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Discussion Starter #1 (Edited)
Outside a temp 64F
Barometric 30.1HG
Cloudy overcast day. Chrono was a brand new competition electronics ProChrono

Rifle uses an Adams Arms free floating gas piston system and Precision Armament Hypertap brake.

Chrono was about 10ft in front of the rifle as per recommendations by the manual.

Hornady 110gr BTHP (American Gunner) = 2569 FPS over a 15 shot string. Max 2607 FPS, min was 2532 FPS.

This is a very accurate load with consistent grouping and expansion (based on other's testing of the projectile in hand loads) and shoots to spec. in their factory loading which lists 2570 FPS as the reference velocity (although they do not specify barrel length for that velocity, clearly it for 16" barrels like their VMAX and SST factory loads).

Wilson Combat 110gr TSX = 2505 FPS over a 5 shot string. Spec for this load was listed at 2550 FPS so it’s shooting a bit slow but still at the 2500 FPS min threshold for a duty load. A bit baffled why it’s shooting slow from my ARP 3R Scout barrel. I was expecting more but saw a bunch of reviews on WC website saying in 2014 they download all of their ammo significantly compared to what they were loading them too prior.

115gr BTHP Prvi Partizan = 2409 FPS
Factory spec is 2624 from a 24” barrel so right about as expected for a 16”. I’d consider this a weak load suitable for close range hunting and plinking, but why buy this when Hornady 110gr AG is same price, 160 fps faster, more accurate and has a far better BC? The BC of this projectile is terrible and closely mirrors that of the short 7.62x39 projectiles. I wouldnt recommend this load if Hornady AG is available.

Feel free to list your results and setups especially if your running an ARP barrel.
 

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Wilson Combat 110gr TSX = 2505 FPS over a 5 shot string. Spec for this load was listed at 2550 FPS so it’s shooting a bit slow but still at the 2500 FPS min threshold for a duty load.
Mine is older (WC ammo) and labeled 2700 FPS with warning for SPCII barrels only.
 

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Discussion Starter #3
Yah I read that on their site, there was one review where a guy bought some in 2013 and then again in 2016 and noted they downloaded the 95gr TTSX from 2850 FPS down to just 2600 FPS. No idea why. Maybe I need to just bite the bullet and get into hand loading to work up some loads that can utilize the enhanced capabilities of the ARP 1:11 3R barrel.

But I was happy that at least the Hornady AG 110gr BTHP, my training / plinking load, shot at 2570 average with a few coming out above 2600 FPS. It's literally one of the cheapest 6.8 factory loads out there and their match bullets perform well in terms of accuracy and BC.
 

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Keep up the good work but in case you hadn't seen this thread before there is a world of info in it where xman did a ton of testing.


PS you will never get the full benefit of the ARP chamber and 3r rifling unless you reload as no factory ammo is loaded to spec2 pressures anymore. I guess lawyers got involved.
 

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Discussion Starter #5
I think was I need to do is bite the bullet and start hand loading. Then I can load to mil spec pressure (58k psi) and really get the most out of the Hornady 110gr BTHP (aka what was their 110gr OTM). Their factory load is decent, I do get the advertised 2570 fps, so it's still what I would consider "full power", but on the slower side. I think of it as a low recoil version of the milspec loading, but eventually I'd like to start working up hand-loads (i'll probably start with a slightly down-loaded version of what Constructor loaded to for 110gr OTM).

It really sucks that nobody loads to mil-spec for this cartridge because of a few barrels that may still exist that were designed to an incorrect chamber spec....
 

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I think was I need to do is bite the bullet and start hand loading. Then I can load to mil spec pressure (58k psi) and really get the most out of the Hornady 110gr BTHP (aka what was their 110gr OTM). Their factory load is decent, I do get the advertised 2570 fps, so it's still what I would consider "full power", but on the slower side. I think of it as a low recoil version of the milspec loading, but eventually I'd like to start working up hand-loads (i'll probably start with a slightly down-loaded version of what Constructor loaded to for 110gr OTM).

It really sucks that nobody loads to mil-spec for this cartridge because of a few barrels that may still exist that were designed to an incorrect chamber spec....
Sadly only a handful ever did in the first place. SSA tactical loads, old Wilson loads, and maybe some double tap are about it as far as I know.
 

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I think was I need to do is bite the bullet and start hand loading. Then I can load to mil spec pressure (58k psi) and really get the most out of the Hornady 110gr BTHP (aka what was their 110gr OTM). Their factory load is decent, I do get the advertised 2570 fps, so it's still what I would consider "full power", but on the slower side. I think of it as a low recoil version of the milspec loading, but eventually I'd like to start working up hand-loads (i'll probably start with a slightly down-loaded version of what Constructor loaded to for 110gr OTM).

It really sucks that nobody loads to mil-spec for this cartridge because of a few barrels that may still exist that were designed to an incorrect chamber spec....
Only 2570? I was getting 2650 from American Gunner factory loads. Ill try a d double check my numbers this weekend.
 

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Discussion Starter #8
Only 2570? I was getting 2650 from American Gunner factory loads. Ill try a d double check my numbers this weekend.
Out of a 16" barrel? I'm running a 16" ARP 3R Scout barrel and my testing was on a cool over cast day at 64F.

Maybe 2650 from 110gr AG from a 18~20 inch on a 95F day...unless Hornady changed their load specs, they advertise 2570 FPS for 16" barrel and that's exactly what I got with my ARP 3R so it's not shooting slow like the WC load was.
 

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Discussion Starter #9
Sadly only a handful ever did in the first place. SSA tactical loads, old Wilson loads, and maybe some double tap are about it as far as I know.
Problem I had with SSA tactical loads was reliably cycling, particularly for their 85gr. Granted I am running a bit of a unicorn, a mid-length AA free floating short stroke piston system where most AR's are DI, but I don't think that's why I had issues.

It would short stroke with SSA, but not with Hornady 110gr AG, WC 95gr TTSX, 110gr TSX and Prvi 115gr BTHP. All four of those worked fine. SSA wouldn't do anything about it either when I contacted them. I suspect the combination of a fast burning powder and light projectile = low port pressure and dwell time.

It did cycle round to round when shouldered with the SSA E-tip so I'll give it that, but I also needed mine to cycle when not shouldered for close quarters use which the others all do. I never got a chance to chrono it though. I sold the remaining 125rds of SSA E-tip I had left from the original order and the guy that bought them for hunting said he also had problems cycling in his 18" WC DI AR but was going to try a lighter buffer / spring. Seems to be a finicky load even if the velocity is up there.

Regardless, 2570 FPS from 110gr Hornady OTM (BTHP) is pretty decent and meet's constructors minimum velocity criteria of 2500 fps for 110 / 115gr loads in 16" barrels as a combat load. Thus I have standardized on it for bulk self defense use (SHFT) and also training use as it happens to be one of the cheapest out there to within a few pennies.

It's very accurate and unlike most of Hornady's OTM's, this is the actual load developed and tested during the development of 6.8 and does expand / fragment from everything I have seen in their testing and with people who actually use this load on hogs. It's a good all around do it all load even if it's not the best at everything.
 

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Problem I had with SSA tactical loads was reliably cycling, particularly for their 85gr. Granted I am running a bit of a unicorn, a mid-length AA free floating short stroke piston system where most AR's are DI, but I don't think that's why I had issues.

It would short stroke with SSA, but not with Hornady 110gr AG, WC 95gr TTSX, 110gr TSX and Prvi 115gr BTHP. All four of those worked fine. SSA wouldn't do anything about it either when I contacted them. I suspect the combination of a fast burning powder and light projectile = low port pressure and dwell time.

It did cycle round to round when shouldered with the SSA E-tip so I'll give it that, but I also needed mine to cycle when not shouldered for close quarters use which the others all do. I never got a chance to chrono it though. I sold the remaining 125rds of SSA E-tip I had left from the original order and the guy that bought them for hunting said he also had problems cycling in his 18" WC DI AR but was going to try a lighter buffer / spring. Seems to be a finicky load even if the velocity is up there.

Regardless, 2570 FPS from 110gr Hornady OTM (BTHP) is pretty decent and meet's constructors minimum velocity criteria of 2500 fps for 110 / 115gr loads in 16" barrels as a combat load. Thus I have standardized on it for bulk self defense use (SHFT) and also training use as it happens to be one of the cheapest out there to within a few pennies.

It's very accurate and unlike most of Hornady's OTM's, this is the actual load developed and tested during the development of 6.8 and does expand / fragment from everything I have seen in their testing and with people who actually use this load on hogs. It's a good all around do it all load even if it's not the best at everything.
I never tried any of their lighter stuff mainly just 110gr tactical loads. Of course back when they were available all i had was a 20" 6.8 ARP with rifle length gas. Still have it and its surgically accurate.
 

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Out of a 16" barrel? I'm running a 16" ARP 3R Scout barrel and my testing was on a cool over cast day at 64F.

Maybe 2650 from 110gr AG from a 18~20 inch on a 95F day...unless Hornady changed their load specs, they advertise 2570 FPS for 16" barrel and that's exactly what I got with my ARP 3R so it's not shooting slow like the WC load was.
Ill double check, but thats what I was getting out of my 16" Bison. Chronograph was about 6 ft in front, since I was at the public range. It was alot hotter than 64 here in Arizona haha.
 

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Problem I had with SSA tactical loads was reliably cycling, particularly for their 85gr. Granted I am running a bit of a unicorn, a mid-length AA free floating short stroke piston system where most AR's are DI, but I don't think that's why I had issues.

It would short stroke with SSA, but not with Hornady 110gr AG, WC 95gr TTSX, 110gr TSX and Prvi 115gr BTHP. All four of those worked fine. SSA wouldn't do anything about it either when I contacted them. I suspect the combination of a fast burning powder and light projectile = low port pressure and dwell time.

It did cycle round to round when shouldered with the SSA E-tip so I'll give it that, but I also needed mine to cycle when not shouldered for close quarters use which the others all do. I never got a chance to chrono it though. I sold the remaining 125rds of SSA E-tip I had left from the original order and the guy that bought them for hunting said he also had problems cycling in his 18" WC DI AR but was going to try a lighter buffer / spring. Seems to be a finicky load even if the velocity is up there.

Regardless, 2570 FPS from 110gr Hornady OTM (BTHP) is pretty decent and meet's constructors minimum velocity criteria of 2500 fps for 110 / 115gr loads in 16" barrels as a combat load. Thus I have standardized on it for bulk self defense use (SHFT) and also training use as it happens to be one of the cheapest out there to within a few pennies.

It's very accurate and unlike most of Hornady's OTM's, this is the actual load developed and tested during the development of 6.8 and does expand / fragment from everything I have seen in their testing and with people who actually use this load on hogs. It's a good all around do it all load even if it's not the best at everything.
So unless my Chronograph is way off. I got the numbers below for Hornady Match. Listed velocity is 2550.
 

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Discussion Starter #13
I'm not shooting Hornady Match, it's American Gunner. It may use the same 110gr OTM bullet, but I believe it may be loaded to a different OAL and charge weight as it's intended for long range accuracy.
 

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I'm not shooting Hornady Match, it's American Gunner. It may use the same 110gr OTM bullet, but I believe it may be loaded to a different OAL and charge weight as it's intended for long range accuracy.
Understandable, but thebpoint was that usually Bison and ARP shoot faster than listed specs. The listed velocity for Match is lower that Gunner, yet as you can see it was about 100 fps faster than listed.
 

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No experience with piston AR's, but im wondering if the difference in velocity is due to bleeding off from the the piston port once cycling begins? Of course you also have the differences in individual Chrono's as well.
 

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No experience with piston AR's, but im wondering if the difference in velocity is due to bleeding off from the the piston port once cycling begins? Of course you also have the differences in individual Chrono's as well.
Good point. Mine is a DI with a superlative AGB.
 

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Discussion Starter #17 (Edited)
I'm running an Adams Arms mid-length piston with their P-series micro adjustable gas block. I could turn it to off so the gas port is closed off and manually cycle the BCG to see if I gain any velocity which would prove or disprove that theory, may be a good point of testing to see if there is any appreciable difference as it would eliminate the piston system all together. The area around the gas seat on the barrel shows no signs of leaking (carbon buildup) so I know at least the gas block to barrel mating surface is not leaking. And I see only the usual minor carbon build up around the gas block adjustment key. With over 1k rounds through it, there's not anything unusual there that I can see.

AA piston system does not bleed off gas like LWRC, H&K 416, PWS or other piston based AR's. The piston cup remains over the gas block guide sleeve and stops at 1/2" of travel, it's limited by the barrel nut, there are no bleed off ports on the piston cup or gas block so the system remains pressurized until the bullet exits the barrel (this was designed to prevent secondary flash for NV compatibility as it was originally designed as a retrofit to convert military issue DI guns to short stroke piston back in 2012 ish time frame). So the only loss of pressure after the bullet passes the gas port (aka the gas system is pressurized) is the very minor leaking around part tolerances (aka the gas flow adjustment key and piston cup) which I can't see being any different than all the leaks around the gas tube / carrier key and piston rings in a DI gun.

All of my Hornady AG is brand new manufacture (just purchased in the last few months). It would be interesting if someone bought a new box of 20 and tested it again to see if there's a difference. Just like Wilson Combat downloaded their ammo some time in 2013 to 2014, maybe Hornady did the same? Either way, I'm at least getting the advertised velocity which to me is the minimum I would expect, even though I was hoping for more. I do run a very hefty 4 port muzzle brake (Precision Armament Hypertap), maybe that could be affecting chrono readings due to the pressure waves but most of the blast is to the sides, not forward, but I can't see how it would affect velocity.

Either that or the inverse is true and Nativeman30's readings are off because of his muzzle brake or lack of one. Maybe I'll try some Horandy Match and see how it compares to their American Gunner. Same bullet, but the box is different and the advertised velocities are different, perhaps the Match has a different powder that is netting a higher velocity than the AG.
 

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Discussion Starter #18 (Edited)
Here's a video of a Bison upper with what appears to be a SS barrel, not sure if it's SPCII or not, but they only got 2519 fps average out of what looks to be either a 16" or 18" shooting Hornady V-Max 110gr, which has the same advertised velocity as the 110gr AG BTHP (aka OTM). V-Max and AG should get 2570 out of a 16". This would be a DI gun:

At this point, I guess we may never know why the significant difference unless we were to both shoot the same ammo out of the same box on the same chrono at the same location. Then we could have an apples to apples comparison. Otherwise there are quite a few variables.

But I'm getting the advertised velocity from 110gr AG at least and it is my understanding the ARP barrel and chamber is not going to net any difference over a 4-groove nitrided or chrome lined or SS barrel unless your pushing hot hand loads which is where the ARP chamber and 3R or 5R rifling comes into play. In that case the 3R/5R rifling and optimized chamber keeps chamber pressures down so you can load a large charge for more velocity without blowing cases or bolt lugs. Unless something is really awry here that i'm just not seeing (maybe my chrono is way out of spec or something off with my upper that I'm just no seeing).

Beyond that I'm just not sure how a bison 16" DI gun with a 4 groove barrel can shoot over 100 FPS faster than a ARP 16" 3R barrel (and the ammo spec) unless your seeing higher than expected chamber pressure with that barrel and that's where your velocity is coming from. I also found reviews of Federal 115gr SP out of a Palmetto Chrome Lined Hammer Forged 16" SPCII chambered barrel (4 grove) and they got 2478 FPS, which is what was advertised on the box for a 16". So I've not see anywhere but this forum where people are getting 100 to 150 fps more than what's on the box for the specific barrel length unless your hand loading.
 

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Discussion Starter #19
Got results from setting the gas key to 0% vs. 75%. I tested on the same day within a minute of each set. 7 shots for each.

2598 FPS average for gas key set to 75%.
2609 FPS average for gas key set to 0%.

So I would say the piston system is not leaky at all. 11 FPS average difference is extremely good and inconsequential. As I mentioned before, the system remains pressurized the entire time the bullet is traveling through the barrel. It does not vent like LWRC's or traditional AK long stroke actions. The op-rod move 1/2 inch and then stops against the collar which rests against the barrel nut.

61915
61914
 

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Discussion Starter #20 (Edited)
I posted this on another thread, but here is the system from a component level:

1/2 inch of travel, note how well the op-rod is guided by the gas block sleeve and how much of it remains over the sleeve. 1/2 inch of travel is how far a DI carrier moves before the gas tube slides out of the carrier key and the bolt has fully unlocked. It mimics this stroke length because it was originally designed as a retrofit system to replace mil-spec DI setups.
61916


One piece forged carrier (this one is standard mass in NiB, but you can get them nitrided for less, in standard mass 9.5oz or low mass at 7oz, I run the Low mass NiB version my ARP barreled 6.8 upper).
61917


End of the op-rod, the collar rests against the barrel nut, this is what stops the op-rod from moving after 1/2 inch of travel, do NOT use aluminum barrel nuts with this system, the collar will shear off the lip of the aluminum barrel nut, but standard steel works just fine.
61918


Gas Block tolerance...spot on for a 0.750 gas seat.
61919


Piston cup internal clearance on the op-rod.
61920


Gas block sleeve size that the piston cup slides over. Only 0.003" clearance, pretty tight for a moving part. And it's not a direct path, gas would need to flow 180 degrees around the end and back out....it's also a self cleaning system. Scrapes off carbon as it returns home. Between myself and my dad, we've fired over 15,000 rounds and neither of us have ever cleaned our pistons once, they still work just the same as new. And that was with mostly dirty russian 5.45 7n6 surplus (corrosive) from the 1980's as we originally started out with 5.45 uppers with Ballistic Advantage barrels.
61921


Gas Key Diameter.
61922


Gas Key socket in the gas block diameter. Only 0.0025" difference here too. No threads to jam up like a set screw. Nitrided for ultra high durability. Gas key rotates and "misaligns" the gas block port hole with it's own port to decrease the size of the orifice, thus choking off flow. You can go from 0 to 100% in about 25% increments. Works awesome for suppressed setups too.
61923


So I think we can rule out a leaky "piston system" as the cause for the differences in velocity. I'm going to chalk it up to these facts:

1. Two completely different chronograph brands and mine has a tolerance of +/- 0.5%
2. I'm in a much cooler environment being in Ohio, I got 29 FPS average more velocity just going from a 64F over cast day to a somwhat sunny 87F summer day on the same ammo, same gun, same chrono and same gas settings vs. last time where I got 2569 FPS average (Hornady spec is 2570 FPS for a 16"). He is in Arizona if I recall, much hotter and sunnier.
3. I used Hornady 110gr American Gunner (OTM / BTHP), he used Hornady 110gr Match, could be difference powder charges / weights
4. Gas piston vs. DI, ARP 3R 16" vs. Bison 4 groove 16"

I think what I'm getting is pretty believable and reasonable. That's basically 2600 FPS on a typical summer day. That's what the military used when the refined the 115gr OTM to 110gr OTM (see attached document) and results were even better with the slightly slower 110gr OTM vs. the hotter 115gr OTM. Higher BC of the 110gr meant you got the same velocity / energy out at 500 yds despite the lower muzzle energy because losses were lower, so you didn't need as much punch from the get go = lower recoil with same performance overall.

At this point, I'm satisfied with my results for a factory 110gr OTM load in 6.8. It's now my de-facto standard load for training, self defense and possibly hunting hogs or deer if I ever get the time. May not be the absolute best at any one thing but its is very versatile and the barrier performance is extremely good, much better than any 5.56 offerings.

The other nice thing is, while it's not exactly "cheap", it's affordable enough that I can train with and shoot the exact same load. This is a really good way to make sure your rifle is 100% reliable with your combat load vs. training with a cheap 55gr XM193 but using a premium 62gr OTM or SCHP in 5.56. You may not know if issues with your premium ammo in terms of cycling, temperature, fouling, feeding until you fire 500 to 1k rounds. For a civilan marksmen, I think this is as good as it gets right now in balancing performance (aka single shot legality), ammo capacity, barrier performance, accuracy, capacity, reliability and cost. I'm really loving this cartridge and it's no surprise, it was designed by actual warriors!

See the attached .pdf. This goes along with the 2008 Roberts report and Constructor's original development info from his time with this cartridge. I think the next step for me is to get into hand loading to actually take advantage of the barrel's capabilities. Pushing the 110gr OTM bullet to 2700~2750 FPS sounds intriguing to say the least.
 

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