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Thread: .410 might be possible

  1. #51
    TRX
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    M-14 magazine with 3" .410s in it.

    The spring is pretty stout; the top shell has been in the magazine for a couple of days. You can see where it has bent under the load.

    I'll have to get some music wire and wind a weaker spring, and balance spring tension vs. feeding later.
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    The bolt is from one of the Romanian parts kits I bought. The pins just pushed out by hand when I took it apart.

    The boring tool is a ground-down 1/2" end mill. I made the toolpost years ago; it has a slot for a 3/8" tool at the correct height, and a 1/2" hole for a boring bar on center.

    The metal cut easily enough, and the sharp cutter didn't care about the interrupted cut. The Romanians put a great big dirt groove around the perimeter of the bolt face, which makes it look funny when the OD is opened up. I'm not sure what it will do to the soft shotgun shells when fired, but from comments on Saiga-12.com some Saigas are like that and it doesn't hurt anything.

    I haven't recut the extractor yet. It sits at an angle, and the rim on the shotgun shell is round and not as tall as a 7.62x39, so I want to grok it in fullness before cutting.

    I managed to salvage the mis-bent Tapco flat. I adjusted the hole positions with a diamond bit, then cut off the screws to the right length. I have a piece of 3/16" steel flat with a 10-32 hole in it. If you grind the screws down until they're just proud of the opposite side, they're correct for the front trunnion. This flat is sacrificial, since I wanted to figure out the magwell mods on a $15 Tapco flat instead of my expensive AK-Builder underfolder flat.
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  3. #53
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    What's the appropriate method for pinning the blocks to the barrel? Press everything on and then drill straight through, or use an undersize drill and a reamer?

  4. #54
    No Hope For Me Coils's Avatar
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    I would use the undersized bit then ream, if you don't have a reamer (just so you don't have to buy one) just step up the bit size until you get as close as you can.
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  5. #55
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    I could give that a shot. The AK parts are pretty hard, and the Mossberg barrel is definitely not hard, so I was wondering if the drill bit would have a tendency to veer off where it shouldn't.

    added: a useful thread on the subject:

    http://www.gunco.net/forums/f43/egyp...ctorial-53251/
    Last edited by TRX; 03-20-2010 at 10:05 PM. Reason: new information

  6. #56
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    Best as I can tell, the extractor groove is cut perpendicular to the extractor body, and the whole extractor sits at an angle to provide a slight hook onto the cartridge rim.

    Looks like I need to put it in without the spring, then keep grinding until the rim will pass the front of the extractor, then grind the groove deeper as needed until it fully grasps the rim.

  7. #57
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    I started to work on the extractor, then realized I had a problem. I'd opened the recess in the bolt head up to the .410 rim size, but it was substantially deeper than the .410 rim thickness. The Mossberg barrel had a simple V chamfer that let the base of the shell sit a few thousandths inside the barrel. Apparently it had been designed for a flat bolt face.

    After considering the situation for a while, I trimmed a bit off the barrel, cutting off enough of the chamfer to expose a few thousandths of rim. Then I put the bolt back in the lathe and faced it off. The gap between the bolt face and the back of the barrel is .003, with zero headspace.

    No metal came off the left (small) locking lug. I don't think the metal I took off the right lug will make any difference.

    I didn't want to trim the back of the barrel flat, since the chamfer is apparently intended to help guide the flat-nosed shell into the chamber.

    From the information I have on paper and what I've gathered on the web, shotshell rims vary quite a bit according to manufacturer. If I run into problems later I'll twiddle things some more.

    As an aside, the bolt faced off easily with a plain HSS cutter. It didn't feel any harder than the 4140 annealed bars I faced off for my .30'06 bolt project, chips looked about the same.
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    Wow I haven't really been following this but from the pics its looking pretty good!

    The rims may have problems feeding from that magazine. If you look at a PSL mag, you'll see the lips extend all the way to the back of the magazine to contain the rim. On those mags you posted, it looks like the rim is exposed, leading for the potential of having it stick on the lip when being pushed forward by the bolt.

    I'm not sure how best to fix it if it does cause feed problems... you may be able to spot weld a reinforcing shim to the back of the lips. Or use needle-nosed pliers to flare out the back of the lips so they "funnel" the rims.

    That will be something to look for when you test.
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  9. #59
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    I expect to do some work on the mag lips. My thought was to either extend them backward so the rim is always under the lip, or to taper them smoothly forward so they push the rear of the cartridge toward the center as the cartridge strips off.

    Fortunately the .410 rims are small and fully radiused. They strip off the unmodifed M-14 mag, but not smoothly.


    On your .45-70 you used a PSL bolt. If I remember right, it looked pretty much like an ordinary AK bolt. How does the breech end of your barrel look? That is, how did you wind up headspacing it with the rim?

  10. #60
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    I'm going to build the breech to look like a 7.62x54R barrel with the tapered face.
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