Breech crowning?

[riarcher]

Same as muzzle crowning (screw and abrasive / self centering)?
I'm a little amist with this.
Noticed the groupings were not as expected and after running through some tightenings, did some experimenting.
Using my trusty new pellet seater, found it to be detrimental to grouping using it the way I think it's intended.
However, By inserting the pellet in breech, then with moderate presure seating the skirt with the ball end while in the breech my groups tightened by a good 50%! Reduced by 1/2 the size! (at minimum) Also reduced the amount of noted fliers considerably too.
I'm assuming I have a skirt / breech seal problem?

Something else I'm finding rather confusing,,
I'd expect the heavier pellets to hit lower at 20 yds. than the lighter ones?
Sighted in for 8.5 Exacts (predators are hitting same POA),, my 10.5 gr. Premiers are hitting consistantly 3+" higher. But like a shotgunner's pattern.
I really don't know what to make of that. I'm guessing I'm running around 900 fps w/ Exacts in a 17.5 long barrel.

Any of this "normal"?

[3n00n]

Ballistic coefficient could play a small part, but with springers,there are several dynamics at work that can alter group size and placement. Piston recoil during the shot cycle can move the action enough to change groups, which is why a smooth tunedaction usinga consistant hold is so important.

[riarcher]

I'll bet you're exactly right!
My hold is near no hold at all. Open fore,  light trigger w/ little to no grip, easy in the shoulder.
It bucks. Staying in the barrel longer could be (probably) makeing it look to be shooting with less drop with the bucking.
At first I thought I may have been getting a better seal (more fps) with the heavier pellets because of stiffer skirts 9more initial resistance) or something. As you can tell, I'm trying to relate it to a powder gun. Knowing I shouldn't, but it's all I have to go on.

What do you think about the skirt sealing at the breech?
Should I try and true it up a bit? or just continue with the ball seating practice?
All is new to me. concerned about making a livable situation worst. If someone can screw something simple up, it's me.  :0