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Posted: 11/11/2012 9:11:35 PM EDT
| I know the 1/7 twist barrels are better at stabilizing the longer, heavier rounds, but how do these barrels perform when shooting the lighter 55gr round? Is it a best of both worlds twist rate? Or is there trade off when compared to the 1/9 twist |
| It is not the twist rate that is the big slice of the pie, as long as you reach certain thresh holds. If the lighter bullets are well made they will shoot well in a 1 in 7. The quality and concentricity of the bullet will most likely determine the accuracy penalty paid by using more twist rate than required for stabilization. |
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Totally over hyped. 1/7 does fine with 55 gr. If you have a 1/7 that doesn't shoot 55 well that's just the gun you have, all rifles have loads they love and hate. Have a colt that loves 55 and 77, but has huge groups with 69gr. Pretty much this. I have 5 1/7 barrels, and they all shoot 55 grain stuff crazy accurate. They also shoot 75 and up grain stuff incredibly as well. Unless you plan on shooting a steady diet below 55 grains, I see no reason to not go 1/7. |
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1-7 vs 1-9 is an argument that will go on forever. In a nut shell with 1-9 you are good to go with bullets up to 75 grains of weight. 1-7 comes into play with 77 grain bullets. I believe this to be true due to my personal experiences. I have had very good results with Winchester WB 45 gr JHPs in a 1/7 (as well as the 1/9) as well, go figure. Over hype? You got it. |
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There is a good article on twist rate in the latest issue of "Rifle" Magazine by John Barsness. Basically it boiled down to "over stabilization" is pretty much a myth. To science/ engineers it is a real thing, but is so miniscule to firearms that it can't even be measured at 1000m with the best equipment and scientific testing procedures.....under stabilization is very real. As mentioned above perceived over stabilization boiled down to poorly manufactured unbalanced bullets. It's virtually impossible to over stabilize today's quality bullets for all practical purposes. YMMV
advntrjnky |
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Quoted: There is a good article on twist rate in the latest issue of "Rifle" Magazine by John Barsness. Basically it boiled down to "over stabilization" is pretty much a myth. To science/ engineers it is a real thing, but is so miniscule to firearms that it can't even be measured at 1000m with the best equipment and scientific testing procedures.....under stabilization is very real. As mentioned above perceived over stabilization boiled down to poorly manufactured unbalanced bullets. It's virtually impossible to over stabilize today's quality bullets for all practical purposes. YMMV advntrjnky then why does lighter bullets do so poorly in 1:7s, ie 22lr |
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Quoted: then why does lighter bullets do so poorly in 1:7s, ie 22lr Most .22LR barrels are 1/16 and I'd read that the .22LR is inaccurate in a 1/7 barrel as well. I have a Cmmg drop in conversion and it's been very accurate in my 1/7 barrels. Mind you I'm not shooting rimfire bench rest just plinking and a few Steel Challenge matches and acurracy is very good. |
| A faster twist reduces velocity to some degree. Fast bullets are hard on barrels, harder on barrels with fast twists. There are always trade offs. The question is can you afford a small amount of increased barrel wear and velocity loss with light bullets in order to extend the range of the rifle with longer bullets? Personally I'd take a dedicated upper with a 1-12" barrel for light bullets and a 1-8" for exclusive use with longer bullets. I think 1-9 is a good compromise for use with bullets in the 40-68 grain range. If you plan to use 77 grain bullets at 2850 so the trajectory will to line up with a standard mil dot reticle, then 1-7" might make sense. but if I invested in a dedicated barrel accurate enough to shoot to 700 yards and beyond, I would use a different gun to shoot M193. |
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Quoted: 1/7 doesn't shoot 22lr very well because 22lr bullets are undersize for the .224" bore. IIRC, 22LR barrels are .220" and usually use a 1/16 twist. 22lr is the same diameter as the 223. So is the 223/556 undersized as well??? still doesnt explain the differences in the AR |
| While overstabilization is real with bullets under 50 grains, and bullet deformation from centrifugal force is possible with thinly jacked bullets under 45 grains from a 1:7 twist barrel, one can find a bullet for every application from either 1:7 or 1:9 twist barrels. 1:8 is probably the most versatile, but every rifle is unique and it is up to the rifleman to test out several loads and decide which works best from his rifle for his applications. |
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Quoted:
There is a good article on twist rate in the latest issue of "Rifle" Magazine by John Barsness. Basically it boiled down to "over stabilization" is pretty much a myth. To science/ engineers it is a real thing, but is so miniscule to firearms that it can't even be measured at 1000m with the best equipment and scientific testing procedures.....under stabilization is very real. As mentioned above perceived over stabilization boiled down to poorly manufactured unbalanced bullets. It's virtually impossible to over stabilize today's quality bullets for all practical purposes. YMMV advntrjnky Since most 22LR ammo is inexpensive plinking ammo, this would be my guess as to why it's inaccurate in 1/7 barrels. |
| only time I have ever seen a negative effect was when I bought a cheap box of reman 36gr varmit ammo, they would fly about 20 feet but were spinning so fast that the jackets literally popped apart in the air, at the time I didn't know what was causing it and just stopped shooting them. |
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I have a 1/8. It shoots whatever I need, big and small. I also have a 1/9, that won't mind shooting 75's, but shits the bed on 77's.
My 1/7 does it all well too. It's just one of those things, that is fun to me. Coming up with dope for your own rifle. I also keep a sniper style log book for each of those three guns. Maybe I'm a bit overboard, but it seems to help. As of right now, I have one sighted in for 60 gr. nolsers, for deer, and 62 gr. fusions on another, for deer as well. L2 |
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.22lr isn't the same diameter as 5.56/.223. The groove diameter of .22lr barrels is generally about .221" with a bullet diameter of .222". Generally lead bullets need to be about .001" over groove diameter to shoot accurately. the 5.56/.223 has a groove and bullet diameter of .224". That means that a .22lr bullet fired through a barrel meant for 5.56/.223 will never reach it's full accuracy potential because it's about .003" undersized for the bore. However, they often shoot decently out to moderate ranges....often attributed to lead bullets ability to "slug up" slightly when they hit the rifling.
advntrjnky ETA: if you have quality bullet designed to handle the centrifugal force incurred from a fast twist barrel you you can not overstabilize it and it will shoot more accurately than the shooter Quoted:
Quoted:
1/7 doesn't shoot 22lr very well because 22lr bullets are undersize for the .224" bore. IIRC, 22LR barrels are .220" and usually use a 1/16 twist. 22lr is the same diameter as the 223. So is the 223/556 undersized as well??? still doesnt explain the differences in the AR |
With spinning objects like bullets it is the effect of excessive rotational spin causing the nose of the bullet to rise above the center line thereby alter its aerodynamics and ballistic coefficient from its "optimum" more neutral state.......engineering term.......and simplified by a simpleton  (me).
advntrjnky Quoted:
Somebody please explain how you can "over stabilize" a bullet  |
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An optimumly stabilized bullet has enough gyroscopic stability to keep its center of mass behind its center of pressure(point forward), but not so much gyroscopic stability that it will fly in a way which is aerodynamically inefficient(ojive forward) as its direction shifts. In other words, when the bullet reaches the point in its trajectory where its direction turns downward, we want the nose of the bullet to change so that the bullet stays pointed in its direction of travel. With an overstabilized bullet, the nose stays pointed at its angle of departure.
Think of football. When a QB throws a nice tight spiral, the nose of the ball turns down when the ball begins to come down, making for a straighter path. Now, consider the punter. When he punts the ball and gets a really fast spin on it, it does not turn over. It just hangs up in the air for a while because the nose does not turn down. The hang time is longer because a football falling with its nose pointing horizontally is aerodynamically inefficient. We want our bullets to hit like a well thrown pass, not like a great punt. |
| So there is no over stabilization as far as accuracy goes. How about terminal effects? Will "over-stabilized" bullets cause less damage or be less likely to frag compared to a just barely stabilized bullet?? Were there less complaints of inadequate effectiveness of M193 fired from 1:12 barrels compared to the M855 fired from the 1:7? |
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Quoted:
So there is no over stabilization as far as accuracy goes. How about terminal effects? Will "over-stabilized" bullets cause less damage or be less likely to frag compared to a just barely stabilized bullet?? Were there less complaints of inadequate effectiveness of M193 fired from 1:12 barrels compared to the M855 fired from the 1:7? Terminal effects are not changed by the overstabilization in air. No .223 bullet is stable in flesh. Accuracy can be affected by overstabilization at ranges over 300 yards because overstabilized bullets are not flying nose first. Terminal effects past 300 yards may be hampered if a bullet needs to hit nose first. M193 does not need to hit nose first, 40 gr vmax does. Ymmv. Air density is a critical factor. |
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