6.8 SPC Forums banner
181 - 200 of 223 Posts

·
Registered
Joined
·
1,091 Posts
I have a big fat slow PCC in 2 cartridges same caliber .
Same bullets both just over super . Both allow me to scare golf balls to death out to 75 yd . The fast twist , which is completely overkill for the cartridge , continues to be plate accurate to 200 yd while the slow twist fails to remain stable through the transition just beyond 75 yd . In 45 cal a 1-32 is fine for subs at pistol ranges or where the shot starts subsonic but a 1-16" will maintain the line of flight from a supersonic start .

Every bullet needs a minimum twist and some designs use aerodynamics to get and stay stable where they are too long for the twist . A 180 gr VLD or X type in a 1-10" 30 cal for example .
On the other side a 1-16 will stabilize a 900 45 cal bullet at anything over 900 fps . I did some work with a design program years ago and a nominal RNFP or TC 7mm bullet will make the window on the nominal twists of 1-8.5 or 1-9.5 out past 250 gr . A bullet over 1.6" long .
In 25 cal you need the 1-10 to get any 120 to fly straight but we step up to .277 or 284 and 1-11 is really enough for most modern fast and flat.
I don't know how the 10 or 11 will handle .277 cal 150s as I haven't gotten there yet . I do have a mould i just haven't cast it yet , 130s are probably about perfect .

Having the 6.8 case in both .277 and .284 dia with 1-10,11,&8.5" twists I'd be happy to try a few at assorted weights if bullets were available . Finding suitable moulds has been a struggle in 27 cal and 7mm ain't a lot easier .
 

·
Premium Member
Joined
·
239 Posts
A "real sniper" isn't going to be hanging out on an internet forum talking about "real snipers". That's my opinion anyway.
Then you don't know Jack Guano nor anything about ground pounder MOSs and testosterone levels per team, squad, section nor platoon.
And you sure as hell never placed your best friend in a da-da-damn bag and didn't get angry when a newbie unit member made a gallows humor statement.

And Constructor owes me another 6.8 Super Bolt that was a POS like the one he replaced that was a POS. I've got pics and back and forth emails.

Pics from the same microscope that I built 8 PCBs for Embedded Systems Designs {Georgia Tech card carrying geniuses, Roger Kromann & Brent WhatsHisFace} to go into the next Space Shuttle {ATLANTIS} after the Columbia burned in.
Six PCBs (three in each wing) were put into the next shuttle{ATLANTIS} and two were sent to Huntsville for g shock and temp abuse. The name: Calorie Counters.

Constructor, I'm supposed to ream out a bolt's firing pin channel with a #XX bit because your QC that day sucked to the point
of taking place of Newton's Law of Gravity? Check you emails, bud. You know it's true. I'll post 'em if'n your memory is failing.

You peckerwoods that think the HSLD are quiet types mulling over their horrific deeds...
[Gen.GeorgeSPattonVoice]You bilious bastages that post in a public forum about the quiet solemness of USMC S/Ss in the
Saturday Evening Post don't know anything more about real snooping & pooping than you do about making babies.[/Gen.GeorgeSPattonVoice]
i.e. constructor, Hobbes96, Strawdawg and 1 other person

How's this for a da-da-dagnabit wrench in the works, folks?
Yeah, I accidently started it after 3 glasses of Merlot.
BUTT!!! I didn't wiz in the thread with a snarky comment or LIKEs first.
Ain't looking for a ban, just responding to the BS stated in this thread towards my cul de sac/left field post.
I better no longer post while taking the Pump Doc's orders on red wine for my ticker. Been shot, fragged, bombed and directly hit by lightning.
He said two glasses and I was well into #3.
I'm hitting the rack, already put in 9.5hrs of work in the Lab on my day off.

EDIT: Constructor, I would not buy anyone else's bolts or barrels than yours.
Why? You remind me... of me.
 

·
Premium Member
Joined
·
18,742 Posts
Discussion Starter · #184 ·
Dave, I don't know your full name but this is probably what I told you 10. 12, 15 years ago. Send the bolt back to me and I'll check it out, if it's a simple deburr I'll do that, If not I'll swap it out. I still have a few bolt bodies and should be able to match dimensions so the headspace is the same. Send me an email [email protected].
 

·
Registered
Joined
·
457 Posts
Wow Dave, I'm glad you got that off your chest.

I never stated or implied that I was ever in any branch of service. If you were in any MOS? that involved any sort of "sniper" training and I am wrong you have my most heartfelt apology. I'm still pretty sure that any "sniper" would not be posting on this lowly website unless they were giving pertinent information to the subject at hand. Seeing that the 6.8SPC is only good to about 400 yards on deer (my farthest shot so far) it's not even something a "sniper" would think about.
My normal self would tell you to GFYS, but I won't do that to someone that went overseas when I did not.

Just to add, I hope you get past your st stutter.
 

·
Registered
Joined
·
63 Posts
Wow Dave, I'm glad you got that off your chest.

I never stated or implied that I was ever in any branch of service. If you were in any MOS? that involved any sort of "sniper" training and I am wrong you have my most heartfelt apology. I'm still pretty sure that any "sniper" would not be posting on this lowly website unless they were giving pertinent information to the subject at hand. Seeing that the 6.8SPC is only good to about 400 yards on deer (my farthest shot so far) it's not even something a "sniper" would think about.
My normal self would tell you to GFYS, but I won't do that to someone that went overseas when I did not.

Just to add, I hope you get past your st stutter.

So as a veteran, you shouldn't hold us to some greater level where you refuse to engage in normal behavior. The only exception would be if the military service is related to the topic, in which in my opinion it's not. We chose a different life, some may hold it to a greater accord, but I like to pessimistically think that the civilian service you provided was/is as equally beneficial for society as my military service.

No matter what though there are definitely "real snipers" that are on this forum, other gun forums. They enjoy engaging with like minded individuals on a topic they really enjoy and for some have dedicated their life to. I also would like to point out that some of the worlds best shooters were never in the military at all and sometimes can go toe to toe shooting wise with some of the best shooters the MIL has to offer. This may be an unpopular opinion because I have some experience dealing with it, but being a sniper is not this glorious sexy thing that a lot of people have built up in their mind in part thanks to Hollywood. Imagine laying down in the prone for days at a time never being able to stand up, having to find out how to use the bathroom in that situation, eating food in the same space, all while trying to stay alert watching for the enemy. Not every situation is like that, but that general concept on actual missions is pretty accurate atleast for AFG.
 

·
Premium Member
Joined
·
1,035 Posts
Thank goodness that on the 'net, we are not liable to be arrested for PUI. It would be way more boring than it is otherwise. Car forums are generally way more entertaining.

I took the original post to refer to the popular precision rifle group often led by the 6.5Creedmoor's, I see quite a few that are totally enamored by rifles and cartridges that are deemed 1000 yd capable. Note that I built one using one of H's barrels and it appears to be a light's out shooter.... I can attest it pops Tannerite at 200 yds! Not sure I ever shot it further than that and the longest distance that I can safely shoot is about 750 yds across one of my wheat fields that has a pretty good hill on the other end.

Maybe we should capitalize Sniper? Abolish Snipercentral? Eliminate long range shooting because it should be restricted to those that are real Snipers by profession?

Some how, I doubt that actual military snipers who are pretty limited in number as far as I know, pay much attention to such things, but, I am guessing that there are quite a few that believe they do. They have my total respect and always will and nothing that uses the term sniper casually that is not an attack upon the profession bothers me as "sniping" is a pretty common term, imo
 

·
Registered
Joined
·
1,091 Posts
No dog here .........
I have a long line of military , civil service , GOCO ammo humping , and several kids and steps both in service and done with long hitches .

I've found that aside from a very small group of elitist sorts that likely were of that mindset beforehand anyway most are pretty humble about their service . Most that did face to face kind of work even more so . A few when asked don't talk at all and a few will talk the ears off a corn field . A tiny fraction are pissed off about what they had to do even decades after .

It's just what it is and how the individual resolves it . You can bury it , sell the book over rye , or hang on to the rage for the sake of holding on to it . In some it never goes away it never eases up and it never just sits quietly sipping rye .

Let the man vent , it might be an anniversary of an/the event that changed everything .

He who brags loudest mostly has the least to brag about . Unknown author but true .
 

·
Premium Member
Joined
·
1,035 Posts
Tofan, when I first read your post, I kinda blew it off, but, I have been thinking about it and I believe your design might be a perfect answer to a everyday truck gun. Out here where I live, it is terribly dusty and it may be getting to be more so. To be useful, a gun has to be quickly accessible without having to open a case or unzip a soft one. When I see something running, I want to be able to grab the gun and shoot thru the window.

I find it very difficult to drive around with an AR on the seat collecting dust. I also don't like trying to manipulate a charging handle with very little room between the scope bell and the handle. I prefer a side charger.

One of my favorite guns to shoot is a Zastavia pistol with a brace. My son has one that he SBR'd. Problem is that they are a bit weak at 100 yds and will barely pop tannerite. The 6.8 carries a way better punch well on out to beyond my range capabilities and it will handle any size of target normally found in Texas. Obviously, it has much better accuracy as compared to the usual AK altho' the Zastavas are pretty good even with surplus ammo.

One of the obvious benefits of the 6.8 is the lack of velocity degradation with shorter barrels. My favorite is my 12.5" ARP. Makes for a great truck gun (other than I don't want to leave it on the seat and collecting dirt/dust and getting scarred up) and kills hogs at distance without a problem. Few lightweight, easy shooting guns in other calibers exist that can cover the gamut as the 6.8 can. It shoots targets well, but, it is really a shooter's round when it comes to performance. As well as a 6.5G or Valkyrie shoot at distance, neither is a good all around hunting barrel when it comes to the person that actually shoots on a daily basis when needed without stopping, getting out of the vehicle and stopping something that is rapidly disappearing into brush, trees, etc.

Your weapon sounds like a hybrid that could work either with a conventional AR lower, or one with a good Magpul mag (or a metal copy that might allow longer loading as suggested by RD). Equip it with a good barrel that provides good accuracy inherently along with the piston that should allow it to be less sensitive to dirt and a reasonable price tag, I think you might be on to something that appeals both to the serious user as well as those that just like something different.

There are some serious Texas hunters here that might love to try it and get some real marketing going instead of just ads especially if you put out some more affordable bullets like the 115 gold dots that Speer made and were used on the Federal rounds. For hog hunting one does not want to use boutique , high dollar rounds.

Obviously, I am not describing a tacti-cool, drugstore gun owner, but it can be uglied up enough to shake their stools as well. LOL



Well you asked, and so I will go ahead and tell you what we have planned and how we feel about it. First the 6.8 SPC round is one that we feel real strong about not only because it was developed by a person in the military, but because it just makes sense. It does great for a lot of things including people killing, hunting, target shooting and just general shooting stuff. Things like the SAAMI spec, weapon variability and one of the most important is being able to use those magpul mags. They are perfect, lightweight, tacticool, etc. I'm not hating on any other brands, but I wasn't willing beyond the ruger mini 6.8 to buy a rifle that couldn't use the magpul mags, i imagine others are the same. With all that being said, what are "we" my company doing about it?

The very first thing is we have been designing a new rifle that utilizes a lot of great technology of the past and future. With that we aren't not willing to share a picture yet, but I will describe the rifle. The V-SH68 will be a gas piston driven, 6.8x43MM weapon system that will incorporate a sheet metal receiver, quick change barrel system, adjustable gas system, user customizable stock and pistol grip system. The magazine adapter will use the magpul mags, but we are working on the other one that will allow use of all other magazines. Along with this we will be releasing stripper clips like we hinted out in the other thread along with some more goodies. There will also be a belt fed machine gun variant too, but we suspect it will just be eye candy at this time. The other caliber choice will be 5.56, but no others are planned or are likely to be incorporated. I have no idea on the time of release, I am waiting on a few other inputs from some important voices in the field and then I will have a good idea of the date of when we will be able to release this thing.
 

·
Registered
Joined
·
63 Posts
Tofan, when I first read your post, I kinda blew it off, but, I have been thinking about it and I believe your design might be a perfect answer to a everyday truck gun. Out here where I live, it is terribly dusty and it may be getting to be more so. To be useful, a gun has to be quickly accessible without having to open a case or unzip a soft one. When I see something running, I want to be able to grab the gun and shoot thru the window.

I find it very difficult to drive around with an AR on the seat collecting dust. I also don't like trying to manipulate a charging handle with very little room between the scope bell and the handle. I prefer a side charger.

One of my favorite guns to shoot is a Zastavia pistol with a brace. My son has one that he SBR'd. Problem is that they are a bit weak at 100 yds and will barely pop tannerite. The 6.8 carries a way better punch well on out to beyond my range capabilities and it will handle any size of target normally found in Texas. Obviously, it has much better accuracy as compared to the usual AK altho' the Zastavas are pretty good even with surplus ammo.

One of the obvious benefits of the 6.8 is the lack of velocity degradation with shorter barrels. My favorite is my 12.5" ARP. Makes for a great truck gun (other than I don't want to leave it on the seat and collecting dirt/dust and getting scarred up) and kills hogs at distance without a problem. Few lightweight, easy shooting guns in other calibers exist that can cover the gamut as the 6.8 can. It shoots targets well, but, it is really a shooter's round when it comes to performance. As well as a 6.5G or Valkyrie shoot at distance, neither is a good all around hunting barrel when it comes to the person that actually shoots on a daily basis when needed without stopping, getting out of the vehicle and stopping something that is rapidly disappearing into brush, trees, etc.

Your weapon sounds like a hybrid that could work either with a conventional AR lower, or one with a good Magpul mag (or a metal copy that might allow longer loading as suggested by RD). Equip it with a good barrel that provides good accuracy inherently along with the piston that should allow it to be less sensitive to dirt and a reasonable price tag, I think you might be on to something that appeals both to the serious user as well as those that just like something different.

There are some serious Texas hunters here that might love to try it and get some real marketing going instead of just ads especially if you put out some more affordable bullets like the 115 gold dots that Speer made and were used on the Federal rounds. For hog hunting one does not want to use boutique , high dollar rounds.

Obviously, I am not describing a tacti-cool, drugstore gun owner, but it can be uglied up enough to shake their stools as well. LOL
We have never talked, but what you describe is extremely accurate as to what I envisioned for it. We have made contact with PRI about the mag design, we will see if they are up to do it. I have one more contact in the industry that I will try to make contact with if PRI is not interested. We are aiming for $750 as the max price point for the gun, barring some world emergency. I don't know about the AR lower, I will have to think about that. The problem believe it or not is the AR15 lower kills the modularity aspect of it. Our design allows you to use an AR pistol grip, a FAL pistol grip, an AK pistol grip, your own pistol grip, I really don't know if there is a pistol grip out there that you can't use. The buttstock is a little more limited for obvious reasons but it will still be modular. It is most definitely a side charger too, cant agree with that POV enough.

We believe in the caliber and all we need in the market is a few more things to happen and it will take "center stage" so to speak. Pictures of animals getting crushed with it, especially the bigger game animals do so much for the caliber, and there has been more bullet R&D these past 2-3 years. There is more but more work needs to be done, thanks for the response it means a lot!
 

·
Premium Member
Joined
·
1,035 Posts
We have never talked, but what you describe is extremely accurate as to what I envisioned for it. We have made contact with PRI about the mag design, we will see if they are up to do it. I have one more contact in the industry that I will try to make contact with if PRI is not interested. We are aiming for $750 as the max price point for the gun, barring some world emergency. I don't know about the AR lower, I will have to think about that. The problem believe it or not is the AR15 lower kills the modularity aspect of it. Our design allows you to use an AR pistol grip, a FAL pistol grip, an AK pistol grip, your own pistol grip, I really don't know if there is a pistol grip out there that you can't use. The buttstock is a little more limited for obvious reasons but it will still be modular. It is most definitely a side charger too, cant agree with that POV enough.

We believe in the caliber and all we need in the market is a few more things to happen and it will take "center stage" so to speak. Pictures of animals getting crushed with it, especially the bigger game animals do so much for the caliber, and there has been more bullet R&D these past 2-3 years. There is more but more work needs to be done, thanks for the response it means a lot!
I was trying to find a means by which people that already owned an AR could use their existing lower with the new upper. Perhaps, longer term-wise, it might be better to build a lower with the new mag well that could use an adapter for use with existing magazines. Trying to think of a means to make it appealing to old or new...but, I am probably overthinking it LOL It needs to be functional and reliable first.

It's a shooter's gun, not a talker's gun.
 

·
Registered
Joined
·
740 Posts
Thanx for the post on exterior ballistics. I have two shelves of books on the subject and still keep all my prep school and college math/physics/chemistry books when required to revisit subjects that have dimmed.
ETA- Notice the part about bullet balance and COG

Barrel Twist and Bullet Stability
By Damon Cali

Posted on April 07, 2011 at 12:13 PM

The barrel twist you choose for your rifle can have a significant impact on it's accuracy. But how and why?
Bullet Stability
Bullets are aerodynamically unstable. Left to their own devices, they will tumble through the air in an accuracy destroying, chaotic manner, hitting the target in a basically random orientation - straight, sideways, or even backwards. If you spin them at a high rate, however, they behave quite nicely, and will keep their nose pointed more or less down range.
The longer the bullet, the more spin it needs. Accurately calculating the amount of spin required to stabilize a given bullet requires the use of some empirically derived constants, not unlike the ballistic coefficient we're all familiar with. Those constants are not generally available. For the mathematically inclined, a more thorough treatment of the math behind bullet stability can be found in Robert McCoy's excellent Modern Exterior Ballistics: The Launch and Flight Dynamics of Symmetric Projectiles - but only if you have a heavy duty math background (a math or engineering degree or equivalent knowledge).
For the less eager, there are several approximate methods of calculating the required spin for a bullet. The simplest is the old Greenhill formula:
T = 150 / L
where T is the twist in bullet calibers, and L is the length of the bullet in calibers.
Unfortunately, it's not a very good method, but I include it here to show that longer bullets require faster twists, which is basically all you need to know. A better calculator that uses a more involved method is available at JBM Ballistics.
So why not just pick a really fast twist and be done with it? It turns out the very spin that keeps our bullets stable also conspires to send our shots off target - it is possible to over-spin a bullet.
Bullet Balance
Perfect bullets are balanced both statically and dynamically. That is, the bullet's center of gravity is on the bullet's axis of symmetry (static balance) and the bullet's principal axis of inertia is parallel to the bullet's axis of symmetry (dynamic balance). Static balance is straightforward enough, but what is this principal axis business?
Think of a tire being balanced - the goal is to add weights until the wheel's principal axis of inertia aligns with the wheel's physical axle. if they are not in line, the wheel will wobble. The same thing happens with bullets.

This bullet is statically imbalanced. Its CG is off the center, but it's principal axis of inertia (Ip) is parallel to the bullet's axis of symmetry.


This bullet is dynamically imbalanced. Its CG is centered, but it's principal axis of inertia (Ip) is at an angle to the bullet's axis of symmetry.

In real life, all bullets have both static and dynamic imbalance. Think of a bullet with a small void or impurity off the centerline. That will throw off both the center of gravity and the principal axis of inertia. So why does this matter?
Lateral Throwoff
The first concept to understand is that of lateral throwoff. When a statically imbalanced bullet travels down the bore, the off-center center of gravity will travel in a helical path since the outside edge of the bullet is constrained by the bore. When the bullet leaves the muzzle, it will fly off in a direction tangent to that helical path. The exact direction depends on what direction the heavy side of the bullet happens to be facing when it leaves the muzzle.
Note that a perfect bullet, if it is allowed to tip in the bore, will also fall prey to lateral throwoff. All that is required is for the center of gravity of the bullet to be off the bore's centerline.
The faster the barrel twist, the more lateral throwoff you will have. In other words, faster twists are less accurate with imperfect (that is, real) bullets.
Aerodynamic Jump
Similarly, when dynamically unbalanced bullet (even if it is statically balanced with the center of gravity perfectly centered on the bore) leaves the muzzle, it will do so with an initial yaw that causes it to fly off in the wrong direction. This is called aerodynamic jump.
Like lateral throwoff, aerodynamic jump can also caused by in-bore tipping. As we'll see in a moment, wind can also cause aerodynamic jump.
In any case, the faster the barrel twist, the more aerodynamic jump you will have. Again, the deflection will be in a random direction determined by exactly how the bullet was positioned when it left the muzzle.
Lets take a break and summarize. Spin is required to stabilize bullets in flight. Defects in bullet balance or in-bore tipping will cause lateral throwoff and aerodynamic jump, which will cause the bullet to fly off in an unwanted and unpredictable direction. The faster the barrel twist, the more deviation in the trajectory.
Cover Your Bases
An interesting side note is that aerodynamic jump can partially cancel out lateral throwoff. It turns out that a defect forward of the bullet's center of gravity (that is, at the nose) will cause this cancelation. The same defect aft of the center of gravity (that is, at the base) will cause the two effects to reinforce each other. Benchrest shooters have long known that the bullet's base was more important than the nose. This is one reason. (Obviously, a perfectly balanced bullet is the best case, but if you're going to mangle a bullet, do it at the nose.)
Aerodynamic Jump Caused by the Wind
A cross wind will cause the bullet to yaw to the side as soon as it leaves the muzzle - creating aerodynamic jump. However, unlike the jump caused by bullet imbalance, this yaw is predictable since its source is the direction of the wind. Oddly, what happens is that the wind-based aerodynamic jump causes a vertical deflection of the bullet's point of impact. The stronger the wind, the more the vertical deflection will be.
Note that the magnitude of this effect is not small. A .308 168 grain Sierra MatchKing at 2,600 fps will experience a vertical deflection of approximately 3/8" at 100 yards in a 10 mph cross wind. Compare that to the almost 1" of horizontal wind deflection that you might be more familiar with.
Imagine shooting in very gusty winds with a very accurate rifle. You might wind up with a target that looks something like this:

A left to right wind causes bullets to hit low. A right to left wind causes bullets to hit high. (Note that this would be reversed for a rifle with a left hand twist.) So rather than wind causing a pure horizontal dispersion as you might picture, it actually causes a a dispersion at an angle. The faster your rifle's twist, the greater that angle will be.
Now I don't know about you, but it's hard enough for me to keep track of the horizontal impact of the wind without having to worry about a vertical component. By the way, the angles of the lines on the figure are drawn to scale for a Sierra 168 grain MatchKing with a right hand twist at 2,600 fps at 100 yards.
It's important to note that this effect is much more noticeable at short range than long range. This is because the vertical jump is a constant angle no matter the range, while the horizontal wind will increase greatly at longer ranges. So at long range, the ratio of vertical to horizontal deflection will be smaller - that is, the angle of the line in the above chart will not be as steep at long range.
Practical Take-Away
For the highest levels of accuracy, pick a high-quality bullet that will give you acceptable ballistics at the range you need. Then get a barrel with the slowest twist that will stabilize that bullet. Adding a little more twist "just to be sure" will degrade your accuracy by a small amount. Ask around and see what others are using - use the slowest twist that seems to work at the ranges you'll be shooting.
Additionally, we've seen why it's important to keep the bullet aligned with the bore through proper chambering and hand loading techniques, and why we need to pay attention to the wind both at the at the muzzle and down range.
Having three of the Bison fast twist barrels would like to comment on this post.

Okay so when someone makes a poll add fast twist barrels to it. Bison has some 7 twist if I remember correctly.
I own three of the Bison quick twist subsonic/supersonic tubes from 8.5" up to 16" and have experimented with them a good bit. The only way to make them good subsonic shooters is buy the Cavity Back bullets made for the task. Can do o.k. with others and get good cast gas check bullets to somewhat shoot well but given a dozen better cartridges to launch subsonic I have four 458 SOCOMs because when set your speed limit at 1,050 fps then only way to increase energy is with mass. I have 300 to 600 grain bullets to select from and mostly use 550 grain cast hollow points which slay hogs like a sledge hammer.

I have run into issues with all of my fast twist barrels using full power loads especially at longer ranges or using thin skinned bullets. They will spin up some varmint bullets at full power to point they come apart in flight. Spin drift becomes a real issue at longer ranges so its not a good general purpose rifle. the 200 to 220 grain limit of 6.8 subsonic and may be better off with a 3000 Ham'r. I am not a 300 BO fan though owned two 300 Whispers I liked in the early days. Unless able to build multiple rifles or at least uppers a fast twist barrel is going to limit you just because of physics and we cannot overcome the laws of physics yet.

I still just want access to affordable Six8 receiver groups like Shulzer tried and convincing Magpul to increase the internal lenth of their Six8 magazines. Then we could keep on calling it 6.8 spc II, be safe with factory 6.8 SPC ammo, spc II loads and give us an option to push spc II that little extra we prove to the Grendell fan boys on the range or field we have a better and more durable rifle. just the ability to seat bullets out a tad more and develop a slippery 130 grain open tip bullet with rebated boat tail and I could take a few thousands or hundredths of an inch and have a range card that shoots just as flat as the 6.5 without worries over broken bolts.

I broke three 6.5 bolts when built my first two, swapped to JP high pressure which held together but realized I was lobbing more expensive bullets that did nothing my 6.8s wouldn't do with just the proper range card and do it better in close.I can use a Whidden bullet point die along with trimming the meplats of exiting 6.8 bullets to make 450 yard coyote hook ups and had guys missing at lesser ranges with their 6.5s. We prove it in the field and that will do more for the 6.8 than anything especially combined with its better durability and performance on two legged critters.
 
  • Like
Reactions: earlytom

·
Registered
Joined
·
680 Posts
Thanx for the post on exterior ballistics. I have two shelves of books on the subject and still keep all my prep school and college math/physics/chemistry books when required to revisit subjects that have dimmed.


Having three of the Bison fast twist barrels would like to comment on this post.



I own three of the Bison quick twist subsonic/supersonic tubes from 8.5" up to 16" and have experimented with them a good bit. The only way to make them good subsonic shooters is buy the Cavity Back bullets made for the task. Can do o.k. with others and get good cast gas check bullets to somewhat shoot well but given a dozen better cartridges to launch subsonic I have four 458 SOCOMs because when set your speed limit at 1,050 fps then only way to increase energy is with mass. I have 300 to 600 grain bullets to select from and mostly use 550 grain cast hollow points which slay hogs like a sledge hammer.

I have run into issues with all of my fast twist barrels using full power loads especially at longer ranges or using thin skinned bullets. They will spin up some varmint bullets at full power to point they come apart in flight. Spin drift becomes a real issue at longer ranges so its not a good general purpose rifle. the 200 to 220 grain limit of 6.8 subsonic and may be better off with a 3000 Ham'r. I am not a 300 BO fan though owned two 300 Whispers I liked in the early days. Unless able to build multiple rifles or at least uppers a fast twist barrel is going to limit you just because of physics and we cannot overcome the laws of physics yet.

I still just want access to affordable Six8 receiver groups like Shulzer tried and convincing Magpul to increase the internal lenth of their Six8 magazines. Then we could keep on calling it 6.8 spc II, be safe with factory 6.8 SPC ammo, spc II loads and give us an option to push spc II that little extra we prove to the Grendell fan boys on the range or field we have a better and more durable rifle. just the ability to seat bullets out a tad more and develop a slippery 130 grain open tip bullet with rebated boat tail and I could take a few thousands or hundredths of an inch and have a range card that shoots just as flat as the 6.5 without worries over broken bolts.

I broke three 6.5 bolts when built my first two, swapped to JP high pressure which held together but realized I was lobbing more expensive bullets that did nothing my 6.8s wouldn't do with just the proper range card and do it better in close.I can use a Whidden bullet point die along with trimming the meplats of exiting 6.8 bullets to make 450 yard coyote hook ups and had guys missing at lesser ranges with their 6.5s. We prove it in the field and that will do more for the 6.8 than anything especially combined with its better durability and performance on two legged critters.
Going supersonic from 1050fps to 2600fps increases bullet spin a whopping 60%. In the example by Damon Cali, his used 14 twist to 10. An increase of just half that at 30%. Not surprisingly bullets did some funky things including midair self-destructing. Sounds like my kind of a fun experiment though.

Over spin can cause other stability issues. When a bullet spins too fast it will tend to fly nose high resisting following the trajectory arc down range. When going transonic this can cause key-holing in a target.

I didn’t see any post in this thread advocating anywhere near those increases in twist rate. At most I’d like to see a 1:9 twist, to aide bullet stability, but also give greater terminal performance went hunting without hurting accuracy to any large degree. YMMV
 

·
Premium Member
Joined
·
18,742 Posts
Discussion Starter · #198 · (Edited)
"I have run into issues with all of my fast twist barrels using full power loads especially at longer ranges or using thin skinned bullets. They will spin up some varmint bullets at full power to point they come apart in flight. Spin drift becomes a real issue at longer ranges so its not a good general purpose rifle. the 200 to 220 grain limit of 6.8 subsonic and may be better off with a 3000 Ham'r. I am not a 300 BO fan though owned two 300 Whispers I liked in the early days. Unless able to build multiple rifles or at least uppers a fast twist barrel is going to limit you just because of physics and we cannot overcome the laws of physics yet."

I hope Robert Silvers doesn't see that he'll build camp here for the next 3 years telling us all about the 4 twist 300BO barrels he made that had absolutely no effect on pressure or velocity.
Come to think of it there have been 3 or 4 guys who said fast twist barrels have no effect on pressure, velocity or accuracy but I haven't seen a big rush by major gun makers to produce such barrels. It's been at least 10 years what are they waiting for?
 

·
Vendor
Joined
·
2,403 Posts
Going supersonic from 1050fps to 2600fps increases bullet spin a whopping 60%. In the example by Damon Cali, his used 14 twist to 10. An increase of just half that at 30%. Not surprisingly bullets did some funky things including midair self-destructing. Sounds like my kind of a fun experiment though.

Over spin can cause other stability issues. When a bullet spins too fast it will tend to fly nose high resisting following the trajectory arc down range. When going transonic this can cause key-holing in a target.

I didn’t see any post in this thread advocating anywhere near those increases in twist rate. At most I’d like to see a 1:9 twist, to aide bullet stability, but also give greater terminal performance went hunting without hurting accuracy to any large degree. YMMV
Litz just recently on his FB page addressed what he calls a myth that rifle projectiles will fly nose high when spun faster. I said that comes from artillery shells with a high arc that hold a nose high attitude when arcing over the top. But that rifle cartridges do not do that as their arc is not severe enough to cause it.
Ballistics have came a long way in the last 10 years.

You are correct though. No one has advocated anything other than saying a 1:9 or 1:95 twist would have no detriment in the 6.8.
With the advances in projectile design it would help with terminal performance. Again not that it needs to be done, just that it would further improve performance.
Projectiles like the Cutting Edge, Hammer, Lehigh that shed petals all would radiate the petals further out with a faster twist.
The 6.8 does not have the power to self destruct projectiles.
Nor does it have the range for spin drift to become a factor.
Nor is it capable of .1 to .2 MOA accuracy like benchrest.

But a SLIGHTLY faster twist would improve terminal performance SLIGHTLY.
You are spot on on that my friend.
 
181 - 200 of 223 Posts
Top