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762cavalier
12-03-2006, 12:44 PM
Will a 1/7 twist barrel stablilize the lighter 55 grain bullets as well as the heavier 72 grain bullets?

NeoWeird
12-03-2006, 12:53 PM
I believe it will stablize both. I am not sure, but it would seem that a faster spin wouldn't destablize the bullet. Like a football; if it doesn't spin fast enough it wobbles, but spin it faster and faster and it just spins tighter and tighter.

I am pretty sure 1/7 would be fine.

hoffmang
12-03-2006, 12:55 PM
Here is an excellent resource for that question:
http://www.ammo-oracle.com/body.htm

-Gene

blkA4alb
12-03-2006, 12:56 PM
Neoweird, if it gets spun too fast the bullet will tear itself apart.

You should be able to fire 55 grain, but not 45 grain. A 1/8 or 1/9 would be better suited to shoot 55 grain however. The 1/7 is designed for heavier bullets to reach out further.

Aluisious
12-03-2006, 12:59 PM
Neoweird, if it gets spun too fast the bullet will tear itself apart.

You should be able to fire 55 grain, but not 45 grain. A 1/8 or 1/9 would be better suited to shoot 55 grain however. The 1/7 is designed for heavier bullets to reach out further.

You're not going to spin a bullet fast enough out of a rifle barrel for it to break apart. Some physics regarding tensile strength and centrifical forces generated will prove that, as well as the fact that people shoot light bullets out of fast twist barrels all the time without any problem.

1/7 would be fine for 45 grain as well. The only downside is that with excessive spin, the bullet will continue to spin along the axis it left the barrel even as the trajectory falls...it will look kind of like a plane coming in to land, nose up. Not good for accuracy.

blkA4alb
12-03-2006, 1:07 PM
You're not going to spin a bullet fast enough out of a rifle barrel for it to break apart. Some physics regarding tensile strength and centrifical forces generated will prove that, as well as the fact that people shoot light bullets out of fast twist barrels all the time without any problem.

1/7 would be fine for 45 grain as well. The only downside is that with excessive spin, the bullet will continue to spin along the axis it left the barrel even as the trajectory falls...it will look kind of like a plane coming in to land, nose up. Not good for accuracy.
Do not put your writing in my quote :mad: .

And second the ammo oracle seems to think different.

http://www.ammo-oracle.com/

1:12 twist rifles cannot stabilize SS-109/M855 bullets and 1:7 twist rifles are slightly less accurate with lighter bullets and will often blow apart the thin jackets of lightweight varmint bullets. The 1:7 twist is used by the military to stabilize the super-long L-110/M856 tracer bullet out to 800 yards, but unless your plans include shooting a significant amount of M856, the 1:9 twist rate is better suited for general use.

Aluisious
12-03-2006, 1:11 PM
Do not put your writing in my quote :mad: .

And second the ammo oracle seems to think different.

http://www.ammo-oracle.com/

1:12 twist rifles cannot stabilize SS-109/M855 bullets and 1:7 twist rifles are slightly less accurate with lighter bullets and will often blow apart the thin jackets of lightweight varmint bullets. The 1:7 twist is used by the military to stabilize the super-long L-110/M856 tracer bullet out to 800 yards, but unless your plans include shooting a significant amount of M856, the 1:9 twist rate is better suited for general use.
I keep editing that post and somehow keep getting it wrong. I'd rather not have my writing in your quote.

Of course bullet construction makes a difference, but take pause and think. A 1/7 twist is only going to result in about 30% higher RPM than a 1/9 twist. Also a 1/7 twist on a 45 gr bullet is only going to result in less than 20% higher RPM than the same twist on a 55 gr bullet.

Either they make those varmint bullets rediculously close to the edge already, or it's an old wives tale.

762cavalier
12-03-2006, 1:12 PM
OK maybe more info. I will be using it in a fixed mag config and I handload. so I guess i wanted to know how it will do with SS109(which seems to be commonly avail) so I can stock up but I planned on handloading heavier bullets

dw1784
12-03-2006, 2:14 PM
though I'm no expert in balistics, I can tell you about my mini14(1:7), bushmaster(1:7), colt match(1-9) and a-1 upper(1-12).
1:7 works for (most) 55gr and heavier. I have mixed result with WWB 40gr varmit and PMC varmit. With the mini, I've experienced jacket seperation- copper jacket on entry side of paper target. Norinco yellow boxed 55gr steel jackets on the other hand, almost always keyholes with my mini(with a huge fireball:D), but not with the 20in bushmaster. Depending on who you believe(especially some armchair generals at arf.com) heyhole may not be all that bad on soft targets...just my 2cents.

oops-yes, 1:7 is designed for ss109 and heavier.

tiger222
12-03-2006, 4:01 PM
the only difference I have found in shooting 1/7 with M193 or 62 gr is the POI shifts to the right with the lighter grain round.

Pthfndr
12-03-2006, 4:20 PM
The 1/7 will work just fine with mil surp / mil spec ammo, match ammo (like the Sierra 52gr Match King, or varmint bullets down to 50-52 gr (lots of high power shooters use the 50/52gr spitzer bullets for 100 yard matches because they're cheap and accurate).

The 45gr varmint bullets WILL come apart because the jackets are thinner (for a reason). Seen it happen with my own eyes.

proraptor
12-04-2006, 7:29 AM
I have a 1/7 and use the 55 grain bullets all the time