barrel twist?

[texasislandboy]

i have a 24'' barrel with a 1/12 twist on it and wanted to know if i took off 4'' of the barrel would it affect shooting much ? i have no clue on this subject

 

[TexMex247]

Would need to know what caliber and action type. Then what weight of projectiles you are firing/want to fire.

 

[texasislandboy]

.308 168g bthp loading around 45.5g of varget with a oal of 2.80 in a bolt action

 

[TexMex247]

I have heard that 24" is the optimal length for accuracy and MV in the .308. You will probably lose 50fps or more w/the 4 inches and some terminal power. It will definitely effect long range shots. Is it a heavy contour barrel ? What ranges(yds) do you typically shoot at ?

 

[texasislandboy]

i shoot 400yrds alot its a very heavy barrel! i just want to make the gun a little lighter

 

[M. Sage]

I have heard that 24" is the optimal length for accuracy and MV in the .308. You will probably lose 50fps or more w/the 4 inches and some terminal power. It will definitely effect long range shots. Is it a heavy contour barrel ? What ranges(yds) do you typically shoot at ?

50 FPS per inch. So he'd probably drop 200 FPS.

As long as you can adjust your dope for it, it shouldn't really affect accuracy. Shorter barrels usually have better harmonics and better overall accuracy potential. Generally, shortening a rifle barrel has the same effect as increasing outside diameter. A friend of mine has a .308 with an 18" barrel and it's deadly accurate at 300 yards. It'll print 2" groups at that range all day long.

Find a good gunsmith that will put a proper target crown on. The crown is extremely important to accuracy.

 

[texasislandboy]

hell its just my go to gun if its dead on at 400 im happy i dont care about much more than that i may get it threaded and cut down at the end of the month

 

[dee]

It'll be fine my .308 is only a 20" barrel and is very accurate.

 

[mikeofcontex]

Fluting the barrel will lighten it, stiffen it, and make it dissapate heat better. It might provide a solution with all the benefits.

 

[texasislandboy]

that would be a good idea but i have a blued barrel and dont really want to get it reblued

 

[Texas1911]

Fluting the barrel will lighten it, stiffen it, and make it dissapate heat better. It might provide a solution with all the benefits.

Fluting it won't increase the rigidity of the existing barrel. However, if you flute the barrel it can run a thicker profile, which is more rigid.

 

[Texas1911]

i have a 24'' barrel with a 1/12 twist on it and wanted to know if i took off 4'' of the barrel would it affect shooting much ? i have no clue on this subject

The bullet is spun up the moment it engages the lands, otherwise it'd strip the diameter of the bullet down. That being said, you are only going to lose velocity with cutting the barrel down, and the 50 FPS rule doesn't apply here since we are talking about barrel lengths exceeding 20". For example, the difference between 18" and 20" is about 30 - 35 FPS in a .308 bolt rifle. The difference for every inch beyond that is even less because of the reduction in pressure and the continuation of friction loss.

In short, you'll lose about 75 FPS and it won't affect the accuracy. You will have to adjust the elevation for a 400 yard shot compared to the 24" dope.

You may also have to adjust your load a few tenths of a grain since the harmonics will be different.

 

[texasislandboy]

The bullet is spun up the moment it engages the lands, otherwise it'd strip the diameter of the bullet down. That being said, you are only going to lose velocity with cutting the barrel down, and the 50 FPS rule doesn't apply here since we are talking about barrel lengths exceeding 20". For example, the difference between 18" and 20" is about 30 - 35 FPS in a .308 bolt rifle. The difference for every inch beyond that is even less because of the reduction in pressure and the continuation of friction loss.

In short, you'll lose about 75 FPS and it won't affect the accuracy. You will have to adjust the elevation for a 400 yard shot compared to the 24" dope.

You may also have to adjust your load a few tenths of a grain since the harmonics will be different.

thanks alot ! im gonna do it when i get my other barrel threaded i want to take it down to 20''

 

[Texas1911]

thanks alot ! im gonna do it when i get my other barrel threaded i want to take it down to 20''

The only thing you'll lose out on is running some big bullets like say a 190 - 208 grain bullet, but the 1:12 won't stabilize those very well anyways so it's a moot point.

 

[texasislandboy]

yea im gonna try to stick with the 168g

 

[Rum Runner]

Just being the technical police here. I want emphasize two common misconceptions.
1) As Texas1911 stated, fluting a barrel does NOT stiffen it. It is pretty IMO. It increases surface area and will cool the barrel faster (though I do not see the point in a .22). It also lightens it. It does NOT stiffen it.
2) Most people talk about bullet weights when it comes to twist. Weight has NOTHING to with twist directly. If it did, the same weight bullet in different calibers would require the same twist, which we know is not true. It is a function of length and diameter (and especially with non lead core bullets, density to a certain degree). It just happens that heavier bullets are usually longer, so weight indirectly affects twist and you can lump certain weights into certain twists for certain calibers.

So, now that I have been annoying, I will try to be helpful.
Lets use Greenhills formula (there are better ones, but they are much more complicated) (Twist=(coefficient / (bullet length/caliber)))*caliber)
The coefficient would be 150 (180 for velocities > 2800fps)

If we assume a 168g Sierra MK in 308: it has a length of 1.210".
(bullet length/caliber) = 1.21/0.308 = 3.9286
Coefficient/result) = 150/3.9286 = 38.1815
(result*caliber) = 38.1815*0.308= 11.7599
So a 1 in 12 twist is close to ideal for this bullet.

The ideal bullet for a .308 w/ a 1 in 12 would have a length of like 1.185 like the Speer 165 Gr BTSP.
Thats hypothetical...dunno how it would play out for real.

 

[texasislandboy]

dam! thanks man with all that math it has to work! my barrel will be cut really soon i hope by next week i want to go shoot the last of my 150g hpbt's so i can start making my 168g hpbt