Expert large frame troubleshooters needed for diagnosis

[smoooth1]

Shot a pieced together a large frame 308 today. Suppressed, 16” BA barrel () gas port drilled / opened up, PSA bolt, live free armory matched upper and lower. New Pmag 20. Heavy buffer and flat wire spring.
147 fmj ZQ (Turkish) reloadable brass case.

First 2 were fine, then double feed, cleared, fire, same with the next 2, etc.
10rds fired, 3 double feeds,WTF?

All fired cases have a lower body dent and the rims are a bit chewed up.

Any suggestions??

Thanks

 

[M4orturnate]

Way overgassed

 

[USK308]

Shot a pieced together a large frame 308 today. Suppressed, 16” BA barrel () gas port drilled / opened up, PSA bolt, live free armory matched upper and lower. New Pmag 20. Heavy buffer and flat wire spring.
147 fmj ZQ (Turkish) reloadable brass case.

First 2 were fine, then double feed, cleared, fire, same with the next 2, etc.
10rds fired, 3 double feeds,WTF?

All fired cases have a lower body dent and the rims are a bit chewed up.

Any suggestions??

Thanks

View attachment 8358133View attachment 8358134

Gas port drilled/opened up FROM? TO?

Gas System --> carbine length? rifle length?

Initial thoughts echo @M4orturnate ... way overgassed! But, the info above will help solidify diagnosis (IMO).

 

[smoooth1]

Don’t know gas port details; maybe opened to .090"? Had been running 175’s and was under gassed.

Appears to be a Mid length gas system.
Non adjustable gas block.
Is the over gassing causing the stove pipe / double feed issue?

Ejection seemed to be 2-3 o’clock.

 

[USK308]

Don’t know gas port details. Had been running 175’s and was under gassed.

Appears to be a Mid length gas system.
Non adjustable gas block.
Is the over gassing causing the stove pipe / double feed issue?

Ejection seemed to be 2-3 o’clock.

2-3 o'clock indicates "hot ammo and/or a suppressor."

If you are running a non-adjustable gas-block, you won't have a means to reduce the amount of gas pushing the BCG back.

Are you running reloaded ammo? Sorry, brain is tad fried from the harried weekend (lol).

Have you tried some factory ammo?

 

[Jsp556]

2-3 o'clock indicates "hot ammo and/or a suppressor."

If you are running a non-adjustable gas-block, you won't have a means to reduce the amount of gas pushing the BCG back.

Are you running reloaded ammo? Sorry, brain is tad fried from the harried weekend (lol).

Have you tried some factory ammo?

Depending on deflector geometry.

 

[smoooth1]

2-3 o'clock indicates "hot ammo and/or a suppressor."

If you are running a non-adjustable gas-block, you won't have a means to reduce the amount of gas pushing the BCG back.

Are you running reloaded ammo? Sorry, brain is tad fried from the harried weekend (lol).

Have you tried some factory ammo?

This was "factory" ammo.... made in Turkey..... Also running suppressed.

Thanks for the diagram!

 

[LRRPF52]

Cyclic rate is too fast, and look at the brass flowing into the extractor shelf.

The extractor is trying to rip the rims off the brass due to early carrier momentum from excessive gas into the carrier.

For MLGS 16” barrels, you don’t want to be over .076” generally speaking.

No bueno

 

[Cascade Hemi]

Cyclic rate is too fast, and look at the brass flowing into the extractor shelf.

The extractor is trying to rip the rims off the brass due to early carrier momentum from excessive gas into the carrier.

For MLGS 16” barrels, you don’t want to be over .076” generally speaking.

No bueno

Agreed.

That barrel configuration may always be hard on brass, even after it's gassed correctly. Hand loading with faster powder can reduce the early unlocking but at the cost of low velocity. A different barrel would be the best solution.

 

[M4orturnate]

You can get a xh buffer from heavybuffers.com that may help, if also install a adjustable gas block. It's hard to base how the gun is gassed based of extraction patterns. The double feeds and bent rims are the telltale signs

 

[bfoosh006]

MKE 308 ammo can be very sporadic .... mine will shoot shotgun patterns at about a foot across at 100yds.
That bargain ammo from Walmart, wasn't

While FGMM , from the same barrel and day, will shot MOA while I hardly try. ( well you know what I mean )

I would suggest trying some other ammo first.

 

[wvfarrier]

Get an adjustible gas block. That should likely solve your issues

 

[Jsp556]

The cost of a X heavy buffer, spring, and adjustable gas block is half the price of a rifle gas length criterion.

Probably isn’t what you wanted to hear though.

 

[smoooth1]

Thanks to everyone for all the helpful advice, very much appreciated!!

I know the barrel leaves much to be desired but a new one is not in the budget at the moment.

Pretty sure I have an adjustable gas block, will have to do some digging.

Will do some tinkering this week and report back with the results.

Thanks again!!

 

[Redlion]

Who "pieced it together?"

 

[smoooth1]

Update:

Gas port was previously enlarged from .072 up to .092 diameter a few years ago.

Did some digging and found a couple adjustable gas blocks (AGB) - JP, Odin Works, and an unknown with an adjustable lever type arrangement which I chose due to the handguard design.

Threw some 308 loads together using 40.5gr - 41.4gr TAC, 170 fmj, S&B and Fed. primers in Federal GMM brass. The brass was bought used years ago, fired 5x previously and neck tensions varied considerably as some pieces were neck turned by the previous owner. This brass was perfect for experimental load use and semi auto abuse.

The AGB worked wonders, was easy to use (swapping gas tubes, however, was not that easy) and made the system reliable! Also, the AGB was the ONLY change made to the rifle. Once the proper setting was found, function was 100% with over 40rds tested.

As to the bought-used-on SH 16" BA barrel, it's surprisingly accurate for what it is, especially considering the wildly inconsistent neck tensions of the loads. Shot a couple groups @100yds, 5 shot 1 1/4", 7 shot 1 9/16". Obviously, not great, but all things considered, not terrible.

Again, thank you to all who offered suggestions!