AR Comp Reloads and new barrel from Shaw

[grendeldude]

I have had a grendel for a few years now, actually its the 6.5 LBC from BHW. I put the rifle together myself and have done many AR builds for about the last 10 years. After some tweeks the rifle runs great now. For 2021 I decided I wanted to deer hunt with the grendel, mine for some reasons unbeknown to me know was cerakoted in a nice silver, not ideal for hunting. Back late in 2020 I started thinking about this build, as it were shaw had some closeout barrels on sale, great deal, but only 18", but the price was very good. I just got around to the build and shooting it the last few weeks and run into a few issues.

I dare not try the same loads in my lbc as my new shaw barreled gun, so I started low. Everyone on this thread seems to love AR comp, and I do as well. I loaded up some 123sst and started at 26 grains and went up to 27.5 grains. Now there is no published data on this load, but a ton of guys on here using this combo as well as a bunch of youtube guys with great success. I started seeing pressure signs early in the string, but probably against my better judgment finished it out. I never blew out any primers, had no ejector marks, but for sure had some cratering and bulging. some this was even at the lowest loads. After thinking about this a while it came back to a tired topic that is probably many places on this forum. Did I buy a type 1 or type 2 shaw barrel, I was positive it was a type 1 the same as my lbc, as I wanted them to be the same and shaw let you choose at the time. After phoning shaw they confirmed that it was a type 1 barrel. Someone posted a video on here of BHW trying both bolts, anyway it does not appear a type 1 bolt would fit and function in a type 2 barrel anyway. So now I am 100% confident I have the correct type 1 or AK style bolt.

Went to the range again, this time same combo but starting loads much lower and rem 7.5 primers, not cci450. Got to around 26.5 before seeing any issues, and again went all the way to 27.5, no ejector marks, less primer bulging but stills some. Velocity at 27.5 with the 123sst is right at 2450, which seems about right. I cannot figure out what is causing this issue with the primers, yes its a probably a hot load, but not excessive based on other reports. Any suggestions on what may be causing this? Next trip I am going to try some hornady factory loads with same bullet, and see if the same issue happens. I must have a headspace issue if it happens with factory ammo I would think... Please help, deer season is coming up fast...

[Bobke]

[grendelnubi]

Your AR Comp 123 grain load data / FPS aligns with my load data so I think you are close to where you need to be. I have found 123 factory loads are slightly hotter than my reloads so I feel they are safe.

You may check a few things;
1. Check for excessive carbon buildup in your chamber.
2. Check to see if you are over gassed. Your bolt could be unlocking a little too early.
3. What is your primer pocket depth in your brass? I have found that I have to ream mine out a little to at least .122 thousands to get the primer below case.
4. What brass are you using and how many reloads?

Reason I am asking about brass is I first started with Hornady brass and over the last several months I have started using Starline brass. I have about 10 reloads on my hornady brass which is starting to show early signs of pressure now, (usually ejector swipes for me) so I believe it is getting soft maybe? In contrast the same loads in my new starline brass shows zero signs of pressure. For you, if this is new brass you may not be seeing pressure signs on the brass yet.

Just my thoughts....

[grendeldude]

Wow, I actually have the same brass situation, I had hornady for a long time, and was able to get 300pcs of starline awhile back. The primers in the starline seat plenty deep enough as far as I can tell, its a brand new barrel so and I did a proper break in and cleaning so dont think it is a carbon build up issue. Brass was brand new, 2 firings on them now... The over gas issue is interesting, as I did not use an adjustable gas block in this build? Was unaware that could cause an issue, just thought it would be about the function of the gun more than anything. I figure I probably losing around 60fps with the 18" barrel.
The accuracy was excellent, Sd was 8, first time out I actually got a 5 shot 1/2" group. By all accounts this should be a safe load, so it leaves me searching what the issue could be... I love the grendel round, I want to get this thing figured out before hunting season... By all accounts I should not have to go into the woods with 2300fps rounds, I should be able to get more out of it safely than that...

[VASCAR2]

https://www.righttobear.com/rca-adjustable-gas-key-1ad-gky/

[grendeldude]

I do not have access to quick load, however I just watched a youtube with Hazzbro, in the comments someone said 27.2 is over 60,000psi per quick load. Does anyone know if this is correct? So many folks seem to be using hotter loads than this... Also, I find it odd that the only pressure sign is the primer, no extractor marks whatsoever, is this normal? In the past like with 300blk I always noticed flat primer and extractor marks on the brass if I was to hot. Hazzbro in his comments claims the starline brass has way less capacity than the Hornady. I think I will shoot some of my hornady brass and see if the same issue happens. As far as the gas condition, if anything it would seem I am undergassed and or as above stated I have a tight chamber. The only time I got a good extraction was in the hotter loads, above 27 gr, the lower loads failed to extract or just dumped on the bench barely coming out of the gun. I was single loading from a Amend 2 magazine. The last round I fired 3 rounds and all worked perfectly with the 27.5 loads.

[VASCAR2]

[grendeldude]

Shaw responded they use a .093 gas hole in their barrels. Don't think over/ under gassed is the issue. Factory loads will be here by the weekend, will do test with starline brass, Hornady brass, factory ammo, using magneto speed chronograph. If I can safely get past 2400fps I can be fine with it. Group size so far has been outstanding.

[mdram]

i tested up to 27.6 with no pressure signs
settled at 26.8 for 2450fps from a 20" barrel

[Mesa1978]

I have an AA Overwatch, Shaw barrel, 27.5 AR Comp works well.

[grendeldude]

I noticed on some other reloading sites that short brass may cause the a primer to bulge. I measured both my 2x shot and brand new starline, and most of them are well short of the normal trim to length listed, which is 1.516. Most once fired are measuring 1.505, my hornady brass measures 1.510 to 1.512. The brass has not seemed to stretched after two firings? Could this be the issue with the primer bulging, factor starline brass is to short? I got two batches from two sources, one from Midway and another cant remember, both seem to measure the same. Should I contact starline and get a response?

[mdram]

I noticed on some other reloading sites that short brass may cause the a primer to bulge. I measured both my 2x shot and brand new starline, and most of them are well short of the normal trim to length listed, which is 1.516. Most once fired are measuring 1.505, my hornady brass measures 1.510 to 1.512. The brass has not seemed to stretched after two firings? Could this be the issue with the primer bulging, factor starline brass is to short? I got two batches from two sources, one from Midway and another cant remember, both seem to measure the same. Should I contact starline and get a response?

per hornady manual max length is 1.52, trim to is 1.51
i run through a trimmer at 1.51 every firing. most cases dont get trimmed but a few do
it will also vary based on your annealing

[Dt219]

My starline brass is well short of what the hornady brass is also

[Lemonaid]

If you have a spare firing pin it might be worth it to swap it and see what happens, better or worse or the same.

[grayfox]

Did anyone mention that seeing "cratered" primers can also be caused by the primer metal flowing back into a somewhat larger firing pin hole... so a "crater" is not necessarily a sign of overpressure.
My batch of starline brass (very good by the way) is a little smaller capacity than my hornady, but not a whole lot. I forget the exact measurements but fraction of a grain of H2O.

I have in two batches of AR comp one batch that wants to go 28.0-28.4 for ~2510 fps (20" barrel), and the other batch uses 27.4 gr for same MV. It is hotter but it's a variation due to lot number. If you have a chrony you should use it to help determine what loads your barrel can do, with that batch of powder. None of my loads are over pressure in my barrels. ymmv and usual disclaimers.

Hopefully your calipers/trim routine can measure to the 0.001, you need that type of precision for good trims. 1.520 max, 1.510 min.

A load that is too underpowered can be limited on its ability to full-cycle the bcg and extract properly.

Also with most new barrels they will "speed up" after about 100 rounds, can give you 50-100 fps more MV, which in reality means your favorite "pet" load will start shooting too slowly and open up on paper.