Just as a datum - I go as high as 13.0 grains of Lil-Gun in my K-Hornet Contender, 14" barrel, 35 grain V-Max.   With a 45 grain Sierra softpoint 11.9 grains.   Best powder for accuracy that I have ever tried.  Never a flat primer or case problem.  Both calculate to less than 45K psi in Quickload.   

If the O.P. is getting problems with that 9 grain load, I'd go to a pistol primer.   Rifle primer may be forcing the case forward, the primer protrudes, then gets flattened as the main charge ignites?   Not a pressure problem at all.   If there are enlarged primer pockets, were they there before the cases were loaded?   I've found an awful lot of "once-fired" Hornet brass with enlarged pockets from the previous shooter using ultra-hot loads instead of a bigger cartridge.   

Using cast bullets, I'd pick a faster powder anyway.  Lil-Gun likes to be pressured up over 20K psi in my experience.  Did poorly in my trials in the .25-21, aiming for 1400 fps with plain base bullet.