Gentlemen,


I reacently received a Belt Mountain base pin and I'm having a bit of trouble installing it on a Ruger New Model Blackhawk. It seems that the pin fits the cylinder snug as a bug, however it just will not clear the first frame hole (the one with the base pin latch). It goes in about 1/2mm and thats it.

I know I probably need to lap the holes in the frame, but how do most of you go about doing this? What material should I use and what tools will I need to do this?

Any help is greatly appreciated. It's obvious this belt mountain base pin is superior to the factory one and I want to use it bad!

You can always get a quarter-inch rat tail file and open the hole in the frame up a bit. Hit it with some cold blue and you are good to go. Otherwise, take it to your gunsmith and pay him to open it up.

I would take a steel rod of about 1/8 to 3/16", slot the end and wrap a strip of 400 wet or dry sandpaper on it for a snug fit. Spin with a drill a little and keep trying the pin. You will have to hold the locking pin open or remove it. Clean out the hole and oil before every fit trial. You might only be looking at .0005" to remove so be careful.

There is certainly no reason not to tackle the job if you use the right tools and take care. I would strongly advise against the suggestion of using sandpaper on a split rod, as you'll surely end up with the hole belled on both ends of the frame. The proper tool for the job is relatively inexspensive, and it's called a 1/4" barrel lap. http://www.jlindustrial.com/catalog/product.jsp?id=LAP-...D&backtosearchpage=Y

You'll add some lapping compound to the lap, expand the lap till it is just snug, then work it in and out of the hole with a drill. My preference is to power the lap with a drill press. You'll also need an extension with the barrel in place.

I will have to take a different approach here. My pistolsmith once told me, "if you can help it, never modify the gun, modify the accessory to fit better". I would chuck the base pin up square and solid and use the 400 grit paper just on the end of the pin as far as it needs to be inserted into the frame. You can reblue it as necessary. That way if, for some reason you want to sell the gun with the old pin, you haven't screwed that possibility up. It should only take .0003" at most.

Paul and Larry, I agree that great care must be taken with the split rod. Both of you have great ideas but I think the fit in the cylinder is what the new pin is about and taking it down makes it no better then the original.
Paul, thanks for the link for the tool as that is much better.

BFR, In my method, you don't take down the entire length of the pin. You leave the snug part of the pin that fits in the cylinder alone. You just polish the very end that fits into the frame again. That way, everything still remains snug in the cylinder and the pin fits without modifying the frame, AND, if you chuck it up square, it will still be just that, square. If you modify the framr, the square part is harder to maintain, IMHO, and is not fixable should you screw it up.

Larry, he said the new pin will not go in the first hole, the one with the latch!

So long as one goes slow and uses a proper lap, it is pretty tough to screw up the frame. You're only removing a few tenths of a thousandth. The stock pin will still work fine, and the new pin will fit.

If one uses a more agressive cutter, it is certinaly possible to screw things up, but go slow and all is fine.

If you're still afraid of the lap, you can get a plus 1/4" reamer, this will cut a 0.2501" hole. Just let the reamer find it's way in the hole and it will clean things up.

I'd venture to say most folks do more damage to their guns cleaning them then by opening up the frame for an o/s basepin. Use the right tools and take your time, it's about as easy as it gets.

BFR, you are right. I apologize. Must be the new contacts.