Backpacker
I too have a 'Backpacker', purchased new, I don't recall when. Great gun to handle, look at, but not to shoot with heavy weight 44 magnum rounds. I believe the reason for the remarkable difference in noise, muzzle blast, and flash with only a one inch difference from the 4 inch is powder burn. Depending on the load, manufacturer, and the powder they use, it is not completely burned in a 3 inch, where the 4 inch has burned up considerably more.....in just that one inch. Same ammo in a 6 inch, less blast and noise. In a 8 3/8's, even less......in that perhaps all the powder has burned completely. Powder that is still burning is still producing the ignition noise and obviously the muzzle flash, having left the barrel still igniting. JMHO.