30BR twist rates

C

caroby

Guest
Comments from the Score/BR 30 cal shooting community...

"If"... I were to obtain a 1-15" twist barrel #7 contour (High End lapped and all blank) and set it up for a 10.5 gun chambered in 30BR for VFS shoots...
1. Would I experience too much torque in the bags due to abit of excessive twist rate for, Ohhhh say 118gr - 125gr bullets?
My thoughts are that a 1-16, 1-17 rate of twist would be Ideal.

2. Torque would be my only issue with the 1-15" twist... Correct ?

Does a 1-17" stablize a 125gr 30cal Flat Base Bullet properly....?

Thanks all,
cale
 
Yes and No

Cale, the 15 twist 30 caliber barrel has had a big following (in the past) by the Hunter Class rifle shooters,..
But reduced recoil by using lighter bullets has become more the NORM...
Yes reduced torque of the gun does play a part of that accuracy gain that comes from using lighter bullets...
A slow twist 17 or 18 twist barrel stabilizes the preferred 112-118 grain bullets built on the .940 jackets...
The idea of shooting a 125 grain bullet in Varmint for Score is not the trend of the winning shooters today...
The best advice is to talk to some of the gunsmiths that make many of the winning 30BR rifles in LV /HV class and go with what they recommend...
Trying to make a rifle win with the 125 grain bullet is going to be more difficult than going with a tried and true combination...
 
caroby said:
Comments from the Score/BR 30 cal shooting community...

"If"... I were to obtain a 1-15" twist barrel #7 contour (High End lapped and all blank) and set it up for a 10.5 gun chambered in 30BR for VFS shoots...
1. Would I experience too much torque in the bags due to abit of excessive twist rate for, Ohhhh say 118gr - 125gr bullets?
My thoughts are that a 1-16, 1-17 rate of twist would be Ideal.

2. Torque would be my only issue with the 1-15" twist... Correct ?

Does a 1-17" stablize a 125gr 30cal Flat Base Bullet properly....?

Thanks all,
cale
Click to expand...

A 1:15" twist barrel will work well - statistically, you'll give up about .040" in agging capability to your neighbor, who's shooting a 1:18" twist of equal quality. Over a long-haul and many barrels, the 17 & 18 twist barrels WILL make you a better shooter . . . but, only when/if you're tuning and shooting well enough to remain in the hunt once the hair -splitting begins! Oh, I almost forgot - for a given amount of wind-drift, the faster twist will produce a LARGER vertical component: you'll miss more of those "oh-so-close" 10"00 -11:00 O'Clock and 4:00-5:00 O'Clock shots!:eek:

While in BR competition, .040" is the GRAND CANYON, differences from barrel-to-barrel can mitigate the gap - whether you get a "hummer" or, a HO-hummer . . . Under standard Conditions (@ sea-level), a [TRUE] 1:18" twist produces Sg of 1.45 for FB bullets of up to 1.050" long - as a rule, this covers just about any BR quality bullet made with the 1.00" long J4 jackets, which includes most of the 125 Gr. thirty caliber offerings.
This is a higher Sg than produced by the typical 1:14" twist 6mm, firing a 68 Gr. bullets based upon the .825" long jacket (finished bullet length of about 0.845"). Unless I were going to shoot bullets in excess of 1.050" long, I would not use anything faster than a 1:17" twist, which will impart Sg of about 1.7 for the thirty caliber bullets based upon the 1.00" long jackets (the longest of which I've measured was still < 1.025" OAL) - I like to keep the table tilted in my favor!:D

Bullets based upon the .925" long jacket are ideally suited (1.5 Sg) to 1:19" twist barrels - were I to decide to campaign the shortest/lightest bullets, I'd go with a dedicated 19" twist barrel. For these bullets, a 17" twist produces 1.9 Sg - the 1:17" twist barrels offer a LOT of goodies/options . . . including 1.4 Sg for bullets of up to 1.10" long, which equates to most of the 135 Gr. BR quality bullets out there!:eek::D

A lot of messing around for the last 12 years has provided enough empirical evidence to convince me that the GURUS are correct: for a praticular bullet, the highest potential [for precision] lies in a velocity/twist combination producing Sg in the range between 1.4 to 1.9 - somewhere close to the middle doesn't hurt. RG
 
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Cale

I have a 30BR with a 15 twist Shilen HV barrel that was the best barrel I ever had, but it's past it's prime now. I won a bunch of Denton score matches and won a 200 yard registered group match with it. (.221 agg.) I also shot the small group two years running, at Tomball, with that barrel with a .045" and a .083".

I think a hummer is a hummer no matter what twist it's in. But, I use 17 twist Shilens these days because Randy Robinette gave me a twist lecture. His contention is that a perfect bullet will shoot as well in a 15 as in a slower twist but a slightly off balance bullet will do better in a slower twist. Randy thinks that a slow twist will agg about .040" better than a fast twist 30 cal barrel. I've tried other 15 twists but I haven't found another fast twist hummer...... yet. I do have another 15 twist waiting to be fit and tested.

As you can see, Randy beat me to his lecture.

Shelley
 
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Go With The Flow

This is one case where the success is obvious. 17 and 18 twist barrels wit 112 through 125 grn bullets rule Varmint for Score.
The fact you are building a 10.5 pound Rifle makes this even more of a no-brainer. I have shot both twist, and it is remarkable how much the slower twist tames the Rifle down in the bags.........jackie
 
The very best

caroby said:
Comments from the Score/BR 30 cal shooting community...

"If"... I were to obtain a 1-15" twist barrel #7 contour (High End lapped and all blank) and set it up for a 10.5 gun chambered in 30BR for VFS shoots...
1. Would I experience too much torque in the bags due to abit of excessive twist rate for, Ohhhh say 118gr - 125gr bullets?
My thoughts are that a 1-16, 1-17 rate of twist would be Ideal.

2. Torque would be my only issue with the 1-15" twist... Correct ?

Does a 1-17" stablize a 125gr 30cal Flat Base Bullet properly....?

Thanks all,
cale
Click to expand...

.30 barrel I've had so far was a 1-17 Lilja. My first one about 7 years ago was a 1-14 Hart...that was no slouch! However the slower twists are adequate and very much less violent in the bags. Good barrels are where you them. I would shoot a 1-8 if it were a hummer.
 
I use 135 sierra MK in my 17 twist with a 30 BR chambering and have no problem shooting tiny little groups out to 500yds.:D
 
Ok....1-17" it is...

Thanks guys, each and every one ... Great info!

I won't be buy'n the 1-15" off a fellow shooter and rather, call up either Wade Hull at Shilen or Chris Dichter at PacNor for a 1-17" ...

Randy, I'll be looking you up fer some 118.;)

Looking forward to shooting little groups with a big hole punch! :D:)
Oh yea, as well as cutting out ALOT more X's in score shoots!;)

cale
 
cale

caroby said:
Thanks guys, each and every one ... Great info!

I won't be buy'n the 1-15" off a fellow shooter and rather, call up either Wade Hull at Shilen or Chris Dichter at PacNor for a 1-17" ...

Randy, I'll be looking you up fer some 118.;)

Looking forward to shooting little groups with a big hole punch! :D:)
Oh yea, as well as cutting out ALOT more X's in score shoots!;)

cale
Click to expand...

one final memory. The first barrel blank I ever bought directly, to take the place of the 1-14 Hart was a 1-15 7 groove. I asked the rep if they made anything slower, like a 1-17. He said no and what idiot would want a 30 caliber barrel in that slow twist rate? Man, have things changed !! Folks should leave their 10 gallon hats on the peg when it comes to rifle accuracy experimentation and changes. Good luck --Greg
 
With the guys I shoot against, you need all the advantage you can possibly get. So a rifle that jumps around in the bags more than theirs means you are toast. I have thought that if I were to build a light gun it would have an 18.5 to 19 twist shooting the lightest custom bullets I could find.
 
Plugger,

Your right on track, no pun intended. The rifle needs to track well (ride the bags) and not get jarred around to be consistant for you shot after shot day after day. I got into a very Heated discussion about this with a fella at Sierra. The conversation was about stabilizing bullets with the minimum possible twist for a length bullet. His veiws were that you can't overstabilize a bullet. For highpower (read Sierra) that may be the case. But for benchrest the idea is not an overstabilized bullet, but an over torqued rifle in the bags. I wouldn't know just how well an 8 twist will shoot a 115 grain .30 cal bullet, but if a 18 twist will stabilize it, I just don't see the need to buy the 8 twist just as I have no asperations of trying a 220 grain bullet.

Paul
 
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