AR10 - can 6.5CM and 308Win uppers use same lower (buffer/spring)?

[kfd518]

I'm not sure if you got this sorted yet.

Dealt with my 6.5 not cycling to lock back by contacting the manufacturer once I realized the "matched" gas block was blocking 0.040" of the port. It was a rifle length+2".
In my experience a 5.2 oz minimum buffer is needed in all large frame AR builds. A good combo to work from that I have noted in my building has been anyone of the 5.2+ short large frame sized buffers with a sprinco orange spring.

I realized this on my first one when it was showing ejector swipes in mid January with factory match loads. It was un locking very early while pressure was still up in the chamber. The problem returned after I suppressed it. I did manage the last part of the equation with an adjustable gas block and I know the settings from one to the other and set the AGB accordingly now.

Another thing to verify as mentioned before is that you are not bottoming out in the LRE. Not enough weight, weak spring, to much gas will increase the bolt speed to a point that it cannot strip the round from the mag.

I diagnosed the short stroke of my 6.5 CM with my iPhone set to slow motion.

 

[epc001]

RABAZ, I can drop powder charges radically for my LR308 w/o issue, whereas those same pressure make my old "steampunk" M1 double tap or lock up. Load 'er down if terminal velocities aren't a critical issue. Most of my iron, bolt or gas, groups better at less than max anyhow.

PS I assembled an old carry top AR15 with a .223 Wylde barrel and a adjustable gas block. What's neat about the adj gas block is for the 100 yd CMP open sight shoots, you can load it down some, and set the gas block to not slam the bolt back hard. Becomes the most gentle shooting .223 you ever did hug. FWIW.

Powder charge is your friend here unless you make a mechanical adjustment in the rifle, which is preferred only if you're wishing to keep velocities high. Otherwise take 2 grains out and see how it runs and groups. HAVE FUN!

 

[RABAZ]

RABAZ, I can drop powder charges radically for my LR308 w/o issue, whereas those same pressure make my old "steampunk" M1 double tap or lock up. Load 'er down if terminal velocities aren't a critical issue. Most of my iron, bolt or gas, groups better at less than max anyhow.

PS I assembled an old carry top AR15 with a .223 Wylde barrel and a adjustable gas block. What's neat about the adj gas block is for the 100 yd CMP open sight shoots, you can load it down some, and set the gas block to not slam the bolt back hard. Becomes the most gentle shooting .223 you ever did hug. FWIW.

Powder charge is your friend here unless you make a mechanical adjustment in the rifle, which is preferred only if you're wishing to keep velocities high. Otherwise take 2 grains out and see how it runs and groups. HAVE FUN!

I seem to have gotten it to work ok by, as several of you have suggested, dialing back my powder charges - it's like magic!! Thanks for the help and input.