Twist rate

[Shadow 300]

Hello everyone,
I just joined in hopes of learning some things about the .300 Whisper cartridge. I recently ordered a 7.62 Phantom suppressor from YHM. The reason is that I have always wanted to build a bolt action in .300 Whisper and use a suppressor. The can came in to my dealer and I'm just about to start the form 4 wait. The first thing I really need to know is what the twist rate must be in order to stabilize this bullet. I have heard anything slower than 1 in 8" will not stabilize a subsonic bullet this heavy with the result of possible baffle strikes. Someone else told me bullet stabilization is dependant on length of bullet relative to length of barrel. What is the truth? Thanks for your help.

[Malaga]

1:8 will work real good....

[Expatriot]

The first thing I really need to know is what the twist rate must be in order to stabilize this bullet. I have heard anything slower than 1 in 8" will not stabilize a subsonic bullet this heavy with the result of possible baffle strikes.

1:8 is only needed for the really heavy or really long bullets. 1:10 will stabilize most bullets under 200gr. It is easily possible to build subsonic loads with 150gr bullets. There is really no reason to use the ultra heavy bullets.

Someone else told me bullet stabilization is dependant on length of bullet relative to length of barrel.

I'm not sure what the length of the barrel has to do with bullet stabilization?

[Hoser]

A 1-8 will work for everything up to 240 Sierras.

I am using a 8 twist in my bolt gun with no problems at all.

[Spook]

Heavy bullets are typically higher in BC and bullets with higher BC's resist wind deflection better than light bullets and maintain downrange velocity better than light bullets.... Given those parameters its less difficult to shoot heavier bullets more accurately the further downrange the target gets.... something to consider when working with a caliber that doesnt offer a lot of bullet expansion on live targets.

That being said if you know your target will be close in and/or you know that you'll never shoot anything heavier than 220gr , a 10 twist will work fine.

[amafrank]

I'd like to point out that the 1:8 twist rate allows you to not only shoot the heavies quite accurately (220-240gr) but will work quite well with the lightweights as well. We have fired 100gr plinkers with good results in the same guns we were shooting 240gr matchkings. The converse however is not the case. I have done a repair on a suppressor for a customer who learned the hard way that you don't want to shoot the 220's out of a 1:10 twist barrel subsonic. Wiped out 3 baffles and the endcap. If you are planning on benchrest shooting of the 300 than you should really pick a particular bullet you intend to shoot and choose the twist rate for that but otherwise choose a twist for the heaviest bullet you shoot and the lighter ones will work too. Overstabilizing of bullets is not normally a problem unless you are shooting extreme ranges, are doing indirect fire at extreme range or if you are shooting very thin jackets at high velocity. The faster twist will spin the bullets up to very high rpm if you get the velocity up. The 100gr plinkers at 2600fps were spinning pretty fast but not enough to blow the jackets up. Some varmint shooters find that they blow up the bullets by overdriving them and there are those who have posted on these boards that this is a concern for our 300's as well. I don't think that is the case however as we cannot load enough powder in the case to get the velocity that will do that. The bullets we use are not superthin jacketed either so the strength is there and the loads are not. Bottom line here is that if you intend to shoot subsonic than the heavy bullets are best for that. They carry the velocity longer and the energy as well. 1:8 is the best rate for those bullets. If your interest is strictly supersonics than 1:10 is fine.
You must choose.......


Frank

[Expatriot]

Heavy bullets are typically higher in BC and bullets with higher BC's resist wind deflection better than light bullets and maintain downrange velocity better than light bullets....

The published BC figures are only valid within a narrow velocity range. None of those BC figures are even close to reality once we go below the speed of sound.

Subsonics have a very short range and do not tend to bleed velocity very quickly regardless of weight.