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300 Remington Ultra Mag in AICS 338 Lapua Magazine

brand692

Gunny Sergeant
Supporter
Full Member
Minuteman
Oct 22, 2009
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Western NE
Well, I'll keep the back story to this short.

I ended up with an NIB AICS 338 Lapua Magnum 2.0 stock a while back in trade. I thought it would be a great compliment to a 300 Remington Ultra Mag that I got on a trade, after all, they have the same COAL of 3.600, so why wouldn't a 300 RUM fit in a 338 Lapua magazine.... right?

So I went all out. I got the 2.0 stock, the Badger IMUNS, the AI bipod (against my better judgement), and three mags. The day it showed up, I was elated. It was going to make traveling with the long barreled 300RUM much easier. I installed the IMUNS, put in the the barreled action, and I thought I was off to the races. Until I attempted to load a magazine. Here is where I was reminded that NOT doing your research can bite you in the ass.

Turns out that despite the COAL of the 300 RUM and the 338LM being identical, their shoulders are in different places. The AI 338 Lapua magazine has two stamped reinforcing ribs that run from top to bottom, as seen here:

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<span style="font-style: italic"><span style="font-size: 8pt">Picture is compliments of Triad Tactical, a site sponsor and a great place to do business.</span></span>

Since the neck of the 300 RUM is shorter and shoulder further forward, the shoulder of the 300 RUM would hit the forward reinforcing rib whereas the shoulder of the 338 Lapua clears it. I thought to myself; "Whoops."

Back to the Snipers Hide Search Engine where I began doing my research I should have done before I started down this path. Keep in mind, I have somewhere in the neighborhood of $1800 into this AICS stock, the magazines, and the accessories. I frantically typed in "300 RUM in AICS" and came up with a few weak sauce hits, but they all said the same thing. The mag would have to be altered to get it to work. Damn. I'm a fool. I should have done this step first.

So I called a friend. He is a member here, and I won't give his user-name, because I don't know how many more of these, if any, he would want to do. Mike, if you read this, feel free to chime in. Long story short, I sent Mike the three magazines and a couple of empty rounds for him to see if he could make it work for me. Well he did.

He simply removed the reinforcing rib. And he did a fantastic job. So now my 300 RUM is back in action.

Here are some pics of the final product. This is still totally compatible with the 338 Lapua Magnum, but voids AICS warranty. In a couple of the pics you can see where the rib was removed and where the shoulder of the cartridge would have it if it was still there. The feed lips did not need to be messed with at all and are unaltered. This obviously poses a problem of foreign matter entering the magazine, but I'm not awful concerned about it this point. That would be a consideration for someone looking at doing this for a 300 RUM.

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I post this in hopes that no one makes the same mistake I did. Thanks to Mike for a fantastic fix to my oversight.
 
Re: 300 Remington Ultra Mag in AICS 338 Lapua Magazine

Man that barrel is to long. You should cut it down.. LOL....LOL...
 
Re: 300 Remington Ultra Mag in AICS 338 Lapua Magazine

LOL. You and the short barrels! Must come from years of riding the short bus.... hahaha.

I should bite my tongue though. You have me spun up on a 20 inch 338LM. As they say, its not always about the size.
 
Re: 300 Remington Ultra Mag in AICS 338 Lapua Magazine

Stacey will also do this for you. As you said though, it will void the warranty on the mags.
 
Re: 300 Remington Ultra Mag in AICS 338 Lapua Magazine

I actually tried Stacey. I sent a PM and an email and didn't hear back. Someone mentioned he was on vacation, so I didn't press the issue. But yes, I've heard he does it as well.
 
Re: 300 Remington Ultra Mag in AICS 338 Lapua Magazine

brand692,
glad that you like them and that they work ok

mike
 
Re: 300 Remington Ultra Mag in AICS 338 Lapua Magazine

Nice fix. Do the mags feel like they are less rigid now after removing the reinforcing rib?
 
Re: 300 Remington Ultra Mag in AICS 338 Lapua Magazine

Nope. Just as stiff as before. I have no doubt they will perform just as flawlessly as with the rib. I'm sure its there for a reason, as is everything AI engineers, but it works great for me without the rib.

Ben
 
Re: 300 Remington Ultra Mag in AICS 338 Lapua Magazine

Well done write-up, thanks. If someone's concerned about debris in the magazine 2 pieces of scotch tape or thin packing tape running on the inside and outside of the mag would solve the problem.
 
Re: 300 Remington Ultra Mag in AICS 338 Lapua Magazine

now i know why you got rid of youre ARD, the IMNUS rail wont clear it, am i correct?
 
Re: 300 Remington Ultra Mag in AICS 338 Lapua Magazine

I'm glad I learned a lesson and that hopefully someone doing a proper search, can save themselves the headache I had. Or, if they are die-hard on making it happen, they now know how.
 
Re: 300 Remington Ultra Mag in AICS 338 Lapua Magazine

Thank you, I may have to do the same thing when I get started on my .338 RUM build
 
Re: 300 Remington Ultra Mag in AICS 338 Lapua Magazine

You'll have to as the same problem exists with using 338 RUM in the 338 Lapua mags. Brand692's post did an excellent job of illustrating the problem and the solution to this situation. This topic comes up every so often and Brand692's post should be made a sticky.
 
Re: 300 Remington Ultra Mag in AICS 338 Lapua Magazine

Thanks for the detailed Post.
 
Re: 300 Remington Ultra Mag in AICS 338 Lapua Magazine

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: brand692</div><div class="ubbcode-body">Nope. Just as stiff as before. I have no doubt they will perform just as flawlessly as with the rib. I'm sure its there for a reason, as is everything AI engineers, but it works great for me without the rib.

Ben </div></div>
Hi. The ribs are there both for reinforcement AND limit forward motion due to recoil. Have you had any experience with bullets getting blunted or pushed back? If you could do this test: keep the bottom cartridge in the magazine the whole time you're at the range, exposing it for many shots and then check if anything negative have happened. You should measure COL before and after. If you use a muzzlebreak (sure u do
smile.gif
) u might want to take this of to check the extremes...
Would really appreciate if you did this, as im thinking about a 338 EDGE in AI mags...

magnus
 
Re: 300 Remington Ultra Mag in AICS 338 Lapua Magazine

thanks for the info....one more thing to check on............
 
Re: 300 Remington Ultra Mag in AICS 338 Lapua Magazine

Forward of the feed lips you only need to cut down 2.250" thats enough to clear 5 rounds.
 
Re: 300 Remington Ultra Mag in AICS 338 Lapua Magazine

good to know, I am in the middle of a 338 edge build and haven't decided between building a repeater or single shot because of the mag problems, this solution seems easy fix enough for my purposes.
thanx again forthe tip.
 
Hello,
You can tell me why that cut full length...?(for dust, sand, and other dirty things...)

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LARS,300 Remington Ultra Magnum (CIP AI magazine)
 
Thanks for the information, great post.
I'd imagine one could TIG in a patch to prevent foreign matter intrusion.
 
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You can cut a piece of foil tape and cover the slot, spray flat black if you want. Don't cut all the way down, just 2.250" from in front of the feed lips to clear 5 rounds.
PS: The 300 WM works better than the 338 Lapua mag for the RUM case.
 
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