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Posted: 12/22/2009 9:34:49 AM EDT
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Looking to take my current AR and make it into a LR rifle to use with heavy bullets (69-90gr) using a 1:7 twist barrel. I don't want to go up to a 24" bbl so should i go with a 18" or 20"? Am I getting that much more out of the 20" to compensate for the extra 2" of bbl length?
Thanks, Hawk |
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Quoted:
Looking to take my current AR and make it into a LR rifle to use with heavy bullets (69-90gr) using a 1:7 twist barrel. I don't want to go up to a 24" bbl so should i go with a 18" or 20"? Am I getting that much more out of the 20" to compensate for the extra 2" of bbl length? Thanks, Hawk I guess it depends on how far you wanna shoot. Any extra velocity is your friend when you start stretching out. Although not a requirement it wouldn't hurt. |
| It don't know what it is for .223 but I recall that every extra inch after 20" for a .308 gave 50fps out of the muzzle. I'm sure there are some ballistic guys that can help you out a little more. But what ever the round you want to shoot, find out what the barrel length was for the velocity testing and use that as a base. Going up from there will give you that added velocity, how far do you plan on reaching? Would a .308 build be a better option if you wanna test limits? |
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I don't know if I would use the 1-7 for the bullets you mentioned. Read this article.
"Twist Rates 223 Rem Remington barrel Twist rateThe .223 Rem shoots a wide range of bullets very effectively, from 35gr flat-based varmint bullets, to ultra-long 90gr VLDs. However, you'll need the right twist rate for your choice of bullet. For max velocity and accuracy with the lightest bullets, a 1:14" twist may be ideal. More versatile is a 1:12" twist that will allow you to shoot the popular 60-64 grain match bullets. (However, a 1:9" twist is needed for the steel-core 62gr bullet used in the M855 military loads, because that bullet is as long as most 70-grainers.) For normal lead-core jacketed bullets, a 1:9" twist will let you shoot up to 73gr bullets. Since most .223 Rem shooters prefer bullets in the 50-73gr range, a good "do-it-all" solution is a 9-twist, unless you're a Highpower competitor. For long-range match purposes, long, high-BC bullets are favored for their ability to buck the wind. You'll want at least a 1:8" twist to shoot the 77gr and 80gr MatchKings and 80gr Bergers. To shoot the new 90gr pills, a 1:6.5" is recommended, though a true 1:7" will work in most conditions. Overall, what twist rate is best? For varminting we like a 12-twist. The slower twist will give you a bit more velocity, and minimize the risk of jacket failure at high rpms. For general use, an 8-twist barrel will let you shoot the excellent 77gr and 80gr Sierra MatchKings and nearly all varieties of non-tracer milsurp ammo. We'd only select a 1:7" or faster twist barrel if we had a need to shoot the 90gr VLDs. Barrel Twist Rate1:14"1:12"1:9"1:8"1:7" or 1:6.5" Max Bullet Weight55gr FB65gr FB73gr BT80gr BT90gr BT VLD After 40 years of varmint and target reloading and shooting I have 1-12 in my bolt guns for light bullets (50 gr range) and on my two long range AR's I went with 1-8 twists as I like the MachKings. In my 16 in carbines I stick with the 1-9s are they are the best compromise for the real-world loads I commonly use in those guns. (55 gr to 62 gr loads) Note on the chart that those are the MAX weights to use with those twists, not the best weights. 1 in 14 works best with 40-50 fr, 1-12 can shoot 45-55gr pretty well, etc. Lots of AR fan boys want you to believe that 1-7 is the "only" twist worth having. Slow down and go research what serious shooters have been learning over the past fifty or so years this round has been around. Tech article on .223 Good read on history of the 5.45 x 45 |
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Quoted:
Looking to take my current AR and make it into a LR rifle to use with heavy bullets (69-90gr) using a 1:7 twist barrel. I don't want to go up to a 24" bbl so should i go with a 18" or 20"? Am I getting that much more out of the 20" to compensate for the extra 2" of bbl length? Thanks, Hawk I am guessing you are also looking for very good accuracy ? If so , I recommend a stainless bull barrel . These are heavy . If a 20" is not too heavy for what you plan , pick it . My target upper has a 24" SS bull barrel . God bless Wyr |
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