Chris how much did the length of the bullet decrease after having bumped up.

Ok, more info.  I have my friends very detailed notebook.  That particular bullet is actually a Dr. Richard Gunn design.  It started as 1.442" long so shortened 0.030".   The nose bumped up from 0.399" to 0.405" after firing which is just a little under groove diameter ( 0.4095"-0.4097" ).

Oh, and it was recovered from a snow bank.

Chris.

It really does not look at all like a Snover (designed by Dr. Gunn) However I think that is the point, the carefully designed and cast aerodynamic bullet that went into the chamber, exits looking like something different. 

For BPCR, I like hard alloys.

Right! 
And, we try to minimize the differences, and to large extent, with strong alloy choice, tight match chambers, and bullet fit by design, we do.

Yep it all goes hand in hand when all is said and done and why Mann could never eliminate his X Factor it being an unbalanced bullet.

gunlaker wrote on Feb 26^th, 2019 at 3:45pm:

I'm re-reading Mann at night before bed.

I once read an analysis that proved that the lead bullet couldn't slump under acceleration down a bore. I wish I could find it.

Faulty math.

That picture is what I have been looking for. Snow or whatever recovery media could (and I stress could) cause deformation of a bullet that looks like slump. 

However, the bore riding portion of the bullet expanding into the groves is irrefutable evidence that the bullet slumped in the bore. 

A proper measurement in my opinion would be the depth of the groves in the bullet, representing the amount it expanded into the groves of the rifling. This along with bore dimensions and bullet nose diameter would complete the measurements.

Steven

My goal is to keep them from slumping.
My solution is to use an alloy hard and strong enough to support the "un-supported" nose  

It works.
One tool to get an idea if your alloy works is two chronograph Bc testing as well as traditional accuracy testing both close and at range from the long lines.

I have also heard of bullets slipping / stripping the grooves but not sure of the cause other than possibly not having the alloy tin rich enough? Also not sure how one could go about identifying it a caught bullet would still show the markings left by the lands once they took hold.