H4198 vs IMR 4198?

[bollox]

Are these powders interchangeable?

I have IMR and am looking to load for .243 win but have data for Hogdon.

Reading on the interweb shows a difference between the old metal can IMR but polymer can stuff may be the same?

Anyone with experience with this?

Thanks.

 

[LUTNIT]

IMR and H powders of the same numbers are sometimes very close and sometimes dangerously far apart. I have swapped H and IMR 4198 and 4895 at starting loads for reduced pressure cast loads before and never had a problem. 4831 is an example where the two brands are quite different and it would be very dangerous to switch between them.

Since 4198 and 4895 (either brand) operate well at reduced pressures I would take data for either brand of the same number, reduce it by maybe 10%, and swap it out. If it's a little under-powered they will both still burn correctly. Then you can work up the load as normal. If you're looking for maximum velocity and want a published number to reach it might not work well but with a 60k psi cartridge like the .243 you could just check for stiff extractions to know your pressure limit.

*edit*
Doesn't the .243 Winchester usually prefer slower powders? Wouldn't 4198 be a tad fast for it? I can't find data for either 4198 for it.

 

[bollox]

^ Awesome, thank you for your insight. Mine will not be cast, does that make a difference starting at -10%?

 

[LUTNIT]

I swap 1 for 1 with cast loads since they're already reduced. For regular loads I'd probably knock it down a bit; 5-10%.
Again, this only works for the powders that are close. Not all H and IMR powders are close to each other even if they have the same number.
How far the two powders are on the burn rate chart also doesn't tell you everything since you don't know how much difference there is between adjacent powders. I'm talking from personal experience, not a chart.

Where is the data from? I just find it odd that a fast powder like 4198 would have data for the .243. I doubt it'll give you ideal velocities as a result.