[Jellysick]

I'm a newbie when it comes to reloading, looking for some direction. I have a box of reloads made for my 6.8 but have yet to make it to the 100yd range to shoot the ladders so my reloading experience has been with 9mm and 45ACP. Given the short range expected out of the 300blk I've made the indoor 25yd range work, zeroing in at 20yds which, according to the charts, keeps me within 4" up to 175yds with the factory loaded 125gr MKZ. I'm shooting an AR Pistol with an 8.3" Ballistic Advantage Hanson barrel with the pinned gas block and an Eotech RDS. I also have a suppressor.

I realize the 300 BLK is not what a lot of folks chalk it up to be. Its anemic as Xman puts it. I really like the idea of the flexibility b/w supersonic and subsonic with the switch of a mag, and the fun factor of the subsonics with the suppressor. Supersonic will use the suppressor as well. I'm also able to participate in whitetail hunting in Missouri during the "Alternative Methods" period with this caliber and the AR pistol. I intend to use the 125gr MKZ if this pans out.

I shot a few strings of reloads recently out of this pistol, subs and supers. Suffering from analysis paralysis currently. The ladders I shot provided good info but the accuracy component of the process was not captured. All rounds were within 6", but only at 20yds. The process rendered an understanding of where I need to be from a charge perspective, but I don't know how wrapped around the axle I need to get from the accuracy standpoint. Keep in mind this is an AR pistol, so I'm not shouldering it, and using an Eotech RDS which can't provide the same accuracy as my Vortex Viper on my 6.8SPC. I'm sure there are plenty of more accurate shooters than myself as well. I do OK, I just don't spend a lot of time behind the trigger.

I'm not trying to squeeze the last .25 MOA out of this round. If I'm within a 4"-6" circle at 100yds I'd be more than happy. With this said, how much variance is one likely to get by testing reloads of varying capacity by a difference of .1gr +/-? For my supersonic rounds using 150gr Berrys JHP I'm using H110, I shot a ladder from 15.4gr to 16.9gr (reloading data shows 17.2gr as max charge). I had a case failure at the 16.9gr load (shooting once fired LC brass, case split around the circumference close to the middle of the case) but I'm fine with the velocity of the 16.3gr and 16.6gr loads. How much testing and refinement from an accuracy standpoint is a casual shooter able to achieve shooting 100-150yds? Are there suggestions on how you'd go about finalizing this load?

The last component is simply time. Range time adds up and I'm looking to minimize the back-and-forth. I have young kids so a small window for a trip to the range can be hard to come by!

Thanks all!

 

[Xman]

Jellysick, I'm going to give it a go. I haven't much luck with reloading the 300 BO. Three things have deterred my enthusiasm.

1. I couldn't find a powder or load that allowed me to achieve the velocities provided by Barnes 110 TTSX factory ammo.
2. My first barrel was defective and replaced by CMMG. The replacement barrel had 0.090" less freebore resulting in a significant loss of powder capacity and MV with heavier bullets.
3. The POI difference between subsonic and supersonic at 50 to 100 yards was so significant I pretty much just use supersonic now. Thus, its more than just switching the magazine.

I initially hunted subsonic until I realized that a 200-grain bullet at 1000 fps was essentially a 45-cal pistol even though I had a "rifle" in my hand. That realization was made when 50% of the hogs I shot at 100 yards ran off. Since then, I have only hunted the 300 BO with the 125 MKZ and it has provided satisfactory terminal performance.

You didn't mention your muzzle velocity. I wouldn't recommend a 20 or even 25-yard zero. With a 50-yard zero with supersonics, I'm on again at 125 yards and 4 inches low at 175 with a 125-grain bullet.

I'm not familiar with the Eotech red dot sights. Suggest you check its parallax. With a steady rest and a target at 20-25 yards, move your head back and forth. Does the red dot stay on the target. How about at 50 and 100 yards. For load development, you would be better served by using your Vortex Viper at 100 yards (50 might be ok also). This will provide a better result/indication of your load's accuracy.

A powder charge variation of 0.1" grain will not make a significant difference if your load is at its optimum charge weight (OCW). For 5.56, 6.8, and 300 BO load development, I use 0.3 grain powder charge steps which looks like you did also. Do you use 3-shot groupings or single shot per charge weight ladders? I usually stop load development when I get a moa load or better. I know my rifles' accuracy potential enough that I can usually (75% of the time), do a single shot per charge weight ladder to find OCW. E.g., by recording the location of each impact, I look for 3 that group an inch or less. I pick the middle weight and load there to see if that provides usable accuracy. I once did a 5-shot ladder, adjusted the crosshairs for the middle location, and shot a hog with the 6th bullet in the ear at 50 yards the next day. If you are not familiar with this load development technique, load two rounds per charge weight. Shoot one ladder, mark you impacts, then shoot the second ladder on top of it. This can be more telling than trying to shoot 3- or 5-shot groups and saves powder/bullet resources.

I find that adjusting COAL in 0.015" increments can fine tune accuracy if I desire smaller group size once I find the OCW. I've never done this with the 300 BO because there isn't much latitude to change COAL. Do you measure your distance to the lands? I've had to do that for every bullet I've loaded in the 300 BO if I want to maximize the powder charge.

I'm a bit concerned about you splitting a case. That is an indication of a headspace issue. How far are you pushing the shoulder back when you resize? Only 0.003" to 0.004" is desired. If you are following the direction that came with your dies, your die may be incorrectly adjusted. Hornady has a good tool for measuring shoulder bump/headspace. Some reloaders use the mouth of a pistol case against the shoulder with their calipers. Make sure you remove the the spent primer so you get accurate readings. A proud primer or crater can throw off your measurements.

Do you crimp? My loads don't leave home without one, but I only use a collet die like Lee offers. Don't use the integral crimp feature in your seating die, it will only cause issues that are hard to diagnose.

Did I cover your questions?

 

[Jellysick]

You're always very helpful. A quick google makes me think the Eotech EXPS2 is supposed to be parallax free. Obviously great points on the POI difference b/w supers and subs. I figured I would just adapt using the reticle on the Eotech. One of the main challenges with all of this is that getting to a 100yd range is difficult. I have access to two, but it takes a decent time commitment which is fine, but at the end of the day it just won't happen very often.

I realize the similarities b/w 300 BO Subs and .45ACP. I'm fine with it and I'm not expecting it to be anything that it isn't. Certainly not intending to hunt with subs. My 20yd zero reference was in relation to some ballistics charts I was looking at which looked like it would work for my needs (and conveniently would work for the 25yd indoor range close by). Below is what I'm referencing, the factory loaded 125 MKZ clocked in at 1947fps out of my 8.3" barrel (I'm using a Magnetospeed chrono attached to the hand guard of the upper). Unless I've really overlooked something, this should give me plenty of usability with 175yds or so. Realistically I'll probably be within 125yds for my needs.

Specific to the reloads, yes .3gr increments. I'm familiar with your ladder approach, find the middle shot of a tight 3 shot grouping and that would be your accuracy node. My problem is, which is only made worse by this red dot and the fact that it's a pistol (I'm not shouldering or resting on anything), I'm not doing the greatest work behind the trigger to remove as much as I can in terms of the human variable.

My initial ladder which also included the ruptured case was a 6 shot ladder. Hornady 150gr FMJ BT bullets w/ H110 (Hodgdon site specifies 14.6gr as starting load, 17.2gr max load, w/ 2.15" COAL. My data is below:

I'm using once fired LC 300 BO brass. I'm unsure if it was 5.56 previously or if it was manufactured as 300BO. It came pre-sized but I am running it through my sizing die just to make sure. I also have a Sherridan case gauge in 300 BO that I'm using along the way to make sure everything looks OK. There's certainly some dented and dinged up brass in the bunch so I've chalked up the rupture with a base case. I'm discarding any others that I come across that may have damage. With 17.2gr of H110 listed as the max and firing up to 16.9gr the primer looked OK I think? Below are the cases after firing them. I never recovered the 2nd one.

The ruptured case (which is the far right case in the above line-up):

I fired a ladder of subs as well, progressing through the ladder to the listed starting load. Nothing very exciting there, captured FPS which indicates I need a bit higher charge to get around 1000fps or so. The chrono didn't capture velocity on the first two because a sensitivity adjustment had to be made.

I'll start at 11.3gr and creep higher using the chrono as a gauge to tell when to stop.

So my next range trip my plan is to simply find an accurate enough load for my needs. Focusing in around the 16.3gr of H110 and the 150gr Berrys bullet, will test a 5 shot group of 16.2, 16.4, and 16.6. From that I'm hoping one of those is "good enough".

Anyways, that's where I'm at. Just struggling with the reloading approach as relates to accuracy given all of the other variables that exist (non-shouldered firearm, no bench rest, red-dot sight, etc). Let me know any thoughts you have on how I've progressed through load development and of the ruptured case.

** Edited to add a few points I left out. I'm familiar with the Hornady gauge to measure head space. I have one that I use for 6.8 but I'm not using it for 300BO. And yes, I've used the instructions provided with the dies to adjust them. Lastly, I'm not using any crimp at the moment.

 

[Xman]

Jellysick,

I can see right off that I was incorrectly assuming the height above bore of your red dot. All my red dots are 2.5" above the bore. The 1" delta makes a huge difference with a 20-yard zero.

I've only experienced two case separations but I wouldn't assume your rupture was due to a nick/dent in the brass. I reload dinged cases all the time. Have you verified your shoulder set-back?

Your 25-yard range seems challenging at best for load development or even a decision on which load is shooting the best. Are there no horizontal surfaces/tabletops elevated above the floor you can put a rest on? Can you shoot from the sitting position? Do you have any shooting sticks or tripod you can shoot from? I think you need to get creative and find a way to reduce the human interaction with the firearm. I've shot my pistols from the bench without shoulding for load development, but I always use a rest. Are your developing you loads with the suppressor installed if you plan to shoot the bullets that way in the future? It can make a difference. Remember to check parallax.

I checked the Barry's website to make sure I understood the bullet you were using. Have you checked the distance to the lands? This is not critical but could be useful data. But what I did find interesting is that Barry's does not recommend velocities above 1650 fps which are easy to achieve with the 300 BO and 1680 powder.

"Don’t exceed the recommended maximum velocities listed. This creates bullet core separation and accuracy issues."

 

[Jellysick]

Your height over bore comment may have brought to light an incorrect value in my numbers. I believe you are right, it is likely 2.5" or 2.6". I'll have to double check. Missed that part. And good call out about the max velocity. I'm already over that with my 150GR load and H110. Appreciate you pointing that out as well.

I'll try to get creative or figure out a rest at the range. It's the typical stalls with the waist height table top for your gear...

 

[Jellysick]

Typo on my part. The 150gr bullets I'm using are Hornady jacketed bullets. They are packaged exactly like the Berrys but they are not Berrys.

 

[just_me_mongo]

I have a few thoughts to help out. I reloaded for a 16" .300 blk rifle that I deer hunted with and I reloaded for a 9.5" SBR. Both of these guns were accurate and the 16" was a very cheap barrel. Both of my BLKS were 1/8 twists (that matters for bullet weight). I am not sure that you will get a reasonable amount of accuracy from a pistol if you cannot shoulder it. The way you hold it, the way you brace yourself, and the way you breathe will change the POI. I consider a 3" group a reasonable amount at 25 yards.

Now, the powder burns up in the first ten inches of your barrel. My 9.5" always had unburned granules leftover in the receiver (when cleaning). If memory serves, I had to zero at 25 or 50 yards. My flip ups and red dots did not have enough adjustment to do anymore than that. It was good to 75 yards then the bullet really dropped off. I used a subsonic load of10.2 grains of Re7 and a 208 Amax.

The 16" rifle's barrel liked a 125 grain SMK and 17.6 grains of H110. I ran supersonic ammo out of this gun because it was my deer gun. I used a 100 yard zero all the time.

A 300 blk pistol is going to be extremely over-gassed with supersonic rounds. In prior years, I ran some and it felt like the bcg was going to blow out of the back of my SBR. From the advice of a Master Gun-smith, I decided to use subs only in my SBR with a 9.5" barrel.

I had a buddy who broke his hammer pin, trigger pin, and other parts of his 300blk AR from doing that. His gun was over-gassed and certain parts were overworked until they broke. Trying to switch back n forth from subs/supers in a short barrel or pistol is not a worth while venture in my opinion.

That said, I am going to respond to your questions in quotes and my responses in italics.

"I'm sure there are plenty of more accurate shooters than myself as well. I do OK, I just don't spend a lot of time behind the trigger." Not shooting is a whole another ball of wax. I have a buddy who shoots once every two years and will go on a hog hunt without practicing. His last hunt, he shot 25 times to kill 3 hogs. That averages about 8 shots per hog. Little time on the trigger can cause you some grief.

"With this said, how much variance is one likely to get by testing reloads of varying capacity by a difference of .1gr +/-?" I do not see a major variance with 1/10 of grain. I see major variances with 3/10 and or 1 whole grain. Variance = groups opening up from say 1" to 3".

"For my supersonic rounds using 150gr Berrys JHP I'm using H110, I shot a ladder from 15.4gr to 16.9gr (reloading data shows 17.2gr as max charge). I had a case failure at the 16.9gr load (shooting once fired LC brass, case split around the circumference close to the middle of the case) but I'm fine with the velocity of the 16.3gr and 16.6gr loads."
What temperature were you shooting in? Case head separation is usually a sign of a headspace issue. How you size your brass matters. The Hornady manual states that 15.9 grains is the max charge for 150 grain bullets (9th Ed.). The Sierra website states that 16.7 grains is the max charge for 150 grain bullets. 16.9 grains is above max in both cases.

"How much testing and refinement from an accuracy standpoint is a casual shooter able to achieve shooting 100-150yds?" I do not understand this question.

I am happy to help with anything that I can.

TC

 

[BoilerUp]

Interesting. I found the 300 BLK to be one of the easiest to load for. I load H110 exclusively for 300 BLK, but only developed loads for 110 gr to match the TAC-TX or 220gr Berry's subsonic for fun.

Xman, FWIW I get TAC-TX velocities and POI at 18.7gr of H110. For plinking, I load Hdy 110gr SP at 20.2gr of H110 and I get the same POI as the TAC-TX (much cheaper to train with!).

Jelly, even with an EOTech at 20 yards, you should be able to shoot a 3-5 shot group you within an inch or two, you just need to get a bench rest and take your time. If you can't shoot tighter than 6" at 20 yards with EOTech (when bench resting) then there is no point in load development because something is wrong with either the gun or the shooter. And if you are shooting off-hand, well, I don't know what to tell you; you're introducing more variance into the target from your shooting then you are from the loads, which is a waste of time and components.

I wouldn't go lower than .2 gr increments for ladders.

 

[Jellysick]

I've got the Hornady Lock-N-Load Headspace comparator kit out this morning. Using the B-.350 Bushing, here are some initial measurements, random sample of 3 shown for each:

• Factory S&B 124gr 300 BO = 1.052", 1.049", 1.052"
• Factory CBB 125gr MKZ 300 BO = 1.072", 1.074", 1.072"

• Once fired S&B 124gr 300 BO, fired from my pistol = 1.083", 1.082", 1.082"
• Fired reloads using LC Brass = 1.080", 1.075", 1.080" (Sample taken from the ladders of varying charges which I account for the range in measurements)

- Sized 300 BO LC Brass that I'm using for my reloads = 1.077", 1.071", 1.073", 1.074"

So it looks like the should set back is more like .006" - .009", depending on which measurements you take the difference from.

Thoughts on these measurements? I've got 29 rounds in 3 separate ladders that I just finished, planning on testing them tomorrow. If I need to pull them all and start over I will, let me know what you would do. But again, I'm not trying to squeeze every last .25MOA out of these reloads.

Also, I'm not sure if I'm understanding the situation as relates to should set back. I roughly understand what it is. Xman's reference to a .003" bump from fired in my chamber is a recommendation to allow the reloads to cycle while preserving accuracy, is this correct? If I followed the instructions that came with my RCBS 300 BO dies (which I did), would the bump that is greater than the .003" introduce danger into the reloads? Or would it simply have the potential to be less accurate?

I want to do this the right way, just trying to understand the situation a little better. I don't understand if what is being stated by following the instructions from the RCBS dies is actually dangerous? Or if there are simply better ways to fine tune reloads? I'm hoping it's the ladder.

@BoalerUp - fair point on the accuracy statement. I might be able to do that from a rest. My goals with reloading are for the economics of it, and for the flexibility in the projectiles that can be used. Certainly not doing it to squeeze every last .25MOA out of every round, but 4 MOA is probably sufficient in all reality.

 

[just_me_mongo]

"Also, I'm not sure if I'm understanding the situation as relates to should set back." - This is a common issue.

Should bump (or setback) is something that you measure and when factoring in "head space." Here are a few steps to give you comparable numbers.

1. Use the same 300blk pistol for the following steps.
2. Measure a loaded cartridge (headspace comparator). Write down that number.
2. Shoot that cartridge and measure post-firing (head space comparator). Write down that number.
3. Compared the loaded cartridge number to the post-firing number.

Here are your numbers below:

• Factory S&B 124gr 300 BO = 1.052", 1.049", 1.052"
• Once fired S&B 124gr 300 BO, fired from my pistol = 1.083", 1.082", 1.082"

If I read your post right, there appears to be a difference of .031. How I came to that number is by substracting the 1.052 from 1.083 = .031. That is a noticeable a difference from pre-fired to post-fired.

Does this make sense so far? Set-back (when sizing your brass) is getting the brass back to the original number or close to it. Example: 1.083 - .003 = 1.080. However, your unfired cartridge measured at 1.052. If you wanted to get back to your original number, your should bump (setback) would be .031.

Headspace (too much or too little can be dangerous).

TC

 

[Jellysick]

Thanks Just_me_mongo, I do get that much of it. For reference, my measurements were not of the same round before and after firing. I simply didn't keep track of them that way in order to make that comparison. The numbers I stated relating to my reloads could be used as a better before/after comparison:

• Fired reloads using LC Brass = 1.080", 1.075", 1.080" (Sample taken from the ladders of varying charges which I account for the range in measurements)
• Sized 300 BO LC Brass that I'm using for my reloads = 1.077", 1.071", 1.073", 1.074"

The numbers I posted relating to setback - are they within reason to fire? They don't meet the .003" measurement of how much set back to apply, however factory loaded rounds measure much smaller than the LC brass I'm using. This is where I don't know how to apply this information to the situation.

 

[just_me_mongo]

.003 setback would apply to a loaded cartridge that was fired from your 300blk pistol. You would know the pre-fired measurement and compare it to the post-fired measurement. A good example would be if your measurement pre-fired was 1.077. Post-fired, it would measure 1.080. 1.077 - 1.080 = .003. You would apply this number to a cartridge/case that was isolated, same case, measured pre/post, and finalized with a specific number of .003. Does that make sense? You would aim for .003 set-back because you knew the number before and after.

Now if you are measuring "random" pre and post fired cases - you can use a general number for setback. .005 is a good general number but you do not have anything to go off. Does that make sense?

In general,.006 seems reasonable. 1.074 - 1.080 = .006.

TC

 

[just_me_mongo]

What type of barrel do you have? Can you give all the details?

TC

 

[Jellysick]

Ballistic Advantage 8.3” Hanson barrel, pistol length gas system, low profile pinned gas block.

 

[just_me_mongo]

Do you have any other factory ammunition to measure with your headspace comparator gauge? I don't have any factory ammunition to measure to give a comparison to your other factory ammo. These are some of your measurements below:

"Factory S&B 124gr 300 BO = 1.052", 1.049", 1.052"

"Factory CBB 125gr MKZ 300 BO = 1.072", 1.074", 1.072"

The lowest number is 1.049 and the highest number is 1.072. 1.049 - 1.072 = .023. These are pre-fired measurements and I subtracted the two in order show the difference between two unfired - factory cartridges.


Now for the numbers below:

• Sized 300 BO LC Brass that I'm using for my reloads = 1.077", 1.071", 1.073", 1.074."
• Fired reloads using LC Brass = 1.080", 1.075", 1.080" (Sample taken from the ladders of varying charges which I account for the range in measurements.

1.071 is the lowest number and 1.080 is the highest number. 1.071 - 1.080 = .009. In this case, you are measuring pre and post fired cases. If you wanted to get back to 1.071, your setback would be .009.

.003 is not an arbitrary number. It is a specific measurement. I hope that helps.

At this point, I would start from scratch. You can do that by shooting one cartridge, measure pre/post, and get yourself some good numbers. An old school re-loader told me to "SLOW down your reloading process." I recommend that you slow your process down (in any way that you see fit).

TC

 

[Jellysick]

A box from Midway USA just arrived at the door with S&B 147gr 300 BO factory loaded ammunition. These are measuring 1.061", 1.060", 1.059", and 1.060" (from 4 pulled out of one of the boxes).

I opened a different box of S&B 124gr (different in comparison to what was opened to measure previously..): 1.053". 1.052", 1.052", and 1.051".

What is not clicking is the sizing portion of the reloads. I understand .003" is the guidance. My 300BO upper is putting out cases that are measuring ~1.080". What is the danger in sizing my reloads to 1.080 - .003 = 1.077 or sizing them back to 1.080 - 0.020 = 1.060 to match what the S&B factory loaded rounds are measuring? Or even further, 1.080 - 0.030 = 1.050 to match the other S&B factory rounds? Either way, the chamber in my rifle is not changing so based on this thread (which is helpful, by the way), one would think the S&B factory rounds are sized too small for my chamber. Is this what we are saying?

There may be a component to my question above that involves pushing the ceiling of chamber pressure, or even exceeding it. To my knowledge I'm not doing that.

 

[just_me_mongo]

"What is the danger in sizing my reloads to 1.080 - .003 = 1.077 or sizing them back to 1.080 - 0.020 = 1.060 to match what the S&B factory loaded rounds are measuring?"

Sizing back to 1.077 does not seem like an issue. Sizing back to 1.060 seems excessive to me but the proof is in the pudding. That measurement is from factory ammunition (1.060).

"Or even further, 1.080 - 0.030 = 1.050 to match the other S&B factory rounds?"

Sizing back to 1.050 seems excessive to me but - again - the proof is in the pudding. The S&B rounds came that way. A good example is the measurement of .003 set back. .030 is ten times that of .003 (points to a headspace issue).

"Either way, the chamber in my rifle is not changing so based on this thread (which is helpful, by the way), one would think the S&B factory rounds are sized too small for my chamber. Is this what we are saying?"

This is an accurate assessment. That number (1.050) seems excessive. This is especially notable when you compare the fact that your sized/pre-fired LC brass is around 1.071 and your fired LC brass is around 1.080. The difference between the two is .009 versus .030.

"There may be a component to my question above that involves pushing the ceiling of chamber pressure, or even exceeding it. To my knowledge I'm not doing that."

In regards to your LC brass (handloads): the tell-tale sign of danger is the fact that you have experienced case-head separation. This is indicative of a head-space issue. I believe that you may have loaded above the maximum load, too. That can cause a high-pressure situation,which is also dangerous.

The case-head separation is proof that you did something wrong. Trust me, we have all messed something up. I would look at your load data and review the maximum charges of H110 and a 150 grain bullet. I reviewed Hornady and Sierra and both published maximum loads that were less than your stated maximum load in the earlier post.

You are dealing with two issues: Excessive headspace and excessive pressure.

For head-space, take a look at this article:

Read Me

For load data, here is the Sierra Data:

Sierra Data

TC

 

[Jellysick]

Fair enough, let's pick at that scab a bit.

My first mistake here was assuming I was shooting Berry's Bullets, at 150gr when in fact they are Hornady 150gr FMJBT. I bought these around 2 years ago and my 300 BO project was put on hold for a bit. You lead me to realization of this by your comment about being over pressure and that Berrys bullets says not to exceed 1650fps. I am already exceeding that which prompted me to dig into my equipment a bit closer.

Secondly, the load data I am using for this load, which is also the load that had the ruptured case is the data published by Hodgdon, noted here:

A couple other areas that I went wrong are now noted. While I used this load data, the C.O.A.L as noted with this data is 2.235". I am using 2.15 (which is specified in the Berrys Bullets spec). So a shorter COAL plus the higher charge maybe is what led me here?

Hitting the reset button

A bit of research leads me to believe the Hodgdon COAL of 2.235" might be a typo as that is a very long round. I sed reference of folks using 2.06-2.08", some 2.1". The Sierra datasheet you referenced shows 2.140" for C.O.A.L. So starting over and dialing things down. I will leave the size of the brass as is since the only way I'm aware of to make them larger is to fire form them in the chamber. Am I correct here? Once that is done I'll revert to the .003" bump based off of measured rounds from my chamber.

I'll load a ladder starting with 13.8 and proceed in increments of .3gr to 16.2.

When you state I have a "head space issue", is this something specific to my chamber? Or the relationship between the rounds and my chamber? So the "issue" would exist with the factory loaded rounds but given they are a milder load the "issue" never presents itself? Is that a fair statement? Furthermore, as I proceed with reloading, as I size/bump appropriately then this "issue" is no longer present? Is that also an accurate statement?

 

[just_me_mongo]

I forgot about something. Now that you have posted the load data, I forgot to mention trim length: 1.363". Are you checking each sized case for the trim length? That can cause pressure issues, too.

Now for head-space, head-space works with two major items: the brass sizing process & your chamber. So yes to it is a relationship between the sized brass and your chamber. I want to separate the factory ammunition and the handloads.

Factory ammunition: the measurement of 1.050 seems excessive to me. However, that is coming directly from the factory. If your chamber is producing fired brass with a measurement of 1.080, I would not attempt to use the measurement of 1.050. I would be more inclined to use the measurement of 1.071 or (1.075).
The reason is that the case is stretching a lot more in the sizing process to get back to 1.050 and that the case will stretch more in the firing process when it stretches out to 1.080. To me, 1.050 is excessive (excessive headspace). 1.050 - 1.080 = .030. Excessive headspace is when your brass has the ability to move back n forth too much. You are looking for a proper fit as opposed to a sloppy fit. If there is too much empty space, you can experience case-head separation. The brass case is literally separating into two pieces upon firing.

Handloads: the measurement of sized LC brass is 1.071. The measurement of the fired LC brass is 1.080. The setback in this case is .009. .009 may be an acceptable number for the AR-15 platform because it is a semi-automatic rifle. This is a platform that can experience feed issues. If it works, I would aim for a setback of .005 (1.075). You are not stretching the brass as much when sizing and you are not stretching the brass as much when firing.

Now let's compare the numbers for setback: .030 versus .005 or .009. The ideal setback would be .005. This is relative to your handloads because you cannot control the setback on factory ammunition. You also want your handloads to feed properly.

Does that make sense?

"When you state I have a "head space issue", is this something specific to my chamber?" - No. Unless you think your chamber is completely out of spec and poorly manufactured. It is possible but less likely.

"Or the relationship between the rounds and my chamber?" -Yes.

"So the "issue" would exist with the factory loaded rounds" - Yes.

"but given they are a milder load the "issue" never presents itself?" - I will get back to this part.

"Furthermore, as I proceed with reloading, as I size/bump appropriately then this "issue" is no longer present? Is that also an accurate statement?" - Yes, given that your bump is around .005 as opposed to .030 and relative to your actual pre/post fired cases.

TC

 

[Jellysick]

My case lengths for this string are noted to be:

1.357
1.354
1.355
1.357
1.358
1.356
1.356
1.358
1.356
1.356

I did not trim them, this is they I received them. In my notes for 300 BO Cartridge data, case trim length is 1.348 - 1.368, so I have left the case length alone.