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Rate of twist vs bullet weight

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Rate of twist vs bullet weight

Old 10-23-2002, 04:46 PM
  #1  
Fork Horn
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Default Rate of twist vs bullet weight

We all talk about certian rifles that like or shoot better with certian bullet weights.

Does bullet weight and rate of twist impact muzzel volicity or accuracy .

ie. my 30.06 will spray Federal premium trophy bond 165 gr all over a target at 100 yards.
Yet at the same distance with winchester super X 180 gr groups tightn to -2" groups

So what is the culprite. Bullet speed , weight, or rate of twist of my rifle? or any rifle for that matter?

Ps the rifle is a sporterized p-17 (not a new one by any means)

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Old 10-23-2002, 06:29 PM
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Old 10-23-2002, 08:10 PM
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Default RE: Rate of twist vs bullet weight

-2" groups, now that's a shooter!

What about the relationship between bullet velocity and rate-of-twist?

Take for instance a .223 and .22/250. Most rifles in both cartridges will shoot 50-55 grain bullets the best. But I've noticed that most factory .223's are rifled 1-in-10 or 12", where most factory .22/250's are 1-in-14".

Using the reloading data on Hodgdon's website, and averaging the velocities produced by all of the powder combinations (max loads) I get the following velocities from each cartridge:

.223 Rem - 3,247fps
.22/250 Rem - 3,608fps

By doing some simple calculations it's found that the rotational speeds of both are:

.223 w/ 1-in-10" = 233,784 rpm
.223 w/ 1-in-12" = 194,820 rpm
.22/250 w/ 1-in-14" = 185,554 rpm

So we see that while the twist rates are significantly different, the rpms are fairly close. If the .22/250 had a twist rate of 1-in-10" it would be rotating at 259,776 rpm.

I'm thinking that maybe 1-in-10"/12" overstabilizes the 55 grain bullets in a .22/250 because of the increased velocity.

Please note that this is just MY theory based on the information I've read and interpreted. Please feel free to point out any errors in my evaluation.

Mike


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Old 10-25-2002, 10:47 AM
  #4  
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Default RE: Rate of twist vs bullet weight

BUMP

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Old 10-26-2002, 08:10 AM
  #5  
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Default RE: Rate of twist vs bullet weight

I would venture to say that twist, velocity, etc., has nothing to do with the fact that your rifle will shoot the 180's well, but not the 165 load you have had trouble with. I suggest that your rifle does not like that particular load (maybe not the specific LOT of that ammo you have), and that your rifle, if accurate with a 180-grain load, could be made to shoot a 165-grain bullet well also! It might require handloading to find the right combo, but there could also be a good factory load that would do well. By the way, there's very little difference between a 165-grain bullet and a 180-grain load!! Like 15 grains, about the same as a .22 caliber air-rifle pellet!!

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Old 10-26-2002, 10:39 PM
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Default RE: Rate of twist vs bullet weight

I agree with driftrider about the twist , Also I want to add somthing I noticed this week on two different Ammo. brands of 30-06 in 150gr.
I shot 10 bulets PMPs and 10 Remengton springfileds. The PMPs grouped so good where the Rem. didn't. I found out that the Rem. projectile is longer than the PMP,and then the PMP has more thick rear part before it starts to get curved to the pointed section. To some the whole thing in two word it is the "weight distribution" of the projectile.

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Old 10-27-2002, 01:25 AM
  #7  
BT
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Default RE: Rate of twist vs bullet weight

bullet lenth all so plays a part in it to. i have sean espicly with the barns X. people haveig to go to lighter bullets with them for the lenth to match the twist
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