[Grayrock]

I have been loading 250gr LRNFP bullets in .45 Colt. I just bought some more bullets, but they only had 240gr in the style I wanted ( they made me a deal I could not pass up.) How much difference can I expect if I just use the same load and substitute a bullet only 10 grains lighter? I was getting 1200fps out of the 250 grains. OH yeah- old 250gr say they are .454 diameter and new 240gr claim .452 diameter. How will that factor in?

[BluesBear]

The lighter bullets will have a slightly higher muzzle velocity.

What is the bore diameter of your revolver?

If it's .454 then you can expect less than stellar accuracy with the undersized bullets.

Also if you're currently using a .454 expander plug you won't get a good crimp with the new bullets.

If your bore is .451/.452 then your accuracy might improve over the oversized .454 bullets. .454 bullets in a .452 bore also creates slightly higher pressures.


There is no danger using 240gr bullets with 250gr data.
But do not use 250gr bullets with 240gr data.

[Grayrock]

Don't know the bore diameter. Do they vary from model to model? Or should all models in a line be the same? It is a Rossi copy of a Winchester 92 lever rifle.

The bullet is 4% lighter, so should I expect 4% increase in velocity? Is it a linear relationship or logarithmic?

[BluesBear]

Is it a linear relationship or logarithmic?Neither.
There is so much to consider besides weight.

Your Rossi should have a .451" bore.

[nothinbutguns]

:banghead:

[BluesBear]

After consulting some friends who own Rossi rifles berhaps slugging your bore would be prudent.
The .44 Magnum Rossi rifles are commonly found with oversize bores.
I don't know if this malady affects the .45 caliber ones as well since I don't know anyone who has one.

[Nhsport]

There isn't going to be a huge difference going from a 250 to a 240. The size difference might have a bigger effect.
At any rate you should deffinately back off your powder level and then slowly work it back up to where you want to be. This is standard safe handloading.
Generally in reloading for pistols a lighter bullet will get lower velocity vs a heavy bullet. The heavy bullet takes more time/power to get it moveing and allows the powder to burn more efficiently createing more power.Heaver bullets also take up more case volumn which tends to also increase preasure