This story starts with a friend gifting me 100 bullets to try in my .32 RKS Miller.

The gift bullets measure .320-1 on the base band tapering to .314 at the base of the ogive and weigh 200.5 grains cast in 20/1 alloy.  My normal bullets measure .324-5 on the base band tapering to .314 at the base of the ogive and weigh 207.5 grains cast in 20/1 alloy.

The best powder charges for my normal bullets are 13.1 grains of AA 4100 and 13.7 grains of 296.  10-shot vertical dispersion at 200 yards stays between 3/4" and 1 1/4" for both loads.

As you have already figured, the gift bullets seat a whole lot easier than the normal bullets.

I first tried the gift bullets with 13.1 grains of 4100.  The performance was very good - 1/2" to 5/8" 10-shot vertical dispersion at 200 yards.

I then tried the gift bullets with 13.7 grains of 296.  The performance was awful - 7" 10-shot vertical dispersion at 200 yards. 

I think that the abject failure of 296 with the gift bullets shows that 296 needs a lot more "back-pressure" (for lack of a better word) to ensure consistent shot-to-shot ignition than the 4100.

Has anyone had a similar experience?

JackHughs

Jack
While the cause of your vertical dispersion could/can be too small a bullet for the bore, I suspect  that the primer used may not be hot enough to uniformly ignite the 296 powder. Pressure tests I have done has shown that 296 and 4100 have similar pressure rise times when breech seated bullets are used. Each formulation of powder has whats called working pressure, if the minimum pressure is not reached pressures/velocities will be erratic. Too light a powder charge may also contribute to vertical dispersion also. Its been my experience that reduced capacity cases (32-40 vs 32 Miller Short) are more sensitive to slight changes of powder charges.
B Darr

Don't rule out the use of Large Rifle Magnum primers as an ignition source to further induce a complete Powder burn. 300MP has been my powder of choice in my 32-40, Pistol Primers and Standard Large Rifle primers will leave unburnt powder in the bore of which is conducive to extreme velocity spreads and increased fouling. The Winchester Large Rifle Magnum Primers for me provide a more complete and clean burn and greatly reduced fouling. The recommendation from several of the leading ball powder manufactures all recommend the use of Mag. Primers with their Ball Powder Products due to them being exceptionally harder to iginite. Unfortunatly that recommendation is avoided like a plague when it should actually be embraced and well worth giving them a try. Taking your current load and simply switching primers for comparison sake for me has not worked me. It requires starting from scratch and developing a new load specifically for there use.

I hope this information is helpful, it has worked extremely well for me as well as others.

JLouis