A barrrel twist rate vs. bullet weight question

[Mark204]

I'm looking for some thoughts, input or personal experience on this question....I've been playing with my 25-06, it shoots 75 and 87 grainers great.... sub MOA at 100yds. The twist is 1:10, but I've been wanting to try some bullets in the 115 to 120 range. From what I've read and understand, my 1:10 twist would be more suited to bullets at or under 100grs.

Should I decide to work up some loads I'll only be out 20 to 25 dollars for bullets, but I thought maybe some of the fellow members may have some insight as to whether this is a total waste of time and money.

As always, thanks for any all replies.

Mark

 

[fyrewall]

I would look up bullet lengths and find an on-line Miller twist program or should the Berger 115 be if interest go to the Berger site and run their twist program. I have shot 120's in a 1-10 but the 120's were flat base bullets. I don't think many .25 bullets are longer than the Berger 115 VLD and their site should produce a recommended twist and Sg (stability whatever) for the 115 given a 1-10 twist.

 

[shoot4fun]

I have a Kimber Hunter in .257 Roberts. I was (maybe still am) concerned about barrel twist of 1 in 10. It seems the 10 twist is a long standing tradition for anything .257 caliber but that doesn't take all the new technology in bullet design into consideration. I believe the 10 twist to be marginal with the non-traditional bullet shapes.
I once tried some 1,000 yard shooting with a 25-06 and bullets of the 115+ weights. It failed miserably.
If your rifle, like mine, is a hunting rifle and your hunting scenarios are like mine (less than 200 yards) I wouldn't worry so much about twist rate/bullet weight as knock down/killing ability.

 

[fyrewall]

I just ran the Berger twist rate program using a 115 .257 Berger VLD @ 3,000 fps. The 115 .257 Berger is 1.19 inches long, a SG value of over 1.5 is recommended.

1-10 SG= 1.32
1-9 SG = 1.63
1-8 SG = 2.07

According to the Berger program a 1-8 or 1-9 would be the correct twist rate for their 115 under almost all conditions. Possibly under 0 F at sea level a 1-9 might go under SG 1.5. All this does not surprise me and a failure @ 1,000 with some .257 pointy boat tail bullets of 115 and over is not surprising. I vaguely remember shooting 120 .257 Sierra GK's in a 1-10 with OK results but that was no varmint bullet.

 

[shoot4fun]

All this does not surprise me and a failure @ 1,000 with some .257 pointy boat tail bullets of 115 and over is not surprising. I vaguely remember shooting 120 .257 Sierra GK's in a 1-10 with OK results but that was no varmint bullet.

I wasn't referring to performance on game. No way I'd take that shot on anything bigger than a prairie dog. I was referring to the fact that the bullets just would not stay stable at that distance.

 

[Berger.Fan222]

Shot the Berger 115 grain VLD from a 1 in 10" twist in a 25-06 for many years. It was a great load. Late in that rifle's life, a family member shot a number of 600 yard F-Class matches with it. Performance was good, and there were no problems with stability. The accuracy was beginning to degrade (no longer 0.5 MOA) because hot loads in the 25-06 were tough on the throat.

Also killed plenty of deer and varmints over the years with various bullets including 85, 100, and 115 grain Ballistic Tips and a 100 grain solid copper X bullet.

Bottom line: I don't think you need a twist faster than 1 in 10" to shoot 115 grain bullets in 25-06.

 

[fyrewall]

Just because a 1-10 twist .25-05 shoots 115 grain Berger VLD bullets good enough for 600 yard F-Class use does not make that bullet an extremely good choice for long range use with a 1-10.

The 120 .257 Sierra GK or Game King bullet is designed for hunting game animals like deer and larger, for 1-10 twist. They have hollow points, relatively thick jackets thus do not expand well on small varmint creatures. These bullets have a relatively large meplat or big opening, thick jackets and are not intended for long range shooting like 1000 yards.

The Berger twist program provides a 1.32 SG for their .257 115 VLD with a 1-10 twist at sea level and 59 degrees F; they say this is "marginal" meaning that the while good groups may occur the B.C. will not be "optimized". Possibly under certain situations it might fail to meet expectations, like low temperatures. The minimum twist specified by Berger, the manufacturer of that bullet is 9.25.

Comparing 85, 100, and 115 Ballistic tip and 100 grain copper X bullets to the 115 Berger VLD does little. Nosler and Barnes need to sell bullets that provide good accuracy to 1000's of shooters owning 1-10 twist .257 type rifles.

Shoot4fun says his 115 bullets shot from a .25-06 failed miserably at 1,000 - no other data was provided like bullet type, length, or environmental conditions. Could I guess that the .25-06 had a 1-10 twist.

Berger.Fan222's .25-06 was used in 600 yard F class matches with the Berger 115 VLD having a Berger twist program derived SG of 1.32 with a 1-10 twist the same as Berger.Fan222's rifle. No other data was provided such as environmental conditions - altitude and temperature. Berger notes 1.32 as marginal - good groups possible but optimum BC not achieved.

I have heard that, the U.S. DOD, that acquires vast stores of ammo containing projectiles that might be used under every extreme condition from sub-zero sea level artic to blazing hot high desert conditions, has tested bullet stability for projectile/weapon use under these extreme conditions. This would ensure optimum results under all conditions. I have not verified this but I hear that the DOD has specified a SG of 1.5.

For my personal use when shooting targets or rodents at elevations greater than 4000 feet at 80 degrees plus or shooting coyotes near the ocean at below freezing I will select a twist rate and bullet combo that provides a SG of over 1.5 just like the Berger and possibly the DOD does.

Shoot4Fun should be commended for not shooting at game bigger than a prairie dog at 1,000. By "failure" I meant bullet stability and more importantly the use of "failure" was used in the context of SG as related to that particular bullet and twist rates.

The attached link provides some info

bisonballistics.com/articles/bullet-stability

Of note is the "up date 10/4/14" that might be refer to Berger SG of 1.5. When 600 and 1000 yard shooting is mentioned vs. 100 yard bench rest the value of faster twists to get to a SG of 1.5 or more is a consideration.

 

[fyrewall]

I'm looking for some thoughts, input or personal experience on this question....I've been playing with my 25-06, it shoots 75 and 87 grainers great.... sub MOA at 100yds. The twist is 1:10, but I've been wanting to try some bullets in the 115 to 120 range. From what I've read and understand, my 1:10 twist would be more suited to bullets at or under 100grs.

Should I decide to work up some loads I'll only be out 20 to 25 dollars for bullets, but I thought maybe some of the fellow members may have some insight as to whether this is a total waste of time and money.

As always, thanks for any all replies.

Mark

As an answer to the question - determine your rifle's twist rate, if not specified measure it with a cleaning rod and tape, measure the bullet length with a caliper or look it up on line should you not have a bullet to measure. Then run the bullet length and twist rate through a twist calculator like Berger's. The calculator will produce a number called a SG and if it is over 1.5 the bullet will have optimum ballistic properties. If the SG is somewhat lower that bullet might be perfectly suited for hunting as like Berger claims gives good groups. At some point there is no stability resulting in bullet profile like holes in paper targets. More than once I have bought, traded for 68 grain plus .224 bullets that failed to shoot out of 1-14 twist barrels.

Doing this should save $20-$25 for a box of bullets that would not shoot. Sierra makes a nice .257 100 grain Match King that would work in a 1-10. Shooting the Berger 115 VLD from a 1-10 twist might reduce the ballistic properties of that bullet making it not much better than a bullet having lower advertised B.C.

 

[texasbilly]

I understand your concern, but the relationship between barrel twist and bullet weight cannot be defined absolutely by pure science. I think we have all shot bullets that were not suppose to shoot well in a given rifle, and lo and behold, they did. Why did they? Variables include the muzzle velocity, bullet bearing surface, bore diameter, condition of the bore, and more. Yes, the general rule of thumb applies in most cases where slower twists are better for light bullets, and faster twists are better for heavy bullets. However, nothing beats experimentation and experience.

Give it a try. What do you have to lose?

 

[RGRobinett]

I'm looking for some thoughts, input or personal experience on this question....I've been playing with my 25-06, it shoots 75 and 87 grainers great.... sub MOA at 100yds. The twist is 1:10, but I've been wanting to try some bullets in the 115 to 120 range. From what I've read and understand, my 1:10 twist would be more suited to bullets at or under 100grs.

Should I decide to work up some loads I'll only be out 20 to 25 dollars for bullets, but I thought maybe some of the fellow members may have some insight as to whether this is a total waste of time and money.

As always, thanks for any all replies.

Mark

Here's a link to a 25 Cal. BR thread, on BenchRest Central, from almost two years ago:
http://benchrest.com/showthread.php?94319-Why-No-25-Caliber-Bench-Rest-Cartridges
Garn, it's not a "hot" link. I'll try to get some pics from Al, shot via his SGR .250Ack. Imp, 1:10" twist - "too fast" a twist will not spray quality bullets!RG

It looks "hot" now!

 

[fyrewall]

I understand your concern, but the relationship between barrel twist and bullet weight cannot be defined absolutely by pure science. I think we have all shot bullets that were not suppose to shoot well in a given rifle, and lo and behold, they did. Why did they? Variables include the muzzle velocity, bullet bearing surface, bore diameter, condition of the bore, and more. Yes, the general rule of thumb applies in most cases where slower twists are better for light bullets, and faster twists are better for heavy bullets. However, nothing beats experimentation and experience.

Give it a try. What do you have to lose?

$ Money $ - would you guess that the folks that apply numbers to bullets have experience and extremely good analytical experimental skills? @ possibly $40$ or more per box, start reading & thinking

 

[Berger.Fan222]

Just because a 1-10 twist .25-05 shoots 115 grain Berger VLD bullets good enough for 600 yard F-Class use does not make that bullet an extremely good choice for long range use with a 1-10.

The 120 .257 Sierra GK or Game King bullet is designed for hunting game animals like deer and larger, for 1-10 twist. They have hollow points, relatively thick jackets thus do not expand well on small varmint creatures. These bullets have a relatively large meplat or big opening, thick jackets and are not intended for long range shooting like 1000 yards.

The Berger twist program provides a 1.32 SG for their .257 115 VLD with a 1-10 twist at sea level and 59 degrees F; they say this is "marginal" meaning that the while good groups may occur the B.C. will not be "optimized". Possibly under certain situations it might fail to meet expectations, like low temperatures. The minimum twist specified by Berger, the manufacturer of that bullet is 9.25.

Comparing 85, 100, and 115 Ballistic tip and 100 grain copper X bullets to the 115 Berger VLD does little. Nosler and Barnes need to sell bullets that provide good accuracy to 1000's of shooters owning 1-10 twist .257 type rifles.

Shoot4fun says his 115 bullets shot from a .25-06 failed miserably at 1,000 - no other data was provided like bullet type, length, or environmental conditions. Could I guess that the .25-06 had a 1-10 twist.

Berger.Fan222's .25-06 was used in 600 yard F class matches with the Berger 115 VLD having a Berger twist program derived SG of 1.32 with a 1-10 twist the same as Berger.Fan222's rifle. No other data was provided such as environmental conditions - altitude and temperature. Berger notes 1.32 as marginal - good groups possible but optimum BC not achieved.

I have heard that, the U.S. DOD, that acquires vast stores of ammo containing projectiles that might be used under every extreme condition from sub-zero sea level artic to blazing hot high desert conditions, has tested bullet stability for projectile/weapon use under these extreme conditions. This would ensure optimum results under all conditions. I have not verified this but I hear that the DOD has specified a SG of 1.5.

For my personal use when shooting targets or rodents at elevations greater than 4000 feet at 80 degrees plus or shooting coyotes near the ocean at below freezing I will select a twist rate and bullet combo that provides a SG of over 1.5 just like the Berger and possibly the DOD does.

Shoot4Fun should be commended for not shooting at game bigger than a prairie dog at 1,000. By "failure" I meant bullet stability and more importantly the use of "failure" was used in the context of SG as related to that particular bullet and twist rates.

The attached link provides some info

bisonballistics.com/articles/bullet-stability

Of note is the "up date 10/4/14" that might be refer to Berger SG of 1.5. When 600 and 1000 yard shooting is mentioned vs. 100 yard bench rest the value of faster twists to get to a SG of 1.5 or more is a consideration.

Those concerns would make more sense in the competition forum than in the varmint forum. We'd started shooting the 115 VLD in a 1 in 10" twist back when that was Berger's recommendation and it performed well for us including a sea-level match in November where a junior took 3rd place (overall, even against the adults) with it. Sure, a few percent may be lost in BC, but it has accuracy that compensates for that compared with other bullet choices.

I hesitate to recommend faster twists in a varmint forum, because I've seen too many thin-jacketed match and varmint bullets explode in flight in the first 100 yards after leaving faster twist barrels. For the OP to switch to a faster twist might gain some BC for the 115 VLDs, but those lighter varmint bullets are often at risk of exploding in flight. It is much easier for him to try the 115 VLDs or whatever heavier bullets interest him.

If I understand correctly, the Berger stability calculator simply applies Don Miller's formula for gyroscopic stability. Reading the available papers on the subject suggests this formula may be overly conservative for bullets with plastic tips or open tipped match bullets such as the 115 VLD. In any event, I've kept my ear to the ground regarding that bullet since 2000, and I've never heard one report of a problem with it tumbling from a 1 in 10" twist barrel.