Using a Compensator reamer

[aclundwall]

I'm building a new open gun. I got a compensator alignment reamer with which to align-ream the compensator to the bore once I get to that step.

This reamer has short pilot bushing... it's about 1/2" long. Then there is a step in the reamer about 3/8" farther up, at which point the reamer goes to it's full diameter.

I notice a couple things... First, the pilot bushing won't go in the bore of a .355 barrel. And even if it did, the reamer has to be inserted almost all the way into the compensator before the bushing even reaches the muzzle.

So, I'm thinking that my original concept of how this tool is to be used is all wrong... I thought that I'd insert the reamer, and the pilot bushing would reach the bore and allow each port wall to be reamed as it went further in. Of course it comes with no instructions....

I don't think that the pilot bushing is there to center the reamer with respect to the next comp port hole... because for one thing, the pilot bushing is loose in the compensator holes. And even if it weren't, what good is centering the reamer with respect to the already drilled holes in the comp? The whole point of the reamer is to center the comp holes with respect to the bore, right?

I have a lathe...so I can make another pilot bushing that will fit in the bore... but even if I do that, the pilot bushing won't REACH the bore until the reamer is already through the comp ports furthest fromt the bore... I guess I could make a longer pilot bushing.. and maybe that's what I need to do... but I am hopeful that someone here can straighten me out before I re-invent the wheel....

Art

[Dancin Dan]

Art, the reamer I have is a Nowlin barrel comp. alignment cutter. The end that goes into the bore is about two and a half inches long before the cutting edge of the reamer starts. I would suggest you find another reamer.

Good luck.

[Toolguy]

Art-

If you have a lathe, chuck the barrel or put it in a collet and use a boring bar. That will do a better job than any reamer. The reamer you have is useless.

[aclundwall]

Thanks guys...

Dan, can you remember where you got that reamer? I googled "nowlin compensator reamer" and got nothing but links back to this thread, and the reamer I already have :-). Other than the one I already have, which I got from Midway, the only other reamer I found is from EGW... but it was the same price and there was no picture, nor did it say who made it. I assumed it was the same reamer I got from midway, but I don't know that for sure.

Warren, I tend to agree that my existing reamer is useless. However, I have a couple problems with putting the barrel into the lathe.... To perfectly align to the bore, I need to indicate off the bore. Normally, I put a gauge pin into the bore, and indicate it at the muzzle, and then again at some distance away from the muzzle. This allows me to both center the muzzle and ensure the bore is concentric with the lathe's turning axis... But in this case, I'll have a compensator on the barrel. I can't use my normal method, because the gauge pin would be obscured by the comp.. And I cannot simply use the outside of the barrel (hoping the bore is concentric), because the hybrid rib prevents me from indicating all the way around the barrel. I could just chuck it up in the three-jaw and hope... but that's really not very accurate. And I'm not even sure if the three-jaw chuck will clear the rib (My actual barrel is waiting for me at the post office, I'll have it in the morning).

Feel free to point out holes in my logic... In the meantime, I think I'll send an email to EGW and see if their reamer has a longer pilot bushing than the one I'm using.

Thanks again guys...

Edited October 30, 2010 by aclundwall

[Pat Miles]

The EGW 38/9mm comp reamer is 9" long of which 6" of it will be in the barrel/comp before the cutter enters the front of the comp to ream it.

Pat

[mike cyrwus]

Art-

If you have a lathe, chuck the barrel or put it in a collet and use a boring bar. That will do a better job than any reamer. The reamer you have is useless.

thats a great idea.

how much over bore diameter is considered safe but still effective, a couple thous? Never built an open gun.

[Matt Cheely]

I had a reamer made that is .375", some are .368, but I found it to be a bit small on short guns.

[Aircooled6racer]

Hello: Since you have a lathe you can make a pilot so you can indicate the barrel true. It will have to match your barrel bore ID and turn it smaller to fit threw the comp. It will be a step down bushing that you can mount in the barrel then indicate it true. You could use a 4 jaw chuck to get it to run true or you can use shims under the chuck jaws so they will clear the rib on the barrel. Most of the comps I have seen are 0.375-0.390" bore when fitted. Hope this helps. Thanks, Eric

[peterdaws]

Hello: Since you have a lathe you can make a pilot so you can indicate the barrel true. It will have to match your barrel bore ID and turn it smaller to fit threw the comp. It will be a step down bushing that you can mount in the barrel then indicate it true. You could use a 4 jaw chuck to get it to run true or you can use shims under the chuck jaws so they will clear the rib on the barrel. Most of the comps I have seen are 0.375-0.390" bore when fitted. Hope this helps. Thanks, Eric

I have had Tanfoglio Polygonal barrels and Schuemann barrels that were too small for my comp reamer and initially I did as above but the setting up drove me potty. So I took one of the pilots I had made, cross drilled it and soldered in a piece of tungsten carbide which I ground to make a single tooth cutter projecting from the pilot the right amount to give me the bore diameter I want. In effect I have a piloted boring bar. Now it's a quick set up to chuck the boring bar in the tailstock and the barrel in the headstock and open up the comp. Cut slowly and clear chips freqently though as there is nothing to channel them away.

Peter