I'm headed to the range in about 10 hours and rather than use the Barret 30 round mag with my Rock Rest lifted way up to shoot about 50 rds from my LWRC 6.8,
I just loaded 20 rounds in a 20 rd Pmag to give it a try. They cycled flawlessly.

The size was 115gr OTM and there was obviously clearance in the magazine. My understanding is that 130+ grain will have a longer footprint and might not feed properly. In fact, my Rem UMC .223 measured 2.2515" and the 6.8 measured shorter at 2.2355.

While I'm not going to rely on the Pmag for a .223/5.56 in a rifle for home defense (I'll likely drop to a 17 rd-er with another one in a picatinny holder by CAA in the stock) should I be good to go for the range with a 20 rd Pmag .223/5.56 magazine? The Barrett 30 round magazine is HUGE! Plus, I'd like to shoot that slowly until I get my Dillon 550 up and running.

Thanks in advance,
Walsh

P.S. I also have some 20 round straight mags if they might be better to try.

Magpul has said that 6.8s wont work in a Pmag.  I know you have done it, but my understanding is that they are too fat and put a ton of pressure on the side walls and isn't recommended.

load the barrett mags short, or get some PRI mags they have 25 rounders. I don't recommend Cproducts