RPM theshold discussion

[Bullshop]

Freedom its freedom! Once I was in a barrel but once I was free I spun faster. It has to be freedom.

[NVScouter]

Larry I'm reading this due to your reference in my 30-06 thread and trying to get all that you are imparting.
Last post you made a great reference to groups. It's what most if us see while shooting not hypothesizing. If a load will shoot close it will shoot farther on a lineir scale. At least until it goes transonic or hits some thing.
This is my frustration with a sub 1" 50y group going to 7" at 100y. By most of my shooting a 50y .50group should be a 100y 1" group and. 200y 2" group 4" 400y group etc.

[swheeler]

Freedom its freedom! Once I was in a barrel but once I was free I spun faster. It has to be freedom.

That's funny Daniel, I laughed but not as hard as I laughed at gears and brads hypothesis, now that's funny

[Larry Gibson]

Larry, would you mind 'splaining to Scot the difference between what happens to a boolit in the barrel vs. after it's out of the barrel? Something about rate of decay of rotational velocity vs. rate of decay of forward velocity?

Gear

Gear

You didn't mention "rotaional decay" in the post Scot quoted. Easy to see how he thought you were still "in the barrel". Scot does understand rotational decay BTW.

Larry Gibson

[Larry Gibson]

Huh? Your saying the boolit rotation increases after it leaves the muzzle?

I am very interested in hearing what would make it suddenly spin faster than the twist it was given in the barrel.

Rick

I didn't want to bring that up to gear but since you mention it it seems someone is really confused doesn't it??????

Larry Gibson

[Larry Gibson]

Sarcasm Rick, sarcasm.

In response to a previous post who doesn't understand that if the barrel twist is 1 in 9 that the bullet only makes one rotation for every 9 inches of forward motion. You know, the "buzz saw" effect in game.

Me? I know better.

Obviously some don't understand that the RPM doesn't increase as velocity drops..........many of us know better too!

Larry Gibson

[Larry Gibson]

Larry I'm reading this due to your reference in my 30-06 thread and trying to get all that you are imparting.
Last post you made a great reference to groups. It's what most if us see while shooting not hypothesizing. If a load will shoot close it will shoot farther on a lineir scale. At least until it goes transonic or hits some thing.
This is my frustration with a sub 1" 50y group going to 7" at 100y. By most of my shooting a 50y .50group should be a 100y 1" group and. 200y 2" group 4" 400y group etc.

Your frustration is caused by one of two things. Either the bullet is too slow to maintained rotational stability....OR.....the load is too fast and the bullets are exceeding the RPM threshold and going off on a tangent or beginning a helical circle around the line of flight. The first wil cause a loss of accuracy and is easily evidenced by keyholing apparent on the target. In the second (RPM Threshold) the bullets holes will stay round as the bullet still has rotational stability but the groups get larger non-linearally as the range increases.

Larry Gibson

[geargnasher]

That's funny Daniel, I laughed but not as hard as I laughed at gears and brads hypothesis, now that's funny

Haha! Those guys are characters, aren't they! I love it when one of them had that "1/2 group" key installed on his keyboard like somebody else we used to know. What a joke! Have you been reading about that glop they're making for lube now?

Gear

You didn't mention "rotaional decay" in the post Scot quoted. Easy to see how he thought you were still "in the barrel". Scot does understand rotational decay BTW.

Larry Gibson

He must have been talking about some really funky gain twist contraption in that quote. Any other explanation?

I didn't want to bring that up to gear but since you mention it it seems someone is really confused doesn't it??????

Larry Gibson

Oh Larry. Thanks for not wanting to hurt his feelings.

Obviously some don't understand that the RPM doesn't increase as velocity drops..........many of us know better too!

Larry Gibson

I'm sure glad I'm with you, Larry. How could someone get that mixed up?

Gear

[duck hollow pete]

A little off topic maybe, mid 70' rem. xp100 221 fireball 6x18 scope 50gr hornady sx fb ,outstanding groups 1&2 hundred yds tried the matchbullet just to see if it would group better. This bullet grouped better at 100yds,but 200yds it shot patterns .The match bullet was 50grs but boattail design,less bearing surface got to be due to rotation speed?

[Nrut]

We're in Kansas now and these little doggies are hurtin'..
I sure hope that there is plenty of green grass when we get to where we are going..

That'll really get them a squirtin'!

[303Guy]

...
This is my frustration with a sub 1" 50y group going to 7" at 100y. By most of my shooting a 50y .50group should be a 100y 1" group and. 200y 2" group 4" 400y group etc.

A perfect example of what Larry is describing. OK, I get what is being meant by RPM threshold. The same damaged boolit that will spiral off in a fast twist barrel should be remain sort of accurate with a slower twist barrel. Thanks for clearing that up, Larry.


So the faster twist barrel imposes a velocity penalty by virtue of RPM threshold but it can be raised by casting and loading tecniques. A good example of casting flaws is my small batch of boolits I cast yesterday from a mold that should drop 192grs. With my alloy it drops 191grs but I was getting 188grs! OK, I thought, more tin than I realized. But on firing two or three I found holes on the surface exposing internal voids! These things looked good on the surface with sharp base edges (small rebate). Those mysterious flyers one gets are no longer a mystery. All the boolits might have a void but when that void collapses there is going to be a flyer, others wise just not so good accuracy.

[303Guy]

We could use these two for sarcasm.



Not quite what we want but better than nothing. Point is we are just kidding and we do need that sarcasm smilie.

[swheeler]

Stick around gear you'll figure some of this stuff out, eventually

[Any Cal.]

Here is a long winded treatise of the subject...http://www.nennstiel-ruprecht.de/bullfly/index.htm It seems like there is a lot of solid info here, and gives many definitions and illustrations that can get everyone on the same page. I have gone through it, but have slept since then...

[303Guy]

Ah yes. That's one that I've read in its entirety. It's the one I've gotten most of my information from and I've posted bits from it in the past. There's one somewhere where they talk about bullet spiral being measurable by radar chronographing. The velocity at extreme ranges appears to slow and speed up as the bullet spirals downward. I'm not sure where I found that one. I see this one has been updated since I last saw it. Interesting stuff!

Yup - the dopplar radar bit is right in this article too although I saw it elsewhere first.