Barrel twist question

[Eric Myers]

I hope I am asking this in the right area.

OK. Bullet weights. .223

I'm no expert here but from what I can find out an ar15 with a 16 inch 1/9 twist shoots up to 62 grains. A 24 bull barrel ar15 in 1/8 twist I believe can shoot from about 68 to 80 grains more or less. These are general observations.

I see many somewhat high end bolt action rifles from remington like the 5R HS stock models and some from Savage that have a 1/9 barrel twist on 20 and 24 inch barrel. Are these rifles not able to shoot heavier bullets, are 20 or 24 inch barrels able to shoot heavier bullets due to their length, what's the deal? I just can't find the info I'm lookin for. I read reloading manuals and they generally list one barrel length and twist for all bullet weights for that caliber.

I hope I am asking the right questions. Thanks for reading and for any info.

 

[LawnMM]

Re: Barrel twist question

It has to do with stability factor, JBM ballistics will give you the stability factor when you plug in all the variables.

Consider military guys with 1:9 twist barrels are shooting 77gr projectiles just fine. A 1:7 twist might produce a better stability factor but the bullet isn't going to drop out of the sky if fired from a 1:9

People make a bigger deal out of this than it is.

 

[MitchAlsup]

Re: Barrel twist question

Air temperature also plays a part. Air is 20% more viscous at 0dF than at 100dF--so you need 20% more (1.2X) stability factor at 0dF than at 100dF.

So, if you shoot heavy 80 gr 224 bullets at 0dF and sea level, you need more twist than somone shooting the same bullet at 1000 feet and 50dF.

The 1/7 AR15 barrels are able to shoot any bullet in any temperature conditions in death valley or antartica without stability issues.

 

[nso123]

Re: Barrel twist question

I can say that my Rem 700 with a 1:12 barrel did not even stabilize a 68gr enough to get it on the paper at 100 yards.