Pulling the trigger and modifying my Polytech AKS223 underfolder to a full stock. Damn near ready to also swap the caliber to 7.62x39 and have the barrel shortened for an AK-104 build and run it suppressed as a modern “Alpha” AK build.

Got me thinking about considering 5.45 or even 5.56. As neat as 5.45 would be, I’m pretty worried about the amount and quality of 5.45 ammo brought into the US. 5.56 is sort of unique if I can have the rifle modified to take Bulgarian 5.56 mags, but I wonder if it’s more or less enjoyable than 7.62x39.

I also have an M16 with a 11.5” upper that I frequently enjoy and am wondering if that’d be a little too similar. Would appreciate any feedback from those of you who have fired AKs in other calibers, especially carbine versions and suppressed.

My 5.56 ak is the smoothest shooting gun I have. Mine is a 12.5

If you are serious, you would be better off not modifying such a valuable rifle.

Shortening a barrel is one thing...which is the easiest of tasks you have suggested.

"Converting" from an underfolder to a fixed stock is gonna be fun. You'll have lots of holes in the receiver after drilling out and removing the rivets and trunnion. Then, after welding them up, you'll get to drill new holes for the new fixed stock trunnion.

Switching calibers on an ak? Is the ejector the same for these calibers? Mag well size? New bolt that may have a different stem diameter, and may use a different carrier?

This ak is not an AR.. You need to do some research.

Sell the Polytech  and buy a 7,62 and a 5,45  AK

Don’t mod that polytech from an under folder , that’s a hard expensive and value ruining mod. If you are serious about chopping her down , I would have it converted to a Bulgarian 5.56 under folding krink. It would still hurt the value though. I’d personally leave it as is.

@TX-Zen

Don't mod the gun and buy a different one in the caliber you want.

A properly set up AK is crazy smooth shooting. I have a 556 AK that is smooth and flat. One of my 545 rifles makes the 556 rifle feel like it has recoil and basically the only way to tell it went off is the giant fireball, huge concussion and brass in the air but it is a 8" little fire breather. KNS pistons are well worth it.

I can't comment on modifications altering the value but if it were me I'd do it in 5.45 and convert to a side folder vs a fixed stock, and end up with an AK105

Tough to say what caliber is more fun in FA because it's so shooter specific. I rarely use my Sendra with a 7.62 upper but it is a crowd pleaser when done safely with new people who want to experience FA for the first time. I personally prefer 223 on the Sendra and shoot that by far the most, but 22lr is even more fun

On an AK it would definitely be 5.45 for me

Most people that shoot a full auto AK in 7.62x39 don't like it nearly as much as either 5.56 or 5.45. I wouldn't do a caliber conversion on yours. I also wouldn't convert the underfolder to a fixed stock for the previously stated reasons. I would seriously consider a shortened barrel to either 12" or  a full on krinkov conversion.

Personally to me an AK is 7.62x39.

I have a fixed stock in 7.62x39 and intially thought about converting it to something more modern like an AK104 but just can't bring myself to modify what is the quintessential and timeless "AK".

If I had a underfolder AK in 5.56 and I decided to convert it to anything I would probably have the underfolder changed to a fixed stock and it swapped over to 7.62x39 if it was my only AK.

In terms of caliber is there any domestic production 5.45x39?  Even any western europe produced 5.45x39?  If I went with a 5.45 gun I would personally also buy a lifetime supply of 5.45x39 as a stroke of an import pen could choke off the Russian supply of 5.45x39 and I have no idea if there is enough demand for domestic producers to ever significantly support that cartridge.

Honestly the best thing I ever did with my 7.62x39 full auto AK was to put the rate reducer fire control parts in it and use the KNS adjustable gas piston.  Those two things completely changed the characteristics of the gun for me.  It went from a pretty terrible shooter with a high cyclic rate and a lot of recoil for a medium rifle cartridge that I rarely shot, to really pleasant and one I have really started to enjoy shooting more.  Especially since I have been shooting more and more 7.62x39 given its cost and availability.   I have all three of the PTR G3 guns in 7.2x39, a traditional M16 set up in 7.62x39, a 1919 set up in x39, and just got a CMMG x39 mutant in this week I am going to set up with a RLL.

I have started to get the itch for a short/Krink style full auto AK and the underfolder 223 guns are reasonable in cost as a donor.  For a second full auto AK I would contemplate changing one over to a Krink length 7.62x39 barrel to have access to better mag availability, more available/cheaper/caliber common ammo to my other guns, but probably keep the top folder for fun/looks and to minimize the surgery to the back end of the receiver.

Good luck with whatever you decide.

Hornady makes 545. I've been loading their brass cases with VMax projectiles too.

can you post your results on the mutant?

I've been thinking about picking one up to use with my Link also

Sure, it should be pretty straight forward.  

Looking at it I will need to mill the bolt to SP1 spec, slightly relieve the interior of the lower, the rear lug is going to need to be slightly milled to square it up, and I think its going to need a paddle ~1 to 2mm taller than normal.

The rest will be tuning the gas and buffer to get a good ROF and reliability.

now you're getting me excited I can't wait!!

Do you think you'll have it finished by the end of the year?

I beleive so.

Only challenge right now is that its one of three RLL projects on the workbench right now.


Have an HK416, M12AR, and the Mutant all in line to finish up as hosts.

Busy busy man, I love it!!!

What is a good price for a mutant? Because I think that's step one for me.

Well… this Russian ammo ban may have completely killed off 5.45x39 for my consideration and probably 7.62x39 as well.

The 5.45x39 round has much better terminal ballistics than the 7.62x39.
When the Soviets invaded Afghanistan the Afghan people were amazed at the damage caused by the 'new' round.

Think it’s down to just 556 vs 762x39 now. Damn this is a hard decision

5.45 was not here prior to 86. I worked for a guy who did a 5.45 conversion on a Polytech in .223. I would personally go 7.62x39. The issue I have seen with .223 AK's is broken bolts.

I've got both F/A's AK-47 and AK-74.  I have the KNS pistons in them, and everyone that shoots them, all agree they love the 5.45 better than the 7.62.  I like it better too.  In full disclosure though, the 74 is a full stock version and the 47 is an underfolder, which affects the cheek weld and in and of itself isn't pleasant to shoot, even in semi IMO.

Good problem to have. I did both. Ted Marshall did my 1st conversion into an AKMSU in 762, and now he is doing my second conversion into a 100% Russian (minus bare receiver and trunnion) AK105 in 545.  Either way, good luck!

Have you checked with Mario at Piece of History Firearms? I would use him, over the years I've heard nothing but impeccable things about him. Personally, I'd go side-folding in x39. As far as it hurting the value I would think not, still a registered machinegun at the end of the day, in a much better form to boot. I see no point in doing a 556 AK if you've got an M16 as well unless you really just like the platform, but to me it sounds like you're debating which to me says go 7.62x39

So is a properly setup M16 / RLL / RDIAS variant.

I run full auto 7.62x39, 5.45x39 (as well as plenty of other calibers) in the M16 platform as it is so easy to tune with the plethora of aftermarket parts....burn out a barrel?   Who cares.  Parts are cheap and plentiful.  At shoots, I will just bring a few uppers and rotate them.

For the calibers above, I really like running a Surefire SOB carrier which has the extended carrier travel due to the shortened key.  I had a buddy mill the carrier so that I use it with unmodified AK47 and AK74 mags.  

5.45x39 configuration below with an A5 buffer tube, Tubb flat spring, fat boy gas tube, hydraulic buffer and it is super smooth with nice cyclic rate..  I stock piled a bunch of 5.45 and love dumping 45 mags through it with no muzzle rise.



Shorty 7.62x39 setup.  Also nice cyclic rate.