A short barrel will not spin up a bullet enough for stability. Some guns have a gain twist like the .460 S&W so to cut it down approaches a smooth bore. I will never go too short. But I don't carry and stick a gun into a BG. I hunt deer. My best is a 10-1/2' Ruger SBH. My BFR's in .475 and JRH are 7-1/2" and the 45-70 is 10".
Twist rate is not affected by barrel length. All revolvers have enough twist for normal blunt bullets that are commonly used.
Spin is dictated by velocity. Lose velocity and spin decreases.
Let me do this. Take a 240 gr .44 bullet with 24 gr of 296 at maybe 1400 fps. RPM's are 50,400. Lose 200 FPS with a shorter barrel and get 43,200 RPM's. STABLE? My 330 gr needs 1316 FPS to be 47,376 RPM's. You say a twist rate is the same RPM's at all velocities.
Sorry, spin goes down with velocity loss. How about 900 FPS at 32,400 RPM's. You think a 2" barrel with the same twist will do the same as a longer barrel with more velocity is the same. I don't know how to explain. You need to get a 2" barrel up to 1400 FPS. A pound of Bullseye?
43 gr of 296 will burn in an inch in the .500 S&W? Get real. You will blow the gun to shreds with the pressure. You are always wrong and have been for years.
