Difference in pressure between small and large pistol primers

[Waffenfabrik484]

Dear all, I have managed to cut 45 Schofield brass to fit Webley .455 revolvers and found reliable and tested loading data on original Fiocchi brass, however i have noticed the Fiocchi uses small pistol primers while the chopped Schofield brass has large pistol primers. Can someone kindly guide me if there are established ratios or percentages of how much do I need to decrease the grains of powder (current sweet spot on SP primers is 3.2 grains of Vithavouri N320, safe maximum of 4.0).

I accept that I am ultimately responsible for any loss of life and limb but any advice welcome before I go 2/3rds load and try to go up that.

Thanks Beforehand
Daniel

[Outpost75]

Have no experience with N320.

I fired charge establishment tests comparing large and small size Federal 100 vs. 150 primers in the .45 ACP loading the H&G #68 201-grain SWC bullet and Alliant Bullseye powder. It required a 0.3 grain increase in powder charge with the small primer to match the velocity obtained with the large primer for my 50-yard load, 4.5 grains Bullseye with Federal 100 primer vs. 4.2 grains of Bullseye with Federal 150 primer, at 1.255" overall cartridge length, in Federal cases. Velocity is 770+/-30 fps from a 6" M1911 accurized wadcutter gun with Bar-Sto barrel.

[Waffenfabrik484]

I read a lot of american based threads and Bullseye seems to be the equivalent of the N320 we have in Europe with a very very close burn rate.

My thanks for your answer, should be of great help!

[17nut]

This is for RWS primers but it will give you an idea.