modify bolt face for a smaller cartridge?

[jason41987]

as ive been playing around with the idea of converting a 5.45 AK to 5.56, theres a general lack of availability of bolt parts.. i have a 5.45 caliber bolt it has a 10mm rim diameter and a 1.5mm rim thickness... 5.56 has a rim diameter of 9.6mm and a rim thickness of 1.14mm

most people just use the bolt as it is.. and it can be a tad loose.. what id like to know though is what the proper procedure would be for adding some more material to this bolt for the proper bolt face or is starting with smaller bolt face a requirements?.. can it be welded up and machined back to where you need it?

im assuming said product would have to be re-heat treated

the other idea i guess would be to somehow fit in some kind of an adapter for the bolt face.. exterior dimensions to match the original bolt face, interior dimensions machined out to match the new bolt face.. maybe solder it in, or drill and pin it in.. see i dont know the proper procedure for reducing a bolt face when a new bolt isnt a possibility

 

[LAGS]

An adapter ring would be so thin, that it wouldnt stay in place.
The Bolt can be rewelded and re- machined, then re- heat treated.
But that is an awful lot of time and expense.
The differance in the bolt face diameter is not that big of an issue if the extractor is set for a smaller case diameter and the rim thickness is not an issue.
Over all the case is only clearing the bolt face by .2mm in reality because the case stays centered in the bolt face.
You have stated the Case head sizes, and the minor differances.
But what is the Actual measurement of the Bolt Face opening ?

 

[jason41987]

if i could find my calipers id tell you, ive misplaced them in my move to this state recently.. but its not so much the case sliding around that im worried about as it is the depth of the bolt face for the thicker base of the 5.45.. about how deep should the bolt face for a 5.56mm cartridge be and could i just machine back the edges of the bolt face to match that.. and maybe make a new extractor?

 

[LAGS]

For that Jason, we need to know How Much recess there in in the Bolt Face.
That will determine where the case is sitting in relation to how much of the head is supported by the chamber.
I am sure you can Mill the end of the Bolt to lessen the recess of the bolt face
But if the Cartridge when Headspaced to the Bolt Face, is still the casing is into the chamber far enough so the front of the Back Web of the cartridge head in inside the Lip of the Back of your barrel, then you are fine.
Let's see if you cant find that caliper, and then we can get down to brass tacks.

BTW
Can the barrel on the AK be set back in the receiver at least the same distance you intend to mill off the face of the Bolt END ?
I am not into Semi autos, and dont know how all the different models Breech Up for the barrel stop.
But chambering dimensions and lock up clearance are universal along with headspaceing.

 

[jason41987]

thats a good question whether it can be set back or not.. if the gas port is already drilled i dont know.. if not, then yeah it can be set back as far as it needs to be.. a couple mm shouldnt matter

how much difference would there have to be for some kind of a bushing to be suitable?.. what i mean is if theres enough material in the bolt would it be possible to machine it out a bit and then add a bushing that would fill in the sides and the depth as well? and how would that bushing be attached?

 

[LAGS]

@ Jason41987
You do not want to mill anything off the face of your bolt more than .010" MAX.
Now, you are going to think I was real stupid on this one , but it worked and to this day atill being shot with no problems.
I had a Mosin Nagant that had .016" too Much Headspace, and there were none of my bolt heads that brought the headspace any closer.
So I cut a disc out of a steel feeler gage that was .020" thick, shaped it to fit in the recess of the bolt head with a hole for the firing pin, Then Silver Soldered it to the Bolt Face.
Now the rifle has good headspacing, and the disc has never come loose because it in in the recess, and all the pressure is going backwards.

You brought up something interesting.
Do you plan to use the Original AK74 Barrel ?
The bores on a 5.45 x 39 bullet are only .221 or .222 NOT .224
And yes if you have to set the barrel back then your gas system will need modification.
I thought you were having a whole new barrel made.?
Those issues would be address in the manufacture of the NEW barrel

 

[jason41987]

well there are some 5.56mm barrels made for the standard AK-74s.. and what i was considering was machining the bolt face out a bit more and a bit deeper, then cutting a metal disc to match the width and the depth of the hole bolt face opening.. with a hole cut out for the firing pin.. machine the face of this metal disk to the depth and width for a .223 casing and silver solder that in.. one solid piece containing the base and the walls for the bolt face to adapt it.. i also thought about drilling and tapping the bottom of the plug and screwing it into the face of the pre-existing bolt.. or pinning it somehow for added strength

but if that wont work then i guess the only option to convert the bolt face to a true 5.56mm bolt face would be to have someone TIG weld it up, machine it out, and then re-heat treat it.. any idea what it would cost to have someone do this?

and yeah, im well aware of the difference in bullet sizes and how the russians like to be a PITA like that

 

[rcmodel]

any idea what it would cost to have someone do this?

Yes.

About two times what a new SAIGA .223 would cost if you can find one.

rc

 

[LAGS]

If there are barrels being made for the AK-74's then I bet they are using the standard Bolts or they would be selling Conversion Bolts too.
We need to get the true measurements of what you are working with before you tear your hear out trying to build a better mouse trap.

But I would not SOLDER a disc into the bolt face on a semi auto.
You have tramendous forces when the bolt cycles to the back.
And the rebound could work your adapter loose.
And if it falls out, and goes out the ejection port, you could have created a Major headspace problem on the next round that loads, and not even know it till you wake up in the hospital.

 

[jason41987]

so what do you think it would cost to have it welded, machined, and then re-heat treated? anyway.. ill probably hold off on this conversion anyway, leave it as 5.45 since i do like the round more.. my concern with 5.56 has more to do with widespread availability throughout the country more than anything else.. most people do use the 5.45 bolt, im just not sure how i feel about having more of the case pushed into the bolt and less of it in the barrel with a little gap around the edges of the base and what that all may do to the brass if i intend to reload it

 

[rcmodel]

You shouldn't worry about reloading steel case 5.45x39 ammo in the first place, as it is not reloadable in the strictest sense of the word.

It is all Berdan primed.
Which means a reloading die cannot push the old primers out.
And new Berdan primers are about as easy to find in the USA as hens teeth.
And there is no source of .220" bullets for them either that I know of.

Reloading 5.45x39?
Fuggedaboutit!!!

That should have no bearing on your choice of calibers.



rc

 

[LAGS]

@ Jason 41987
The gaps from the case to the bolt collar will not effect the expansion of the case at all.
And as I said before, as long as the case head web is supported in the chamber then there is no issue, when the headspace is correct.
What is the Actual differance of the case web depth or thickmess on a .223 and the 5.45 round ?
I think you can buy a .223 bolt for the Velmet AK for far less than you can what it will cost for the welding , Machining and heat treating.
But milling the bolt face is still an option if you feel it will be supporting the casing better.
When you set a Barrel back, you do it in Full Turns so everything in the chamber and gas ports line up as well as the sights.
How many Threads Per Inch are on the barrel thread ?
Figure the travel in thousands per turn and figure probably one turn maybe two turns max to compinsate for what you mill off the bolt face.
What ever you set your barrel back, is the same amount you will have to shorten your Gas Tube, and Gas Piston rod.
And after setting the barrel back, you have to machine the back of the barrel to retain the proper clearance between the END of the bolt, and the back of your barrel.
Then you have to ream the headspace to the proper depth.
It is a lot of work isnt it, and a lot of critical measurements, and should be left to the professional Gunsmith /Machinest with the proper Tools to do the measurements.

 

[jason41987]

ak barrels are pressed and pinned in.. im going to look for my calipers and measure the depth of the bolt face and see how that compares with the thickness of the case webbing of the 5.56mm cartridge.. how far should the case webbing be above the edges of the bolt carrier?

 

[jason41987]

.395" is the diameter of the opening in the bolt face, and about .111" for the depth

 

[LAGS]

@ Jason41987
The bolt head provides No support for the case head,
If the casing is inserted into the chamber, the start of the extractor groove should be very close to the face of the back of your barrel.
But you can not check the case protrusion because you do not have a barrel in the correct caliber for the cartridge you are using.
You have to measure the thickness of the case web between the two casings, to see if the 5.45 is really that much thicker.
You can do that with an 1/8 ' rod about 2" long and a Dial caliper.
But when you put the .223 casing on the bolt face, is the Rim of the case totally inside the recess, or only part way.
I think the actual Rim thickness of a .223 casing is about .040" thick.
So that means the rim is not thicker than the depth of your recess.
And where is the front edge of the extractor groove on the casing in relation to the end of your bolt ?
And on your rifle right now, what is the clearance from the end of your bolt to the back of your barrel ? Or is ie a zero clearance fit ?

 

[LAGS]

@ Jason41987
I found an old .223 casing in my scrap brass and measured it.
From the back of the Case Head , to the front edge of the extractor groove is about .110"
That is right about right where you want to be if your front of your bolt is touching the back of your barrel when locked up.
If your bolt recess is .111" deep, and the front of your bolt touches the back of your barrel when locked up ,then the case protrusion out he back of your barrel to get .004 headspace is .107 ".
From what I can see, you are right where you need to be with the bolt face right where it is.

 

[jason41987]

looks like the 5.45 has a narrower space between the base of the body of the case itself and the top of its rim, so although the rim is thicker, the overall case web thickness doesnt seem to be that much difference.. possibly because 5.45x39 is designed to be a steel cartridge and 5.56 is designed to be a brass cartridge, webbing thickness comes out to about the same with the 5.45 having the thicker rim

a lot of people say 5.56mm works fine in a 5.45 bolt, but rather than take their word for it i wanted to either have a proper 5.56mm bolt or be sure it would actually work.. and it looks like yeah, theyre probably right

anyway, im holding off on the 5.56mm conversion for now, turns out there are no suitable 5.56mm barrels for the AK-74 that are chrome lined.. there are barrels, but unlined with anything and id rather hold off till someone starts chrome lining them

 

[LAGS]

@ Jason41987
I am glad we could help you.
Good luck on finding your barrel, and let us know if you are able to start up this project in the future.

 

[jason41987]

ill probably get a new AK parts kit to build a new one from a flat up for the purpose of being a 5.56mm, and leave the one i have now as a 5.45, but yeah, the information helped a lot, thanks

 

[LAGS]

@ Jason41987
Building one from a AK parts kit is a good idea, because you end up having to install a new barrel on most of the parts kits I have seen to replace the 14" 7.62x39 barrels anyway.
Either that or register it as a NFA short barreled rifle.

 

[jason41987]

i build my last one on an NDS receiver, ill be building my next one from a flat.. i dont have a 7.62 AK right now though and i really have very little motivation to get one my AK is a 5.45x39 caliber model.. if i was going to get a 7.62 AK it would only be for a 6.5 grendel conversion which would be easy enough since the grendel and 7.62x39 have the same exact rim, base, etc

i actually prefer 5.45x39, just wanted atleast one AK in 5.56 for commonality amongst friends and neighbors that tend to have AR15s and my complete lack of interest in ARs