Dented case help

[Jgault]

308 I built did this to 2 rounds out of about 100, the other 98 fired correctly and the cases didn’t show any damage. It seems some rounds are getting caught while chambered, these two rounds chambered but didn’t fire, and took mortaring to get out. Any ideas on cause?

 

[KZP]

Assuming ar-10 type rifle? What magazine are you using & brand of barrel?

 

[Jgault]

Assuming ar-10 type rifle? What magazine are you using?

Yes lr 308. I considered the mag, both these happened using steel duramags, could it be the round is sticking in the mag just enough to cause the carrier to crush it upwards? I’m going to the range tomorrow and loaded a few duramags and pmags to see if it happens again,

 

[KZP]

I had the same issue using Larue steel mags. Switched to pmag & lancer then the problem went away. But it may also be the BCG group speed/timing, barrel feed ramps, magazines not sitting properly in the lower or more.

 

[Jgault]

I had the same issue using Larue steel mags. Switched to pmag & lancer then the problem went away. But it may also be the BCG group speed/timing, barrel feed ramps, magazines not sitting properly in the lower or more.

How do you like the 308 lancers? They are my favorite 5.56 mag, is the 308 worth the price tag? I think your probably right, this hasn’t happened with pmags, and the pmag sits just a little lower in the magwell.

 

[KZP]

Both types function fine so far. Have had about 1k rounds between two pmags, 500 through one lancer. But I like the potential longevity of the Lancer because of the steel top instead of being 100% polymer....plus the translucent plastic is extra tactical.

 

[FuhQ]

I agree with above, you might want to try running a heavier buffer and/or spring to slow down that BCG. Also, I'd check your feed ramps in your barrel to ensure they're cut right and chamfered properly. Trying a PMag won't hurt either. Might be a simple fix. Even if the new mags work, I'd still run a heavier buffer and spring to slow down that BCG. Will also help with felt recoil, too.

 

[Jgault]

I agree with above, you might want to try running a heavier buffer and/or spring to slow down that BCG. Also, I'd check your feed ramps in your barrel to ensure they're cut right and chamfered properly. Trying a PMag won't hurt either. Might be a simple fix. Even if the new mags work, I'd still run a heavier buffer and spring to slow down that BCG. Will also help with felt recoil, too.

I’m using a 4.5 ounce buffer now, think another ounce would help? The feed ramps are good.

 

[FuhQ]

An H3 probably wouldn't hurt regardless... But I don't know if that will fix it. AR's are a finicky design. It could be as simple as swapping to an H3, and maybe a new type of magazine. Or swapping in an adjustable gas block? I wish it was more definitive than that, but sometimes diagnosing AR's over the internet is a very hard thing to do.

 

[Jgault]

An H3 probably wouldn't hurt regardless... But I don't know if that will fix it. AR's are a finicky design. It could be as simple as swapping to an H3, and maybe a new type of magazine. Or swapping in an adjustable gas block? I wish it was more definitive than that, but sometimes diagnosing AR's over the internet is a very hard thing to do.

I know but I appreciate it, kind of like trying to tell someone how to fix a carburetor over the phone. It already has a adjustable gas block I will click it down a click tomorrow.

 

[FuhQ]

I know but I appreciate it, kind of like trying to tell someone how to fix a carburetor over the phone. It already has a adjustable gas block I will click it down a click tomorrow.

Honestly, the best way to find your rifle's ideal gas, is to tighten it until it stops picking up the next round, then go back up 1 click. It should be ejecting them backwards over your right shoulder. Anything forward of a perfectly straight 90º imaginary line to your right, and you are overgassed (technically speaking). And adjusting that gas block way down will slow the BCG down by pushing less gas into it. That might even solve your issue without having to go up in buffer weight.

 

[Jgault]

Honestly, the best way to find your rifle's ideal gas, is to tighten it until it stops picking up the next round, then go back up 1 click. It should be ejecting them backwards over your right shoulder. Anything forward of a perfectly straight 90º imaginary line to your right, and you are overgassed (technically speaking). And adjusting that gas block way down will slow the BCG down by pushing less gas into it. That might even solve your issue without having to go up in buffer weight.

Just got back from the range. 200 rounds without a hitch from steel and pmags. The only odd thing I noticed was about 5 rounds only ejected about a foot, while 195 ejected normally, no damage to the cases I checked. I set the gas to just past bolt lockback.

 

[Tillerup!]

Having a similar problem. With my AR10 build w/ P-Mags. Criterion "M118" barrel. Ramps are smooth, but there are traces of brass/copper on the ramps.
Running the 175 SMK with XBR powder.
But I'm hearing, gas block adjustment rectified your problem?
I was thinking my mag latch was a bit sloppy. Any rec's for a "good" mag latch?
Def try adjusting the gas block next time out.
Appreciate this group!!