[Slowpoke Rodriguez]

This is an older style crimp die for Pacific shotshell reloaders.

It has no spring between the die body and threaded section that screws into the die head of the reloader.
The newer ones are spring loaded so the crimp plunger is a bit independent of the die body.

Is this what you are describing?

 

[Tom in Pittsburgh]

It would be helpful to see a photo from the OP.

Thanks.

 

[poacherjoe]

Here it is

 

[Tom in Pittsburgh]

Thanks for the photo. I’m afraid I can’t help - have never run across one of those.

 

[Nebs]

Judging from the printing on the top of the instructions, it goes to a model 350.

 

[Slowpoke Rodriguez]

In the photo above of the instruction sheet, obscured by the pre-crimper itself, I think I see the words "used on all current model shotshell reloaders, and judging by the part number #250-A-61 it would be applicable to 150, 250 or 350.
But I can't see how it would assemble to the die head.
See the part numbers on the attached pages from the DL-250 and DL-350 Manual.
Edit: Ebay photos of a Bair 600 (Pacific 350) show a very similar pre-crimp.
See image below.