Quote Originally Posted by gwpercle View Post
No need to change loading data . The load listed for a gas check boolit can be used for a plain based boolit and vice versa ... all other things being equal of course .
If I remember correctly member Larry Gibson did some testing which revealed the gas checked boolit developed LESS pressure than plain based boolits !
Larry G. ...correct me if I'm wrong on this .
Gary
My initial testing did indicate that. However, subsequent testing with other cartridge bullet combinations tend to indicate "it depends"..... Thus like numerous pet theories we used to assume were correct there are variables that can skew measured results one way or the other. The biggest variations are the cartridge type used and the seating depth (not to be confused with the OAL). The biggest variation I've found so far is going to be in handgun cartridges because of their smaller case capacity over larger rifle cartridges. Those variations include bullet design which influences bearing surface and close weight of the bullets within practical consideration. Example; in the 44 magnum with a given load a 240 gr Lee TL SWC seated to the 1st lube groove and the Lee 240 GC'd SWC consistently give higher psi than the heavier 429421 (252 - 255 gr) bullet. Both the Lee bullets seating depth is the same and the psi with a given load are also pretty much the same. The Lee 240 SWC GC'd However, a 429360 PB'd 240 gr SWC gives less psi than all the other bullets because the seating depth is less than the others.

In handgun cartridges the seating depth [with a given load in a given cartridge] appears to be the critical variable that effects pressure the most over GC'd vs PB'd or even with jacketed bullets. In larger regular bottle larger rifle cartridges variation in seating depth and GC'd or PB'd falls within test to test variation and is basically meaningless. In smaller capacity rifle cartridges such as the 22 Hornet, 30 Carbine, cartridges based on the 223 Rem case and other AR length cartridges seating depth can also be a critical factor if approaching maximum pressure loads.

This is why we should follow most all manual suggestions to work up loads watching for pressure signs. The use of a chronograph is very beneficial if developing maximum psi loads or approaching those. If you are getting higher velocities than expected with a load combination then you can pretty much bet you are also getting higher pressures. I do not believe in "fast barrels". Those barrels that give higher velocities with a given load have chamber/bore/ rifling dimensional differences that create higher pressure with that given load/cartridge.