With an old daisy Milbro 250. You mean the breach is too tight, right? Can't seat the pellets all the way flush, then they get pinched when you close the action? Well, I have that problem. Mine is a .22. The best-fitting pellets are Beeman Silver Aces. I have yet to try the JSB 5.51, but they might work good, too. I like the gun enough that I might dare to work the breach with some bore past or lapping compound.
Good luck,
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Dan (in NY)
I assume you are referring to the gun's dinging the skirt when the action is closed, though it's a bit hard to tell from your post.
Try either using a seating tool to push the skirt past the breech face, or finding another brand of pellets with a smaller skirt diameter so that you can fully seat them with your thumb.
What I've done is to purchase a small tappered reamer. Insert it into the breach end of the barrel. Give a few turns without much pressure and remove it to check how deep your pellets now seat. Continue untill you are satisfied. Now take a small tappered fine stone on a dremel tool at low speed and polish the area where the metal was removed. A drop of fine oil might help here. No more deformed pellets and easier to load. RWS did this on one of my guns years ago to improve accuracy and I have had good luck doing it ever since.
Good luck!
Chris