Thread: .410 might be possible

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.

I tried a 3" shell in a G3 mag. Fits fine. The M-14 mag, not so well - the lips don't go all the way to the back of the mag, and snag the rim, which then jams solid. The lips need to be extended to the back, or trimmed forward at an angle.

Hmm. If I'm figuring it right, the Saiga mag tilts the shell sharply up at the front, where it touches the top barrel extension? Then it just rides the extension right into the breech?

I guess that's easier than trying to guide a flat-nosed shell into a small hole.

Hmm, looks like the ordinary AKM trunnion rivet pattern instead of the inline pattern of the Saiga-12.

That U-shaped(?) shell guide(?) looks like it's held in place with a small rivet on the right side.

I've been playing with some bits. An M-14 magazine can be slid up high enough in the trunnion for the shell to have an almost straight shot at the chamber. The bolt and bolt carrier vs. the mega-spring in the M-14 mag would beat the heck out of a shotshell, I bet. The M-14 spring is noticeably stiffer than a G3 spring. Never having seen a Saiga .410, I have no idea how stiff one of those springs is.

The M-14 follower has nothing much to keep it from tilting. The last shell would get flipped up in the front as the folower tilted. The next-to last and other shells have no problem, as far as I can see. Also, the rear of the lips need to be beveled to accept the rim, and the same for the back of the follower.

The G3 feed is nearly perfect, follower, lips, and all, but either the front of the mag or the trunnion need to be thinned for the trunnion to accept the magazine. Though this could be done, it would leave no room for a rivet, and maybe two threads on a screw. I know several .308 conversions have been done with G3 mags, but I think the M-14 might work out better.

I think some experimentation with magazine springs would be indicated; winding progressively weaker springs until feed problems manifested, then going back to a stiffer spring. You could wind music wire over a wooden form.

This sort of thing is why many early bolt-action rifles had weird double-lever arrangements under the follower - the spring(s) gained mechanical advantage as the follower went up, so as you fed or emptied the magazine, the pressure of the cartridges against the feed lips was fairly constant. With a straight coil spring, the pressure is drops linearly as the magazine empties. With the 50- round magazine on my MAC-11, the coil spring is so tight it sometimes double- feeds the top rounds, while the last few don't come up fast enough for the bolt to catch them on the rebound. Basically, the magazine doesn't work very well, though it's an OEM factory part.

The lever-follower mags went away because simple leaves or coils worked well enough for metallic cartridges, and because they were complex. Most of them only handled five cartridges; it would have required a stack of levers to feed more, which would have been a hassle.

Still, it would be nice for something like that to feed shotshells, so they wouldn't get all mashed out of shape if you put the gun away while loaded.

.410 is Go

Okay, the Voices wore me down. I ordered a Romanian underfolder kit and a 24" .410 barrel, originally for a Mossberg. I'll have to fill the dovetail on the bottom that was to hold the forend.

I made a deal with a friend for his Chinese underfolder FSB, so eventually I should have a double underfolder .410. It doesn't have a bayonet, but I should be able to score one eventually.

I could justify it as a "close quarters weapon", but really, I'm doing it because it should look cool when it's done...

I ordered a Romy underfolder flat from AK-Builder for $35, and went ahead and got a 2XTM flat for $30 for the other build.

I need an FAL magazine to compare to the G3 and M-14 mags, but it will have to wait until I find one somewhere where I can combine shipping with some other stuff.

From the picture it looks like the Mossberg barrel has an extension built onto it already.

I'll take a picture when the barrels come in. (I ordered one for the AK, one for the SMLE)

I'm not sure you could press the ribs out without warping the magazine. You might take a cut-off wheel and cut a slot down the indent to give the metal some place to go. You could weld it up, or if you make the slot neat, and you could just leave it open to tell how much ammo you had left.

The front follower stops need to be trimmed back or re-angled; they catch on the fluted plastic of the cases.

They don't seem to exist in my local area. And once I paid an FFL and shipping to get one here, I'd still have to convert it.

$120 Romy underfolder kit, $35 AK-Builder flat, $25 Numrich .410 barrel, and the parts box is cheaper than I could get a .410 Saiga to my door... and then I'd be out about the same time and money to convert it to AK configuration.

I kind of have my heart set on a double-underfolder .410 now.

Other than that, "just because" ought to cover it!

Midway sells 32 gauge shells. Considering how oddball it is, I thought the price was surprisingly reasonable.

If I remember Ed Hubel's 12gaFH thread on Accurate Reloading correctly, he got a ruling from the ATF on his .720 caliber rifles. The ATF said that even if the barrel was rifled and he was shooting blown-out BMG in it, if it would still accept a standard shotshell, it was still a shotgun as far as they were concerned.

Of course, shotshells have tiny rims, and with enough extractor hook travel, there's no reason you couldn't shoot a rimless brass shell, as long as the rifle could still shoot a standard shotshell. At least, that's how I understood the thread. It's something like 65 pages long now...

I have a 4140 bar cut up to make bolts from. Depending on how the feed issues work out, I could always make a Saiga-length bolt if I had to. I'd like to do it without going that far, if possible, so others could duplicate it without a lathe and heat treating a bolt.

My underfolder kit came in today. Yee-haw!

Looks like, other than the kit, the most expensive part of this build will be the bayonet. eBay and Gunbroker prices reflect the average selling price I found on various fora - $100 to $125! Yow!

On the other hand, Polytech's web site has brand new underfolder bayonets for $75... sometimes I wonder how people set prices on things.

The .410 barrel showed up today. It says "NEW HAVEN BY MOSSBERG MODEL 283T - .410 GA. - FULL CHOKE 2 1/2 AND 3 IN SHELLS - NORTH HAVEN, CONNECTICUT - MADE IN USA" on it. Quite a lot, for a small barrel...

The breech end is threaded. The picture at Numrich showed dovetails cut for the pump bits, and fingers going back over the breech. This is just threaded, no dovetails, which is good. I suspect the picture was generic.

Interestingly, the threaded tenon is small enough that when I make a bushing to press it into the AK trunnion, the barrel pin shouldn't intersect the threads.

I think most of the "finger" function, if needed, could be taken care of by an extension to the rear sight block.

The barrel is .812 where the RSB goes; the RSB ID is .790. It would be easiest to turn the barrel down to accept the RSB. The barrel is tapered where the gas block goes, .625-ish. The gas block is .595 ID.

SAAMI pressure for the .410 is 13,500, so shaving .022-.025 from the barrel diameter shouldn't hurt anything.

Hmm. One barrel says "New Haven" and the tenon is .725x24tpi. The other says "Western Auto" and the tenon is .715x24tpi. Otherwise the barrels are identical.

23/32 is .7188", or 8.256mm. Close enough for 8.25mm, except for the thread pitch. Weird.

I was going to order a tap, but I guess I could pin the barrel to the spacer sleeve. It's an AK, after all... My internal threading skills are shaky, and I'd just as soon avoid that if possible.

I think I'm just going to turn the threads off the tenon and press-and-pin it into the sleeve. It's good enough for Kalashnikov, it's good enough for me...

My lathe is a 1950s Atlas 10x60. The Atlas design doubles the leadscrew as the power feed screw. It hangs right out in the open, for rust and swarf. By the time I got the lathe the screw was noticeably worn; despite my best attempts to preserve it, it's now worn to almost a V thread.

I could thread something long enough to hold in the steady rest, over an unworn portion of the screw, but it's all enough of a hassle I'd as soon avoid

it.

So, I'd ordered a nice Romy underfolder flat from AK-Builder for $30, and a couple of Tapco flats from DPH for $15 each. I pulled the Tapco flats out of their bags and the outer sides have a very coarse belt-sanded finish, not at all like the one I bought a year ago.

So I set the first one up to bend... and bent it wrong.

[unprintable: deleted]

The top rails weren't completely bent at the front, and I'd measured across the outside. That made the sides .020" different in height.

My fault for not triple-checking. I measured to the inside of the (partial) bend on the second one, and got it right.

The AK-Builder flat, by comparison, is a whole different thing. Nice and smooth. No locating pin holes, so I had to drive my roll pins down flush. Stepped top rail! And properly bent and trimmed up front, no Dremel work needed to get the flat to fit into the slots in the trunnion. Beveled sides at the ejection area.

AK-Builder's equivalent (non underfolder) flat is $20. Next time I'll pay the extra $5, even if they don't come with lower rails.

Originally Posted by 1biggun does the mag you plan to use clear the demples on a standard blank?? People have made G3 mags fit without grinding completely through the dimples. If I grind completely through, I'll just cut the dimples out and weld patches in.

Bending the Tapco flat -

It's a variant of 555th's fixture. The flat bolts between two shoes, then some fine thread 3/8" rod pulls it through.

The miscellaneous holes are because the angle iron is recycled from a previous project.

I set the barrel up with the breech at the tailstock end so I could turn the threads down. There's a radius on the end of the tool to prevent a stress riser at the end of the cut.

Flip the barrel over, cut the step for the RSB. There was no way the Romanian bits were going to work, but the Chinese bits were all bigger. I only had to turn .020 or so off the barrel for the RSB.

Moving up to the handguard retainer area, I discovered the barrel wasn't straight, though it looked okay sighting down the bore. It was also out-of- round. The kicker is, it appeared to be rolled and welded, like muffler pipe! There was a dark line on the inside that I thought might have been rust from condensation. There's a definite lump on the outside, though, and you can see some imperfections where it was welded. I know Ford uses welded brake lines in their cars, and welded tubing does fine for hydraulic cylinders, and the .410 isn't a high pressure cartridge, but it was a bit creepy just the same.

The handguard retainer bit cleared up. I repositioned the barrel to reduce the unsupported area. When I bought the lathe, it came with TWO steady rests. Unfortunately, I just discovered one is apparently for a South Bend, or at least a 10" lathe with a single pyramidal way. The other fits the Atlas, but it's for a 12" lathe. [sigh] I sharpened the tool and made teeny tiny cuts, holding onto the barrel with my hand to damp the vibration.

Unfortunately the combination of warp and out-of-round on the gas block area made it impossible to turn concentric. After cogitating a while, I dressed the high spots with a file, then filed it down to the right size. It's a bit out of round, but it shouldn't affect the press fit.

I'll have to cut the barrel for the FSB later.

Fortunately, the Chinese parts were almost perfect. Even opening up the Romanian RSB and GB as far as they would go, I don't think I would have had enough barrel thickness to be safe. It would have required custom parts, or cutting and welding tubes to the Romanian parts.

I have two Romanian handguard retainers and an AMD-65 retainer. They have keys on the sides to keep the retainers from twisting on the barrel.

The Chinese retainer is from a 1966 milled military rifle. Besides being larger in diameter, it has no keys; it's retained only by the flip lever and shaft.

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.

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.

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?

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/

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.

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.

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?

Bushing to step barrel diameter up to the Romanian trunnion ID. The interference is .003" to the barrel. 3/8" threaded rod to pull them together.

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...

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.

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.