Chambering Benchmark 2 groove .22 rimfire barrel?

B

Boyd Allen

Active member
Today I had my first chance to look down the bore of a Benchmark 2 groove barrel. The first thing that came to mind was to wonder how one rigs a chamber reamer's pilot for one, given that there is so little land width to work with. It almost looks like you would need to cut clearance in the pilot so that you could have half on the lands and the rest on the grooves, or perhaps pre-bore, and chamber without a pilot. How have you done one of these?
 
Fairly easy. Since the chamber is so short and so little metal to remove, dial in VERY CLOSELY at the freebore then bore the chamber body to almost full depth and to full diameter, then ream. The reamer body will act as a pilot. Care must be taken to not ream too deep.

Oh, I use a solid carbide boring bar. Some early RF chambers even have a very slightly tapered chamber body.
 
Thanks Jerry. I thought that it might be something like that. This thing looks to be very well made, and quite different. A friend will be using a cast in place slug (done like a short lap) to investigate the bore dimensions, and see if there is any choke, where it is, and how much. That should be interesting. Recently, he has done this on all of the barrels that he has chambered, for bench and hunting rifles. He has sent several barrels back, and learned a lot. This is kind of like when bore scopes first became affordable, and came into more wide use. From what I have learned about his experiences with this, I would not want a barrel that had not been evaluated that way.
Boyd
 
I just chambered my Benchmark 2-groove a few months ago. I too had questions about how the reamer pilot would stay centered. Turns out it was a non-issue. I just sized my pilot for a good fit on the top of the two lands and went at it. The fact that the barrel is spinning when you ream it keeps the reamer centered in the bore. The chamber was round when I checked it with a test indicator, no lobes that I could detect. I did use a floating reamer holder and made sure the pilot was centered when I started the cut. I don't know what would happen if you used an undersized pilot and started it out off of centerline.

Eric U
 
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