Questions about handloading for AR10. Pics inside

[mattmcg]

I am looking for some help with reloading for a new GAP AR10. I'm fairly experienced with reloading for bolt guns but the AR10 is somewhat new to me and I'm a bit confused about what I'm seeing. Figured it best to query somebody with some experience on this.

Yesterday I put together a set of loads to work up to see where pressure signs might arise. I walked away scratching my head a bit as I didn't quite get the typical feedback that I was expecting.

The gun is a DPMS based GAP build with a DPMS upper, DPMS bolt carrier group, and a Bartlein 24" 1-11.25 twist 308 Win barrel with Surefire suppressor adapter.

The loads consisted of Federal GMM 308 Win brass (once-fired), Lapua 155gr Scenar, Fed 210M primer, and Hodgdon Varget powder.

Here are the loads that I put together and the velocities reported by the chrono. These were 5 shot groups.
o 44.5gr, MV=2814fps 1.0" group
o 45.0gr, MV=2846fps 1.3” group
o 45.5gr, MV=2874fps 1.3” group
o 45.7gr, MV=2879fps 1.6” group
o 46.0gr, MV=2891fps 1.2” group
o 46.2gr, MV=2909fps 0.9” group
o 46.5gr, MV=2917fps 1.6” group
o 46.7gr, MV=2929fps 1.1” group

I happened to see extractor marks on pretty much all the loads with slightly heavier marks on the 46.7gr loads (but not terrible). There were no primer expansion marks and all exhibited a bit of gas along the sides of the case (again 46.7gr more so than 44.5gr). All primers were flattened along the top but nothing out of the ordinary. There were no popped primers or other case damage except for the rough brass handling by this setup. I have a feeling that the 46.7gr load was overpressure knowing what other folks are seeing for velocities in a similar gun but I was left thinking I could go higher still. I guess I was extremely surprised to see >2900fps in a gas gun in this caliber.

My questions are:
1. Is it typical to see extractor marks on all AR10 loads?
2. What signs do you look for to signify max pressure? Do you think I was over the limit already on some of these?
3. Given the data above, do the results within a safety margin seem reasonable?
4. Any other thoughts that can help me better understand how to load for this gun?

Thanks in advance for your help. I've included high-res photos of the load lots to look at. I know its a lot of data but am hoping to turn this into a 1K paper punching gun but want to do so without blowing anything up in the process due to my lack of experience with large caliber auto-loaders.

 

[okiefired]

Re: Questions about handloading for AR10. Pics inside

Cant see for sure but are'nt those ejector swipes? If so, its pretty common on 308 AR's. Some say Fed brass is a little softer too.

okie

 

[mattmcg]

Re: Questions about handloading for AR10. Pics inside

Yeah, if you click on the high-res photo links (FYI.... those are 3MB files each) you can clearly see ejector swipes on pretty much all of the cases. Figuring the 308 bolt head turns approx 30 to 40 degrees before going out of battery, the ejector drag seems like it is just the nature of the beast.

And yes, Federal has been soft. I figured working with Federal brass first would display issues with going into/out of battery before other brass manufacturer's. Figure it a good test piece to showing anything seriously out of whack.

 

[bfoosh006]

Re: Questions about handloading for AR10. Pics inside

http://www.davidtubb.com/ar15_cws.html ...have you considered one of these? I don't know if it will fit your DPMS, but the one in a AR15 worked wonders on recoil (softened up the recoil "impulse")and pressure signs. Give them a phone call and check to see if it would work with your rifle.
And while you are at it...check n' see if their Chrome Silicon buffer spring will "fit" your DPMS. http://www.davidtubb.com/tcom_images/ar15_images/cs_buffer.html

Any-who..if it was me working up those loads...I'd get those two items, and then try the same loads over again. Keep the pictured brass and compare the second identical set. ( I'd love to see the next batches photos.)

 

[coues7]

Re: Questions about handloading for AR10. Pics inside

tag

 

[mattmcg]

Re: Questions about handloading for AR10. Pics inside

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bfoosh</div><div class="ubbcode-body"> http://www.davidtubb.com/ar15_cws.html ...have you considered one of these? I don't know if it will fit your DPMS, but the one in a AR15 worked wonders on recoil (softened up the recoil "impulse")and pressure signs. Give them a phone call and check to see if it would work with your rifle.
And while you are at it...check n' see if their Chrome Silicon buffer spring will "fit" your DPMS. http://www.davidtubb.com/tcom_images/ar15_images/cs_buffer.html

Any-who..if it was me working up those loads...I'd get those two items, and then try the same loads over again. Keep the pictured brass and compare the second identical set. ( I'd love to see the next batches photos.) </div></div>

Bfoosh,

Frankly, I'm not at the stage to know if I have a problem where the Tubb extra weighted buffer would solve it.

If I read between the lines, I think you are suggesting that the gas pressure from the fired cartridge is prematurely forcing the bolt out of battery with high pressures still in the barrel. Thus the reason for external gas remnants on the case and heavy extractor marks on the brass base. Am I correct in interpreting why you suggest the Tubb products?

 

[okiefired]

Re: Questions about handloading for AR10. Pics inside

I'm a little comfused about your querry. Are you asking about ejector swipes or extractor marks? BTW, the Tubb CWS did'nt effect the ejector marks on my AR10T but it sure tamed the recoil and violent cycling of the 308.

NEVERMIND, I answered my own question. Sorry.

okie

 

[mattmcg]

Re: Questions about handloading for AR10. Pics inside

Sorry, a lot of detail there I know. As listed in OP:

My questions are:
1. Is it typical to see extractor marks on all AR10 loads?
2. What signs do you look for to signify max pressure? Do you think I was over the limit already on some of these?
3. Given the data above, do the results within a safety margin seem reasonable?
4. Any other thoughts that can help me better understand how to load for this gun?

 

[Jumper]

Re: Questions about handloading for AR10. Pics inside

Nothing about you loads seem abnormal to me. The ejector spring on my AR10T is extremely stiff. So I'm not surprised to see ejector marks on relatively soft Federal cases. I looked at your primers and they don't look like they are high pressure to me.

 

[sinister]

Re: Questions about handloading for AR10. Pics inside

1. Is it typical to see extractor marks on all AR10 loads? <span style="color: #3333FF">Yes</span>

2. What signs do you look for to signify max pressure? <span style="color: #FF0000">Flattened primers; cratered primer impacts (the rim around the firing pin indent will be raised as brass tries to flow between the firing pin hole and the firing pin tip); pierced primers; primers backing out of their pocket; brass flowing into the extractor hole; smeared extractor marks on the case head; rims partially pulled off the case head. </span>

Do you think I was over the limit already on some of these? <span style="color: #3333FF">No.</span>

3. Given the data above, do the results within a safety margin seem reasonable? <span style="color: #3333FF">Yes.</span>

4. Any other thoughts that can help me better understand how to load for this gun? <span style="color: #3333FF">Use a reloading manual (I recommend the Lyman 49th Edition as they seem to have the most realistic loadings of all major loading component manufacturers' manuals). Recommend you not exceed the requirements for the M14 and use a medium burn rate powder (IMR 4895; Varget; N135; Reloader 15; IMR 4064).

Although the ARs don't have a piston the bolt carrier group will start to unlock as gas pressure overcomes the inertia of the bolt carrier group and buffer assembly. Smoked brass indicates the cases were not obturated to the chamber walls and gas pressure was still high enough to foul them as extraction began. Your primers look like they still have nicely rounded radii and case smoking isn't bad at all.

The Tubb CWS in an AR-10 seems to help in NOT abusing your brass (unlocking and extracting is delayed long enough your cases aren't all dinged up or elongated). I use one in conjunction with a Slash very heavy buffer. </span>

 

[mattmcg]

Re: Questions about handloading for AR10. Pics inside

Yes, I use the Speer and Lyman manuals as well as worked up all of these loads in Quickload before putting them together. On paper they looked good although the pressure estimates north of 46.0gr were above SAAMI specs.

Sinister, what was the difference when running the Slash very heavy buffer? Was it simply increasing lock time and reducing barrel pressure before case extraction? How much of a change did you see? Was brass smoking reduced?

I guess I was a bit surprised to see >2900fps on these loads without overpressure scenarios.... I'm still skeptical.

 

[mattmcg]

Re: Questions about handloading for AR10. Pics inside

Also with increased lock time, would I see a reduction with ejector swipe marks?

I also happened to come across LowLight's debate thread about AR10's prematurely going out of battery and displaying a flash from the ejection port. If true on KAC SR25 rifles, this would lead me to believe this is endemic to this type of gun thus requiring a heavier buffer than currently specified. So why aren't folks like KAC and DPMS increasing the AR10 rifle buffer weight then?

 

[sinister]

Re: Questions about handloading for AR10. Pics inside

Lock time is the time from pulling the trigger to the primer going off -- this is faster with a striker-fired bolt action than a hammer-action semi-automatic.

Dwell time is the time from initiation of the firing chain (the primer starting the ignition/burn of the powder charge) to initiation of movement of the bolt carrier and buffer groups as gas pressure pushes the mass to the rear.

Yes, both the Slash HSS buffer and Tubb CWS (tungsten insert) help delay unlocking and extracting. Cases are much cleaner and ejector plunger smear is minimized. On the down side they can add up to a half-pound or more to the overall weight of the weapon.

The designers and manufacturers of semiautomatic rifles are concerned with the weapon cycling and shooting accurately -- they are NOT concerned with the condition of your brass and components. The rifle may be specified to shoot GI Ball/tracer and AP, and a heavier combined bolt carrier/buffer group weight may affect the cycling of a rifle fitted with a suppressor.

Manufacturers must tolerate the criticism of the jackass using surplused 3rd-world ammo as well as the precision shooter. They can't make everyone happy.

Let's say 1,000 people buy an AR-762. My guess is over 75% will shoot random .308 ammo, perhaps surplus bulk-pack 7.62 surplus. 20% will fire premium match ammo, with perhaps half of those reloading. Many will never shoot more than 500 rounds (if that many) with the original owner.

Maybe 5% (or less) will compete or work with their weapon and possibly ever wear out the first barrel and fit a second.

 

[Falar]

Re: Questions about handloading for AR10. Pics inside

I have 0 experience with a DPMS LR-308 like yours, but I do handload for an AR10 and the same principles should apply. I've posted a tech note from Armalite in this forum before about how swipes are normal with the AR gas system. I do get them with a few factory loads in both my AR15s and my AR10. Here is what my brass looks like with 46.5gr Varget and 155gr Scenars:

That isn't a loose primer, I decapped it to look at it. I get those swipes down to even 46gr and the primers never get flat. Your velocity is much better than mine, so condsider yourself lucky. My 21" Noveske barrel only gets me about 2800fps with 46.5gr. I've since added the Tubb CWS and it has decreased the swipes about the equivalent of losing .5gr powder charge. I've never loaded over 46.7 myself, so I don't know what max truly is in this gun with 155s, Winchester brass, and Varget.

 

[mattmcg]

Re: Questions about handloading for AR10. Pics inside

Falar, that is great feedback. It seems that your data aligns well with what I posted.

I do believe after discussing this with some knowledgeable folks that AR-10s or notoriously overgassed and the ejector swipe is a direct result of too short of dwell time leaving too much rearward pressure on the bolt face while it rotates out of battery.

I'm going to play around with what Sinister recommended and see if I can make an apples to apples comparison with the same loads and only increasing the buffer weight. Should have some good comparison photos in about two weeks to see if the hypothesis is proven.

 

[Slash]

Re: Questions about handloading for AR10. Pics inside

Hazardus - Your buffer will ship tomorrow and you should have it on Saturday. Please keep me posted on the results.

Thanks for your business.

 

[sinister]

Re: Questions about handloading for AR10. Pics inside

Slash, you the man.

 

[mattmcg]

Re: Questions about handloading for AR10. Pics inside

Thanks Slash. Increasing the buffer weight from 5.4oz to 9.5oz should increase dwell time but I'm not sure how much effectiveness this will actually display. Thus the reason I'm keeping my test brass for an apples to apples comparison.

Here are my priorities in testing this.

1st priority: Maintain weapons reliability & usability
-No increase in FTF
-Retain consistent lock back on last round
-No short stroking
-Similar or reduced recoil properties
-Acceptable brass extraction properties

2nd priority: Brass treatment & ballistic performance
-Reduced ejector swipes
-Reduced extractor marks
-Reduction in smoking of external case (back pressure)
-Increased bullet velocities

If any of you can think of others, I'll add them to the list.

 

[sinister]

Re: Questions about handloading for AR10. Pics inside

1st priority: Maintain weapons reliability & usability
-No increase in FTF <span style="color: #3366FF">Shouldn't be a problem</span>
-Retain consistent lock back on last round <span style="color: #3366FF">Shouldn't be a problem</span>
-No short stroking <span style="color: #3366FF">Shouldn't be a problem</span>
-Similar or reduced recoil properties <span style="color: #3366FF"> The rifle will definitely recoil differently as the reciprocating mass is heavier -- you may not like the result -- I have a muzzle brake</span>
-Acceptable brass extraction properties <span style="color: #3366FF">Should improve</span>

2nd priority: Brass treatment & ballistic performance
-Reduced ejector swipes <span style="color: #3366FF">Check, but I use both the Slash HSS AND a Tubb CWS, combined</span>
-Reduced extractor marks <span style="color: #3366FF">Check, but I use both the Slash HSS AND a Tubb CWS, combined</span>
-Reduction in smoking of external case (back pressure) <span style="color: #3366FF">Check, but I use both the Slash HSS AND a Tubb CWS, combined</span>
-Increased bullet velocities <span style="color: #3366FF">I doubt it</span>

 

[mattmcg]

Re: Questions about handloading for AR10. Pics inside

Just to update this thread. Slash sent me a solid stainless steel extra heavy AR10 buffer (10.2oz) that wouldn't insert easily into the buffer tube without a shim as it didn't have the side relief cuts. It was also lacking the reciprocating weights inside since it was a solid buffer.

With the buffer not able to be installed easily or easily removed in the field, I exchanges the solid SS buffer for a modified AR10 regular buffer with the standard steel weights swapped out for tungsten weights (5 I believe). This retains the reciprocating weights which were originally designed as part of the buffer to reduce bolt carrier bounce. I'm pleased with the construction of the modified buffer. It also weighs in at 10.2oz.

This evening I loaded up identical rounds to those listed above and will be heading to the range tomorrow to go through the exercise again. I also included a few extra light loads to function test (bolt locked back on last shot). I should have some good comparison photos as well as comparative field data tomorrow evening.

 

[mattmcg]

Re: Questions about handloading for AR10. Pics inside

Wanted to close out this thread with a summary of my findings. I did take pictures but frankly, it was difficult pictorially to tell any difference from the photos in the above posts. So rather than post them, figured I would provide a point-by-point summary. Here are my findings.

1st priority: Maintain weapons reliability & usability
-No increase in FTF: Achieved. All rounds fired without a hitch.

-Retain consistent lock back on last round: Achieved, I did not experience a single failure to lock back on last round and loaded 2 rounds per mag, the same as before.

-No short stroking: Achieved.

-Similar or reduced recoil properties: The perceived recoil was definitely reduced by about 10%-15%. Frankly, the whole mechanism felt like it ran better than with the lighter buffer, almost as if this 24" barrel with full gas was designed for the heavier buffer. I can explain it by saying there was a reduction in the violent movement of the BCG before, tamed with the heavier buffer. Definitely felt like a functional improvement and would seem to lighten the load on working parts to increase their lifespan (especially the locking lugs). Things ran much smoother with less jerking.

-Acceptable brass extraction properties: Achieved. Brass extraction functioned well.

2nd priority: Brass treatment & ballistic performance
-Reduced ejector swipes: Achieved. The ejector swipes were reduced across all load variations by about 25% if I had to put forth a percentage.

-Reduced extractor marks: Achieved. This was a more noticeable reduction than the ejector swipes and was quite pleased with the result. The brass was not as torn up as the original lot and could only be attributed to increased dwell time lowering pressures before extraction.

-Reduction in smoking of external case (back pressure): Achieved but to a lesser degree. I'd guess a 5%-10% reduction overall but smoking was still apparent, even on the lower charged rounds.

-Increased bullet velocities: Inconsequential. My second day was 10F less in temp and the velocities were consistent with what I had witnessed during the original shooting session. I was using Varget as well which is a temp insensitive powder so while it might have been a bit better, it was in the noise. Increased dwell time in this case didn't have an effect on increased velocities.

So there you go. I can recommend Slash's standard heavy buffer weighing in at 10.2oz and think it was a worthy tuning for this gun. I'm pleased with the result and will try to run some hotter loads than this to see where the performance well is.

 

[Ghogs Nightmare]

Re: Questions about handloading for AR10. Pics inside

Thanks for the info...was noticing my brass was getting beat now an then as well.
.
Anyone ever do any longevity testing in regards to if these measures weren't taken how long before the brass started becoming weak?

 

[Grump]

Re: Questions about handloading for AR10. Pics inside

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hazardus</div><div class="ubbcode-body">Yes, I use the Speer and Lyman manuals as well as worked up all of these loads in Quickload before putting them together. On paper they looked good although the pressure estimates north of 46.0gr were above SAAMI specs.
[snip]
I guess I was a bit surprised to see >2900fps on these loads without overpressure scenarios.... I'm still skeptical.
</div></div>
A couple of cautionary notes here:

1. Did you run QuickLOAD with YOUR chamber's actual water capacity value, based on at least three readings for that brass? If not, re-do it. I have found that available case volume is a major factor.

2. Do your velocities closely match what QuickLOAD predicted? If not, I would NOT rely much on the pressure predictions.

Because primers *can* mushroom and look nasty-overpressure with short ammo fired in a long chamber, my skepticism in using them for pressure signs extends even to primers that look as "nice" as yours. IME, tight tolerances and/or harder primers can fail to warn of pressure--and they don't quantify pressure at all.

The dwell time discussion above is spot-on. Metals flex, and unlocking the action after the bullet has passed but before pressure has subsided below some (unknown to me) value will result in ejector swipes. I'm more concerned with bumps being left in the caseheads--did the brass flex back??? I know older FC brass could show damage like that from being once fired in factory loads at 110 F or so. Those loads, however, just might have been overpressure in those rifles at those temps (two bolt guns).

Specifically, I've decided to NOT use 46.0 VARGET in my 22-inch rifle because with my case capacities, the only way for QuickLOAD to predict the velocity I was getting basically was to increase the burn rate to a point where the pressures were too many thousands above spec for me to like it. I tried fudging bore cross-sectional area to equal a full .001 tighter bore, but that didn't come close. 2826 fps out of a 22-inch barrel was the real-world result, but adjusting QuickLOAD to get that velocity predicted too much pressure. For reference, 46.0 VARGET is 1.2 grains over Sierra's max load using FC cases, and their max of 44.8 is supposed to go 2800 fps from a 26--TWENTY-SIX inch barrel. Educated guesstimates of 25 fps per inch says I should have been getting no more than 2700 fps with that powder (others can beat it by 100 fps, according to Sierra).

So, when QuickLOAD--as adjusted--said 46.0 could give me 2826 fps with 155s out of my chamber, but only with a pressure I didn't like, I believed the primers.

I'm not confident that your 24-inch barrel can get more than 2800 fps with any powder and 155-gr bullets without being overpressure. You'll have to decide for yourself what you're willing to live with, regardless of what the brass and primers *might* be trying to tell you.

FWIW, current-production FC factory loads and 1x-fired brass do NOT give me any ejector swipe in my M1A, unless the reload is hot enough for QuickLOAD to be giving me warnings for the actual velocities obtained.

 

[Pogo57]

Re: Questions about handloading for AR10. Pics inside

I'd suggest a reading of Zedicker's "TThe Competitive AR15: the ultimate technical guide" and concentrating on the big Rifle section to see how to fix these problems common to the big AR's.

http://www.zediker.com/books/ar2/ARII_main.html

 

[fredreded]

Re: Questions about handloading for AR10. Pics inside

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hazardus</div><div class="ubbcode-body">Just to update this thread. Slash sent me a solid stainless steel extra heavy AR10 buffer (10.2oz) that wouldn't insert easily into the buffer tube without a shim as it didn't have the side relief cuts. It was also lacking the reciprocating weights inside since it was a solid buffer.

With the buffer not able to be installed easily or easily removed in the field, I exchanges the solid SS buffer for a modified AR10 regular buffer with the standard steel weights swapped out for tungsten weights (5 I believe). This retains the reciprocating weights which were originally designed as part of the buffer to reduce bolt carrier bounce. I'm pleased with the construction of the modified buffer. It also weighs in at 10.2oz.

This evening I loaded up identical rounds to those listed above and will be heading to the range tomorrow to go through the exercise again. I also included a few extra light loads to function test (bolt locked back on last shot). I should have some good comparison photos as well as comparative field data tomorrow evening. </div></div>

Where did you get the heavy buffer with the reciprocating weights?

 

[fredreded]

Re: Questions about handloading for AR10. Pics inside

Or... Where can you just get the tungsten weights?

 

[fredreded]

Re: Questions about handloading for AR10. Pics inside

What would be the advantages of increasing BCG mass rather than just installing an adjustable gas block?

 

[MitchAlsup]

Re: Questions about handloading for AR10. Pics inside

All I can say, here, is that the primers are showing no excessive pressure indications, and the soot on the necks are a general indiation of too low a pressure not to high {But with semis it can indicate unlocking with pressure still in the barrel.}

You might want to rerun this load workup with Win or Lapua brass.

 

[mattmcg]

Re: Questions about handloading for AR10. Pics inside

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fredreded</div><div class="ubbcode-body">What would be the advantages of increasing BCG mass rather than just installing an adjustable gas block? </div></div>

Frankly, the adjustable gas block is a preferable solution to just adding reciprocating mass. Adjusting the gas volume to tune the rifle is really the correct solution. I've got a 22 inch LR-308 upper (a JP variety with adjustable gas block) that I'm going to begin testing soon with a standard AR10 weight buffer. Reduction in reciprocating mass should also help with decreasing felt recoil as well. We'll see how it goes.

It is apparent that the gas block on my original rifle in the OP was overgassed and Slash's extra heavy buffer was needed since the gas port was already drilled and fixed gas block mounted.

 

[mattmcg]

Re: Questions about handloading for AR10. Pics inside

Another couple of points to add to the above post.

Some folks like slightly overgassed as this ensures better semi-auto reliability, especially when the dirt, sludge, and other crud gets into the action. For military applications, this may be preferred.

The other downfall with adjustable gas blocks is that most are clamped on rather than pinned. This can reduce the reliability of the gas block as well for those folks that must have their gas block pinned.

 

[338LM]

Re: Questions about handloading for AR10. Pics inside

Did you try replacing your GMM brass with Winchester brand .308 brass?