Welcome to AR10T.com, the world's first forum dedicated to AR-10™ rifles .  We invite you to JOIN our friendly firearms enthusiast forum.

I Need .300 RSAUM Magazines

  • Posts: 11
  • Thank you received: 1

I Need .300 RSAUM Magazines was created by MeatAxe556

I bought a AR10T Ultra .300 RSAUM many years ago (sitting NIB all this time while I've been sidetracked with other projects). Now that I've dusted it off to start shooting, I cannot find magazines. Armalite does not sell any, followers or otherwise (thanks Armalite for your stellar customer support -- I'll remember that next time I'm in the market for a rifle!). Armalite has been no bloody help whatsoever.

Of course, I would rather have hi-cap magazines than the few anemic 5 rounders I have on hand that came with the rifle. My question: can the Gen 1 or Gen 2 Armalite .308 mags be used with .300 RSAUM or can they be modified to do so?

Any other suggestions? Can M14, FAL, etc. mags be used or modded for this caliber?

Thanks!
Last edit: 10 years 9 months ago by MeatAxe556.
10 years 9 months ago #26307

Please Log in or Create an account to join the conversation.

  • Posts: 459
  • Thank you received: 111

Replied by SOC on topic I Need .300 RSAUM Magazines

If you would have contacted Armalite they would have told you that the new Gen II mags work for 300 RSAUM.

You can turn a 15 round Gen II into a reliable 10 round mag for your AR-10TU. Anything over 15rd size the friction of the rounds stacking in the mag is just too much to allow feeding.

The follower needs slight alterations and the feed lips need trimmed back to the same length as the ones on the 5 rounders the rifle came with. I'll post a how to once I find more 15 rounders.

Also if you want the last round bolt hold open to function with gen II mags you'll need the new bolt catch.
The following user(s) said Thank You: jtallen83
10 years 9 months ago #26311

Please Log in or Create an account to join the conversation.

  • Posts: 11
  • Thank you received: 1

Replied by MeatAxe556 on topic I Need .300 RSAUM Magazines

Thanks for the prompt info!!! Will try to scrounge up some factory Gen. 2 15-ound mags for this project!

I did contact ArmaLite directly by email about this, and one of the Lead Tech's emailed me back basically telling my I was SOL -- no help at all, obviously. Pissed me off!
10 years 9 months ago #26312

Please Log in or Create an account to join the conversation.

  • Posts: 1785
  • Thank you received: 212

Replied by faawrenchbndr on topic I Need .300 RSAUM Magazines

Send MrRaley a message here asking if he has any suggestions.
That is the problem with uncommon calibers, finding mags can be a bear
NRA Life Member
USAF(ret)
10 years 9 months ago #26313

Please Log in or Create an account to join the conversation.

  • Posts: 11
  • Thank you received: 1

Replied by MeatAxe556 on topic I Need .300 RSAUM Magazines

Thanks for the info!
10 years 9 months ago #26326

Please Log in or Create an account to join the conversation.

  • Posts: 737
  • Thank you received: 153

Replied by mrraley on topic I Need .300 RSAUM Magazines

I've ran into this a few times so far and this is what I have on this...

The RSAUM rifle was a short lived era. It did not go over as well as planned. After production ran out, the rest of the parts on hand were either sold or sent to repair shops for fixes.


The GEN II magazines will not work properly. The feed lips are short and have a wider gap.

The GEN I magazines for this rifle were hand picked before modification for there longer feed lips.


If you can find M14 magazines with the longer feed lips, you can convert them to work in the AR-10. The down side though. Is that the followers will not hold the bolt back after the last round has been fired.
"Attack the issue NOT the individual"

“Fix the problem, DON’T affix the blame”

"Prosecute the position, NOT the person"
10 years 9 months ago #26335

Please Log in or Create an account to join the conversation.

  • Posts: 11
  • Thank you received: 1

Replied by MeatAxe556 on topic I Need .300 RSAUM Magazines

OK, I'm getting confused with conflicting info here: either the Gen 2 mags can or cannot be used and the feed lips of Gen 1, 2 and modified M14 mag bodies are either too short or too long and need to be trimmed...

I did notice on the followers of my 5-rd .300 RSAUM mags that it looks like part of the hump has been neatly shaved off at an angle.

Are these .308 followers that have had their humps shaved down to accommodate the wider .300 RSAUM case? Or is it a totally different follower?

I'm hoping I can get either a Gen 1. Gen 2 or a modified M14 mag body and shave down a Armalite .308 follower just so and put it all together to feed .300 RSAUM...or simply stick the few .300 RSAUM followers I have in modified M14 mag bodies...am I on the right track?

The solution to this would make a good submission to the Articles section.
Last edit: 10 years 9 months ago by MeatAxe556.
10 years 9 months ago #26357

Please Log in or Create an account to join the conversation.

  • Posts: 459
  • Thank you received: 111

Replied by SOC on topic I Need .300 RSAUM Magazines


Go see my post "SOC's AR10-TU Magnum 300 RSAUM"

Here are some pics to show you what actually needs to be done.

RSAUM on left Gen II on right. Trim Gen II to match the ones that came with the rifle.

This image is hidden for guests.
Please log in or register to see it.



To make a 15rd Gen II function reliably you'll need to trim this corner off the follower.

This image is hidden for guests.
Please log in or register to see it.

The following user(s) said Thank You: jtallen83
10 years 9 months ago #26359

Please Log in or Create an account to join the conversation.

  • Posts: 11
  • Thank you received: 1

Replied by MeatAxe556 on topic I Need .300 RSAUM Magazines

Thanks, SOC, for the info! You ought to put that in the Articles section so that noobs like myself won't be asking so many questions.

Searching for Gen 2 15-rounders!
Last edit: 10 years 9 months ago by MeatAxe556.
10 years 9 months ago #26361

Please Log in or Create an account to join the conversation.

  • Posts: 459
  • Thank you received: 111

Replied by SOC on topic I Need .300 RSAUM Magazines

Please let me/us know where you find them.
10 years 9 months ago #26362

Please Log in or Create an account to join the conversation.

Show 'em Off!

Add your rifle to the AR-10 Photo Thread!