My 35 Rem contender has never misfired and it has been fed only Federal primers. I think the "head space problem" in the Contender is way over rated. It gets blamed for a lot of things it has nothing to do with.
WRONG! At least on the rimless rounds it is the main reason for misfires. The shell goes too far forward, the firing pin can't reach the primer, or it doesn't hit hard enough to fire it. This has everything to do with how the shell was sized. If the shoulder is pushed back too far, the shell can go into the chamber too far.
The reverse is true if the shoulder is too far forward, this prevents the shell from entering the chamber far enough
, the barrel does not lock up completely preventing the hammer from falling all the way.
Rimmed cartridges headspace on the rim so they can't go too far into the chamber. BUT if the shoulder is not pushed back far enough, it CAN prevent the rim from contacting the chamber in front of the rim, causing incomplete lock-up of the barrel lugs, causing the hammer to not fall completely; light hammer strike on the primer.
I had a 35 remingtom contender barrel, I used for IMHSA shooting. I never had one misfire, and never had case head separations. It was quite accurate as well. It's one I'm sorry I ever sold!