Quote:


Sorry but I disagree. All three of the things you mention all end up being a bullet not spinning around its centroid. Certainly that's bad. But it degrades the flight path by a) magnifying the magnus effect and by b) nutation and precession. These are characterized by random bullet strikes and more dispersion. If you fired a series of shots from 0 to 100yds in 1 yd intervals you would record an elliptical pattern of the classic corkscrew flight path.

Similar to gunlaker,  I have a Saeco bullet that tips in my 16 twist barrel.  It weighs in at 202 and my other two bullets: a Darr  190, and a Barnett  204 shoot clean holes.  (All three tend to avoid the 25 ring, but I think it is a loose nut  behind the trigger.)

I have tried upping the charge on the saeco to no success,  I've used 4227 and AA1680 and  I don't think the powder is the culprit.  I am looking at the calculators that Seanmp posted to see if it is a center of gravity or center of pressure.  CP is a new term to me and not sure if I understand it.  Would love to see explanation.

-06

Here are the pictures I'm posting for BoHo.
His bullets:
First these are the bullets. #1 as cast PJ bullet, #2 PJ with .080¡ turned from the base. and #3 is the barnett as cast.

This was shot with the cut down Paul Jones, tipping now very light. And no broken 32-20 cases! This many shots with the as cast bullet would have broke a standard case after 4 shots. 

Seanmp,
If you'll play with the ballistic program that we both like. Make a long sharp spitzer with it. You'll find that the farther back the CG, the less twist you need to stabilize a bullet. I learned it first by shooting a 1.180 long bullet (Ideal 320366) in a 16 twist. When I found that program on the Border site 2 years ago, it varified that it could be done in the ballictic program. All the other programs said no.

That program is thee best at helping to understand things. 

Frank

Those are some nice looking bullets. Looking at the bullets its hard to imagine you have an unbalanced spin causing nutation.
But the tipping smears are oriented in random directions. That leads me to say what your looking at is gyroscopic precession.

Meaning the bullet is traveling along the straight flight path which is passing through the centroid but the nose and the tail are orbiting in balance, Normally drag would settle this down but you have a high spin rate causing the gyroscopic effect to be too strong for the tiny drag force at the tail of the bullet.
If you hold a spinning gyrscope on the tip of your finger you can see gyroscopic precession

In short there is little to worry about IMHO. This will cause a slight reduction from calculated BC but little else.

frnkeore wrote on Aug 5^th, 2014 at 8:59pm:

Your absolutely right and I'll be the first to admit I'm a transonic guy. All of the work I've done on bullets and barrels focuses on that boomerang dip at the transonic zone. Mainly because the big bore airguns and BP loads I like pass through or even spend their entire flight in this zone.

The trouble with an aft CG is when it enters the transonic the center of pressure suddenly jumps to the nose of the bullet or strangely out in front of the nose. This creates a large moment of inertia and the bullet invariably flips end for end.
We had some great success counteracting this with a stepped boattail (similar to the Corbin design) on the airgun side but sadly the steps just get squashed in the BPCR

Here you go, Wayne.

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Frank