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Posted: 8/5/2013 11:56:27 AM EDT
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I've been wanting something a bit different so I bundled all the parts for the new build and shipped them to:
Kurt Buchert Post Office Box 1398 Sulphur, LA 70664 [email protected] If you followed my last project with Kurt, he built my 7.62x39 upper and documented it nicely on this site. He was able to get that 7.62x39 to shoot .5" groups. http://www.ar15.com/forums/t_3_121/616985_.html&page=1&anc=bottom#bottom I like (REALLY LIKE) his work so I sent him a takeoff barrel last Thursday that came from a bench rest gun. I asked him to reconfigure into a nice AR varmint gun for me. That barrel is a Hart or Llija and I know that the shooter was measuring groups in the upper ones and twos. He took it off at 1500 rounds. Kurt should be able to re-chamber it and clear out the throat erosion at the same time. With a straight case and sharp shoulders of the 6mmTCU I know that there can be feeding issues. I want to shoot 70 gr. bullets in it so with the right choice the OAL should not be an issue. More to follow... Bill in OR |
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Quoted:
I've been wanting something a bit different so I bundled all the parts for the new build and shipped them to: Kurt Buchert Post Office Box 1398 Sulphur, LA 70664 [email protected] If you followed my last project with Kurt, he built my 7.62x39 upper and documented it nicely on this site. He was able to get that 7.62x39 to shoot .5" groups. http://www.ar15.com/forums/t_3_121/616985_.html&page=1&anc=bottom#bottom I like (REALLY LIKE) his work so I sent him a takeoff barrel last Thursday that came from a bench rest gun. I asked him to reconfigure into a nice AR varmint gun for me. That barrel is a Hart or Llija and I know that the shooter was measuring groups in the upper ones and twos. He took it off at 1500 rounds. Kurt should be able to re-chamber it and clear out the throat erosion at the same time. With a straight case and sharp shoulders of the 6mmTCU I know that there can be feeding issues. I want to shoot 70 gr. bullets in it so with the right choice the OAL should not be an issue. More to follow... Bill in OR Bill, what twist is the bore...If its slower than 1:9 it might not stabilize the bullets much past 75-80 gain weights as the 6mm bore is typically very sensitive to twist rate and moderate velocities that come from the 6x45mm and 6mm TCU rounds (although slightly less w/ the TCU version). Since Kurt is doing the work himself, It's in very capable hands and one of the best Smiths' around for AR work...Good luck. |
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The old bbl owner custom swaged his own bullets for competition. They were 62.5gr. Damn accurate too. I don't know the twist but Kurt will when he gets it. I'd love to be able to shoot 80's out of it but the reality is that I'll only use it on coyotes and maybe the small blacktail deer along the OR coast so 70-75 grain should do just fine.
Bill in OR |
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Hi Bill,
Thanks for the kind words....made your link hot... x39 Russian Thread It may be worth mentioning that the reamer we'll be using has the freebore reduced to make it a little more agreeable with the AR mag length.... We'll look at the blank and run a similar drill as we did with the 1:15 x39 to figure the useable bullet weight.....I'm thinking this one will be similar to the x39 in that we'll start the new TCU chamber at the first available good spot in the barrel and try to salvage as much length as we can to maximize the expected velocity....figure in a little back extrapolation and come up with the useable weight range.... We also do the entry into the chamber a little different for the 'straight' 'steep' TCUs.... Thanks again, Kurt |
I picked up the package of parts today for the 6mm TCU build... Looking over the barrel it appears to be: a former 6mm PPC broach cut 1:14.75 twist.... once the PPC chamber is removed and get to a good spot they'll be around 19 to 19.5" of barrel remaining.... with the velocity expected from the ~ 19" TCU, it looks like the useable weight range of the bullets for testing is going to be 68gr flatbase 'match' to 70gr ballistic tip boat tail....a 1:14 twist would of helped getting closer to the 80gr weight range, but right now I'm gonna stay a little conservative and start out with the flatbase 68s as they should offer a little more inherent stability.... more to come..... Kurt |
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I ended up forming some fresh 6TCU brass for the project... Started with some virgin Lake City 5.56x45mm.... Original brass length: 1.755" Die formed brass: 1.745" Fire-formed brass should end up around ~ 1.740" Will be testing 62, 68, and 70 grain projectiles.... 
The PRI and HK 5.56 mags both allow loading out to ~ 2.320" 
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Great info on the mag's and the extra OAL they allow. I've been limiting my OAL to 2.225 - 2.230 in the mags I have. A few more thousandth of length can make the difference between a good group and a great group. Looks like another purchase in my future.
Excellent pictures. I'm a visual learner so those really help me understand the process you are using to produce and wring out the best these uppers have to offer. Keep up the great work. Bill in OR |
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Quoted:
I ended up forming some fresh 6TCU brass for the project... Started with some virgin Lake City 5.56x45mm.... Original brass length: 1.755" Die formed brass: 1.745" Fire-formed brass should end up around ~ 1.740" Will be testing 62, 68, and 70 grain projectiles.... http://www.ar15.com/media/viewFile.html?i=54917 The PRI and HK 5.56 mags both allow loading out to ~ 2.320" http://www.ar15.com/media/viewFile.html?i=54918 These are typically the brand/type of mags we use to get the best COL/performance out of our 6.5mm PCC wildcat...very well made especially the HK. |
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I loaded up a bunch of 6mmTCU brass two nights ago and topped off the case with a bunch of misc 6mm bullets that I have saved over the years. Perfect for fire-forming. It was quickly apparent that I could not get the bullets to seat deep enough to work in the OAL limits of the AR mags. Not with the RCBS dies that I have. I have used this caliber for years in IHMSA (Pistol Silhouette) where the bullets were seated out to within a few 1000th of the lands. I never thought about them not being to be seated to a deeper depth. Anyway, I dropped off the die to a local machinist and he is turning down the seating stem to allow for a deeper bullet seating. I pick it up today.
These are the joys of working outside the norms and make our build more interesting. Bill in OR |
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