Last time I took my R9 out to the range, I had about 4-5 double-feeds out of maybe 75 shots. I'm wondering what could be causing this. FWIW, I changed the recoil spring relatively recently... it had probably had 50 rounds through it before this last range session, with no issues.
I will say that it was with Remington UMC ammo, so that could conceivably be the problem. I only had one mag full of Gold Dot, and it went through the gun just fine. 7 shots isn't really enough of a data point to make me comfortable though.
I'm used to getting the occasional malfunction using cheap ammo, and I'm alright with that (as long as it performs flawlessly with my carry ammo). But these double-feeds are kind of a concern... they are real a bitch to clear, especially with the R9's mag release being where it is. If one of those comes up in an emergency situation, you might as well just throw your gun at the bad guy.