The new IMR 4198

[Marlin Junky]

Has anyone tried IMR 4198 with the new features (from the IMR website: Proven metering and necessary elements were added to make it extremely insensitive to hot/cold temperatures)?

I need to make a powder purchase pretty quick and was wondering how the "new" 4198s (H and/or IMR) compare to those profiled in Quickload. I've got an old metal can of IMR 4198 that I've been using with RCBS 30-165 and I'm getting 100+ fps more velocity compared to QuickLoad. I'm going to try c309160 with my old IMR 4198 next week (in my '06). The RCBS boolit weighs about 15 grains more that the Lee boolit when both are barrel ready.

MJ

[felix]

Being canister grade, I would suspect the peak pressure would be very close to any previous lot, but also would suspect the pressure curve itself to be somewhat different even though the average pressure would also be somewhat the same. The chemical used which keeps the ignition temp less dependent on ambient temp also introduces its own variability. That variability deals with humidity, much like black powder does. So, the powder would be better when shot in changing ambient temps; but, somewhat worse when shot in changing ambient humidity. So, what else is new, right? Dis for Dat. ... felix

[nighthunter]

Felix ... I have thought cartridge cases to be pretty much sealed when loaded. Especially so when useing lubed cast bullets being that the lubricant and neck tension combined would create a seal. I don't mean 100% sealed but enough so that outside humidity would have an extremely low effect on the cartridge contents. Perhaps I am wrong in my thinking but could you explain better the effects of humidity. I have no problem understanding the effects of temperature. Thanks.
Nighthunter

[felix]

Of course, you are correct, NH. It does not seem logical, but there is enough "time" for the powder to absorb/adsorb the ambient moisture from within the barrel as the projectile passes by. It would obviously be worse to load these kinds of powders at the range, but then various sighter shots (show and tell, not for record) are used to detect the compensation needed to bring accuracy back into the standard groove for the gun. That is the usual BR practice anyway, and makes the outing's powder choice a moot point unless the powder speed is not kosher in the first place. ... felix