45 Colt - Chamber Pressures Unique Compared to Herco

[321BMT]

I have read that Herco is very close to Unique as far as charge weight to velocity - a little more Herco to get same velocity as Unique. Is the relationship the same for relative chamber pressures for the two powders? Does it take the same charge or a little more of Herco to reach the same chamber pressures?

Brian Pearce lists 10 grains of Unique under a 280 gr. SWC as a safe Tier II load. Would 10 grains of Herco under the same bullet likewise be a safe Tier II load?

I'm working up loads for mid-frame Ruger Flattop, and I have some Herco on hand and some 45-270-saa's from Matt's. I don't need to max out the load, but I'd like to have an idea of where that max is for this bullet before I start.
Starline cases and CCI 300 primers. OAL ~ 1.65"

If anyone has actually pressure tested similar loads or run them thru Quickload that would be really helpful.

Thanks

[flint45]

I have made up some 10 grain herco loads with a 260 gr. RCBS bullet seems like a good mid range load. 300 grs. bullet and 8.0 and 9.0 grs. herco no signs of being to hot.

[Outpost75]

Herco is a bit slower than Unique, but works very well in the .45 Colt with the heavier 260-grain+ bullets. In my Ruger NMBH I use 10 grains with the Accurate 45-290H at 1.65" OAL in Starline brass with the WLP. I think you would be just fine with the 270 Matt's in your Ruger Flattop, but I would not increase it further in the mid-frame. I have gone as far as 11 grains in my large frame, but the load was less accurate, so I went back to 10 grs. which seems a good full-charge load which is powerful enough without getting snotty.

Larry Gibson pressure tested a Bullseye load for me which also shoots very well, the data sheet attached.

Attachment 259288

[321BMT]

Thanks for the replies. I'll work up to 10 grains and use that as a ceiling.

[GSP7]

Ive used Herco in .45colt also. I like it.