Ammo Manufacturers do not use canister powders like we use, however they are many times very similar
Like 100% similar except in kegs or caddies instead of pound cans.
Think, if the powder mill turns out a production lot - in Phil Sharpe's day it was a carload lot, 50000 - 60000 lbs - that is dead nuts on spec for Acme 39/95 and they only have orders for 20000 one pound cans for retail, they will surely sell the rest to an OEM as "bulk powder."
The caution is, you can't KNOW that to be able use the same charge of store-bought as what is in factory, not that there was any INTENTIONAL difference or agreement between bulk and canister that week.
Trivia Alert:
On the other hand, when Vihtavuori powder first hit the US market, it was said that they made 33 powders of which only 13 were canistered for the hand loading market. Frex, it was a while before they would sell N330 by the pound, it having been their wholesale powder for 9mm OEM.
An early Handloaders Digest had a piece that said Hercules made nine different grades of Red Dot shotshell powder; listed Red Dot 10, 20, 30, 40, 50, 60, 70, 80, and 90. What you got at the store was Red Dot 30, the other grades wholesaled by spec to OEM.
Hodgdon got their start selling surplus powders like 4895 originally made for military ammo by DuPont.
I wonder if they only sold one of those carload lots, or if they back blended lots for consistency, or if they got lucky and had matching lots. Whatever the case, when they ran out of surplus, they started having something they called H4895 made by foreign contractors. Close enough.
Not all was so close, I read of one well known lot of surplus 4895 from another source, maybe DCM, that was "almost as fast as 3031."
Jac Weller wrote of loading to military match specifications, using surplus 173 gr bullets and
his lot of 4895.
For a while surplus 4831 was sold as "4350 Data Powder." Being slower burning than 4350, any 4350 charge weight would be safe with 4831. Only later did Hodgdon test and publish specific loads. I don't know of anybody who uses Jack O'Conner's load in .270 any more.
Their second lot of Winchester Ball powder was enough different from the first that they labeled it Ball C 2, later Bl C2 after Winchester got ugly about their trademark.
Of small brands, a gunzine writer with Connections once got samples of all calibers from Corbon and tested them for pressure and velocity. All but one were right at the top of SAAMI pressure and at or near the claimed velocity. The .38 Special +P+ was considerably overloaded.