https://castboolits.gunloads.com/archive/index.php/t-328499.htmlAll the early .45 ACP collector ammo I have has either a large (.210"), or the Frankford Arsenal 0.206" diameter primer. I have never seen a US example of small primer .45 ACP factory ammunition manufactured before 1980. If somebody can show one I would appreciate a photo of the headstamp.
Here are some typical early .45 ACP rounds, all large primer:
188990188991188992188993188994188995
Modern use of small primers in .45 ACP ammunition was brought about by the need for nontoxic range ammo with lead free primers. The small primer pocket was used as a manufacturing expedient so that the ammunition factories only needed to produce one size of nontoxic, lead-free primer for use in all calibers of handgun training ammunition in .38 Special, 9mm Para, .40 S&W and .45 ACP. The small primer also serves as positive identification of nontoxic .45 ACP work-in-progress ammunition moving through the plant.
In my .45 ACP testing a small pistol magnum primer produces the same pressure, velocity and accuracy as a standard large pistol primer.
Using standard small pistol primers with H&G #68 200-grain SWC bullets and 5 grains of Bullseye powder, the velocity drop over a large primer of the same manufacture is about 40-50 fps. When using standard small pistol primers and Bullseye powder to obtain the same velocity as obtained with the large primer, simply increase the powder charge by 0.2-0.3 grain of Bullseye.