Drilling the main barrel pin hole on a new AK barrel

[GunsRFun1]

I have started an underfolding Romanian AK kit. So far, no problems. I bought a new barrel and was wondering what size/type of bit to use to drill the main barrel pin hole(7mm). I will be using a drill press to do this. Any tips or tricks would be much appreciated.

[DocAV]

Centre-punch the site of the hole, with the receiver and barrel set up and "lined up" (sights etc) in a vice. Remember once you have drilled the hole, even the pilot hole, you will be committed...no more sight alignment adjustment after the drilling.
Drill using a 1/4 inch or 6,5mm drill. Then get a 7mm parallel reamer ( an adjustable one may be needed) and finish the hole to 7mm...assuming you have set everything up correctly,and drilled True ( ie 50% in the barrel, 50% in the wall of the receiver, and come out horizontally "level". All this requires a professional Drill press, or better still a Milling Machine or a heavy Mill-drill combo...NONE of your $99 Walmart specials....

Once the hole is cross drilled ( by setting up to drill Vertically in the Milling Vice) and reamed, you can prepare the Locking Pin. It needs to be very slightly tapered ,with a "rounded" lead edge. The Back edge can be flat.

DO NOT Hammer the PIN; lube it lightly, then Tap it in to start it. Check that it is square to the receiver with an engineer's square...Then Move the whole lot to a 5 ton Arbour or Hydraulic press, and Press--Repeat--Press the Pin in, using a flat face on the press to do the job. The Job itself should be kept square by locking up in a Milling Vice, firmly bolted to the press table. Use form-fitting clams if possible ("receiver Blocks")

That is the way they do it in the Factory, so you can't go better than copying the system.

Good luck,
Doc AV
AV Ballistics Film Ordnance Services

PS BTW NB

I am assuming above that the receiver is "unfinished" ( ie there is no hole in the trunnion part yet...)
If there is a 7mm hole already in the trunnion, but no corresponding slot in the barrel, proceed as follows:-

Try to get a 7mm End Mill ( four flutes--an "Unconventional" size), and use in a Mill Drill, using the receiver trunnion hole to "Guide" it true. The four cutter edges will cut the "half groove" in the barrel, and line it up with the existing holes in the Trunnion. Then clean up with the 7mm reamer. Everything must be "square" otherwise the cutter will "run out" and bugger your hole. Work the mill drill, advancing slowly...patience is a virtue here--and clear chips regularly, with either compressed air, or a squirt bottle of cutting fluid.

Replacing an existing barrel in a gun is easier than fitting a new barrel.

Doc AV

[AbueloMark]

I had this same challenge putting a Romo barrel into an Egyptian trunnion. There were several challenges. First, the barrel was not snug. I had to punch a ring of dimples to give it enough diameter to fit snug but not tight. Once I timed the barrel and head spaced it, I began to use the correct end mill. I had several problems. The barrel was harder than the trunnion. I know, soft Egyptian steel? No way. The end mill would drift and simply enlarge the hole. Also, there was enough looseness that the trunnion would slide off the barrel. This was driving me nuts.

Eventually, I managed to mill enough of a starting cut into the barrel. I pulled the barrel and used hand files to rough out an undersized slot in the barrel. I re-dimpled, reinstalled, head-spaced and timed it. I ran the end mill in again and it cut the correct-sized slot in the barrel. I eyeballed the results, checked headspace and then drove in a lubed roll pin. I check headspace again and was satisfied. I used cutting fluid and cleared chips as I went along. I had the drill pressed slowed down to the recommended speed. High speeds are not necessarily your friend.

Doc AV is the default setting for correct info.

Obviously I met the standards for a Kyber Pass built. Not proud but I believe the rifle is 100% safe. I will check the headspace repeatedly in the future. Once I had started I felt I had crossed the Rubicon and needed to complete the rifle. It will have all the ugly charm of a Bedouin shoulder arm.

I offer this not as a guideline, but simply as an example of what can and will go wrong. The experience has killed my desire to ever build with anything other than a already slotted barrel into a proper trunnion such as a Bulgarian barrel into a Bulgarian trunnion.

[DocAV]

Thanks, AbueloMark,
for the experiences with "non" matching Barrel and Trunnion" and the roll pin...That was a feature I had not anticipated....AK barrels are made to be an initial "press fit" to the trunnion, then the Pin is just a Locating device...it should NOT be used to carry all the load of the linear pressure of the gun firing.
The Use of the Roll pin is good for initial setting up,( can be easily removed) but I would not use it for permanent use...a solid pin ( slightly tapered) should be used for the permanent set up, and remember to always drive it in and out the same way. (Thats why I said above, "round the leading end, and flat the "pressing-in "end.")

I have done "barrel Pin" removals on SKS, SKK (AK magged SKS), AKs and RPDs; on nearly all of them I had to either "press out" the PIN, with a Hydraulic set up, or Drill the pin out ( use a smaller than diameter drill, very slowly, and set up in the Mill.) the Remnants can then be reamed out or a screw extractor used to leave a "clean" Pin hole.

Replacing the original Barrel once "re-watted" ( most of my guns are used for Movies), everything can be re-aligned sights etc to the vertical, and one finds the cross Pin hole is almost "true"...a simple long taper Drift Punch will "line it all up," then the New Pin can be pressed in.

The SKS types are usually taken down to shorten barrels for "FA" type Conversions, or making "HB" LMGs -- new, heavier Barrel, usually made from a SMLE .303 barrel, which even has the essentials of the 7,62x39 chamber already in it. ( front end of a .303 chamber is identical to 7,62x39, except the .303 has longer neck.) Cutting off the threads from the shank of a .303 SMLE barrel will give the correct length for Headspacing to 7,62x39, and with very little polishing out of the head part of the chamber. Body tapers match in both cases.


Enough technical waffling...
regards,
Doc AV
AV Ballistics Film Ordnance Services
Brisbane Australia

[jjk308]

That is the way they do it in the Factory, so you can't go better than copying the system.

Good luck,
Doc AV

To duplicate the way the factory did it I believe you'd have to drink a bottle of Vodka the night before, come to work with a hangover, find that Ivan, at the station just upline from you, has cut all the pins a little oversize because the factory manager wants to reduce scrap waste, and then press or sledgehammer the pin in by brute force.

Either that or there was a Communist plot to cause orthopedic injuries and mental derangement in the Yankee counter-revolutionary demillers they'd be selling the AKMs to in 30 years.

[GunsRFun1]

Well thanks guys, I think you have given me enough instruction to get the ball rolling. Last night I ordered the correct end mill cutters and reamers to get the job done. I'll let you know how it turns out and post some pics. Unfortunately we are leaving for Kalifornia next week, so it'll be a few weeks before I can complete this thing.

[Florida Mike]

To duplicate the way the factory did it I believe you'd have to drink a bottle of Vodka the night before, come to work with a hangover, find that Ivan, at the station just upline from you, has cut all the pins a little oversize because the factory manager wants to reduce scrap waste, and then press or sledgehammer the pin in by brute force.

Either that or there was a Communist plot to cause orthopedic injuries and mental derangement in the Yankee counter-revolutionary demillers they'd be selling the AKMs to in 30 years.

Ahhhh de milling a parts kit without destroying the parts in the process. I have about smashed up 3 rear trunions demilling them. De milling is the part that takes the most patience some times.

[GunsRFun1]

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I think they turned out pretty good for my first AK builds! Thanks to everyone for your good advice. I ended up using a drill bit and a 7mm hand reamer. I dont know what I was nervous about, drilling and reaming was the easy part.

Well my gun building days are over for now. The day before the earthquake in Japan my wife got orders stating we would be moving to Misawa Airbase in northern Japan. As far as I can tell the only thing I might be able to take with me is a trap gun.

We wont be leaving until September so I should be able to pound several hundred rounds through these babies!

[Setlock77]

Hello, after reading the responses given, I had to give you a "back to reality" check. Ak47 are built all around the
World, some in caves. These rifles are among the easiest to build. I have built 6 so far. Using a mill helps but is really nessasarily needed. The most important fixture is a v-block clamp. This will hold the barrel at the proper angle (90deg) so you can drill your holes. For a barrel pin hole, I use a drill with the letter "I" on it, which is a .2720" hole, if you measure the drill, it has a smaller dia. (can't recall off the top of my head). For the rear sight, I use a drill size "20" which is .1610" on the chart. For the other pins, I use a size "31" which is a .1200" (on the chart, they measure less). If you ever have a pin that is too "loose", you can always make a pin by cutting a drill bit which is the next size u and use the shaft of the bit. I would recommend using a "go no-go" set of gauges and also use a real bullet for checking headspace. Before I drill any holes, I put all the pieces parts on the barrel, I also put the piston tube in place and even make sure the top cover fits (no spring at this point, as I do not have the trunion riveted to the receiver yet. Once I spend about an hour making sure everything is square, I then drill my barrel pin hole, using my delta bench top drill press. I have a mill and do agree that it is easier to get these holes in place, but my first 4 builds we're using the drill press. Use plenty of cutting fluid and go slow. There is NO reason in the world why you would ream these holes... They are pin holes for god sake, this reminds me of a saying " too little knowledge can be dangerous", now of course reaming or not reaming is not dangerous. It just adds a boatload of in-nessasary work (and extra cost in purchasing the tools). I purchased a "kit off a guy once (gunbroker), guy didn't disclose that he screwed up the barrel. He didn't align everything as I said earlier and drilled his holes in the wrong places, including the barrel pin. I used a TIG welder and filled in all the drill slices that the guy had previously made. I then used a dremmel and cleaned up the welds ( using a barrel sander). I then put all the parts back on and re- drilled the holes, he wasn't far off, so my drill holes were partly through the welded area. The heat from welding had "hardened" the metal, so the drilling process was much slower. So I guess what I am saying, is that IF you screw up, you have another chance, but it adds a lot of extra work, so please take your time when aligning. Building an AK-47 is not rocket science, as I should know, I've worked as a NASA engineer for 25 yrs.

[Grandpa Mark]

I bought a cheap Egyptian kit and a Romo barrel. I ended up doing it and would not do it again. Doc AV has given a very good set of instructions.

I will share how not to do it.

1. Press fit barrel into trunion. If it is too small, take a cold chissel and cut in grooves on the exterior of the shank with a slight left or right hand twist. press in barrel until it feels deceptively tight.

2. Clamp barrel and trunion into a home-made jig bolted to a drill press with enough wobble to be slightly discouranged but not dissuaded. Sadly, you will still think this is going to work.

3. Using an end mill from a mail-order company, slowly and almost straightly begin to cut into barrel. Press hard without checking until you discover that the barrel is barely scratched but you have now made the hole in the trunion a nice oval shape.

4. Curse profusely as you remove the barrel. Replace and try again with same results.

5. Using the slight scratches on the shank as a guide, clamp barrel into Harbor Freight vice and take a small round file and roughly begin to cut a groove. Avoid doing this in a straight line. Do not think about head spacing using the fact that it's an AK and they build these in caves and how significant can it be?

6. Gouge and fit until, well hell, it looks like it will work.

7. Find a roll pin that fits snugly and pound it into place. Check the head space by putting bolt and carrier assembly up against the trunions and eye-balling it.

8. Convince yourself that this incredibly ugly rifle looks much more authentic than all those others. Fill in center of roll pin with some sort of hard, gooey stuff.

9. Curse the ATF for the damned barrel ban and conclude that your AK building days are over.

10. Break out the three Francotte-pattern falling block rifles you bought from IMA when they were on sale, disassemble, clean, assemble the best parts from each rifle, use files to make them fit and then convince yourself that all those other people who talk about exploding Francottes are just a bunch of worry-warts.