Hodgdon web site says 6.4 gr is max for titegroup with a 225 FTX getting 863fps.
That's not your bullet, but a place to start. 13,200PSI

Your 7.5gr seems a little hot. It looks like the Brian Pearce load at 986fps. He still calls that a Tier 1 load under 14,000psi.


The real issue:
I have a 25-5 with 8 3/8" barrel and .454- exit holes on the cylinder. Barrel accepts a .452+ pin gauge. I bought .454 cast SWC and then tumble lubed them to about .4555 diameter.

Some lube is left as they exit the cylinder, but they are not swaged down below .454. The hardness is around 15. That seems perfect as they obturate well and fill all the way down on the grooves. I measured the recovered bullets base at .455 with most lube gone.
When they don't expand their base and fill down to the grooves, hot gases escape by the base and melt your lead bullet in the barrel.

I get a nice little star of lube at the muzzle.

Accuracy is 1 inch at 25 yards and 3.5" at 100 yards. No leading.
Your specs must be known and used. Powder choice will never matter if specs aren't right.


Prescut