Hi
how short the barrel of a 375 HH could be cut and still getting 2450-2500 FPS with 300 grain bullet?
regards
yes

2450 would be easy with a 20" barrel. 18" might work as well, but it would be close.

I did a 19 incher a while ago for a WELL known gunmaker; he loved it and the guy who bought it insisted he sell it to him for more than he had in it.

I was shooting "Thumper" yesterday and he is a salvaged P-64 Mod. 70 action, had been nicely reblued so was only $550.00, a Mod. 70 "Classic" sts bbl, at $100.00, un-fired, a Micky P-64 style MC stock, used, $100.00, Recknagel "skeleton glow sights with same on banded front, pricey, Weaver steel Grand Slams and Burris low Zee rings, opened to 8/40 and J-B'ed to receiver, metal Gun-Koted and, of course, Leupy 2.5XC-MHD, new, not expensive with a Decelerator at my LOP.

All in, an inexpensive rifle, my 7th-.375H&H and it does MOA with 300 NPs at a chronoed 2400 fps-mv from it's 20" tube. It is superbly balanced, easy to carry and shoots well off-hand; my buddies ALL want to buy this rifle and will pay me serious coin for it as it is the ideal B.C. Grizzly defence gun.

This started as a "joke" project with a buddy and now is a very nice looking custom rifle and one I automatically reach for when going alone with my backpack into Grizzly country. I have another in a re-bored P-64 .30-06 now a 9.3x62 almost finished and it also has a 20" tube....I CAN load hotter, but, a 286 NP or 300 NP of these diameters at 2400 is SO nice to shoot and simply will WHACK anything that lives in North America, that I see no reason to increase my loads or barrel length.

I like H-4350 for this, 76.5 grs., WW brass, CCI 250s and the 300 NPs....can't beat it.