Over spinning bullets

[86alaskan]

So, suppose you had a fast twist rifle set up for heavies. Now, suppose you wanted to send a lighter round downrange at scorching velocities through the same barrel. I've heard of 22-250 bullets coming apart due to high spin basically ripping the bullet apart. Could you get away with that by using a barnes, CEB or Matrix? Case in question... 1-9" twist 25-06 set up to stabilize the 115gr berger or 115gr barnes tsx, wanting to run the 80gr barnes at approx 3750fps. Will the 80gr set up for 1-10" be over spun by the 1-9"?

 

[HARPERC]

I believe there are velocity thresholds + bullet construction + twist rates + barrel quality that will 1) Will spoil accuracy 2) Destroy a bullet completely. Tolerances likely play a role, a bore at minimum (tight), combined with bullets from a run that come out at the maximum may show more tendency to the other stresses involved.

I had a .358 Ackley with a 1-12 twist that shot fireform loads at Whelen velocities just fine. Moving out of that zone never worked, the more velocity past that point, accuracy declined. Flyers more frequent etc. i believe twist was a component.

Generally though I believe more twist, improves BC (Lytz I believe speaks of this), and at worst doesn't seem to hurt accuracy when using quality bullets (hunting accuracy).

The example of a 25-06 given I'd guess you will be OK, but in some of the intense 25 wildcats you might run into issues.

 

[Frank in the Laurels]

I had a buddy a few ERS back that has a .243 AI buil on a Blackstar barrel...8 twist rifling...while shooting at the 200 yard target he noticed that no shots were hitting anything..no even dust was being kicked up on the target bank...what the heck !! When someone noticed about 10 yards from the barrel a split second shimmer similar to oil on water appeared and was gone..Quit a crowd was treated to watching this while he used up the rest...too much spin, too thin a jacket, sharp edged rifling ?? Who knows.,was pretty neat to see however .

 

[RockyMtnMT]

A copper mono will not have trouble with deformation from faster than needed twist. Cup and core bullets can have trouble if the jacket is not heavy enough. It is a balancing act for the cup and core bullets. Light enough jacket to have terminal performance and heavy enough jacket to survive the launch. Remember Berger had to redesign their Hybrid bullets when they first came out because guys with hot rods couldn't keep them together when launched over 3300fps. And that was not over stabilized.

Steve

 

[barefooter56]

86alaskan,
Bryan Litz's - "Modern Advancements in Long Range Shooting" Chapter 5 "Effect of Twist rate on Precision". Explains it all. Get Volume 2. All of Bryan's books are easy to read and understand. You can get them either on The APPLIED BALLISTICS or BERGER BULLETS websites.

 

[86alaskan]

nice, ok. that's kind of what i figured. as long as i stick with better bullets and mono metal bullets, i should be ok. I think its worth letting a few off the leash to see what happens. I think a have a box of sierra varminter bullets that are lighter than 80gr that i can try. we'll see, should be able to get those over 3700 without even trying.

 

[WildRose]

Every rifle has sweet spots with respect to bullet weights, charges etc but other than the really big, slow, African Magnum type calibers I really don't believe it is possible to over spin bullets without doing some pretty insane things like getting down below a 1.8 twist in something that is really screaming at which point you could have problems with bullets coming apart due to jacket failures along with severe pressure problems.

If you are within 1-1.5 times the recommended twist rate for a given caliber and bullet I think you'll be just fine.

I've shot a lot of light bullets in relatively tight twist .30's and .284's and never noticed a stability problem.

Some of the benchrest guys tell us that if you over spin a bullet it won't "tip over" properly meaning dropping the nose as it comes down but I have yet to see any evidence that it is true or that it makes any real difference if it can be shown to be true.

 

[AZShooter]

I had a 1 in 7 twist lilja chambered in 7 rem mag, that Dan Lilja told me would be just fine. WRONG!

At round count 200 it began to destroy the 180 berger VLD hunting at the mild velocity of 2950 fps. I switched to the 140 accubond. Even with the 140 going 3350 fps from that 30" barrel, the accubond held together and was accurate.

RPM for the 140 with that twist was 344,571

The 180 VLD was 303,428 rpm

 

[HARPERC]

.............Every rifle has sweet spots with respect to bullet weights, charges etc but other than the really big, slow, African Magnum type calibers I really don't believe it is possible to over spin bullets without doing some pretty insane things............

Why the exception for the African Magnums? I think I'm missing what you're saying.

 

[engineer40]

I had a buddy a few ERS back that has a .243 AI buil on a Blackstar barrel...8 twist rifling...while shooting at the 200 yard target he noticed that no shots were hitting anything..no even dust was being kicked up on the target bank...what the heck !! When someone noticed about 10 yards from the barrel a split second shimmer similar to oil on water appeared and was gone..Quit a crowd was treated to watching this while he used up the rest...too much spin, too thin a jacket, sharp edged rifling ?? Who knows.,was pretty neat to see however .

I saw the same exact thing at the range once but the guy was shooting a 243 WSSM. I don't know what twist he had or what what ammo he was shooting. But the experience was just as you described.

 

[WildRose]

I had a 1 in 7 twist lilja chambered in 7 rem mag, that Dan Lilja told me would be just fine. WRONG!

At round count 200 it began to destroy the 180 berger VLD hunting at the mild velocity of 2950 fps. I switched to the 140 accubond. Even with the 140 going 3350 fps from that 30" barrel, the accubond held together and was accurate.

RPM for the 140 with that twist was 344,571

The 180 VLD was 303,428 rpm

That's not a mild velocity for the 180 out of a 7mm Mag, that's getting very close to the top end for a safe load.

7mm Remington Magnum Load Data

 

[WildRose]

Why the exception for the African Magnums? I think I'm missing what you're saying.

Because of the shape and BC the twist rates recommended for them are much slower than what we're used to with our high velocity bottle neck cartridges.

 

[WildRose]

I saw the same exact thing at the range once but the guy was shooting a 243 WSSM. I don't know what twist he had or what what ammo he was shooting. But the experience was just as you described.

When we first started loading .17Rem's back in the early 70's this was a fairly common problem. We'd see a little puff of smoke between 50-100yds where the lead core bullets were shucking the jacket and flat burning up.

That led us to using the original Barnes X in the 17.

My how time, technology, and bullets have changed since then with the explosion in the market for high velocity magnums.

"They don't make'm like they used to"... . Thank God!

 

[AZShooter]

WildRose,

The 7 Rem mag had a 30" barrel that is why the velocities seemed high. Actually worked up to 3050 with no signs of pressure but accuracy suffered.