AK barrel contours?


March 24, 2013, 05:09 PM
im buying a new barrel for my bulgarian AK-74.. im actually converting this to 5.56, and taking some steps to make it more accurate.. (yes, AKs can be pretty accurate with good ammo and better barrels)

so anyway, i was wondering if someone know the barrel diameters of the AK-74 at the trunnion, rear sight block, gas block, and front sight, as well as the same dimensions for the RPK-74 rifle so that i can compare them to the medium and heavy contours of the AR15 to determine what size contours i can use on this AK

AK barrels are very, very light contour, many of them are not of the greatest quality either, so since im converting to a new cartridge anyway, i might as well upgrade to a better barrel while im at it

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March 24, 2013, 05:34 PM
Wait, are you trying to use an AR barrel on an AK?

If you are going to the trouble to recontour an AR barrel, why not just buy a barrel blank and and work with that?

March 24, 2013, 07:07 PM
no, im trying to get an AK barrel that has a similar contour to the medium to heavy contours used in an AR15.. point is once i can figure out what the stock contour is, the RPK contours, and look at the contours of the AR15 barrels i can determine the contour i would need for better performance in an AK barrel

the goal is to get a barrel manufacturer turn me a custom 5.56mm AK barrel, and to get an idea of what i need, id need to determine the contour i intend to use.. i need to determine whats going to give me a good balance of weight and accuracy, but i first also have to know the limitations of the rear sight block and gas block so i can determine my limits.

March 24, 2013, 07:25 PM
heres what i found so far..

for the bulgarian 74, its 22mm at the trunnion... its going to be about the same for the rear sight block, .667 at the handguard retainer.. .592" at the gas block, and .572 at the front sight block

the RPK-74 would be 23mm at the trunnion .944" at the retainer, .808 at the gas block.. and no idea what the diameter is at the front sight block.. anyone know?

comparing this to the AR15 barrel contours it would seem that the RPK barrel contour is only about as thick as a medium-contour AR15 barrel... the standard AR15 military contour is listed as .750" at the gas block, considerably thicker than the standard AK barrel

my goal here is a heavier barrel for increased accuracy by using a higher quality barrel, 1 in 7 inch twist, and going with a heavier contour to limit flexing of the barrel.. comparing this to the AR15 contours because i am converting this AK to 5.56mm in the process and trying to determine if an RPK barrel contour is good enough, or if i should try to match the contour of an AR-15s heavy-barrel in a custom AK barrel

March 24, 2013, 10:51 PM
Ohhh, that makes a lot more sense. Why not go for a bull barrel and mount that in the trunnion. Then you could fabricate a two piece gas block that would bolt on like an some ARs have, mill down the end for your sight and then widen the handguard channel on some RPK handguards.

March 24, 2013, 11:57 PM
i was actually thinking of leaving the front sight block off as i was planning to run it with optics (red-dot sight) im not sure if i wanted go with a full on heavy contour or not.. i wanted accuracy, but im not sure if i want to make the rifle that much heavier

im on the fence about the front sight though.. i mean, i could have it machined down for the AK front sight, use AK muzzle brakes and bayonet.. or just have it threaded for the AR-15 muzzle devices (since it would be a 5.56mm rifle)

basically my goal is to improve the AK, while still remaining the AK, so id most likely keep the front sight.. and try to keep the gas block though i believe my gas block might just be too small for a heavier contour.. and i should buy an RPK gas block from kvar

i think an RPK contour would offer me a large increase in accuracy, and be easy to find parts for to fit the barrel

March 25, 2013, 12:57 AM
AK's are already front-heavy with the very thin barrel on the 7.62x39. Only get's heavier on the 5.45 and 5.56 versions (all are the same contour, just different bores... on saigas, at least).

I wouldn't want a contour any thicker than that of your current one. Barrel quality will make more difference anyway, unless you're planning on sustained fire.

March 25, 2013, 09:39 AM
front heavy isnt necessarily a bad thing though, aids in reducing the climb of the muzzle, but those barrels are even thinner than the thinnest 5.56mm barrels, i should think an RPK contour at LEAST would offer a significant improvement, if made by a reputable barrel manufacturer, but you are right on them being a tad front heavy, so it raised the concern of whether or not someone would actually want to go with a full on heavy contour by AR15 standards

and as i said earlier, ive been considering dropping the front sight, having that giant block of metal dangling off the end of the barrel cant possibly be doing much in the form of accuracy, and AK sights are about useless anyway (ive considered a combination gas block and front sight like on the krink) but many modern red dot sights have a built in back-up so i dont think that would even be necessary

anyway, im torn between whether i want to take further mods for accuracy and go with a heavier barrel, possibly even free float, take the front sight off, or just leave it a straight up AK-74 with a heavier RPK contoured barrel... at roughly 7.5lbs weight for a standard AK-74M, how much extra weight do you predict it would add going from the paper-thin AK contour to an RPK contour, and to a contour that would be considered heavy barrel by AR15 standards?

April 4, 2013, 08:48 PM
Here is a front sight gas block combination. Looks like a ultimak gas tube rail also. I think the new version of this pins to the barrel. http://www.rifledynamics.com/services/bolton_block.php

April 5, 2013, 09:42 PM
green mountain sells a .223 carbon steel barrel blank, 1-7 twist for under $90.. are these any good?.. any idea what the groove pattern/shape is?.. and where would be the best place to go to have this contoured to probably an RPK countour, but for a 22mm trunnion?

April 5, 2013, 10:12 PM
I would contour the barrel as thick as possible still allowing standard handguards, use a standard '74 front sight base, but thread it using 1/2x28 so you can use an AR muzzle brake. but as for harmonics, that would be going to far for this application. however, if you can mimic a M4 carbine style barrel contour, then that might help. but i wouldn't focus too much on contour. you could also reduce weight by fluting it while still maintaining a stiff barrel. but that's my 2 cents.

April 6, 2013, 10:38 AM
so lets say i went with the equivelant of a heavy barrel, then fluted it, its weight would be similar to what contour if left unfluted?... its an idea ive considered to add greater rigidity without adding a lot of weight because for such a rifle, being light weight is very helpful

also, im most likely going to go with a combination gas block and front sight to save weight on the front end, and since theyre just for backup, the sight radius isnt THAT important, as ill be using a red dot for the most part...

so the gas block is going to be a limiting factor, if i cant find a larger gas block, i simply cant go with a larger barrel because i dont think theres enough meat on the block to ream it out

April 6, 2013, 12:20 PM
Here's an RPK gas block.

I don't know if it's exactly what you need, but it's what I'd look at. And the fluted barrel sounds like the better way to go.

April 6, 2013, 12:24 PM
expensive it seems. hmm.. roughly an added $150 for front end parts

April 6, 2013, 02:39 PM
Well nothing is cheap with AK modifications.

I've had a Saiga .243 project on the back burner for years now because of cost lol.

April 8, 2013, 10:21 PM
well you could flute the barrel up to the gasblock/sight then have the rest milled down to fit said parts, plus this would probably be around the same size needed for the 1/2x28 threads for a muzzle device. It would be ridged for the most part, and with the front end of the barrel turned down, would reduce weight. But i would look at the possibility of the RPK gas block.

April 10, 2013, 04:09 PM
you know.. i read a chart that lists the contours of AK barrels where certain components are pressed onto the barrel, and when i look at actual AK barrels you can see that at these points the barrels widen where these parts are installed... so my question is just how thick are the AK barrels not including these sections? theyre even thinner

what id like to know if anyone here has the ability to check, is how thick the RPK barrel is immediately before or after the segment the gas block attaches to?

what im going to end up doing is having a custom gas block made, since id like a combination block, but would like to go to a thicker contour.. so im trying to determine what contour the RPK really is to determine if its what im looking for for a custom barrel, or if i should determine something else

on milled AKs, the rear sight block is 18.5mm, im thinking a contour that is 18.5mm straight, forearm retainer from a milled ak could probably be enlarged, but a custom gas block would need to be custom made but thats something i might be willing to have done

if you were going to go heavy barrel on an AK, what would you do?

April 10, 2013, 10:08 PM
Well if you're going to build a custom sight/gas block, just run the barrel as a bull barrel the full length. have your FSB/GS made to fit it. *If I were doing this project*: I would find out what the max width i can go for the handguards to fit normally, then i would use this as my overall thickness up to the gas port, which the barrel will be turned down about .010" less which would run the rest of the way until the threaded 1/2x28 muzzle. Then i would have a custom FSB/Gasblock be made (or pre-existing one) to fit the gas port diameter. the length of said barrel would depend on whatever length of gas tube i was using. and the barrel would be fluted the whole length. but again, that's me.

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