9X21 brass

[dwtt]

I accidently picked up some 9X21 brass along with my 9 X19 brass at the last match. I don't have any information about this cartridge in my Lyman manual, so I'm asking the experts here. Can I trim down 9X21 brass to 9X19 to work safely? Are the case heads the same or equivalent to 9x19?
thanks.

[NotEnufGarage]

If the headstamp says 9x21, I wouldn't trim it. It would be confusing.

Accumulate it and sell it. It's probably not something that's easy to come by cheaply.

[ireload]

Since you said the last match, I would err on the safe side and just leave it as it. Maybe just give it someone who uses that caliber
.

[noylj]

It is the same. If you don't have a 9x21, it could be of more value to sell the cases--probably back to the original shooter.
9x21 has two loading styles:
1) For places where civilians can't own military calibers, the desire for 9x19 is met by loading 9x21 with the same charge and same COL as 9x19.
2) For places where major PF is desired/needed and the person does not consider 9x19, loaded hotter than proof loads to make major, as within their comfort zone (i.e., they have a stronger desire to save their guns and limbs then to save money on the cost of cases).
I have two 9x21s and they are both excellent guns. However, having to sort out the 9x21 from the 9x19 really focuses my case sorting and inspection time.
These cases could also become your primary match cases if you trim them to 0.750-0.753".
I try to save all my 9x19 cases, that are actually 0.750" or longer after sizing, for my target loads (what few I have) as they minimize head space and will almost always shoot more accurately. I obviously can not trim down 9x21 case as they are needed for guns I have on hand...

[dwtt]

Thanks for the response guys. Since I don't have many cases, ~40, it's not worth the effort to trim them down and I'll likely give them to someone. I suspect these might have been from someone shooting major in 9mm, in open.