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Thread: One removable mag stock setup for 308 through 338 Lapua

  1. #1
    Basic Member
    Join Date
    Dec 2015

    One removable mag stock setup for 308 through 338 Lapua

    I have 4 different long action stocks and chassis that are milled for the longest magazine - 3.850" - that Accurate Mag offers. Two MPA's, one HS Precision, and a factory Savage Accustock from a 338 Lapua rifle. I wanted to stick with that platform - 3.850" mag length, for my long range guns.

    I bought the following magazines for these stocks / chassis to see what I could feed out of them - tested 22-250 AI, 243 Win, 6-284, 6.5-284, 6.5 CM, 308 Win 300 WSM, 300 RUM, 338 Edge and 338 Lapua

    • 300 Win Magazine - The 300 Win Mag, unmodified magazine will of course feed 300 Win Mag but none of the other cartridges I tested worked without feed lip adjustment. With the feed lips bent inward until a 308 Win cartridge was at the right height to be picked up by the bolt, the 300 Win magazine would feed one or two 308 Win cartridges, but after that the round below the one being stripped from the magazine would dive deep down into the case and stay there. I remembered reading about some guys who modified the followers, feed lips, ribs and put spacers in the AI mags to get them to feed various rounds for which they were not designed. Not really wanting to do that, I thought about some way to keep the next round coming up from diving down into the magazine. The idea of sticking a 300 Win cartridge in first to give it more spring pressure and to help stop the follower from diving down popped into my brain. I tried it and it worked. As long as you cycle the bolt smartly in both directions it will feed five 308 rounds every time. Even when the shoulders are pushed all the way forward into the retaining ribs. Since the feed lips were moved inward, the 300 WM cartridge is no longer picked up by the bolt face, so it stays down in there through the entire process. I am going to paint a dummy round bright orange so it will be obvious I am out of ammo when it hits the top. I don't have any 300 WM barrels so I don't see ever changing the feed lips on that magazine unless I find a deal on a 300 WM barrel down the road and have ended up not shooting the WSM much.

      None of the other cartridges in the list above would feed reliably with the adjusted feed lips. Though I expected the 243 to work, it kept hanging up on the small tabs near the front of the magazine or diving down under them.

    • 300 Ultra Mag Magazine - The 300 Ultra Mag magazine would only feed the RUM cases. Too skinny for the 338 LM, WSM and RSAUM cartridges and the 308 and smaller cases didn't come close to working as there was no case shoulder rib to keep the cartridges from moving all they way forward in the magazine and jamming every time other than sometimes on the first round only.

    • 338 Lapua Magazine - The 338 Lapua magazine from Accurate Mag is the most reliable detachable magazine I have ever used. In 5 years I have never had a failure to feed. Surprisingly, it was also very reliable with the 300 WSM and 300 SAUM cartridges with no feed lip adjustment or other tweaks. I have been running that mag on a Savage 338 Lapua "Hunter" Accustock with 300 WSM cartridges for several years with zero failures to feed. If I can find my 300 RSAUM cartridges for an old DPMS AR308 rifle of mine, I will test those as well, though not many people shoot that dying round.

    This makes my long action detachable mag kit a lot simpler with more options and less money spent. Four 3.850" AI Mags, various barrels and three bolt heads will allow my 338 Lapua actions to function with a bunch of different rounds and my long actions to work with the same group minus the 338 LM. What I usually do is swap barreled actions among the 4 stocks / chassis I have on hand that accept the AI mags, as needed, since I have more actions than stocks at the moment. Those MPA chassis are pretty spendy. Two is about my limit. Return to zero in the metal chassis is very close when a torque wrench is used.

  2. #2
    Basic Member
    Join Date
    Dec 2015
    I tested some 270 Win cartridges in the Accurate Mag 3.850" long 300 Win magazine just now. This is the magazine with tweaked inward lips that feeds 308 Win rounds, plus the added "follower" which consists of a dummy 300 Win cartridge. Without that "follower" the 5th round almost always dives deep down into the mag and gets stuck there. It will feed 5 rounds of 270 Win reliably with snappy cycling of the bolt in both directions. I couldn't find any 30-06 cartridges as I rarely shoot that one, but I do have some. When I find them I will test them as well. Most likely they will feed fine.

  3. #3
    Basic Member big honkin jeep's Avatar
    Join Date
    Mar 2007
    Metro Atlanta Georgia.
    Good info here. Makes me wonder if a follower modified with epoxy, or perhaps a .308 follower with velcro stacked on top of the win mag follower might be worth looking into. Maybe some other tinkers will chime in with possible additional theories.
    A good wife and a steady job has ruined many a great hunter.

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