In the example given, a .284" bullet was shot through a .277" bore, with no apparent damage.
This was obviously accidental, to use the wrong cartridge, but the shooter had some luck!
Parker Ackley proved that a larger diameter bullet could be shot in a smaller diameter bore, IF THE CASE SEALED THE GAS. In this instance, the 7mm cartridge case was just barely long enough to seal the case to the chamber. That is, had it been a bit shorter, like maybe a 7-08, pressure would have leaked around the end of the cartridge case and blew out every where it shouldn't have. Most likely blowing the stock off.
The reason the larger diameter bullet didn't blow things up is because by the time the bullet had gone the length of itself into the bore, it was sized to .277" diameter and the extra pressure to do this occurred before the cartridge had reached its maximum pressure.
And don't try this at home.
What about going in the opposite direction ,,,,,shooting a 7mm (.284) bullet out of a .308 (30 cal.)? On my first shot last week at my back yard range I accidentally chambered and shot one of my 7-08 reloads out my .308. I had grabbed it from the wrong box and because it was full length sized it chambered easily. When the shot didn't even registered on the target I though WTF and then noticed it was the wrong case. Could this cause any damage to the rifling? It didn't appear that it had because my groupings were quite good.
I was actually surprised at how easily it chambered because my sako is pretty fussy in that regard. My 7-08 cases are trimmed to 2.025 whereas my .308 are 2.005.
That could have turned into a major owie.
I've always wondered with a degree of fear as to what would happen in one of those situations. Apparently the person who fired the shot made it out OK...probably going to be a while before he goes back to the range.
How? Please explain.
Bruce




























