1911.COM : AR-10 General Discussion : AR-10 General Discussion : DPMS Panther 308 AP4

Posted: Oct 16th 2009, 04:27 PM

Hi, I am new to the AR-15 forums and I was hoping this would be a good place to get some ideas to resolve some of the issues I am having with my AR-10. I recently put together a custom AR-10 that would be California legal. I am using a CMMG (DPMS compatible .308) lower and a DPMS Panther 308 AP4 upper assembly. My lower assembly has a bullet button installed to make it California legal. An easy fix to a very convoluted and irrational legislation against assault rifles.

At the range, the first round fired just fine. However, when I attempted to fire off the second round, (click), nothing happened. When I pulled the charge handle, no round came out. I am guessingthe consecutive rounds after the first one did not get stripped from the magazine. I have to pull the charge handle after each shot in order to strip the round from the magazine. This problem is intermittent. Sometimes it will strip the rounds fine for a couple of shots, but eventually the bolt misses the round. Other times I have to charge the round manually after every shot. I have put a lot of thought into this problem and I believe it could be a number of different issues.

I am using the correct DPMS .308 buffer spring and buffer pad, so I think the problem could be related to the spring tension of the factory .308 buffer spring. Maybe the bolt carrier group is not being forced far enough back for the bolt to catch the rim of the .308 case.

When I was cleaning my bolt carrier assembly after my day at the range, I realized just how big and heavy the bolt carrier group was. I think the problem could also be the amount of friction against the inside of the upper assembly that is slowing the bolt down before it can reach the rim of the .308 case.

Is there anyone out there that has experienced the same problem or a problem similar to this one? What did you do to fix it? Any suggestions to fix this issue? I appreciate any suggestions. Thanks.

Joined:
Location:

Oct 16th 09
CA US

Posted: Oct 16th 2009, 08:55 PM

Easy to check the friction issue, lube it up real good. Is the gas tube in order? Try a new magazine or
two, and is the ammo factory?. Can't hurt to try another box of ammo. Doubt if it's the buffer spring because I don't think it would work intermittently. Someone w/ an AR10 will probably chime in.

Joined:
Location:

Nov 29th 08
CT US

Posted: Oct 16th 2009, 10:05 PM

I like Rangers idea about a mag. Most of the problems I have had with my AR's similar to what you describe turned out to be a mag. issue.

Good Luck

Joined:
Location:

Jan 6th 08
MN US

Posted: Oct 17th 2009, 12:32 AM

Thanks for the advice. I think I am going to try factory ammunition first to see if that resolves the issue. Although I have been reloading and swaging for years, I know that reloading manuals suggest a maximum powder load under the actual maximum load in order give a little extra cushion to compensate for user error. I was using hand loads with 165gr. Hornady SST Interlock Boat Tail projectiles with a polymer tip loaded at the mid range of the suggested charge (42gr. H4895 powder). Every round was charged in a single stage press and the charge was measured using the RCBS charge master 1500 (digital scale). These rounds were identical and loaded very, very carefully.

I was confident these rounds would be flawless. However, it seems that it is possible that I may need to work up the loads slowly for a hotter round that can create enough gas pressure to move the bolt back far enough to strip the next round from the magazine.

I will buy some factory ammo to see if that resolves the issue. If the problem still occurs with factory ammo, then I will work on the magazine next to see if that is causing the problem. Thanks for the information. I will keep you posted on this issue until it is resolved.

I did check the gas tube, and I even gave it a good cleaning for good measure. There are no obstructions in it and air passes through it nicely.

Are there any experienced reloaders out there that have built up the perfect recipe for their AR-10 chambered in .308? Please let me know. Thanks.

Joined:
Location:

Oct 16th 09
CA US

Posted: Oct 19th 2009, 07:16 PM

I think the problem worked it self out. I shot 20 rounds through my AR-10 on 10/17/2009 without a single malfunction. I think the problem was the bolt carrier group in my new upper. The tight tolerance between the bolt carrier group and the inside wall of the upper receiver was likely causing excess friction and short stroking the action. Here is what DPMS said:

It sounds like a short stroke issue being caused by gas pressure loss somewhere in the system, possibly the wrong buffer and or spring or too little or too light of lubrication.

Be sure to check your bolt's gas rings, ensure there is no gas loss at the front sight base. Also make sure you run the gun wet during break in. Our 308s do have very tight tolerances and if they are run too dry, they will short stroke. Make sure the carrier is visibly wet with oil, shake off any excess and give it a go.

Thanks for all your help.

Joined:
Location:

Oct 16th 09
CA US

Posted: Oct 19th 2009, 10:41 PM

Looks like you've got everything nailed down, but just to recap in case it starts happening again:

Shortstroke - Change out your ammo, find some XM80 and give it a try, it's hotter than usual off the shelf ammo. Or, give some match ammo a try. Federal Gold Medal Match, no matter the bullet weight.

Magazine - Is it seating all the way, each time you insert it? Are the feed lips bent inwardor distorted in any way?

Lube - I agree, run that phucker sopping/dripping wet with some good quality lubricant.

Gas rings - Great advice. Give them a good check.

Gas block - Make sure the forward gas block hasn't rotated any, which could partially obscure the hole.

Gas Key - Is it staked properly? Has anything moved or loosened?

Break in - DPMS gave you some great advice there. It'll take several hundred rounds for it to loosen up somewhat.

Spring tension - I really don't know how this could be the problem, I mean, I do, but I seriously doubt the spring is having anything to do with your particular problem. I'd let this be the last thing I checked.

I hope your AR continues to run smoothly, but just in case it doesn't, keep this thread handy. Best of luck...

Joined:
Location:

Dec 27th 07
AL US

Posted: Oct 24th 2009, 03:27 AM

Okay, I got a field report update on this issue. I took my AR-10 to the range yesterday and sighted in the gun at 100 yards using new Leupold High rings with my Bushnell Elite 4200 scope. I put 10 hand loaded rounds down range without any issues at all. The hand loads were loaded in middle range according to the Speer Manual using H4895 and Remington CorLokt 165gr projectiles. I then shot 10 of my hand loaded hunting rounds down range without any issues at all. The hunting rounds were loaded in the middle range according to the Speer Manual as well using H4895 (my favorite gun powder) and Hornady SST Interlock 165gr. projectiles.

That's 20 rounds without any malfunctions and the bolt was stripping the rounds from the magazine nicely from two different projectile tips (soft point and ballistic tips). I was very pleased with my gun.

Then I went to the 25 yard line to practice holding over mil dots (my elevation adjustments are maxed out on my scope) and every shot after the initial shot failed to strip the round from the magazine again. Although this was frustrating at the range, at least I have a pretty good idea what was causing the problem. The problem is intermittent which leads me to believe that the gun oil is drying out after so many shots. If the problem occurred consistently I would suspect the buffer spring or magazine. All of my hand loads are identical in powder charge and powder type. Therefore, I think it is just a new gun that I need to break in with sufficient gun oil. Of course I forgot to bring the gun oil to the range and I was not able to test this theory. Next time I am bringing the gun oil and I will be able to see if that solves the problem. I will keep you posted on this issue until it is resolved. I am learning a lot through trial and error (and frustration). Hopefully what I learn is useful to others.

Joined:
Location:

Oct 16th 09
CA US

Posted: Nov 14th 2009, 07:09 PM

Another field report update. I went to the range on 11/11/09 to sight in my AR-10. After about 12 shots of my reloaded .308 ammunition, the bolt of my AR-10 seized shut with the bolt in the closed/chambered position. I tried pulling the charge handle with no luck. The bolt was stuck closed. This is not the first time my bolt became stuck on the range. There was a live round in the chamber and I was not able to get it out. I had to leave the range with my unsafe AR-10. Embarrassed and determined to resolve the issue I headed home with a mission.

I did a lot of online research and determined the problem was either a stuck case or a lose primer pined against the bolt. The solution was the same. Beat the bolt carrier out with a hammer, or kick start your charge handle. I used the less evasive method, by separating the upper from the lower and mounting the upper on my vice upside down. I used a punch (with tape on the end) and a medium hammer to tap the bolt carrier out. The live round came out of the chamber with a few taps and there was no loose primer anywhere to be found.

After hours of research, and the process of elimination I narrowed the problem down to the brass shoulder dimensions/head spacing. I figured this out by manually feeding a round into the chamber of my barrel and attempting to eject the round manually with the charge handle. I noticed some rounds ejected with ease, while others needed to be tapped out with a hammer. In the chamber of the barrel there was a bunch of brass shavings from testing multiple rounds manually. I compared the case dimensions and noticed that the cases were identical except for the datum line on the case shoulders.

The stuck cases had a very slight bulge in the case shoulder. The good case measured 0.396" at the datum line on the case shoulder, and the bad case measured 0.408" at the same point. After even more research I determined the case shoulders bulge was created in the crimping process. Yes, I crimp my reloads. I know there is a lot of debate on whether to crimp or not. I like the idea, so I am going to try and make it work.

I wanted to correct this issue, if possible. The thought of throwing out all that once fired brass because of my noob crimping mistake was unbearable. The only reasonable solution was to try and re-size the live rounds in my sizing die. I know, everyone is probably cringing at that idea. Believe it or not It worked great and I still have all of my fingers! I figure, as long as nothing hits the primer, or the case doesn't get to hot in the process, I am likely to make it out of this experiment alive. I destroyed several cases in the re-sizing process to figure out a method that works, but I finally figured it out. In order to get that consistent 20 degree angle in the case shoulder you have to resize it, very slowly, in a full length sizing die so that the shoulder is pressed against the die wall. The de-capping pin assembly must be removed for this procedure to work, and you have to use plenty of case lube or else you will crush the shoulder. I am sure this is old news to all the veteran shooters out there, or a very backwards and dangerous way of doing it. I am open to any suggestions. Is there a better way to correct over-crimped shoulder bulges?

I would have never guessed this problem was related to head space. I purchased some head spacing gauges and I should be receiving them soon. I also purchased a primer pocket swaging kit and a Harts case saving kit to hopefully resolve any other case dimension issues I may have in the future.

The next post will hopefully be the last on this thread. I am guessing this should resolve the issue I am having with my AR-10. I think Lone Ranger, and Recoil were right about this issue. I will be buying some factory ammunition as well to be used as a control group. I will let everyone know when I have the results of my next batch. Thanks for all of your help so far.

Lone Ranger and Recoil for President!

Joined:
Location:

Oct 16th 09
CA US

Posted: Dec 6th 2009, 01:30 AM

Sure enough, that solved the problem... I tested several rounds after ensuring each case's heaspace was within S.A.A.M.I. conditions using a LEE headspace gauge, and every round worked great! No jams, no short-stroking, no stuck cases. Every round worked great, and every round was consistent.

Joined:
Location:

Oct 16th 09
CA US

Posted: Dec 11th 2009, 12:08 AM

Glad you got it all worked out Seph! Don't thank me, I'm no guru by any means. I just had some problems with my AR10 and tried just about everything in the book to solve them before I finally got a tech. rep. from Armalite on the phone to help me out. Some of the stuff I posted was from notes that he passed on to me. I won't take full credit for the advice...I'm just a squirrel trying to get a nut!

Best of shooting...

Joined:
Location:

Dec 27th 07
AL US

Posted: Dec 16th 2009, 06:00 PM

the crimping problem can be helped by using a lee factory crimp die, I like the way it works, doesn't set the shoulder back, doesn't even touch it.For no more than they cost, they remove a lot of headaches. I use it on my .223 rounds, always works fine once you set how much crimp you want.

Joined:
Location:

Nov 1st 09
AL US