Need help for a friend on how to do a deeply counterbored crown

B

Boyd Allen

Active member
A friend who is putting a new barrel on his rimfire rifle, has opted for the popular benchrest sporter contour that has an bigger diameter section at the muzzle, with the crown counter bored a couple of inches. He has done his own work for a number of years, and gotten good results, but he has never done a deeply counter bored crown. What tooling do you use, and if you would, walk us through the procedure that you use. He does not use computers, so I am doing this bit of research for him.

Thanks

Boyd
 
I've done 3 barrels counterbored to 1 1/2" inches using three slightly different methods. 1st one I simply used a 5/8 4 flute center cutting end mill set up in the tailstock. Slow but effective with a really sharp new end mill. Next one i predrilled with a 1/2 inch drill then went back in with said 5/8 end mill to clean up. In both cases the end mill left a surprisingly good crown. Last one i predrilled then used a boring bar then crowned with a piloted reamer. Boring bar is a real PIA as far as I'm concerned. If I do another I think I'd just stick with the well lubricated SHARP endmill, and maybe a slight touch with a piloted reamer. I'm no pro so I'm sure there are other ways but that has worked for me.

Dennis
 
Dennis D. said:
I've done 3 barrels counterbored to 1 1/2" inches using three slightly different methods. 1st one I simply used a 5/8 4 flute center cutting end mill set up in the tailstock. Slow but effective with a really sharp new end mill. Next one i predrilled with a 1/2 inch drill then went back in with said 5/8 end mill to clean up. In both cases the end mill left a surprisingly good crown. Last one i predrilled then used a boring bar then crowned with a piloted reamer. Boring bar is a real PIA as far as I'm concerned. If I do another I think I'd just stick with the well lubricated SHARP endmill, and maybe a slight touch with a piloted reamer. I'm no pro so I'm sure there are other ways but that has worked for me.

Dennis
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Dennis, thanks for sharing the counter boring procedures you used. I am considering a Sporter build in the future. Being somewhat of a novice on my lathe, however I'm catching on quickly. Have threaded and fitted couple of new barrels on my rifles and bored a couple of tuners as well. My concerns would be not necessarily how to perform the task, but more so, what depth and diameter (dimensions) to counter bore the enlarged section (tuner) at the muzzle? For a gunsmith there must be an enormus trail and error process (range time), and that is why top Sporters go for very high dollars. As one can only counter bore too deep and too wide one time and the barrel is ruined. I believe the place to begin is to evalutate the muzzle area of a good shooting Sporter, that was fitted by a top notch gunsmith and start from there. Now if someone who owns one of these great shooting Sporters, were kind enough to post the exterior and internal dimensions (diameter & length) for the fixed tuner on their rifle, this information would give us something to start with. Thanks, ... John
 
I'd be surprised if most smiths do their own sporter barrel contouring from a blank, not cost effective when you can buy the barrel already contoured and lapped after contouring from the maker and the changes to the barrel after all that machining could be pretty big. I can give you a few rough measurements from the Benchmark barrel I have. The "knot" on the end is 1.150" od and 2 inches long then sharply tapers down to the reverse tapered barrel which is .760 at the juncture. The counter bore is aprox. .640 in dia. and 2.5 inches deep. Hope this helps.

Dennis
 
Dennis,
From your description, it seems that the crown is in the sharply tapered section behind the knot. What would you say that the diameter at the crown is?
Boyd
 
Yeah, I was pretty surprised about that too. Since there is a taper going from the knot to the actual barrel it's got enough material there but I didn't measure it. I'd guess close to an inch or so od.

Dennis
 
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Dennis D. said:
I'd be surprised if most smiths do their own sporter barrel contouring from a blank, not cost effective when you can buy the barrel already contoured and lapped after contouring from the maker and the changes to the barrel after all that machining could be pretty big. I can give you a few rough measurements from the Benchmark barrel I have. The "knot" on the end is 1.150" od and 2 inches long then sharply tapers down to the reverse tapered barrel which is .760 at the juncture. The counter bore is aprox. .640 in dia. and 2.5 inches deep. Hope this helps.

Dennis
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Dennis, I would not begin with a blank. Noticed a Shilen Ratchet Calfee Sporter contoured barrel on KSS website and was under the impression that the 2" long knob at the end was solid SS, except for the bore. Thought that all the counter boring would have to be performed by a smith. Now it appears that the factory performs most of the counter boring as part of the profile. Am I correct? I much appreciate the measurements you have provided. John
 
I bought my barrel directly from Benchmark and it was already counterbored. All I had to do was thread and chamber and cut extractor slots. I don't know how Shilen supplies their barrels but a quick call to KSS will let you know. I'm assuming that my BM barrel was calculated to give a mass that would work for their particular barrel taper, it could well be different for the Shilen.

Dennis
 
Dennis D. said:
I bought my barrel directly from Benchmark and it was already counterbored. All I had to do was thread and chamber and cut extractor slots. I don't know how Shilen supplies their barrels but a quick call to KSS will let you know. I'm assuming that my BM barrel was calculated to give a mass that would work for their particular barrel taper, it could well be different for the Shilen.

Dennis
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Just might consider the Benchmark sporter profile, as most of the difficult work is performed by the factory. Do you recall groove count, twist rate and finished weight of the barrel you installed? How would you rate the accuracy of your Benchmark sporter barrel? Thanks, ... John
 
Mine is a 3 groove 16 twist reverse taper. I don't recall the weight of the barrel but they would be able to tell you that. Pure accuracy is as good as any of my heavy guns though it takes a whole lot more concentration to get as good a score as I find it much more difficult to hold off for wind with the 6X scope!

Dennis
 
Dennis D. said:
Mine is a 3 groove 16 twist reverse taper. I don't recall the weight of the barrel but they would be able to tell you that. Pure accuracy is as good as any of my heavy guns though it takes a whole lot more concentration to get as good a score as I find it much more difficult to hold off for wind with the 6X scope!

Dennis
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That's good news! May I ask what action and trigger group you are using? John
 
Dennis D. said:
The action is a ULA with a Jewel trigger in a Stith stock and a Weaver T6
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Dennis, thanks for the valuable & informative experiences you shared with everyone in this thread. Few would reply with as much detail and honesty. Don Stith happens to be my go to guy when I need a stock. Another quality individual in our sport. I'm sure there are many more. John
 
Benchmark would be a good choice, I finished third at nationals with a six groove sixteen and a half twist benchmark with seventytwo year old tired eyes. Benchmark did all the work all i had todo was put it on a sako finfire.
 
Their website has no prices. How much do they charge for one of these reverse taper gems? Is it chambered, too? Threaded to order?
 
Give them a call, they'll answer all your questions about price and contours. The SAKO is a slip fit into the receiver so it doesn't need threading so it's easy for them to offer a drop in barrel. Anything with threads you'll have to fit and chamber yourself or have someone do it for you.
 
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