Parker hard to open

[Mike of the Mountain]

Usually soft primers and they puncture easily or very hard primers and the firing pins hang up in them. The shells we see here a lot too especially with the cheaper shells. Seems the heads swell up in some guns and hang up in the chamber preventing the gun from opening. 99.9% of the time as soon as you switch primers or use a better quality shell the problem goes away.

[Double Lab]

It's the steel vs. brass on the head. Older ammo and quality ammo usually solve this problem.