300 rcm in a ar-10

[assasinator]

my 6" sand roll arbor arrived today. i will be following my gunsmith's advice concerning modding the pmag 308.

he told me to alter it for case length before the neck. hopefully it helps. what is strange is, at the bottom of the pmag, the 300rcm stack fine. in other words i removed the bottom and spring.....

i added 5 rounds of 300rcm, then added 308 rounds to finish 10 rounds, then put the bottom/follower/spring back in. it fed and only swelled when the RCM got about 1/3rd to the top.

the guide clears the rcm (doesn't touch) until about half way to the top.

is the guide the real issue, or is it simply the diameter? would 284 winchester brass at .500" totally custom wildcat the answer?

i could care less if i have to design a completely wildcat higher capacity round that will feed.

i ROUTINELY ORDER custom reamers, and form brass to my specs..... i realize that is not what most can or will do.

i really hope 300rcm will work..... later....

 

[ARlife4me]

what model mag? ty. wow 112.00 per magazine? they are proud of a mag that barely works.....

that they are. i paid 92 per last year

 

[assasinator]

so, i sand rolled the 20rnd pmag. it held 10 rounds, but i noticed the last round nose diving.

it at least loaded them decent. i am in a holding pattern for getting my barrel reamed for 300rcm. i might buy another 20" 308 and get it reamed for 300rcm. for now im over it. the entire purpose for building a ar-10 is 25 rounds of 308. not 5 to 10 rounds of what ever else. its home defense first.

last thing i am doing is loading brass only and using a hot gun to change the feed lips on the mag to match 300 RCM.

later. -bill

 

[cohunt]

Try a ss mag and tweak the feed lips

 

[assasinator]

Try a ss mag and tweak the feed lips

I WILL ORDER A 20. hope it is better.

its on the way.

 

[Old Rooster]

I have had brand new mags(pistol and AR mags)that would not even pick up a case in the mag.
You can use a pair of pliers but there is a tool just for that job and it is not expensive:

MPA Mag Feed Lip Adjustment Tool - MasterPiece Arms, Inc.

This tool comes in handy when adjustments are needed to the feed lips of your metal AR15, AR15 or Bolt Action Box Magazines to improve feeding. If your feed lips get tweaked, if you drop your magazine or simply have feeding issues due to feed angle of your loaded cartridge, then use this tool to […]

masterpiecearms.com

Thanks for reminding me cohunt!

 

[kfreeze]

I have ar10 mags made for me. The same ones I sold on this site previously. If your base to case shoulder dimension is the same or really close to a 308, let me know. I'd do a little work on some feed lips and follower and send you a mag just to see if it works.

Kyle