milanuk
Well-Known Member
Hello, all.
Well, on the topic of Ballistics, here's a question for those of you who specialize in Long Range: How important is minimizing Extreme Spread and Standard Deviation to long range accuracy? What is a good thumbrule, per se, for a max acceptable value of either or both?
A little background to the question: I have a Remington 40XB-KS in .220 Swift, w/ an Answer Rifle brake, Leupold 8.5-25x50mm LR scope. Everything else is pretty much 'out-of-the-box', w/ the small exception of the folks at Answer Rifles deemed it necessary to lop off an inch of my barrel whilst installing the brake (grrrr...), so I have 26 1/4" vs the normal factory 27 1/4", FWIW. I got this gun for long(er) range prairie dog and rock chuck hunting. I'd been working up loads using 50 Hornady Frontier brass that had been selected from the 80 rds of factory ammo that went down the pipe prior to me getting dies for it. The brass was neck-turned to clean up ~75-85% of the circumference, primer pockets uniformed, trimmed to length w/ a Wilson trimmer, chamfered, deburred, etc., so on and so forth. Loading was done on a Redding turret press using Redding Competition Neck and Seating dies. Total Indicated Runout per round was usually under a thousandth.
Some loads would shoot fairly small little holes @ 100 yds (0.2 is pretty small by my standards for a factory Swift), but the 'average' for most loads was ~0.4". But when I would try these loads (tried multiple powders, bullets, primers) @ 200yds, the groups would open up to somewhere between 1.5-3.0" Some would actually be say, 4 into 0.6-0.7", but never 5 shots into less than 1.5" I realize some of this is probably due to the nut behind the trigger, but it struck me as kind of odd, even so. The tests were done over multiple days, w/ pretty consistent (sadly) results, so I would guess that weather/wind probably wasn't a major factor. Oh, I forgot to mention: my group(pattern!) was more or less vertical in shape. I was always taught that that meant one of two things (usually) : a) shooter error, or b) muzzle velocity variations. So I unpacked the chronograph on the next trip to the range, and lo and behold, I'm getting extreme spreads of _over_ 100fps, and standard deviations of 50, 60, 70, and more. Yikes!!!
After some conferring w/ the local gunshop, I chunked that lot of brass (fired 6-7 times, I think) and am starting over w/ 200 new Winchester brass. I neck turned the entire circumference (on most; on some the setting only did 90-95%), removed the ejector from the bolt and am fire-forming the cases to the chamber and the bolt face, to eliminate any questions of crooked or otherwise 'weird' brass. Once I have all the brass fire-formed, I planned on sorting by case weight, but when I originally posted this on the Long-Range-Rifle mailing list, at least one fellow suggested chrono'ing each round and segregating any that shot abnormally faster or slower than the rest as a better method of culling out the inconsistencies ( a 'performance' based sort, if you will).
In the end, I hope to get things stabilized to where I can get a load that consistently performs out to (at least) 500 yds. Again, any comments or suggestions are welcome.
Thanks in advance,
Monte
Well, on the topic of Ballistics, here's a question for those of you who specialize in Long Range: How important is minimizing Extreme Spread and Standard Deviation to long range accuracy? What is a good thumbrule, per se, for a max acceptable value of either or both?
A little background to the question: I have a Remington 40XB-KS in .220 Swift, w/ an Answer Rifle brake, Leupold 8.5-25x50mm LR scope. Everything else is pretty much 'out-of-the-box', w/ the small exception of the folks at Answer Rifles deemed it necessary to lop off an inch of my barrel whilst installing the brake (grrrr...), so I have 26 1/4" vs the normal factory 27 1/4", FWIW. I got this gun for long(er) range prairie dog and rock chuck hunting. I'd been working up loads using 50 Hornady Frontier brass that had been selected from the 80 rds of factory ammo that went down the pipe prior to me getting dies for it. The brass was neck-turned to clean up ~75-85% of the circumference, primer pockets uniformed, trimmed to length w/ a Wilson trimmer, chamfered, deburred, etc., so on and so forth. Loading was done on a Redding turret press using Redding Competition Neck and Seating dies. Total Indicated Runout per round was usually under a thousandth.
Some loads would shoot fairly small little holes @ 100 yds (0.2 is pretty small by my standards for a factory Swift), but the 'average' for most loads was ~0.4". But when I would try these loads (tried multiple powders, bullets, primers) @ 200yds, the groups would open up to somewhere between 1.5-3.0" Some would actually be say, 4 into 0.6-0.7", but never 5 shots into less than 1.5" I realize some of this is probably due to the nut behind the trigger, but it struck me as kind of odd, even so. The tests were done over multiple days, w/ pretty consistent (sadly) results, so I would guess that weather/wind probably wasn't a major factor. Oh, I forgot to mention: my group(pattern!) was more or less vertical in shape. I was always taught that that meant one of two things (usually) : a) shooter error, or b) muzzle velocity variations. So I unpacked the chronograph on the next trip to the range, and lo and behold, I'm getting extreme spreads of _over_ 100fps, and standard deviations of 50, 60, 70, and more. Yikes!!!
After some conferring w/ the local gunshop, I chunked that lot of brass (fired 6-7 times, I think) and am starting over w/ 200 new Winchester brass. I neck turned the entire circumference (on most; on some the setting only did 90-95%), removed the ejector from the bolt and am fire-forming the cases to the chamber and the bolt face, to eliminate any questions of crooked or otherwise 'weird' brass. Once I have all the brass fire-formed, I planned on sorting by case weight, but when I originally posted this on the Long-Range-Rifle mailing list, at least one fellow suggested chrono'ing each round and segregating any that shot abnormally faster or slower than the rest as a better method of culling out the inconsistencies ( a 'performance' based sort, if you will).
In the end, I hope to get things stabilized to where I can get a load that consistently performs out to (at least) 500 yds. Again, any comments or suggestions are welcome.
Thanks in advance,
Monte