HK 91/G3 barrel re-install

[legaleagle]

Any simple ideas on how to drill the barrel retaining pin straight through the trunion without enlarging the existing hole. Simple jigs, hand filing, etc.?

[DOC]

You can't drive it out with a punch?

[jreifsch80]

drill it from one side about half way the switch to the other side, take your time untill a flat spot develops so your drill bit stays more or less straight. i do it this way drilling ak barrel pins which would be basicly the same way.

[BPTactical]

Find a short piece of tubing that will slip inside the pin hole but will allow a drill bit to go through. This will act like a bushing and keep the bit off of the trunnion. Once you have the pilot hole drilled subsequent bits will follow the pilot hole. Also if you grind your bit to 135 degrees included angle it will not tend to wander like 118 degrees will.
Sneak up on the hole size and instead of tying to drill out to the entire pin diameter just get it to where you release the "bite" or tension on the pin. Once you do that the pin will almost fall out on its own.
As far as drilling for the new pin you can do the same thing but you are really the best drilling close to pin size and reaming to final size.
Example-AK FSB and Gasblocks get drilled with a 2.5mm and reamed 3mm.

[spyder]

What my brother and I have done in the past with our own rifles was drilling a small hole through the center that was just big enough to fit a compressed air cans little air straw through, tilted the can upside down, and sprayed inside the pin hole. Pins pretty much fell out at that point and it was very easy to do.

[legaleagle]

Point of clarification - the pin is out. It came out with a punch no problem. I am curious about re-drilling the barrel to install the pin. When the barrel repressed inside the trunion only about half of the barrel is visible through the trunion. Obviously drilling this will cause it to wander. Even with an end mill how do you guys keep the bit centered and true. What about key files.

[DOC]

Mark it and a hand file will work.

[spyder]

Point of clarification - the pin is out. It came out with a punch no problem. I am curious about re-drilling the barrel to install the pin. When the barrel repressed inside the trunion only about half of the barrel is visible through the trunion. Obviously drilling this will cause it to wander. Even with an end mill how do you guys keep the bit centered and true. What about key files.
Took ours to a machine shop. Charged us $50 a barrel. It looked like their set up clamped onto the barrel and then they positioned it on the press just right, clamped the clamp down in place and drilled. Took a whole 20 minutes and $50 bucks. Before you put the hole in the barrel though, have you gapped the bolt head?

[BPTactical]

Point of clarification - the pin is out. It came out with a punch no problem. I am curious about re-drilling the barrel to install the pin. When the barrel repressed inside the trunion only about half of the barrel is visible through the trunion. Obviously drilling this will cause it to wander. Even with an end mill how do you guys keep the bit centered and true. What about key files.

You will make yourself nuts trying to file it.
It would take about 10 minutes in a mill. The action is locked in the mill vise, it aint gonna move- an indicator rod is placed in the trunnion hole and you index in on the rod for vertical plumb and centering. The mill will not wander.
Do you have access to a drill press? If so you can do pretty much the same. If not don't despair, it will just take a little more care.
Find a short piece of tubing like I described above to act as a drill bushing. It will keep the bit centered and keep the flutes from chewing into the trunnion. Once you have the barrel "notched" from the smaller diameter drill move up to the final diameter. You need to really pay attention here-the bit will really want to grab as it is only taking a partial cut- the trick is to use very, very little pressure and make sure to keep the drill plumb in the hole.
If you are not comfortable doing it shoot me a PM- we will get ya squared away.

Spydyman is right on the headspace/bolt gap issue- you have a little adjustability with roller size but you need to get the barrel depth right.

[spyder]

I would take BP up on his offer, doing that by hand... [ROFL1][LOL][ROFL3]

[jreifsch80]

If you do it yourself with a drill press also use your ears, if you hear a high pitched sound from the drill bit it means it's trying to eat the trunnion low pressure is the key let the drill bit basicly chip the material away.

Btw anyone have an g3 flat bending jig? I still need to build my cetme ;)

[legaleagle]

Thanks everyone. I understand the bolt gap issue. THis is why I need to redo as the new barrel installed was done by a friend who is a smith, but got the numbers backwards. Final gap was .010. While not terrible, I would like it closer to the .020. Fortunately the front sight pin is not re-welded yet, so I figured this would be a good starting place.

BP - I like the bushing idea. Don't know why I didn;t think of that myself. THe AR jigs do that already too. Guess I am too pissed about it to think outside the box.