AR10 Failure to Feed Match Ammo

[Klong415]

Hey guys, need a little help. Built an AR10 .308 earlier this year. It has shot all the ammo I put through it until I tried shooting Sierra match king. If I release the bolt on a fresh magazine it will load the first one but after firing it will not load the second. It bullet gets half way into chamber then it jams and dents the casing. It appears this bullet is slightly longer than the non-match ammo I normally shoot. I set the adjustable gas block with a 150gr bullet and have shot everything g up to 180gr no problem. It only happens when I load the longer match bullets.

Any ideas as to what is going on here?

 

[LG65CM]

Hi Klong415- Don't take this the wrong way, please. But, I noticed 58 people have viewed your post since you posted. No one has replied. I think you need to give much more information to get some opinions as to what is causing your problem with this particular bullet. Info about your build- like its: Buffer/Spring, BCG, Gas System, Magazine used and its inside length. Info about your cartridge: particularly its COAL (over all length). Does that vary from the other cartridges that are feeding?

Hopefully with that extra info and anything else you might think of, people might have enough to get started and reply.

I'm not shooting a 'build' , and occasionally, I'll get a FTF with results being the same- dented brass. But for the most part it likes pretty much anything that fits inside the mag. Good luck !! lg

 

[BCP]

Magazine sitting too low and bullet catches on the feedramps or bolt not coming all the way back (short stroking) and it shoves against the side of the case instead of the rear, smashing it against the feedramps?

 

[hermosabeach]

this might sound different...

Load a magazine and look or measure where the tips of the projectiles are in relation to the font edge of the mag body.
Fire one round, eject the magazine and look. Have the bullets moved forward? I am guessing - that the extra COAL might have the bullet tips hit the mag body under recoil.

if the bullet is further forward, will it them hit into the barrel extension and not move up the feed ramp?


it's just a guess..... now tell us about ball ammo. Where does it land when you fire a magazine?

1:00- 3:30- 5:00 position? how far from the firearm?

Now your match ammo- where does the brass land? position and distance. Is this the same or does it show over or under gassing?

oh- your 150 grain ammo- is it commercial or reloaded by you?
If reloaded, is it the same powder as with the match king? (not same powder charge obviously) Longer extruded powders and shorter powders have a different peak in gas pressures some peak and burn faster and others slower.... some will run a semi well.... others have the gas pressure dropping before the gas hits the gas port

This is common with some steel cases 5.56 ammo... some gives great chrono results, but does not run in a semi auto

 

[FreQRiDeR]

If you load and chamber a single round and fire it, does the bolt lock back on an empty mag? If not, open your gas block a half a turn till it does. If you’re shooting FMMG 168 ammo, it’s not a hot load by any means.