1/4-1/2MOA but then very poor accuracy at 300

[BoydAllen]

Thanks for the followup. I think that your conclusions make sense. The issue of bullets having velocity limits if best accuracy is to be achieved, is pretty commonly overlooked.

 

[jmd]

It appears to be exactly what happened. I just never expected that. Lesson learned & I'm glad I got it taken care of. I guess it didn't really make sense to shoot a light flat base bullet anyway

 

[JustinP]

I've often wondered about this v-max design issue. Why is it that you can't shoot the heavier v-maxes at higher velocities without potentially damaging the jackets or having them self-destruct in flight - but the smaller ones (like the 22 cal 40/50/53/55) can be propelled at 3500+ with no issue? Is the construction that different? Is it something to do with core to jacket ratio, or something? Perhaps someone can enlighten me.

Excellent that the 140s are working for you. I've been trying to get the 95 v-max to shoot out of a 260 but precision is off and I suspect the velocity problem is rearing its head. There is a lot of copper fouling, so perhaps the jackets are getting damaged. Perhaps I'll try some 120s B-Tips. The 140s are too long for the 260 case, as I need to seat to mag length.

 

[Turbulent Turtle]

jmd, thanks a lot for posting the follow-up. I was kind of grasping at straws but that was the only theory I could think of that fit the data. This has to be one of the best examples of dynamic instability I have ever heard of. These events are rare nowadays because bullets are so much more uniform than they ever were so one of the few ways for this to occur was damage done in the barrel.

 

[jmd]

Yeah, the copper fouling is definitely no longer a problem now that I'm not leaving half of the jacket in the tube. Some may say my experiment is flawed because I changed bullet weights. However, I did shoot a handful of 120gr Nosler ballistic tips as well and I did not have any issues. No erratic accuracy problems & no major copper fouling.

JustinP,
That heavy copper fouling is exactly what had me questioning the bullet construction. I honestly have no idea why you can push a Vmax out of a 22-250 at a much higher velocity without damaging it, but my guess would be that it has something to do with rpm's. I'd like to hear the explanation myself.

 

[Turbulent Turtle]

It may not be so much the RPM but the initial engraving of the bullet into the lands. If the twist rate is faster, there is a possibility that the bullet will skip for a few inches before engraving totally and turning at speed. The other possibility might be that the initial land angle is too steep for this combination and a shallower angle might be more gentle for the bullet, something in the 1 to 2 degrees, instead of 3.

It could also be a combination of both, but it's difficult to guess without more information, such as the angle of the lands.

 

[JustinP]

My 260 has an 8" twist krieger on it. Leade is about 1,30d. Suspect there could be something to the RPM theory and the 'skip' in a tighter twist barrel. I guess it then follows that the heavies, moving slower would have less skip/RPM?

Perhaps the light v-max/b-tip type bullets moving at 3500+ can do so because of slower twist barrels?

Would be interesting to do a side-by-side comparison. Same weight of projectile through a faster and slower twist barrel...

Justin

 

[Turbulent Turtle]

My current theory is that the bullets were damaged during the initial engraving into the lands and then experienced a dynamic instability once in flight. Later, when the temperature was a little warmer and the bullets were flying faster, they also started flying apart and never even getting to the target. The bullets skipping the lands and the jackets coming apart also left their trace in the barrel, especially near the throat and that stuff was probably distributed further down by the subsequent bullets

My thinking is that if there is any jump between the chambered bullet and the onset of the lands, the bullets were probably not engraving precisely but skipping for a few inches and thus damaging the jacket causing the problems described above.

A longer (heavier) bullet will be seated closer to the lands and will not be hitting the lands at the same velocity and thus will engrave cleanly and the jacket integrity will be preserved.

The angle of the lands may have contributed to the issue also, but now knowing what the angle is or even what rifle we are talking about and if it's a custom chamber, it's all conjecture.

 

[Erik Cortina]

My current theory is that the bullets were damaged during the initial engraving into the lands and then experienced a dynamic instability once in flight. Later, when the temperature was a little warmer and the bullets were flying faster, they also started flying apart and never even getting to the target. The bullets skipping the lands and the jackets coming apart also left their trace in the barrel, especially near the throat and that stuff was probably distributed further down by the subsequent bullets

My thinking is that if there is any jump between the chambered bullet and the onset of the lands, the bullets were probably not engraving precisely but skipping for a few inches and thus damaging the jacket causing the problems described above.

A longer (heavier) bullet will be seated closer to the lands and will not be hitting the lands at the same velocity and thus will engrave cleanly and the jacket integrity will be preserved.

The angle of the lands may have contributed to the issue also, but now knowing what the angle is or even what rifle we are talking about and if it's a custom chamber, it's all conjecture.

The bullets were hitting the target.

 

[Turbulent Turtle]

Go back and reread the thread, with special emphasis on reply #11 from the OP, which I reproduce in part here:

Bayou shooter,
I probably didn't explain it, but I did go back to 300. I initially started there for the day & then checked grouping at 1 & 2 to verify it was shooting well there. After that I did try at 300 again & I wasn't even on paper. Could you elaborate on the instability you speak of?

So at first he was getting horrible groups at 300 due to dynamic instability. He went back to 200 and 100 and was getting good groups there because the bullets did not have the time to stray from the trajectory due to dynamic instability. But when he went back to 300 later on when things had probably warmed up some, the muzzle velocity was now high enough to make the bullets go poof. The bullets were probably damaged at lands engraving.

 

[Erik Cortina]

I see.

 

[langenc]

Is there a need for you to shoot 300 or a want??

I guess you asked it correctly--"why should I burn up a barrel trying"? if there is no need??

 

[jmd]

I think Bayou Shooter is right on. Justin P, I would like to see that experiment at some point. Maybe two 22-250's with one in a 1:14 twist and the other in a 1:9 twist. Both chambers would have to be cut with the same reamer to rule anything else out & then see what happens to vmax bullets between the two.

Not sure if the 300 yard question was directed at me. Some may call it a want, but I'd say it is a need. Shooting woodchucks at 200 yards is kind of boring especially with a custom 7mmWSM. It gets a little better around the 600+ range in my opinion.

 

[JustinP]

More grist to the mill on this v-max jacket issue. Shot some more 95s out of my 260 yesterday to recheck. Velocity at bottom of ladder was 3200fps MV and top was 3300fps. Obviously the combination of speed and barrel twist (8") was too much for these pills as stability was off and I could start a copper mine with what came out of the barrel afterwards... I reckon a slower twist barrel would rectify a lot of this problem. Unfortunately, the state of the treasury doesn't reach to a slower twist barrel just for comparison purposes..

 

[savageshooter86]

I'm sure y'all have thought about it, but if you call Hornady they are pretty helpful about telling you if the bullet would work in your twist barrel and length. Just a thought

 

[jmd]

I did talk to them & they did suggest dropping the velocity to around 3000-3100fps just "in case" the jacket wasn't holding up. I opted for a different bullet. I don't like to load that low & not use the potential of the cartridge.

Justin P kind of started a new portion to it. It sounds like he's having the same problem in his .260 and he questioned why there is an issue with larger diameter vmax bullets since there are plenty of .22 cal vmax bullets getting pushed over 4000fps.

 

[CatShooter]

Justin P kind of started a new portion to it. It sounds like he's having the same problem in his .260 and he questioned why there is an issue with larger diameter vmax bullets since there are plenty of .22 cal vmax bullets getting pushed over 4000fps.

The 22 cal V-Maxs that are driven at 4,000 fps are usually shot from 14" or 12" twist barrels, but even when shot from faster twists, there is a difference.

The force that is trying to rip the bullet apart from spin, increase with the square of the distance from the central axis.

Add to that, as we seek longer bullets for their BC advantage, we are forced to spin them faster and faster... and as we double the spin rate, we also square the forces inside the bullet, trying to rip it apart.

So putting that together, a 6.5mm, 140gr A-Max at 3,500 fps is under hellova lot more destructive force, then a 50gr V-Max at 4,000 fps.