The problem with the Remington Ultramags in the AICS magazines is the length of the rim to the shoulder. The two deeply stamped strengthening ribs in the magazine body are placed too far back for the Ultramag brass to fit. The .300 Ultramag is 2.387" from rim to shoulder. The .338 Ultramag is 2.296" from rim to shoulder. The .338 Lapua is 2.161" and the .300 Win Mag is 2.196" from rim to shoulder. That's the reason why neither the Lapua or Win Mag AICS magazines will work with Ultramag brass without modification. One solution is to remove the strengthening ribs via grinding or machining. The magazines then have an open slot machined in them that exposes the cartridges,follower and spring to foreign material. People have done the modification,but they have to come up with some way to cover up the slots.
It has been done successfully with the use of the .338 Lapua magazine, the front ribs have to be machined out to allow for the RUM's extra shoulder requirements. This will allow the .300 and .338 RUMS's to function with x5rds very successfully. Of course, once this modification has been done, it will void any warranty/repair/replacement with AI on that particular magazine.
, Australia So which AICS model would be the best for me to obtain to make the modifications needed to house the 300 rum as well as have a magazine feed ? Is there someone that has contact with a fellow 300 rum owner that can give me specifics on the mods required ?
Loc: Elizabeth City, NC You will need the LA AICS in either Stage I.5 or II, your choice, ordered with the .338Lapua magazine not the .300WM and amount of mags you desire. I have done the modification for years for customers and can assist, just contact me direct. On the AICS LA, I believe Bauer Arms has them instock in several different configurations.
Accuracy International North America
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Loc: Ireland, Indiana My 'smith done up a 338 Edge using modded AI 338LM mags. Worked out very nice.
Thank you for your email and the link to the Snipershide post. We are aware that it can be done but it is not an amateur gunsmith job and it voids the warranty on the .338 magazine, which has to be bought separately, and as we are not sure what part of the world our emails come in from, we can be rather vague with dispatching information. Stacey at Accuracy International North America will have the most information to help you with your requirement and would be the best contact.
Yes it can be done says AICS but 338 mags need smithing.
Check under gunsmithing at snipers hide if anyone is interested