I'm no expert on inlines, but have learned a few things -- I think. If your rifle is hard to close with primer in place, "headspace" is too tight, so try tightenening either the firing pin bushing or the breech plug just slightly. Or try a slightly shorter primer. More blowby will of course occur with more powder charge, but the primers themselves do vary. Get a cheap digital caliper at Harbor Freight or elsewhere and measure both length and diameter of your primers.
Here's what I found by measuring the 209s I had on hand, Length and Diameter:
W209 (Winchester) .298-.303" L .242 D.
Rem Premier 209 .295 L .240 D.
Win Triple7 .304 L .242.5 D.
CCI inline ML .302.5 L +- .240.5 D.
So I measured all my selected Blackhorn 209-suitable primers (Win.), and chose the ones best suited to my primer pocket length and diameter. I needed the .303" L and .242 D. ones for best fit. The best fit does reduce fouling around and behind the primer, it seems to me. Try it.
Aloha, Ka'imiloa