Monday, June 1, 2009

Tabuk Build Log – The Barrel

As promised, the next installment of the Tabuk build log involves actually building the rifle. It’s been a long road to collect all of the parts for this build, and I still have a few on the way (front plunge pin / detent and spring, rear sight block pin, butt pad and screws), but I’m far enough along that I can actually start working on the sub-assemblies for the rifle. The most challenging part of this build will most likely be setting up the semi-virgin barrel, so that’s where I decided to start.

Having never worked with a virgin or semi-virgin barrel (all of my previous kits had the barrel set up – just pop the pin out, remove the barrel assembly as a unit, and drop it back in when the trunnion was installed), I did a lot of reading on how others have set up their barrels. There’s a good post by Rahatlakhoom over on Gunco on installing a new barrel on an M70 kit. As the Tabuk is based on the M70, that’s the route I decided to go to help guide the work on this project. Not all of the steps were needed or could be followed exactly as I didn’t have an existing barrel to work from. However, as it turns out, the Green Mountain barrel already had some of my work done for me.

The first step is setting up and aligning the rear sight block. The extractor notch is already cut on the Green Mountain barrels as is the chamber, so there’s no fiddling around with that. Using the extractor notch as I guide, I aligned the front sight block per the instructions using a blue sharpie to create alignment marks. The question was how far back to put the block, with the instructions indicating that most sit roughly 1.880" from the chamber end of the barrel. Green Mountain has already cut a step in the barrel exactly at 1.880" so getting that part on was a breeze. It also turns out that they have steps pre-cut for the lower hand guard retainer and gas block as well (you’re on your own with the front sight!).

Once I got the rear sight block on, then the next major install was the gas block – which I got aligned perfectly and installed (see picture below).

Only problem is I was a complete dork and forgot something . . . the lower handguard retainer (I almost had to do this twice more as I remembered the sling loop at the last minute as well!). I just ended up using my AK-builder jigs to help me with this. The brass nut set up for the chamber works great to serve as a buffer between the ram of the press and the chamber end of the barrel – especially since you aren’t using anywhere near the full 12 ton capability of the press.

Once I got the gas block close, I tested it with the gas tube, everything lined up and fit perfectly! It was then on to the front sight (okay – being honest – for the second time!). The M70 front sight is a fairly loose fit on the barrel – it will stay, but only barely. The pins will help.

Once I got everything set up and aligned, I drilled out the pin holes for the retaining pins per the instructions above. Even though I had to go through some extra material from the virgin rear sight block and gas block, the cutting proceeded fairly easily with a little cutting oil. As mentioned in most virgin barrel builds, DON’T FORCE IT! You’ll just bind up your bit and then have to pray it comes out without snapping off. Of course, at this point I realized I didn’t have a rear sight block pin. I did, however, have ample pins for the front sight and the gas block. They did take a little sanding to fit easily because I didn’t have decimal drills to use, but the end result is very snug. I also haven’t put in the front pin on the front sight because I’m still working on the front sight plunge pin (detent) and spring. I pulled one off of an AMD-65, but the spring is too short. I have a longer spring, but it’s almost too long. I’ve therefore ordered a new one (along with the rear sight block pin) from AA-OK. Hopefully they’ll have them in stock and can get them out to me soon.

The only other part I had been missing was the butt pad, but I’ve found one of those online as well and hope to get it in the mail soon. Now I just need to find someone with a spot welder so I can get the scope rail attached to the receiver. Looking ahead, I’ve test fit several of the other parts to the receiver, and so far the fit looks good. The next major challenge will be headspacing the rifle so I can set the barrel properly. I’ve got a nice match grade trigger group to drop in the rifle once I get to that point.

So far the project seems to be going fairly well. I still need to cut the gas port hole, but I’ll do that after I get the rear sight block pinned. The finish on the stock is just about ready to go as well – and I just can’t say enough good things about the Ironwood Designs stock. The quality is absolutely first rate.

Until next time!!!

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