Oversize barrel pin?

[GOH]

I posted this over in "WTB Hk Parts and Accessories" but received no reply. I've been working on my latest G3 project and I was able to get the barrel pressed in exactly where I want it. I drilled the barrel pin hole with the correct 5mm bit, but the barrel pin only taps in with moderate pressure. I'd like a tighter fit just in case there is a bit of settling in the parts after the rifle is fired the first few times. Bolt gap is just a bit over .020, so a small amount of settling is desirable, but I'm worried that if the barrel pin isn't tight, it'll settle too close to the low end of the spectrum. Does anyone here either have a slightly oversize(5.01mm) barrel pin or know where I can get one?

Thanks,
Rich

[AviatorDave]

I posted this over in "WTB Hk Parts and Accessories" but received no reply. I've been working on my latest G3 project and I was able to get the barrel pressed in exactly where I want it. I drilled the barrel pin hole with the correct 5mm bit, but the barrel pin only taps in with moderate pressure. I'd like a tighter fit just in case there is a bit of settling in the parts after the rifle is fired the first few times. Bolt gap is just a bit over .020, so a small amount of settling is desirable, but I'm worried that if the barrel pin isn't tight, it'll settle too close to the low end of the spectrum. Does anyone here either have a slightly oversize(5.01mm) barrel pin or know where I can get one?

Thanks,
Rich

I've never actually seen any oversized pins for sale, so don't worry about it.

The problem is that a 5mm reamer is too large. The pin is about 5mm, the hole needs to be smaller than that. And the tolerance of a 5mm drill bit is even bigger. A 5mm hole is .1968", the barrel pins are .197", only a .0002" interference. And a new reamer (did you stone the edges first?) is likely to grab more and be on the high side. Using gage pins, the holes through the 93 trunnion will let a .195" pin slide in easily and go all the way through. A .196" pin will start in either side of the trunnion, but won't go all the way in. I only have 2 trunnions here to check, and they are both about the same.

So for anyone else reading this, you really should use a new .195" reamer, or perhaps a well stoned or worn .196" reamer would work.

But unless you have a black-ops hole shrinker like I do, what's done is done. But don't fret, it's an easy fix. Go to www.jlindustrial.com and order a few hardened gage pins. They will be longer than you need, but you can easily grind them to length. You're really after about a .001"-.002" interference fit, and if you already have resistance with the pin, I'd get a few of them, maybe .1975", .198", and .199".

Grind it to length, press it into place, and you can even cut dimples in the end so it looks like an HK pin after installed. I did the same exact thing on my first one, since I used a 5mm reamer too, without checking what the actual hole diameter should have been. And I also didn't make my normal check of drilling and reaming a hole first in a critical application like this to check what size the actual hole will be. Chalk it up to excitment of getting my first complete build done.
So I now use a .195" or .1955" reamer and the pressing forces are back up to what they are in the original.

[darthvictor]

snip

But unless you have a black-ops hole shrinker like I do, what's done is done. But don't fret, it's an easy fix.

snip

Dude, why you gotta send him on a wild goose chase after a bigger pin like that? I've used an actual hole shrinker, but if it's all you have access to a chest freezer will work if you turn it up all the way.

[AviatorDave]

Dude, why you gotta send him on a wild goose chase after a bigger pin like that? I've used an actual hole shrinker, but if it's all you have access to a chest freezer will work if you turn it up all the way.

I also built a board stretcher, for those times when you cut it off twice and it's STILL too short.

[my2cents]

Just a quick related question. What is everyone using to support the receiver while pressing the pins in/out? I've seen a pic of an aluminum jig but it looks like it would be a lot of work to make one and no one seems to sell them. Is there a trick to do it without a jig or does everyone just happen to have a jig laying around somewhere?

[AviatorDave]

Just a quick related question. What is everyone using to support the receiver while pressing the pins in/out? I've seen a pic of an aluminum jig but it looks like it would be a lot of work to make one and no one seems to sell them. Is there a trick to do it without a jig or does everyone just happen to have a jig laying around somewhere?

I don't know how you'd do it without chewing up the receiver. You probably saw my fixture. I've been meaning to make some, but I'd have to sell them for about $300 each if I were to make them on my manual mill, as they do take a lot of time. I want to get a CNC to crank some out, but I keep getting sidetracked by buying more guns. :(

[GOH]

Thanks for the replies!

AviatorDave: The problem with the oversize hole is completely my fault. My drill bit cut the proper hole, but I didn't get the pin straightened properly when I first tried to press it in. It went in a tiny bit sideways and gouged the side of the channel. Stupid Me--I used a 5mm reamer to clean up the gouge mark before I tried pressing again, but it took out too much out of the channel. I still have to use a hammer/punch to tap it in, but like I said, only with moderate pressure.

I'll try ORF and see if they have an oversize pin. When they were still performing custom builds, they installed a new barrel in an FMP rifle for me, and he said that they used oversize pins for that.

Again, guys, a sincere "thank you" for the replies,
Rich

[AviatorDave]

Thanks for the replies!

AviatorDave: The problem with the oversize hole is completely my fault. My drill bit cut the proper hole, but I didn't get the pin straightened properly when I first tried to press it in. It went in a tiny bit sideways and gouged the side of the channel. Stupid Me--I used a 5mm reamer to clean up the gouge mark before I tried pressing again, but it took out too much out of the channel. I still have to use a hammer/punch to tap it in, but like I said, only with moderate pressure.

I'll try ORF and see if they have an oversize pin. When they were still performing custom builds, they installed a new barrel in an FMP rifle for me, and he said that they used oversize pins for that.

Again, guys, a sincere "thank you" for the replies,
Rich

If they don't have any, and you have some gage pins so you can find out the exact size of the existing hole, let me know before you order anything. I have a few extra gage pins since I bought 3 or 4 in different sizes and only used one.

[darthvictor]

I also built a board stretcher, for those times when you cut it off twice and it's STILL too short.

Most valuable tool I own! hehe

[Shattered Mind]

I also built a board stretcher, for those times when you cut it off twice and it's STILL too short.

I'd be lost without my cordless electric hammer...