Mallory commented in his book, "The Krag Rifle Story", 2nd edition, page 173, ... "Peyton powder was used initially in the 2,200 f.p.s. cartridge, but a switch was made to Laflin & Rand W. A. when it was found the latter powder gave lower average pressures".

Mallory reported the 2,200 f.p.s. round as developing 45,000 p.s.i. breech pressure and the 2,000 f.p.s. rounds were loaded to 40,000 p.s.i. pressure level.

I would assume, high temperatures would have increased these pressures.