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Backyard barrel install/headspacing tool set


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Just installed and headspaced a barrel with this little setup. I figured it might be useful to some doing home builds without a press. This is a good alternative to a press, it will not damage the receiver, trunnion, barrel, or bolt carrier, and you can use parts of the same tool set to install barrel components once you have the barrel headspaced and pinned.

 

First off you will want to check interference fit of the chamber to the trunnion, and relieve some material as necessary. This is an Arms of America 5.56 barrel (same as AK Builder I believe) and it checked out spot on to go into the Bulgarian AK-74 trunnion. None the less I polished the trunnion to smooth out any rough surfaces, and lubed the trunnion with a thin coat of anti-seize.

 

Aligned barrel with trunnion by spotting the lower handguard retainer to the trunnion "flat" where the RSB goes. Barrel looked perfectly straight., so I gave it a starting whack with plastic dead blow to begin the process.

 

Parts used here are 3/4" galv pipe, 3/4" joints, 3/4" to 1/2" brass joint, and 1/2" adapter. Wrap the 3/4" pipe in electrical tape to avoid marring the receiver. The brass joint will sit perfectly in the rails and can be secured with zip ties to help hold steady. The tail end of the galvanized pipe has a 3/4" joint installed to place against a concrete surface - I actually used a brass puck below it to avoid cracking the concrete.

 

To support the trunnion to whack the barrel in, it's common to use a bolt carrier. This process uses an unmodified AK-74 carrier. Now in my case I had a couple spare AK-74 carriers so I just used a non-matching carrier. Use brass washers on the right hand side to support the carrier-trunnion contact surfaces, as there is usually a small gap here. The carrier should sit true against the trunnion when pressing forward from the tail. The 3/4" brass joint pressed up against the tail carrier does NO DAMAGE to the carrier, don't worry about it - not even a slight indent was detected on the carrier after this was finished.

 

Also not pictured is a small threaded brass cap which I placed over the crown/muzzle. When I moved from the plastic dead blow to a steel sledge, this brass cap prevents damage to the crown/muzzle. The AoA/AKB barrels are very hard (one guy on Youtube brought the Rockwell tester up to 28 on them, Romy CHF barrels come out around 25, so yes they are harder than the gold standard of Euro CHF barrels) so the brass cap does nothing to the barrel, don't even worry about it.

 

Set the assembly on the ground and carefully whack the muzzle true with the plastic dead blow. If you don't get results, move up to using the brass cap and steel sledge, but be careful not to hit too hard. It only requires light hits with the sledge to move the barrel in.

 

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In my case, I ended up hitting the barrel in just a touch too far, past bolt lockup. So I flipped the brass cap around and it just so happened to fit into the trunnion perfectly against the chamber face. I supported the chamber face in the extractor relief cut with a couple additional brass washers. I added an additional length of galv. 3/4" pipe to the pipe assembly, as well as a 3/4" to 1" adapter to use as a base. I used three soft steel washers to support the trunnion face, making sure that the forward chamber journal turn down did not contact the washers. I then used a long 8" brass drift punch that fit inside the brass cap head. A few delicate taps at a time with the sledge, and checking often with the bolt inserted into battery using a live Wolf .223 round and NO-GO gauge, I was able to get it headspaced perfectly.

 

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Your little bolt head that you sent me didn't correctly buck the rivet heads, it was allowing some contact of the bit to the receiver even with aluminum foil "shims" - I guess rivets were slightly different dimensions than yours. So I had two basically do it twice. The inside of the rivets was formed properly on the first go, but there was a gap at the outside head, so I had to punch the heads in further to the receiver and crush them some more. I probably could've filed some material from the face of the bolt head tool, but I ended up using the trigger guard bit to set the heads instead, as the fit was very tight and allowed to get more crush pressure with the bolt cutters. I was able to get them very tight using that bit, but it left a little "nipple" on the rivet head that will just need to be filed off to look perfect.

 

Getting the swell neck holes counter sunk into the fully hardedned NDS receiver was a PITA. Took both ball bearings and drywall screw heads in the bench vise to sink the receiver into the trunnion holes, and even then I had to chamfer them a little bit in the drill press to get the rivet heads to fully seat.

Edited by mancat
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My swell neck rivet dimples were a royal PITA as well (I guess my torch heat-treating was effective). I used vise-grips, a BB, and a washer.

 

Your rivets look nice!

 

Be careful not to file too much off the lower rails. Tapcos are the only mags that don't wobble at all, in my build (facepalm).

Edited by Sim_Player
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this is a 5.56 build so it will probably only ever see Polish or Bulgarian 5.56 mags.. though I understand that the low cap Tapco 5.45 mags work flawlessly.

 

I'm already thinking of doing another as I have another barrel and partial kit, just no FSB/GB. Might have the barrel shortened and do Ak-102 build with combo block.

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  • 2 weeks later...

I really need to show up at your place some time with a kit and a case of beer or whatever you like.

 

then nothing would get done

Check mag wobble as you file the lower rails.

 

Use an average (thickness) magazine to gauge the space.

 

NDS receivers have the rails pre cut and welded

 

there is zero wobble with Polish Beryl mags, even the ones I have modded for the Saiga

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