Advice on twist and weight

[Dean]

I will be building a 6mmBR.My yardage will be between 100-300.
I don't plan on shooting competitively,just bragging rights between my shooting buddies).

Given that info what bullet weight and barrel twist should I use.This will be a 26"??? Pac-Nor barrel.

I was thinking 12" with a 68-88gr Berger.

Anybody else have distance limitations like this,I would be interested in your set-up.

Thanks in advance
Dean

 

[Eddie Harren]

If I were going to build a 100-300 yd. rifle, I would use a 14 twist and stick to 68-70 gr. bullets.

 

[tightneck]

DocEd is correct. If you wish to have bragging rights over your buddies at 100-300, go 14 twist and any of the match bullets from Fowler, Barts, Euber and others in the 65-70 grain weights.

 

[Dean]

Thanks guys.I'm glad I asked before I bought the wrong one,not that haveing an extra barrel is a bad thing).I would rather get it right from the start.

Thanks again,

Dean

 

[Pbike]

Dean also consider that if you are trying to get bragging rights between your buddies, and speed is not an issue you may want to rethink the 26" thing... In benchrest competition where we undoubtedly have bragging rights, it is seldom you see any barrel over 24", and most are about 22". It's all about accuracy. We get great results and don't need long barreels to do it.

Paul

 

[Dean]

Thanks Pbike,

When it came time to order the barrel I was going to pic the brains of the Pac-Nor folks to see what they recommended.

I have noticed that short barrel lenghts,as opposed to the 26" I use for varminting)are not unusual.

Thanks for the input,

Dean

 

[egwyn]

I had a 20" barrel made for my T/C with a 1/14 twist. I find that it is easy to move around in my truck when hunting ground hogs. From the bench my best group is .435" at 200 yds

 

[chino1969]

Dean,
I have a 24" Hart 1-14" light varmint contour in a 6mm BR with a .265 neck. I can regularly put 5 shots into a one hole group @200 meters with 65 grn. Hornady V-Maxes and 68 grn. Fowlers. I just shot a 5 shot group last week @200 meters that measured approx. .270 and the V-Maxes are close to that. I've shot 70 grn. Nosler Ballistic Tips and other custom bullets but the Fowlers and V-Maxes are on top of the heap. It doesn't get much better than that for a varmint rig.
Chino69

 

[BoydAllen]

Another thing that I would look at is reloading dies. A Harrell FL die,ordered by sending in a fired case from your chamber) and a Wilson seater should help keep things straighter. Also, a set of wind flags.,Even a few sticks with some surveyor's ribbon tied to the top are better than nothing.)You might also take a look at your bags to see if they are up to snuff.

 

[Forum Boss]

I'll break from the pack a bit and recommend a 1:12, IF a good % of your shooting will be at 300 yards,your max).

Consider this. 300 meter,330 yard) competition is a very well-developed, "mature" discipline worldwide. 95% of the shooters are using 90-107 grain high-BC bullets at that distance. If the shorter bullets were a major advantage I think we would see more people shooting them.

No question, if most of your shooting is at 100, then go 1:14" twist. But as you move out, having a bullet with a higher BC can trump the pure accuracy of the lighter bullets. Remember the effects of wind increase, roughly speaking, with the square of the distance. That means a full-value,90-degree) cross-wind will push your bullet NINE times as far at 300 yards as at 100 yards.

And don't think you'll be giving up that much at 100 with the longer pills. With Berger 80s, my 6BR can group in the high Ones at 100 yards. And the Berger 88s have proven effective from 100 to 600,these require a 10-twist however).

 

[Shooter32]

I agree with Paul, my gun has a 1/13 twist and if i was building another i would go with at least a 1/12 . You can shot the lighter bullets as well as the heavy .:thumb:

 

[Dean]

Thanks for all the great info...its food for thought,good thing I'm a big eater).

Mod,when you said I would need a ten twist,was that for the disstance,out to 600 yards)or was that for the bullet weight?

Thanks again guys,
Dean

 

[JimW]

When determining optimal twist rate, much of the recommendations are on the conservative side, but to adequately asses whether one will be able to stabilize a bullet depends on air density, bullet weight, shape, and velocity. Using the computer model from Dan Lilja, an 80gr. Match Berger bullet at "standard metro" conditions,59degrees, 78%humidity, sea level), and a velocity of 3150fps, requires only a twist rate of 1x16 to achieve a stability factor of 1.5, which most consider entirely satisfactory. In colder weather, or less humid conditions, the twist rate needed to stabilize would be faster. However, the most significant factor is elevation, and if you are significantly higher than sea level, air density decreases a great deal. Yesterday I was shooting in 35deg weather with a new 26in Hart barrel, 1x14 twist, and brand new Lapua brass, with 10-20 mph winds achieved 3 shot groups of approx. 1 inch. I am at 6500 feet elevation, so that is a factor, but with 3100 fps and reasonable temperatures, it would appear a 1x14 twist would be entirely satisfactory in the US.

 

[Dean]

I live in Phoenix,1400 feet elev.,temps anywhere from 40 to 120,humidity is very low most of the year,6-10%).

Shooting in the summer months means getting to the range as the sun comes up and your done by 10am,at that point it will be over 100.I tend to do more bass fishing this time of year anyway.

Thanks
Dean

 

[Forum Boss]

Thanks for all the great info...its food for thought,good thing I'm a big eater).

Mod,when you said I would need a ten twist,was that for the disstance,out to 600 yards)or was that for the bullet weight?

10 Twist is what Berger recommends for the Berger 88s. Yep, you could probably get by with an 11. A 12-twist is what Berger recommends for the 80s.

 

[Dean]

Thanks Mod.

There is alot to learn...my head is starting to hurt.

Dean

 

[AlNyhus]

having a bullet with a higher BC can trump the pure accuracy of the lighter bullets.

Respectfully....I strongly disagree with this premise. -Al

 

[Kodiak99317]

My 1:8 twist shots 65g FB into the high 1's at 100 yds and low 3's at 200 yds fire forming for my 1000 yd rifle. I use 105's usually but had these on the shelf so I thought why not, and it worked. Yes I'm way over spinning these pills and I know a 1:14 would out shoot it at the shorter ranges, I've owned them before shooting a 6BR in SR benchrest, but this way you can also go long. It would depend on the game you want to play and how seriously, SR or LR.

Here's a 100 yd group with the 65g FB, no flags with a wind. 3500 fps. 36g N135 in a 6-250 30 Degree IMP,like a 6XC)