I want to load some 25 cal cartridges for a lo wall. I have 25 cal PB (plain base - no gas check) bullets of about 88 gns. I can find loads for lymans 257312 which is close in weight but is a GC (gas check) bullet. How different (if any?) is a load for a GC bullet from a load for a PB bullet of equivalent weight with the same powder in the same cartridge case? I know bullet shape and alloy come into it but the bullets I'm looking at are similar in shape and I have no idea what the alloy is/was for either bullet. Is there a rule of thumb for GC vs PB bullet loads?

Far as load data could be some more pressure created by the gas check however My guess is it's minimal.

Big difference is plain base is limited in velocity while gas checks can be pushed faster. My break in 30 calibers is 1500 to about 1600 fps over use gas checks under plain base.  Switch from Plain to Gas Check may be at lower velocity in smaller calibers.

Alloy is going to be important in getting good results Smaller bullets more sensitive to temper than large.  I recommend high tin/lead ratio.   

And of course Plain Base is required by ASSRA rules

Boats

Agree Gas Checks are largely a waste of time. Go fast use jacketed. Stay under 1500 or so not needed. I don't shoot much 30 caliber cast anymore, if starting fresh would only use plain base molds

Boats

I usually save the GC bullets for my hunting loads in 38-55 and 45-70. However, in this same line of questions, I have always wondered if there was an increased barrel wear concern with some of the older/softer steel barrels with gas checks (thinking primarily of the Lyman 257420 gas checked bullet).
Tom