Hello Peter Larson,
Dr. Kevin Robertson wrote of similar problems when he used older Kynoch ammunition, particularly with their full metal jacket or "solid" bullets, in his excellent book; "Africa's Most Dangerous".
This was in regards to his personal experiences with it in his .505 Gibbs, when shooting animals in situations that definitely called for full metal jacket bullet penetration.
He was disappointed.
From reading his observations on this old ammunition, the evidence strongly points to the jacket material as being too thin in their vintage loadings.
Robertson wrote of also experiencing more than one or two failures to fire, with the old Kynoch ammunition that came with his Dumoulin Magnum Mauser, when he bought it 2nd hand.
So, he pulled all projectiles from his ammunition, dumped the powder and removed the primers.
Then, reloaded the brass with new primers and new powder.
He crimped the "solids" back into the cartridges but only used them as though they were softs.
He indicated the jackets were so thin that they tended to deform on buffalo about, like a premium, tough soft nosed bullet should do.
I believe now that Kynoch may be using Woodleigh projectiles in their ammunition these days.
If so, then the problem is likely solved.
Woodleigh bullets designed for velocities around 2,000 to 2,400 feet per second, by reputation are quite good.
They also make bullets for black powder velocities that, if by mistake any hand-loader tried to use them at more than I would guess about 1,500 to 1,700 feet per second maximum, they can expect over-expansion on large, tough animals.
In conclusion, I believe the over-expanded bullets you witnessed in buffalo, were due to much too thin of jacket metal.
Cheers,
Velo Dog.
