In general, it would not be a wise practice.
I can understand the desire , but, biting the bullet and ordering out BP is a wiser course of action,
Or, actually using published recipes for sub cartridge use.
If you were stuck in 1944 Warsaw ghetto, it would be considered an acceptable expediant, but then so was cooking your own chemicals to make primers and expediant powders and risking the almost inevetible kaboom.
Let us count the "downsides"
- rattling around
- considerable airspace
- inconsistent loading
- inconsistent compression
- the fact that most if not all pellets have an "igniter" side that facilitates being set off by normal primers.
And the fact that pyro pellets, specifically, are a modified BP recipe, so BP rules should be followed
Ad it all up, and I would say
Don't do it.
Loose pyro is an acceptable cartridge powder, with adequate cleaning
Loose APP is better
Loose Triple 7 is better... Still corrosive, more energetic, but not quite as corrosive as pyro.
I myself would not load any of the above in a bottleneck case for reasons too numerous and esoteric to list here.
Bear in mind, YMMV, and others may have "done it" with impunity... Until s?!$t happens.
It is worthwhile to note, I have been personally pursuing the mystical realm of short shotshells.
Specifically 2" and 1.75" roll crimp shotshells.
Specifically in order to shoot g-grandpas old shotgun safely. Thus li am seeking pressures on the order of
8000 cup or less.
Whilst I know I can make a square load of black, I am investigating the duplication of early slow smokeless and semismokeless loads, finding slow shotgun powders that have a pleasant elongated pressure curve.
I am also resigning myself to the inevitable need to buy a pressure transducer system.
In this pursuit, I have engaged professionals in the shotgunning field, to my great advantage.
They actually have a service that you can send shotshells in for pressure testing for a small fee.
$25 for a couple hsells plus hazmat is a small price to save your face.
They have all to a man recommended ignoring the u-tubers who are merrily disassembling store
Bought shells, cutting them down, CUTTING THE PLASTIC WADS, and reassembling. All these guys are
Finding they have extraction problems which is THE ONLY SIGN OF SHOTSHELL OVERPRESSURE you will get before a serious incident. What the u-tubers have done is
- modify case volume (reduce significantly)
-modify components ( to wit, the combination powder seal/compression wad/shotcups )
- kept powder and load weight the same.
This would be similar to taking a .45 Colt, using the same 9.5 great of unique, cutting the case down to .45 ACP length, and loading a 255 gr jacketed bullet.
Recipe for kaboom.
Thus myoverly verbose point :
Follow the recipe.
If there is no recipe, buy a chrony, pressure barrel, pressure transducer, and good insurance.
Last ... If the company does not publish a recipe... I personally do not trust the "next available talking head" that answers the phone... They publish recipes for a reason.
Yhs
Prof "no accidents in 937 days" Marvel