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.410 might be possible

9K views 63 replies 7 participants last post by  TRX 
#1 ·
Saiga .410s aren't $149 any more, and you'd have to find one, pay the FFL fees at both ends, plus shipping, and then you'd still have to buy all the parts and do all the work to convert it to AK configuration.

Building a parts kit into a pistol is legal. Same should apply to building a kit into a shotgun.

Kits are back down to $119 right at the moment.

Doing some preliminary doodling, it looks like it should be possible to build a standard-length AK in .410, bypassing the whole "buy and Saiga and convert it" thing.

A .410 conversion should be roughly similar to a .308 conversion. A .410 shell will fit in a .308 magazine. Do the usual mods to fit a .308 mag.

Unlike a regular cartridge, a shotshell is longer after it's fired. This should not be a problem.

The Saiga 12 and 20 gauge rifles use a two-piece bolt head, but the .410 is one-piece. I figured the two-piece bolts were for ease of manufacture or to make extraction easier, but Saiga figured the .410 didn't need it.

The .410 rim diameter is .524", a 54R is .567", so there's room to open up a standard AK bolt to .410 size.

Numrich has 3" chambered .410 barrels for $50-ish. As a wild guess, I'd expect they'd be thinner than AK barrels and would require bushings at the tenon and to mount the RSB, GB, and FSB.

Lore has it that Saiga went to the new gas block with the oversize floating piston to get sufficient zip to cycle the action with low-pressure shotgun shells. Given the AK's flexibility in handling lower pressure metallic cartridges, I'd give the stock configuration a try before getting fancy. Then I'd open up the gas port a bit, space the gas piston to put it deeper into the gas block, and maybe ream out the gas block as far as practical and sleeve the piston. If none of those worked, a homemade gas block with a Saiga-sized piston ought to work. The floating tappet shouldn't be necessary.

If you started with a Yugo gas block, you could make it adjustable by modifying the gas shutoff.

Looking at pictures (I've never had the opportunity to handle a Saiga in the metal) it looks like the front trunnion is designed with some kind of guide ribs to help the shotshell go into the breech straight. The bolt also has fingers going forward, supposedly for that purpose. A shotshell's flat front means it has little room for deviation from the barrel centerline, whereas a pointy rifle bullet just has to hit the hole somewhere.

Again, I'd try it and see how things worked before over-planning things. Put a mark on the top of a shell with a felt tip, use that as a clock to see where the end of the shell hits the breech face. I can think of half a dozen ways to add guides or fillers to direct the cartridge if needed.
 
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#54 ·
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.
 
#56 ·
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.
 
#57 ·
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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#58 ·
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.
 
#59 ·
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?
 
#62 · (Edited)
So I'm an idiot who can't read his own drawings... I didn't get the step distance right in the bushing, so I had to press everything back apart. Which meant making a press block and a pusher first.

There were a couple of pieces of grotty steel I had failed to throw out, suitable for a one-shot tool like this. Of course, I put more work into squaring and flycutting than it was worth...
 

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#63 ·
I found an SKS underfolder bayonet at a reasonable price and tried it with the Chinese AK trunnion. No go; the sleeve is about 5/8" too short to engage the lugs. This is a 1966 military FSB, so I don't know if the Polytech ones are the same.

I found up with one complete bayonet and three sleeves and springs. I think I'll splice two of the sleeves together to make one longer sleeve. If I can find someone who can make pretty a fish-scale TIG weld across the knurled sections where the join will have to be I'll do it, otherwide it'll probably get MIGged and some cover-up lathe work to hide the mess.

I went with the spike bayonet. The knife bayonet just didn't look right, for some reason.

No other progress; Real Life(tm) has been keeping me too busy for much quality time out in the shop.
 
#64 ·
In our last thrilling installment, I found that an SKS bayonet won't fit an AK underfolder FSB.

Just a moment ago I found the picture below. The text near where I found it mentioned it was an add-on bayonet lug for an SKS, and that the author had used it to attach an SKS bayonet to his AK. Note the standard AK FSB.

I just spent twenty minutes trying to find out who might sell those, but any combination including both "SKS" and "lug" just kept turning up bipod mounts.

Anyone know who might sell one of these? I could make one, but if it's cheap enough I'll just buy one and move on to the next thing.
 

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