I'm building a 30-284 (30-06). First custom gun for me i'm excited. I'm using a 1:13 twist barrel to stabilize the 165/168 gr projectiles, nothing heavier. the reloading manual guns have a 1:10 twist barrel. How does the barrel twist affect my starting load when it comes time to load ammo for this?? I do have a chrony if that affects your reply! Many Many thanks

"1:13 Twist tight bore 30 cal. barrel starting load"

How tight is the bore? I don't think that the twist will matter pressure wise. You have to work up anyway.

You can use starting load data from any manual and should be just fine. However, I do feel that you will have a hard time finding 165-168 grain loads that show extreme accuracy at long range as the twist rate is rather marginal. You may have to go with something such as Berger's LTB (length tolerant bullet) or other flat-based projectiles as opposed to traditional accuracy choices such as the Ballistic Tips or MatchKings. And you may also find yourself having to drop back into the 150 grain range. A 1:10 would have been perfect. Keep in mind that, within reason, you can't overstabilize a projectile but that you can certainly understabilize one.

You can overstabilize a projectile in the sense that spin + inbalance = wobble. A 1-13 sounds perfect for conventional 165 gr. bullets.

nate, the 1-13 twist is ment for the 155 palma bullets,it will stableize 150''s also ,give sierra a call 1-800-223-8799,they''l get you on track, i don''t know if that twist will work with the 165 or 168s but they sierra will, happy 4 you ,jjmp

quote:

How does the barrel twist affect my starting load when it comes time to load ammo for this?

Actually.....it seems that it should.....but it don't.

popenmann wrote:

quote:

You can overstabilize a projectile in the sense that spin + inbalance = wobble

He will NOT run into overstabilization issues with a 1:10 as I suggested. He'd be much better off with it than with a 1:13 -- and that comes from real world experience, not some formula in a book.

Mnay thanks for all the reply's. I'll double check and make sure a 1:13 twist will stabilize the 165 bullets i wanna launch. I thought less twist would allow me more velocity than a faster twist barrel, and thus play into a good starting up load. Many thanks.

quote:

Originally posted by Bobby Tomek:
popenmann wrote:

quote:

You can overstabilize a projectile in the sense that spin + inbalance = wobble

He will NOT run into overstabilization issues with a 1:10 as I suggested. He'd be much better off with it than with a 1:13 -- and that comes from real world experience, not some formula in a book.

You Sir are mistaken.

The 1:10" twist rate traditionally used in 30-06's is intended to stabilize 220gr bullets and is entirely adequate to stabilize RN 250gr bullets.

a 1:12 is usually quite sufficient for 190-200gr bullets.

a 1:13 and probably even a 1:14 twist is in no way "marginal" for any 165gr bullet including the solid copper Barnes bullets.

Let me point out that several manufacturers
(Including Remington) have made 308Winchester rifles with a 1:12"twist rate, and I've heard no stories of 180's keyholing from those rifles...

The difference between 1:12" and 1:13" is insignificant if he's sticking to 150-165gr bullets.

Personally, I'd have gone with a 1:12"... as a matter of fact I did! I only went with a twist That fast because I didn't want to forever close the door on using long pointy Boattailed 180's

1:13 will probably be fine even with 180's provided he stays away from Bullets like the 185gr Berger VLD bullets. and even if he does have "issues" with SOME BT'd 180's keyholing there are always flat based bullets...

Will twist rate affect pressure? No.
Will it affect Muzzle velocity? Yes, somewhat.
slower twists are good for some additional velocity, but the difference is small, other parameters are more critical.

AllanD

Here's another opinion on twist.

1-13" is the classic Palma twist for 308 Winchester. These shoot 155 grainers.

168 grainers tend to go along with 1-12" twists.

I seem to recall that the US sniper platform (rifles) shooting 7.62/308 Win use 1-11.25" twists. This was with the 168 grainers (pre-175 Siera MK), with the idea to provide additional stability at ~ 1000 yards-particularly in cold weathr (lower mv).

1-10" match up with 190 - 200 grainers. I have never shot a 220 grain bullet from my Rem 40x with 1-10 twist-so I can't say it WON'T stabilize. The 30-40 Krag rifles (bolts) had 1-10 twists, and shot 220 grain bullets-so it should get the job done. My Rem 40x (1-10" twist) groups 168 grainers (and 165 grainer flat base-slight shorter in length) into .4 to .5 moa groups. So much for "over stabilizing."

I have shot 175 grain Sierra MK (boat tail) from my rem 700 Varmint Synthetic (1-12" twist), and get 0.5 MOA groups to 200 yards (haven't shot further with that bullet/gun).

I can't say the 1-13 WON'T stabilize the 165/168 bullets, but I think it may be marginal. I can say that my 1-12" Rem VS 308 Win DOES shoot 155 grain Sierra MK to ~.6 moa to 200 yards with the first few loads I threw at it (again, so much for "over stabilization.")

I think the word "overstabilize" is a bad (non-existing?) word. There are folks shooting 6mm BR rigs with 1-7" twists (for 105+ grain bullets) and can also shoot 75 grain (and lower) VERY accurately.

I know I would rather have a slightly faster twist than a too-slow twist-just for this issue. Just what (or when) is a projectile OVER stabilized? It's more critical to know when it WON"T be stabilized right out of the starting blocks.

Hope you get lucky, but a 1-13" twist and 168 boat tail may by on the edge of stability.

If you haven't picke d up the subtle message I'm sending, use a 1-12 twist if you want to shoot 168 grainers. Even though you aren't shooting a 308 Win, and your 30-284 will have a higher MV than a 308 Win-you may still want to look at a 1-12". Higher MV will aid in providing addition rpm to the bullet. It was awhile ago that I actually worked the math on what increase of MV is needed to equal 1" of twist, but I seem to recall it was significant ( not just ~ 30-50 fps). You may get by with the 1-13, but barrels aren't cheap. You'll kick your self for going "too slow" in twist if it doesn't work out for you, when the next step "faster" twist is the same cost, AND will shoot lighter bullets (150's) nearly as well (perhaps equally).

Ask your barrel suppier (ie Hart, Shilen, Pacnor,Lilja etc) for their opinion on it-they are the ones who deal with this stuff every day. Keep us posted.

Good luck.

It is not the weight of a bullet that determines the twist needed to stabalize it, but its length. Although they naturally run together.

You won't have a bit of trouble with the 168's in a 1 in 13 twist. I have shot 175's through a Krieger 1 in 13 twist with excellent results, the rifle was chambered in 308 Win. I have also shot the Berger 190 VLD through a 1 in 12 twist barrel out to 1000 yds. with very good results. Personally, I would never have a 308 Win barreled with anything faster than a 1 in 12 twist.

PaPa 260......May I Be Half The Man My Grandsons Think I Am

Nate D:

Please do yourself a favour and learn more on the importance of the correct twist rate required for the different bullet lengths (not bullet weights) you are planning to use in your rifle.

Always remember, the longer the bullet (longer = larger weight for calibre size) the tighther the twist rate should be.

Visit GS Custom's web site and check the technical data as well as required twist rates for specific bullets.

Papa 260,
I want to thank you especially for replying. you are what i was looking for the Been there done that, got one and its goes whatever, Guy. Many thanks to you especially and to everyone else that has replied and thank you all for your input. spanks

Thanks Catboat for that post. I've also done the math now and i'm OK with the barrel twist selection.