I just drilled my first barrel pin. I started with a 1/4 end mill, followed by a 17/64 drill, followed by a 7mm reamer. The pin was tight enough that there was no way to start it by hand, but it pressed into the trunnion very smoothly. I'm a little worried about how easily it went in. My saiga 7.62x39 was far tighter. That saiga is my only experience removing barrels.

Should I be worried that it pressed in smoothly? Should I consider reaming to .300 and using an oversized pin?

Thanks!

A smooth press just means that you have a properly sized hole for the pin. So long as you can't press the pin out with a punch it should be fine. I'm fairly certain that Izhmash and the like don't ream their barrel pin holes which can contribute to their tighter fit.

Hi folks,

As I kind of anticipated, I have messed up my first attempt at a barrel pin. On one side of the trunnion, the hole is egged out facing down. I went ahead and got a larger barrel pin, but there is still visible egging. I believe the flaw in my process was to start with an undersized end mill, then go to a drill bit, then ream. I believe if I skipped the drill bit, this would have gone more smoothly. Reaming to 300 didn't seem to help.

With that said, the hole looks perfect on one side, and it is only slightly egged out on the bottom on the other side. The top, left and right of the hole are true. My gut tells me that having a proper hole on the left and right, and either the top or bottom on one side, with a proper hole on the other side, should be sufficient for safety. Is my intuition correct?

And for the next barrel, I'm going to delete the drill bit. Having read further on akbuilder, I believe the hole made with the quarter inch end mill should be sufficiently close to use the 7mm reamer for a standard barrel pin, and that the existing trunnion hole will guide the reamer if I go slow. Does this seem correct?

Well, barrel one is toast, as is sight block one and trunnion one. Some takeaways for the other wannabe AK gunsmiths from my $350 lesson.

1) Do not follow the 1/4 end mill with a 17/64 drill bit for the barrel pin. Just go from 1/4 end mill to 7mm reamer. It was the drill bit that caused the barrel pin to go off center. I realized after pressing the components off that I had partially drilled through the top of the trunnion when I attempted the oversized pin. I should have set the reamer to the bottom of the egged out hole instead of the non-egged out hole, as that hole was too high up. Again, I suspect this hole situation would have been avoided by going straight from the end mill to the reamer.

2) Apparently, rear sight blocks can be drilled off center. I'd judge that the hole was at least 4 degrees off center. With the rear sight block lined up, the hole was 1/8 of an inch higher on one side than the other. I attempted a 5/32 end mill from both sides to meet in the middle. Obviously, these holes went perpendicular to the side of the sight block rather than following the angle of the hole in the sight block. By the time I realized the angle, it was too late. By my math I was only a few thousandths from punching through the bore.

I guess the rear sight block could potentially be reused, especially if I welded up the other side of the hole, but the trunnion and barrel are definitely toast. Trying to decide if I should attempt to repair the rear sight block or not. I fear I am a shittier welder than I am a hole driller. But it should be a fairly easy weld, and since I was going to refinish it anyway, filing the splatter isn't a huge deal.

At today's prices, I figure buying the trunnion and rear sight block is nearly half the cost of another Romanian parts kit.

ETA: I'm so glad my triangle side folder Saiga conversions, which gave me the confidence to attempt this, went much better.

Lets see some pics, you can probably just weld up the egged hole in the trunnion clean it up with a dremel, drill out a clean hole for the barrel pin from that side stop half way, make sure you've got it lined up/cleaned from the otherside as well. Follow back through with reamer for the new oversized pin from the side you originally screwed up, press  the pin down from the side you screwed up. I've fixed several trunnions people egged and I scored a deal on.

With proper setup, and minimal runout; the end mill, drill bit then reamer works just fine.
You either had the trunnion setup wrong or excessive runout, most likely a combination of the two.





Again, setup and run out matters. Check parts, do the math before drilling.



You could just be back in AZ and use Jereds's method; wait a year or so for me to build stuff.

Reamers just follow existing holes. If the hole is drilled true you can ream it with lots of oil and a good hand drill. In fact in some ways this is better than trying to force a reamer to follow a specific path with a drill press.

The better question is did you use a PRESS FIT reamer? These are intentionally undersized to generate an interference fit for a pin. Most reamers are slip fit unless otherwise stated.

As you found out, never assume that a used barrel component will be drilled perpendicular to the barrel. It's better to drill with an undersized bit, half a side at a time, until the holes meet. Then enlarge the channel with the appropriate drill bit or even a small round file - worth it to take your time versus ruin surplus parts. Then ream it to press fit size. If you have to move up one pin size don't sweat it - e.g. 3mm to 1/8"

Why not just move up to an oversized barrel pin