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Bolt Stuck on DPMS LR 308

dustinlotz

dustinlotz

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Mar 9, 2008
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Naples, FL
#1
I went to the range today with my DPMS LR 308, and I had some trouble. After firing a few rounds my gun started to misfire, so I decided to break it down and take a look, and that is when the trouble began...

Apparently some small metal, see here:

IMGP0129.jpg


got lodged between the bolt and firing pin. With this metal lodged between the bolt and firing pin, the bolt would not manipulate in the BCG. This made breaking the gun down next to impossible because the bolt would not extend out to its longest position allowing it to unlock from the breech. Anyway, once I removed the BCG from the gun (which took about 45 minutes)I had to force the firing pin out of the bolt(another 30 minutes). Once I did, the small metal pieces seen above fell out of the bolt.

I was having feeding issues with my mag (double feeds) which I have always suffered with the DPMS mags, and the double feeding was deforming my projectiles. (I know DPMS had a bad run of mags, but these are supposed to be the 'improved mags')

The only thing I could think was the mangled projectile was leaving a small amount of debris in the breech which was in turn getting forced into the pin hole of the bolt and seizing the firing pin, but this is where I am confused....

After I noticed the small pieces of metal, I cleaned the Bolt, BCG, and breech thoroughly. I inspected it, and the range officer inspected the rifle, and we both gave it a thumbs up. The next shot I fired shot normal, but the next shot misfired, and then the process repeated (bolt was stuck and firing pin jammed by small pieces of metal). I think the gun misfired because the metal was blocking the firing pin from striking the primer, but my question is, <span style="font-size: 11pt"><span style="font-weight: bold">where is the metal coming from??</span></span> Could the firing pin be destroying the primer, and a piece of the primer getting lodged in the bolt? The primers looked good, and the firing pin looks normal.... I don't get it, does anyone have any ideas?
 
#2
Re: Bolt Stuck on DPMS LR 308

those look like blown primers to me and when they blow they get stuck in the firing pin hole. Also when a primer pierces its like a plasma cutter on your firing pin sometimes and can cut up the tip of the pin. This also causes the firing pin to shoot back really hard and impact the retaining pin. Yours might have bent. I had it happen on mine a few times and it eventually ripped broke retaining pin. What does your fired primers look like? What loads?
 
#3
Re: Bolt Stuck on DPMS LR 308

Yep, primer blanking. I've had it happen with CCI's but not with Winchester primers. This was with my M2008 using 6.5x47L. (SR primers with a LR primer type firing pin.) Interesting thing is that it didn't bind the bolt at all. I'd say with an AR, it's a serious pressure sign. Also, you could have already eroded the firing pin and the hole in the bolt face for the firing pin if you've pierced primers in the past. Could be another reason for your current issues.
 
#4
Re: Bolt Stuck on DPMS LR 308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Salmonaxe</div><div class="ubbcode-body"> primer blanking. </div></div>

Thats a better way to explain it
 
#6
Re: Bolt Stuck on DPMS LR 308

Looks like the primer is blowing.

Can you find any of the fired brass and look at the primer?

May be one of several things. Maybe when the round is feeding it may be jamming the bullet deep in the case and causing an overpressure situation, thereby blowing the primer.

If handloads, I would look carefully at your process.

I'd send the gun back to DPMS (or find a gunsmith familiar with gas guns)and have them fix the double feed problem.
 
#7
Re: Bolt Stuck on DPMS LR 308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hellbender</div><div class="ubbcode-body"> Maybe when the round is feeding it may be jamming the bullet deep in the case and causing an overpressure situation, thereby blowing the primer.


</div></div>

This is very possible too!!
 
#9
Re: Bolt Stuck on DPMS LR 308

You guys are right. It is definitely signs of overpressure. Half of the cases I shot looked fine, but the other half were showing signs of overpressure.

These are handloads, but they have shot fine previously on the same load. I think Hellbender hit the nail on the head by the double feeding causing the bullet to get jammed down in the case more. I would still shot the round even if it was double fed as long as the projectile was fine. I didn't even think about the projectile getting pressed into the case more.

The shells that had overpressure signs had pierced primers and ejector swipe marks on them. The other half of the shells looked normal. I think my load is good, but my mags are bad.

I am going to order a new firing pin and retainer pin today. I just can't wait until the 308 PMAGs come out. I really think that will solve a lot of my problems. I may get some SR25 mags for now.

Thanks for the help guys!
 
#10
Re: Bolt Stuck on DPMS LR 308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: HiTechTactical</div><div class="ubbcode-body">You guys are right. It is definitely signs of overpressure. Half of the cases I shot looked fine, but the other half were showing signs of overpressure.

These are handloads, but they have shot fine previously on the same load. I think Hellbender hit the nail on the head by the double feeding causing the bullet to get jammed down in the case more. I would still shot the round even if it was double fed as long as the projectile was fine. I didn't even think about the projectile getting pressed into the case more.

The shells that had overpressure signs had pierced primers and ejector swipe marks on them. The other half of the shells looked normal. I think my load is good, but my mags are bad.

I am going to order a new firing pin and retainer pin today. I just can't wait until the 308 PMAGs come out. I really think that will solve a lot of my problems. I may get some SR25 mags for now.

Thanks for the help guys! </div></div>

If you can wait a few weeks you'll be able to pick up the new Larue Tactical SR25 pattern mags for about $50 each. They're made entirely in-house at Larue to support their OSR project. Larue could not find any reasonably priced SR25 type mags that they trusted, so they built their own. These are true 20 round mags that are sized to work correctly with M118LR.
 
#11
Re: Bolt Stuck on DPMS LR 308

I don't think you have a mag problem, it seems VERY odd that SEVERAL mags are causing this same malfunction. Didn't you post before that you had some other mags before that were exchanged or something?

I think your reloads are causing the problem, sounds like the noses are dragging slightly on the front of the mag body, what is your cartridge OAL?? You need at LEAST .010" of nose clearance for reliable function.

DPMS brand mags require .050 LESS OAL length than my C-products mags will allow.

Try some factory ammo and see if the problem replicates itself.

Also, disassemble the mags and check the spot welds where the bullet noses drag, make sure it is smooth.

If not that...

It sounds like either the mag is sitting too high in the gun or your mag lips are spread too wide and allowing the bolt to catch the rim or body of the 2nd round in the mag.

Sounds like your lower may possibly have a mag catch location out of spec...

You don't have an aftermarket AMBI catch or something in there, do you? Also, try a different mag catch, they are standard AR15, so it is easy to check

With the gun unloaded and a mag inserted, work the bolt and make sure the mag lips do NOT contact the bolt or carrier in any way, even when you are pushing up on the mag, and rocking it back and forth.

Do the mags drop free OK?

Anyway, just some things to look for, but I would try some factory ammo first.

HTH, HB
 
#12
Re: Bolt Stuck on DPMS LR 308

Yesterday I was only using one mag. I bought the gun used and it did not have any factory mags, so I purchased some DPMS mags recently.

My OAL is 2.800". I checked the rounds and they were clearing the mag when I was loading them. I checked this when I was in front of my press.

I'll check the mags again to see if there are clearance issues, and I will run your suggested tests. BTW - the mags do drop freely...
 
#13
Re: Bolt Stuck on DPMS LR 308

OK, went through all this with my DPMS .260 upper, pierced 80% of primers (factory and reloads, federal and cci primers).
Box upper and bolt group - sample brass and send it back to DPMS. They fixed mine and mailed it back in a short time and everything is good to go now.
 
#16
Re: Bolt Stuck on DPMS LR 308

I have had this happen with a .308 AR10 of mine.
Some cases (about 25%) were overpressure but the others were fine.
I also saw flyers with about the same frequency too.

Here is what was causing it for me:
I loaded 0.010 off the lands and, while single loading, saw that pressure and accuracy were acceptable.
When I let the rifle do the loading was when I ran into the pressure and accuracy problems.
The bullet was sliding FORWARD from kinetic effect (and sometimes) into the lands causing a pressure spike during the violent slamming home of the BCG.

Question:
If you hand fit your ammunition into your chamber, does it fall back out under its own weight?
It should not stick as that may mean that it is jamming into the lands and that will cause an increase in pressure.
Do you know how far off the lands you are to begin with?

If you fully seat the bullet into the chamber and then drop the BCG does the overpressure then disappear?

If it does, like I suspect it will, then you may need to increase neck tension.

A lee factory crimp die and canelured bullets can solve this but may bring up accuracy problems.
 
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