We're prepping for the uppers that will be here this week. Lord knows that anything that actually SHOWS UP is cause for celebration. Now if the other $XX,XXX worth of 'stuff' would just show up,......
Some folks may care, most won't, but this is how we install a pre-drilled front sight base onto a non-drilled barrel. Something like that may happen when you change out your old barrels and/or are too cheap to buy a new front sight base. In our case, it was a decision to buy a boatload of new pre-drilled front sight bases in a market that didn't have un-drilled ones in stock. These front sight bases were from a large company who decided that they wanted gas blocks on their rifles instead.
Pre-drilled makes for some interesting hoops to jump through to get them installed. I've outlined some of them below. Let the fun begin!
1: Line it all up. The straight edge goes across from barrel indexing pin on the barrel extension to the center point of the end of the barrel opening. The jig I built has 2 index marks on the top. Sight across them, and line up the sight post in the middle. Once the Loctite hardens, you're good to go. This ensures you won't be shooting the guy to the left or right of the one you REALLY want to shoot. Great thing to make sure of when you have to shoot just the terrorist and not his hostage.
2: Center your .125 end mill in the existing hole on the front sight base. You're drilling into the side of a round object, and unless you have the patience of Job, the drill bit will wander. An end mill is the only real option here. Chuck it up in my fancy $27K drill press, and get things ready. The blue stuff behind the sight base is blue Loctite. It holds everything in place while you drill it out. It's coolant soluble, so all the extra disappears here in a few minutes. Once you're finished drilling it all out, you just whack it with a hammer, and it pops free. Just need to make sure it doesn't get down into the gas port, but the first shot usually takes care of it.
3: Always turn on the lube...I mean coolant before you plunge into this hole, and make sure it flows to the right places. You definitely don't want to hit a dry spot here. Enter the hole slowly, working it in and out, making sure the coolant flushes all the nasties out of the hole.
4: After you're done milling out the hole, change to a .131 drill bit, and open it up just a bit more. Makes it the perfect size for the taper pin reamer to start. Turn on the coolant, push it in until it comes out the other side.
5: Taper pin reamer, run in by hand. Dip in the cutting fluid, frequent wipes to remove all the chips, re-dip and ream some more.
6: Taper pin reamer ends up just shy of the full length of the pin. Gives the pin enough depth to be tight so you can ream out the other side. Sending this through too far means you screwed up. Badly. Several fixes, none easy. This is what holds the front sight in place, affects accuracy to a large degree as well as functioning of the gas system. Not hard to do right, but it wouldn't be the first time I've seen someone do it wrong.
7: One pin in place, held just proud of the surface. Once the other pin hole is reamed, and the pins lightly tapped in place, the front sight base is nearly ready for use. Since we're waiting on uppers, everything gets torn apart and put back into the box. Once the upper is here, we'll reassemble it, finish ream the holes to their exact depth, and tap the pins into their final resting place flush with the surface.
8: The holes? They kinda look like this. Very hard to accomplish using a regular drill bit, using pre-drilled bases. Not impossible, but the mill definitely makes things much easier.