signal5 Posted July 21, 2005 Share Posted July 21, 2005 What would be the best bullet weight for an 18 in. barrell with a 1/7 twist? I will only be shooting out to 200-250 yards. Will 55grn. fmj work fine or will i need something heavier? Link to comment Share on other sites More sharing options...
wsimpso1 Posted July 21, 2005 Share Posted July 21, 2005 Signal5, Really fast twist barrels (1 in 7" GI barrels qualify) may have trouble with thin jacketed light bullets. There have been plenty of reports of 40-45 grain varmint bullets pushed to max velocities where the bullets will not make the trip to the target. Some folks have reported seeing a gray puff through the telescope or spotting scope during a string and less holes in paper than rounds fired. The internal centrifugal forces when shot from a 7" twist are three times that for the 12" twist (and sometimes lower velocities) that they were designed for, and can cause the bullet to come apart shortly after leaving the bore. 400,000 rpm is a pretty spectacular number... Everything else is used by High Power shooters with fast twists - the 1/7" twist is needed by folks shooting 90 grain bullets for 600 through 1000 yards. The same people use the same barrels with 52-69 grain match bullets on reduced courses (target sizes are reduced to simulate 200/300/600 yards on 100 and 200 yard ranges). Stick with 55 grain and up bullets, and you should be fine. After that, you get to choose between wind bucking ability, drop, accuracy, and cost, and then test ammo to see what it does in your rifle. So much shooting, so little time. Billski Link to comment Share on other sites More sharing options...
wsimpso1 Posted July 21, 2005 Share Posted July 21, 2005 Sorry, I did not get to the rest of the answer - there is another hot thread started by M4Mike right on this forum with the bullet choices being discussed. Billski Link to comment Share on other sites More sharing options...
Stumpnav Posted July 21, 2005 Share Posted July 21, 2005 I've got an 8 twist Armalite barrel that will shoot 52-80 grainers with no bullet blow ups. Link to comment Share on other sites More sharing options...
PacMan Posted July 21, 2005 Share Posted July 21, 2005 What would be the best bullet weight for an 18 in. barrell with a 1/7 twist? I will only be shooting out to 200-250 yards. Will 55grn. fmj work fine or will i need something heavier? <{POST_SNAPBACK}> Yes. Link to comment Share on other sites More sharing options...
cking Posted July 21, 2005 Share Posted July 21, 2005 Feamster in his book/tests show that all bullets weights work just fine as long as you don't push your velocity to the roof. So stay below 2900 fps and all bullets will hang together. Start getting over 3000 and some bullets will just go puff. Supposedly for three gun the ticket is a light bullet with just enough velocity to make minor and you got a no recoil, flat shooting gun. May have trouble on steel beyond 200 yards. Link to comment Share on other sites More sharing options...
wsimpso1 Posted July 22, 2005 Share Posted July 22, 2005 More detail on the topic of exploding bullets - I was not saying that light bullets won't work, I was just cautioning that using the thin jacketed very light bullets might leave the shooter looking at a target with less hits than rounds fired, confusion over where the other bullets went, and then finally a box of bullets that they don't want to use anymore. The 8" twist puts about 2/3 of the centrifugals on the bullet that a 7" twist does (same muzzle velocity), so what works OK in an 8" *might* still cause bullets to disappear from a 7". The bullet puff problem was primarily with 7" twist barrels, 40 and 45 grainers, with thin jackets, and, as was mentioned above, high speeds. I think that they were 0.223" diameter too, which also allows more leakage past the bullet and possibly gas cutting of the jacket, just to help things along. I was not intending to say "don't try 52's and 53's". Anything in 0.224 diameter of 52 grains and above should work fine, particularly if you only load to velocities needed to be comfortably in the match. I have a 52 grain Sierra Matchking load that is an absolute hammer in several rifles including my NRA Match Rifle, 7.7" twist Krieger barrel NRA Service Rifle, and I expect that it will shoot great in my 7" twist Tactical Rifle but have not tried it yet. I agree that more speed really does not buy much in the way of drift or drop, so go for ammo that shoots little groups. Reliability on steel and drift are covered nicely on other threads in this forum. Have fun with the rifle! Now if there were more Tactical Rifle Matches about.... Billski Billski Link to comment Share on other sites More sharing options...
George Posted July 22, 2005 Share Posted July 22, 2005 Try some 55's and if they hold a group well, then OK, but sometimes lighter bullets won't shoot in 1:7's. My 1:7 shoots most 55's OK, some not. If you want closer to optimum in your 1:7, try a 68-69 gr. for longer stuff. It's a good matchup to that twist bbl. for this game. Link to comment Share on other sites More sharing options...
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