I have been making ammo for my vintage 16 bore shotgun and have run into problem. The recipe I am using was selected because it is said to develop 7500 PSI @ 1250 FPS. It published by BPI and also is among RickBin’s data. It is: Fiocchi primed hulls with Fiocchi 616 primers, 22.5 grains of Longshot powder, BPI 1/8” card over powder, SG16 wads with 1 OZ of shot. 6 star crimp. Loader is a MEC JR. During a patterning session I noticed considerable amount of unburnt powder, which looks like Longshot “mud”. Wads look to have quite a bit of carbon on them. I chronongraphed several loads and was surprised to see between 910-930 FPS for 5 loads. Stopped there.
I was having trouble with case capacity affecting my crimp. Somebody suggested I take up the space by adding enough 1/8” card(s) over the powder to make a good crimp. I am pretty sure this may be when the problem started.
I have eliminated the following. I check powder charges. The powder and primers are both fresh. The MEC Jr drops 22.5 grains very consistently. Also, I checked the chrono by shooting some AA trap loads over it. They registered 1250 exactly.
Very clearly this load is not burning the powder correctly. I need to understand how to manage the hull capacity while getting a correct burn.
I would appreciate hearing your ideas.
BTW, I am a very experienced metallic cartridge reloader for the past 40 years. Pretty new to vintage shotshell reloading.
