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Old October 31, 2012, 10:14 PM   #1
barnbwt
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What Makes for a Good Magazine?

Is there an established way gunmakers design magazines/feed systems to ensure the design should function properly? I hear of folks with "buggy mags" tweaking feed lips, honing ramps, reshaping mag catches and all sorts of other stuff. Is there a formula to the madness, or is a brute force guess-and-check the only way to approach the problem?

I'm contemplating converting a Steyr M95 from 8x56R to 45/70, which would require more than just rebarrelling for a repeating rifle. Other conversions attempt to use the existing feed system with similar-enough cartridges (7.62x54R and 30-40 most common). The en bloc clips used to feed the action would need to be substantially modified for the wider, shorter 45/70 round, and are themselves not very durable (disposable, even) in any case. Even successful conversions require frequent readjusting of the feed lips in the flimsy clips.

Since 45-70 would require major clip surgery anyway, I thought it may be better to replace the innards of the entire magwell with something purpose built for the new cartridge, that would hold together much longer. That said, I have no idea where to start. If some guidelines exist for how a cartridge needs to be angled relative to the breech face, how high on the bolt face, etc. I may be able to put something together that would suffice. At least be a closer shot to a working solution, and a much more durable starting point than 100yo sheet metal disposable clips . The dream is a hi-cap using a modified Madsen or Bren mag, but I'd be equally pleased with a 4-5 shot

Thanks for the expert advice,
TCB
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Old November 2, 2012, 07:22 PM   #2
James K
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When a gun uses an en bloc clip or a removable magazine, the feed lips and initial guiding of the round, as well as retention of the round, are built into the clip or magazine. There is usually also a feed ramp designed to handle the appropriate bullet and guide the cartridge once it is released from the clip or magazine.

But rifles made with a built-in magazine, like the Mauser 98, have the primary guide and cartridge retention built into the side rails of the receiver. That is why changing a Mauser or a Springfield M1903 to another cartridge can require work on the feed rails as well as on the ramp to get proper feeding.

There is also a third way, used by some sporting rifle makers. A magazine box is inserted into the space between the receiver and the bottom of the magazine well; it has the feed lips and guide built in; this allows the maker to change around among similar calibers by changing only the magazine box rather than the feed rails, an easier proposition.

For your purposes, it seems to me the problem is not proper feeding but retention of the round in the magazine. To do that requires not only rails of some kind but also a properly shaped follower, plus magazine walls to guide the rounds. Just fixing a clip in place might work, but it would be difficult to load the rifle and, as you note, the clip would soon wear out.

I suggest studying magazines like the Mauser and the Remington 700 and seeing if a magazine box of some kind can be rigged.

Perhaps some of the other folks have done this job (I have not) and can tell you exactly how to do it. Lots of luck.

Jim
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Old November 2, 2012, 10:31 PM   #3
barnbwt
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Thanks for the reply, I know this one of those "stupid questions" people like to say don't exist but totally do

I think door number 3 might be the best option, and the only hope for a non permanent solution (damn, that'd be a marketable product with all the cheap, unsellable M95's out there) for the reciever mods. Would also give me more tries to screw stuff up (unlike tack-welding bits of metal up in there).

I think if I rig up the system to work such that the top of the cartridge is at the same elevation as with the original loading, points roughly the same direction, and leaves the mag at the same bolt position as before...it just might work. The M95 is controlled-feed, so the real trick is likely to be getting the extractor to grab the round reliably; at that point, chambering should be just about guaranteed, right?

Supposedly, a Sako, and even Remington extractor has been modded to the M95 bolt by others (crappy factory extractor tends to break); have either of those actions been done with rimmed rounds (especially 45-70)?

TCB
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Old November 2, 2012, 11:51 PM   #4
Ben Towe
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Maybe I'm crazy but I thought the Steyr M95 had a built in magazine rather than an en bloc clip...
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Old November 3, 2012, 10:46 AM   #5
barnbwt
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Nope, it has a Mannlicher (sp?) style clip that falls out the bottom when the last round is stripped (said hole is why the guns were notorious for getting full of grime). If the internal follower/spring and floorplate are removed, there appears to be enough room for some sort of box (whether internal or detachable), but the round retention would have to come from that box, it looks like, since there is just no good way to attach feed lips well in there (no metal on the sides of the magwell).

I need to get measurements of some type of single-stack curved mag (Madsen comes to mind; SVT mags are too pricey ), since this is likely the route I'll have to take. I'd probably shorten the things to <10 rounds to cut down on the ridiculous factor, and weld/rivet feed lips over the end (if they don't come with them).

Does anybody know how Mosins, Enfields, SVTs and the like keep from getting rim-lock due to recoil josteling rounds in the magazine? Or is proper loading the only solution (a la .22LR magazines)?

TCB
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