On one hand, it seems this has been beaten to death. On the other hand, this cartridge is new to me, so I don't know what to do.
Bought a used Borden action with a 6br barrel and benchrest stock. Barrel was very fouled and looks questionable at best when cleaned. So. The doubt is already in my mind. Thinking of a rebarrel.
Want to go with a Kreiger blank. That much I do know. I'm restricted to 200 yards now and for the foreseeable future.
Given that distance restriction, what would you choose regarding the rate of twist, bullet weight and reamer selection? I've never turned necks before. Understand the process, just never done that.
I don't even know if I'm 'cut out' for benchrest. Just 'dipping my toe' in the water to see what I think about it.
Thanks for looking.
DShortt
Here is an article that I saved a while back. I hope it helps...
Chambering the 6BR and 6 Dasher
The Right Reamer Makes All the Difference --
Dave Kiff
Q: What are the advantages of a custom reamer
You get better accuracy, reduced ES, longer brass life, and most importantly you get exactly the chamber that you want. The throat will be set precisely to match the bullets you shoot and the seating depth you want. And you can pick a neck-size to suit your needs. Whether you want a .272" no-turn neck or a minimum-turn .269" neck (which is very popular now), we can make that, or any other neck diameter you want all the way down to .261". Because you can set the exact neck-wall thickness you want, you get better control over neck tension which reduces velocity spreads. And the body dimensions are ideally matched to Lapua brass so you get less case expansion, without sacrificing feed reliabilty. Brass that isn't worked as much during sizing lasts longer.
Let me give you an example of how important a good chamber is. We've seen super-expensive barrels on thousand-dollar actions that did not shoot well at all, because the throating was bad. The throat will make or break a benchrest gun. When they were rechambered with our reamers, group size was reduced by 50% or more. We've had other customers that start out with non-premium, inexpensive barrels, but still end up with very competitive guns because they have perfect chambers and throats. A concentric, close-fitting chamber and a good throat are the keys to accuracy.
Q: Without revealing any trade secrets, what throat lengths do you recommend for a 6mm BR case?
We normally go with a 1.5 degree lead angle, unless the customer wants something different. For 60-68gr bullets we recommend a .060" freebore. For the 80gr bullets, .080" is a good setting. For the 100-107gr VLDs, a .115" -.120" freebore will allow you to get the base of the bullet up out of the doughnut area. This will save you lots of aggravation over the life of the barrel.
Q: There are a variety of 6BR Improved case profiles out there. Which wildcat version works best, based on reports from your customers?
We have prints for all the popular 6 Improved cases including the Dasher, the 6 BRBS (Shehane), and Bob Crone's 6 BRX. Based on customer reports, it is our strong opinion that the 6 Dasher is by far the best for 1000-yard accuracy. You get a bit longer neck, and the Dasher has a 40° Improved body. This 40° shoulder provides the most ideal turbulence pattern for consistent powder ignition. Bottom line, the 6 Dasher is the winningest 1000yd cartridge based on the 6mm BR parent case. If I built a 6BR wildcat rifle for myself, it would definitely be a Dasher.
Q: What kind of chambering reamers are preferred by your customers?
By far, the majority of our custom reamer orders are for removable-pilot reamers (live pilot) for the full chamber (neck and body). Definitely go with a live pilot for any custom reamer you have ground. Solid piloted reamers can scratch the lands.
Q: What about neck-only reamers--do you recommend doing the neck with a separate neck reamer?
No. We always recommend using a full neck+body reamer for a high-grade custom rifle, particularly if you plan to have more than one barrel. Yes, a very talented smith can finish a chamber with a separate neck reamer (which we sell), but to get absolute 100% consistency from barrel to barrel it is best to cut the chamber with our live pilot reamer that does the neck and body at the same time. When the barrel is shot out, you can take that reamer, give it to any good smith, and get an identical chamber.
Q: If my smith has a 6BR reamer in stock, why should I buy my own reamer?
First and foremost, we can give you a reamer with the throat set ideally from your dummy round, with freebore measured from the bullet ogive. And the body diameter will be a perfect fit for Lapua brass. Having the throat and lead set for your case and bullet choice will provide the best accuracy for the gun. You can spend thousands on your action, barrel, stock and scope, but if the throat is not right, your gun may not shoot to your expectations.
Also, consider that your smith's reamer may be an older model designed for 6 BR Remington brass. This will cut a chamber dimensionally incorrect for Lapua brass. The neck will be short and it will be tight at the casehead. Second, if it is a full SAMMI-spec reamer you may end up with a neck diameter much larger than you want, .276" or even larger, when .272" is all you need for a no-turn neck. Order from us and we can give you precisely the dimensions you want for both neck and body. Lastly, your smith's reamer may have a lot of miles on it. Worn-out reamers cut poor chambers.
We always recommend that you use a sharp reamer that cuts on all flutes. A worn reamer or a reamer that does not cut on all flutes can give you a small or short throat also a larger body than needed. Always check your reamer before you use it.
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