Barrel and gas system lengths

[kfreeze]

So I've got a pair of AR10s and I use that term on purpose.
One is an Armalite AR10 that was originally a 300 SAUM. I rebarreled it to a 6.5 PRC with a 24" barrel and a +2 gas system. I've just about got it dialed in to cycle perfect...but the Armalite mags are dog-spit and I think I'm gonna end up having to 3d print a self leveling follower for their Gen2 pattern mags.
The 2nd is a Matrix upper lower set that is still the Armalite pattern, but takes SR25 mags...that one is 22" with a +2 gas system. Pmags don't work 100% but so far ACS mags have been doing great. Seems to be tuned and feeding/cycling but with both systems...I'm thinking I should have just made them 16 or 18? from the jump.

Has anyone ever taken a barrel with a +1 or +2 gas system and shortened the barrel down to 16 or 18"??
I assume this is going to drastically reduce the gas and potentially start short stroking, but with the buffer, springs and gas block I have...I assume getting it tuned to run suppressed again would be fairly easy.

Really thinking I should have gown shorter.

View attachment 640486

Shortening that barrel will give you problems if you don't open the gas port up. The dwell time gets way to short to give enough gas. Better off to use a good click adjustable gas block and tuning it right in most cases instead of going to a longer gas system unless using slower burning powders.

As a side note, I sold a bunch of dpms/sr25 pattern ar10 mags on year a while back. We could take those and and remove some of the follower and they worked for saum stuff. Maybe bend the feed lips out a little if needed.

On the armalite factory ar10 300 saum I had for a while, the follower was modified by having the rib that sticks up in the follower modified to not touch the fatter case was the only difference that I could see.

 

[liber]

I rebarreled it to a 6.5 PRC with a 24" barrel and a +2 gas system.

The part I'm confused about still is how you handle the magazine? A 6.5 PRC won't fit in a short action mag, which most all LR-308s are. How did you overcome that on a semi-auto gun?

 

[ARlife4me]

The part I'm confused about still is how you handle the magazine? A 6.5 PRC won't fit in a short action mag, which most all LR-308s are. How did you overcome that on a semi-auto gun?

getting the correct mag is key! most will be 2.830" and shorter, but larue, acs and a few others get you past 2.860" problem i have is the follower with both short mags i have. i've tried 10-25 round mags as i know when fully loaded you can get and average of 70-80% of 308win ammo capacities. what's worse is keeping them from tilting which limits it even more to 40-60% of 308win capacities. say my 20 round mag could hold 14 rounds it won't fit into the magwell due to the mag swelling which limits capacity even more (maybe down to 8-10). the poly doesn't swell as much as steel or aluminum mags does, but cartridge length is lessened by .040" or more. if i'm staying under 2.830" magpul m118 mags are the ticket as they give me more capacity with less swelling and/or tilting. using the 6.5prc in conjunction with m118 mags holding 8-7-8 rounds in a 25 round mag feeds the factory norma ammo of 143golden targets which is around 2.830". i need a 3d printer to make followers that utilize short mag cartridges. i might totally remove the cartridge portion of the follower and somehow use a dummy round in its place? i've talked to places that offer short mag ar firearms and their response to my mag question(s) is they use standard 308win mags.

 

[kfreeze]

getting the correct mag is key! most will be 2.830" and shorter, but larue, acs and a few others get you past 2.860" problem i have is the follower with both short mags i have. i've tried 10-25 round mags as i know when fully loaded you can get and average of 70-80% of 308win ammo capacities. what's worse is keeping them from tilting which limits it even more to 40-60% of 308win capacities. say my 20 round mag could hold 14 rounds it won't fit into the magwell due to the mag swelling which limits capacity even more (maybe down to 8-10). the poly doesn't swell as much as steel or aluminum mags does, but cartridge length is lessened by .040" or more. if i'm staying under 2.830" magpul m118 mags are the ticket as they give me more capacity with less swelling and/or tilting. using the 6.5prc in conjunction with m118 mags holding 8-7-8 rounds in a 25 round mag feeds the factory norma ammo of 143golden targets which is around 2.830". i need a 3d printer to make followers that utilize short mag cartridges. i might totally remove the cartridge portion of the follower and somehow use a dummy round in its place? i've talked to places that offer short mag ar firearms and their response to my mag question(s) is they use standard 308win mags.

You are right. I forgot to mention the swelling. Removing the cartridge portion on the follower will help you. That's what dpms did on the 30 rem ar mags to allow for the fat case. You only have to remove enough of it though. Not all of it as they did on those mags.

 

[liber]

getting the correct mag is key! most will be 2.830" and shorter, but larue, acs and a few others get you past 2.860" problem

I guess I've been living under a rock. I've always used magpul mags in my LR-308 with 308. I just got a Lancer mag I'm anxious to try. I have never had any that I haven't had to bend the feed lips. Have had feed issues with 6.5 Creedmoor and 8.6 blackout. Seems odd as 308 has always fed fine in that lower. I had some AR Stoner mags in 6.5 Grendel / 6.8 SPC, but sent them back as they didn't feed well. Different cartridge, so could be different issues.

 

[ARlife4me]

I guess I've been living under a rock. I've always used magpul mags in my LR-308 with 308. I just got a Lancer mag I'm anxious to try. I have never had any that I haven't had to bend the feed lips. Have had feed issues with 6.5 Creedmoor and 8.6 blackout. Seems odd as 308 has always fed fine in that lower. I had some AR Stoner mags in 6.5 Grendel / 6.8 SPC, but sent them back as they didn't feed well. Different cartridge, so could be different issues.

IF, you're lucky enough to find any knights armament company (kac) it'll go 2.880ish from what i've read. key to knowing and finding mags that'll give you more oal is how the mag is welded. most are lap welded so you loose 1 thickness of the metal due to this. some are laser/tig welded together on 1 side or the other by the bolt catch part of the mag, so you gain 1 thickness of the metal. poly is just due to thickness needed for enough strength which keeps them under or at 2.830ish give or take .005-.015".