I have a Ruger M77 chambered in 260 that I have shot for some time. I am wanting to try the 125 grain partitions in my gun, but am not sure how they will stabilize with a 1:8 twist. ( i emailed Ruger and they told me that it has a 1:8 twist.) I know generally people would be shooting 140 grain with a 8 twist, but I am wanting to go lighter. Anybody try these with a 8" twist? I have also been looking at the swift scirocco in 130 grain. I want to go lighter than 140, and increase my velocity.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
125 Grain Partitions in 260 with 1:8 twist
- Thread starter Jevyod
- Start date
603Country
New member
All I shoot in my 260 are 100 and 120 gr Nosler BTs. The 100's over IMR4064 and the 120's over R17. My rifle twist is the same as yours. I started out with the 120's and shot a good number of deer and critters. Then I went to the 100's to see if it made any difference in killing effectiveness. With deer and coyotes, the 100's seemed about as good as the 120's. With pigs, however, the 100's didn't exit and my tracking skills were required, though they didn't go very far. So, back to the 120's I went, and they have exited in the most recent pig hunts, and the pigs went less far. The last couple of hogs were actually knocked flat, and I hadn't seen that with the lighter bullets, so I've decided to stay with the 120's.
So, I expect your 125 grain Partitions will do just fine, though from my experience the 120 gr Ballistic Tips would be more accurate (probably).
So, I expect your 125 grain Partitions will do just fine, though from my experience the 120 gr Ballistic Tips would be more accurate (probably).
Thanks for pointing me to the Bergers website. I was looking earlier if I could find a chart, and I found one. That one, however, said that for best results you should have between a 1.5 and a 2. I could not get that low no matter what I tried. But according to Berger, as long as the number is higher than 1.5 it should stabilize. So I guess I should be ok. Just another question on that, I got a 2.38 with a 125 partition, and a 3.41 with a 100 grain partition. Does that mean the 100 grain should stabilize better?
ShootistPRS
New member
Generally speaking faster twist than necessary doesn't hurt accuracy. "Over stabilizing" a bullet is only a real thing if it spins fast enough to self destruct or if you are shooting competition targets. The holes in the paper at long range can become slightly oblong because an over stabilized bullet keeps its nose above the path of travel. At shorter ranges, and for hunting especially, a bullet that is more stable is better due to the fact that it opens better on impact.
Jevyod,
You don't have much to worry about. I'll correct a few minor points. Gyroscopic stability factor is defined as breaking even at 1.0. So anything 1.0 or higher will not actually tumble, though they will not typically shoot very precisely that low. Sierra recommends 1.3 to 3.0 for "hunting accuracy" and 1.4 to 1.7 for best match accuracy.
Spinning too fast creates three problems. Already mentioned is actual disintegration, which can happen to very fast, lighter construction bullets. Another is core stripping. This is where the bullet jacket's grip on its lead core is not great enough to pull the core up to the jacket's rate of angular acceleration, so the lead slips inside it. Because the jacket engraving looks like speed bumps on the inside, this beats the lead our narrower and loose inside the jacket, so when the bullet exits the muzzle not only is it no longer unitized, the lead is spinning more slowly than the jacket and the two have to come to an equilibrated spin rate that is slower than the rifling nominally produces. That can be unstable and even if it isn't that slow, the bullets usually make a pretty scattered group on paper.
Another problem with over-spinning is it exaggerates drift caused by any degree to which the bullet center of gravity is off the bore axis. This is caused by imperfect bullet alignment with the bore and by bullet defects. It used to be the latter was a bigger issue than it is today. Jacketed bullet manufacturing quality in this country has increased a lot over the the last several decades. Oe result is you can spin bullets faster than you used to be able to do before the drift and wobble in flight due to eccentrically spinning center of mass becomes a problem (though you can still find it in some cheap bulk bullets).
Bullet holes will not be made visibly oblong due to over-spinning. It is true that the stable bullet yaw angle (yaw of repose) increases with spin rate, but a normal value is in tenths of a minute of angle early in the bullet's flight, growing to perhaps a full moa at 1000 yards, by which time the bullet's trajectory velocity has decreased much more than its spin rate has, causing stability factor to increase. A grossly overstabilized bullet might reach several moa of yaw, but you're not going to discern the oblongation of the bullet hole by an angle that small without optical comparators or other special instrumentation.
The stability calculator used by Berger is very similar to the one Don Miller devised by adding modifiers for atmospheric conditions and velocity to the Greenhill formula. That is available at the JBM site. The JBM site adds and argument for a plastic tip, while the Berger site adds and argument for BC. The latter takes into account the overturning forces and is probably the better approach. The JBM site, however, has a convenient and fairly extensive list of bullet lengths worth having access to.
A still more rigorous stability calculator that requires more information about the bullet is based on Robert L. McCoy's program, McGyro. It is available on Geoffey Kolbe's site. The results are in graph form, so you have to adjust to that. I think Berger's use of the BC is meant to replace the drag estimates produced by that information. But what McGryro does, IIRC, is also estimate center of gravity location and moments of inertia of the bullet, which should make the estimate more accurate.
You don't have much to worry about. I'll correct a few minor points. Gyroscopic stability factor is defined as breaking even at 1.0. So anything 1.0 or higher will not actually tumble, though they will not typically shoot very precisely that low. Sierra recommends 1.3 to 3.0 for "hunting accuracy" and 1.4 to 1.7 for best match accuracy.
Spinning too fast creates three problems. Already mentioned is actual disintegration, which can happen to very fast, lighter construction bullets. Another is core stripping. This is where the bullet jacket's grip on its lead core is not great enough to pull the core up to the jacket's rate of angular acceleration, so the lead slips inside it. Because the jacket engraving looks like speed bumps on the inside, this beats the lead our narrower and loose inside the jacket, so when the bullet exits the muzzle not only is it no longer unitized, the lead is spinning more slowly than the jacket and the two have to come to an equilibrated spin rate that is slower than the rifling nominally produces. That can be unstable and even if it isn't that slow, the bullets usually make a pretty scattered group on paper.
Another problem with over-spinning is it exaggerates drift caused by any degree to which the bullet center of gravity is off the bore axis. This is caused by imperfect bullet alignment with the bore and by bullet defects. It used to be the latter was a bigger issue than it is today. Jacketed bullet manufacturing quality in this country has increased a lot over the the last several decades. Oe result is you can spin bullets faster than you used to be able to do before the drift and wobble in flight due to eccentrically spinning center of mass becomes a problem (though you can still find it in some cheap bulk bullets).
Bullet holes will not be made visibly oblong due to over-spinning. It is true that the stable bullet yaw angle (yaw of repose) increases with spin rate, but a normal value is in tenths of a minute of angle early in the bullet's flight, growing to perhaps a full moa at 1000 yards, by which time the bullet's trajectory velocity has decreased much more than its spin rate has, causing stability factor to increase. A grossly overstabilized bullet might reach several moa of yaw, but you're not going to discern the oblongation of the bullet hole by an angle that small without optical comparators or other special instrumentation.
The stability calculator used by Berger is very similar to the one Don Miller devised by adding modifiers for atmospheric conditions and velocity to the Greenhill formula. That is available at the JBM site. The JBM site adds and argument for a plastic tip, while the Berger site adds and argument for BC. The latter takes into account the overturning forces and is probably the better approach. The JBM site, however, has a convenient and fairly extensive list of bullet lengths worth having access to.
A still more rigorous stability calculator that requires more information about the bullet is based on Robert L. McCoy's program, McGyro. It is available on Geoffey Kolbe's site. The results are in graph form, so you have to adjust to that. I think Berger's use of the BC is meant to replace the drag estimates produced by that information. But what McGryro does, IIRC, is also estimate center of gravity location and moments of inertia of the bullet, which should make the estimate more accurate.
Thanks Unclenick, your explanation is most helpful. It does bring up a simple question though. Would a bonded bullet resist core stripping simply because it is bonded? Or does that not make much difference? In other words when going light for caliber, is one better off purchasing premium (bonded) bullets?
I didn't see where you stated your 77's barrel length, but, assuming it's 22" (perhaps even 20") I would think you should be able to get the 125 gr. partitions going 2800 fps mv safely with the right powder choice. Perhaps over 2900 fps if you have a 24" barrel. If you experience poor accuracy I suspect other factors rather than "over stabilization" will be the greater culprits.
My 6.5 Creedmoor (as you may know, is very close to a 260 and with 1:8 twist) shoots the partitions +- 3/4 moa with RL 17. I haven't chrongraphed it yet but Noslers' load data suggests I should be in the 2880 fps range. Their max load is listed as producing 3000 fps. This is a very effective load for hunting whitetail.
My 6.5 Creedmoor (as you may know, is very close to a 260 and with 1:8 twist) shoots the partitions +- 3/4 moa with RL 17. I haven't chrongraphed it yet but Noslers' load data suggests I should be in the 2880 fps range. Their max load is listed as producing 3000 fps. This is a very effective load for hunting whitetail.
Last edited:
alaskabushman
New member
I have been using 129 grain Hornady SST's in my .260 for years with no problems.
Jevyod,
Yes. Bonded should be a significant improvement in resistance to core stripping. I say "should be" because I haven't tested it personally. Obviously, solids won't core strip, either, but they are longer for their weight in an otherwise similar design shape, so they need a little more twist than lead bullets do to stabilize. In this instance, that's actually just fine for what you want to do.
Yes. Bonded should be a significant improvement in resistance to core stripping. I say "should be" because I haven't tested it personally. Obviously, solids won't core strip, either, but they are longer for their weight in an otherwise similar design shape, so they need a little more twist than lead bullets do to stabilize. In this instance, that's actually just fine for what you want to do.