Thanks for all the concerns, blunt or otherwise, but I have never been as careful on anything as I am on this. Believe me when I see signs of pressure I will back off.
As for 100fps it will be more like 300 when done SAFELY.
Reloading can be viewed by ANYONE as stupid at any point if one chooses. When one reloads, you go by published data because that is where someone tells you to go. If your rifle shows signs of excess pressure before you hit published maximums you're done what every reloader SHOULD be doing in the first place, watching for signs of pressure.
If you take the powder charge straight from a 450 Marlin factory round and put it directly into a 45-70 brass the pressure will be lower automatically because the 45-70 brass is thinner and therefore more volumous. Sound familiar? The pricipal is the same here. You never hear anyone saying not to use the 45-70 brass at 450 pressures cause we all know 45-70's were meant for trapdoor rifles.
The limiting factors at play here are the brass, the chamber and the usual signs of over pressure. That is all I am doing, this is not russian roulette.
I don't claim to be him but if Elmer Kieth had never experimented this exact same way, you would never had the 44 mag. Even the gun manufacturers were, at first, reluctant to load them as he described.
It was understandable why they wanted an entirely new casing, but the point is he did it on his own. I have no desire to "magnumize" the 375 but if I can gain 250-300fps over the published loads, I will. I won't be the first or the last STUPID person to do so either.
By the way, my Hornady manual #26 says the max velocity with a 200gr loads is under 2100fps. Yet the HORNADY 2004 annual manual, says 2400fps?

? More pressure? probably, but it was no boubt dont by slowly experimenting.
One manual publishes loads almost 6 grains higher with the same powder and bullet, both manuals from the same company.
As I said, I'll continue untill I see signs of excess pressure then back off.
I'm not pushing the limits of this cartridge, just finding them.