Primer seating problem

Well just for a sanity check, you are using small pistol primers right? Are these once fired, or new brass? If once fired, I suppose its possible they're crimped primers, if they were police issue maybe... 40S&W is not a military issue cartridge, but I suppose there my be a department or departments that specifically requested crimped primers, in any event, you may have to ream the primer pockets. Could go as low tech as a hand reamer Lyman Reloading Primer Pocket Reamer (Small) https://www.amazon.com/dp/B000NOOQY4/ref=cm_sw_r_apan_glt_fabc_Y5S8VES4VECG5EBJN5FQ
Or the whole hog with a full on brass prep center.
Lyman Case Prep Xpress 115V 7810220, Gray https://www.amazon.com/dp/B004TABTWU/ref=cm_sw_r_apan_glt_fabc_14NTHGH1WNX2VMN3YNJB

Swage those pockets if the primer is correct. I just bought a RCBS combo unit for that purpose.

Many other options too.

What’s the headspace? Is it S&B? They’re pretty snug.

If you know you have the correct primers and they are hard to seat, swage or ream the pockets.

If they are not starting then you may have a crimp???? The best option is to give a very slight champfer to the pocket. A tight pocket is good, a pocket that will not accept primers or deformes them needs correction.

https://www.midsouthshooterssupply..../primer-pocket-prep/crimp-removal-and-reamers
Something like these will fix you up without breaking the bank. If you have thousands to do then you may want to get something faster.
Just google Primer pocket swage or go to you tube videos and search for it . You'll find the one that will work the best for you.