The perplexity of ar10 loads

wvfarrier

wvfarrier

Ignorant wretch
Full Member
Minuteman
Dec 7, 2012
2,892
5,466
West (By GOD) Virginia
#1
I am currently running a 20" Wilson Super Sniper in 308 Win lately. It been amazing and is absurdly accurate. I also shoot a Seekins PWS MK218 which is another excellent rifle. Something I have noticed with both as I develop loads for them: Even factory 147 gr FMJ tend to have substantial ejector swipes and flattened primers. I was running Aguila today and all the casing are non-reloadable due to ejector peel marks, from both rifles. I tried some handloads I was working up for a bolt gun, a minimum charge of Varget, same thing. Is this a common issue with AR10s? I will admit I do not shoot mine often, its usually a 300blk or one of my bolt action rifles. It seems a waste of good brass.
 
#5
It's really the nature of the beast. Fine tuning the buffer weight, spring selection and gas does help but doesn't 100% eliminate the problem. I've managed to greatly reduce the severity of it but it still happens inconsistently. I can fire five of the exact same cartridge/load and I might get three with light peeling and two with none. No rhyme or reason. I've tried different buffer weights and went to a Tubb spring. But running a slightly heavier buffer and then the next weight up, no difference. The only thing that does eliminate it is turning the gas way down to the point the rifle won't cycle.
 
#7
Throw the Aguila brass away.
I had found a good load using hornady brass for a gas 6.5cm and decided to play with different types of brass. All exact same trickled charge weights. I got really bad pressure signs with the Aguila brass. Swipes, cratered/pierced primers, you name it.
I now only use hornady brass in my gas 6.5cm (because it doesn't bother me if I lose it) and peterson in my bolt 6.5cm.
 
#8
FWIW, I run KAK 9.3oz 308 length buffers in my rifle stocked LFAR's, with a 308 Tubbs Flatwire recoil spring. SLR Adj. GB

You might consider up'ing the buffer weight. And then re tuning the Adj. GB.

BTW... Pics of the brass ?
 
#12
Assuming the case damage is rough treatment of the brass due to the gas system, and not actual pressure signs, run the case head across a file to knock down the burr and reload the brass.

As noted above, you can mitigate the worst of it with gas system tuning (gas block, buffer weight, buffer spring), but AR10s are harder on brass than bolt guns.
 
#13
Lake city brass is heavier and hits pressure faster that's a max load you made not minimum if you want a benchmark I shot lots and lots of LC brass, 175smk and 41.5 H4895 or 41.5 Varget through my M1A, for plinker loads 42-42.5 grains of TAC and a 150gr bullet.

Ohh damn those aguilas look rough maybe you have a sharp edge on the extractor/ejector too.
 
#15
It's gassing and dwell.
Here's 155gr Hornady Match, 45gr Varget, and Starline brass. This is over 100% case capacity and doesn't ruin brass.

Edit: Low Mass BCG, 2.2oz buffer.

 
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#17
Yesterday. Some have the swipe marks, some don't. Each row of five is the same load, ladder test. So even the hotter loads don't always show swipe. It's consistently inconsistent. Was using a higher back pressure can this time around. She cycles 100% of the time now and is ejecting at 3 o'clock exactly. Locks back on empty mag. I may try a smidge more buffer weight and see what happens.

I wet tumble with stainless media so any raised portions get knocked flat. I have no problem reloading them.

 
#18

Barrel length and gas system length? The gun is unlocking early and looks pretty consistent. It is always gassing and dwell with DI guns. 308 Win is more sensitive to dwell than 223/556, especially with shorter gas systems.
 
#20

Lake City 7.62 brass is all over the place regarding internal capacity...as in you'll see a 2% spread across that many cases. That may explain why you are exhibiting pressure signs on some, and not on others.
 
#22
Good point on the LC brass, I should probably sort by year but I'm going mostly for practical accuracy out of the gas gun. I will say that it does it on mild loads, factory loads, pretty much anything. They aren't pressure signs though, it's the ejector making marks from the bolt unlocking early. It's always done this, three different bolts, two different barrels, numerous springs, buffer weights, charges, and on and on. A cold gun does it less. As the gun heats up, it sort of stabilizes and does it more frequently but still ejects a few pristine cases every now and again.

I do need to check with my Huxwrx and the new spring. These were shot using the RD LS3 which is a low back pressure can but not a true flow through like the Hux.

On Cascade Hemi's last question, yes I can turn the gas down but it won't cycle as reliably as it does now. I'm actually debating purchasing another barrel but I really don't want to go much longer than 16" as it's a lightweight (under 7 pound) rifle and I'd like to keep it that way. I could likely be talked into an 18", maybe.
 
#23
Heavy buffer with a JP FMOS solved all of my ejection/feeding/brass problems on two different AR10s.

I am in the process of building a lightweight .308 so I'm going to try the LMOS and a lighter buffer on that one...we'll see.
 
#25
I saw the OP said he can’t run JPs parts but this info may still be helpful. I had a conversation with a JP engineer last year regarding same issue and not the best accuracy (reloads). He explained that I’m not seeing pressure, but the bolt unlocking a bit early while the case is still expanded (not moving) in the chamber. The ejector is being run across the brass as the bolt unlocks, sometimes causing the swipe. This is a byproduct of a lightened carrier / buffer. He suggested a heavier carrier (I was using their lightened carrier). He also said that the heavier carrier will help with accuracy as well. He also said to ensuring my adj gas block was adjusted properly and not over gassed. I bought JP’s adj weight carrier and started with the weights that come on the carrier. I also re adjusted my adj gas block. I immediate saw a significant difference in (less) ejector marks and accuracy increased. JPs engineer said that the downside of the heavier carrier is more recoil as there is more mass traveling back and forth. He said if the rifle is mainly for LR precision than the weighted carrier isn’t a big deal, and I didn’t really notice a difference (20” barrel / NF ATACR 4-16). He said if you are running 110gr Hornady’s in a 16” 3gun rifle for HM Div, then the light carrier is what you want. Hope this helps.
 
#26
Ok I gotta talk through this so excuse my potential ignorance. The gas port is more than adequately sized to cycle the bolt despite the fact there isn't a lot of dwell time vs say an 18" barrel. If it's unlocking early, that would come down to the gas port location as well as the gas port size (amount of gas entering the gas tube) if it's a non-adjustable, no? The dwell would only figure in to uncorking the system and stopping the flow of gas through the gas tube to the bolt carrier. Assuming the gas port is theoretically sized properly and the port is 100% open, and the gun would NOT cycle reliably, it'd be a dwell time issue, no?

If my bolt is indeed unlocking too soon, I don't think that's a dwell issue. I need to hold the bolt closed longer so that'd be a heavier spring (preferred) and then a heavier buffer in that order of trial with possibly a gas adjustment to fine tune. I have adjustable buffers so I can do just about any combination I want of tungsten, steel and aluminum weights. I also have two different buffer bodies, one heavier than the other.

I'm currently on the .917 plunger with the Riflespeed gas block but I'm on the lower end of the operating range. Going to try the .924 which should put me right at 6 in the adjustment range.
 
#27
I'll have to weigh my carrier. Not sure if it's full weight or not but pretty sure it's not. It's not made out of titanium and not lightened/relieved in any way but it's essentially a small frame AR10 though so the bolt is lighter/smaller and I'm guessing the carrier is lighter than something like DPMS or Armalite. Interesting info none the less. Food for thought.
 
#29
LaRue solved the ejector extrusion swipes with a large kidney-shaped ejector in bolts on the newer .308 and 6.5CM gas guns.

LaRue’s biggest fan/ie @bigjake83 posted pics of all those new updates in his detailed threads about those rifles.
 
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#31
For the OP, make sure your ejectors outside edge is free of any sharp edges. And smooth the radius edge.

Not a fix, but a smoother surface on the case head.
 
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