I had a 41 a while back, and it seemed as only CCI Std Vel would function 100% (tried the Wolf spring kit and all). Wasn't as accurate as I hoped with it, either. Ended up selling it.
Another one came up at my club recently, for a great price, so I picked it up. Accuracy is much better, as is functioning. So far I've tried CCI Std Vel, Federal Gold Medal 711B, and Wolf Match. Benched at 50ft, CCI held well within a dime, all shots touching. Federal a little better, and Wolf, a single hole with enough distortion to let you know it was a couple shots. Very impressed, as it was better than my Euro guns shot with these brands (I don't even tease myself with the Eley Tenex, etc... Maybe when shooting give s me a paycheck!
). All functioned 100% with the exception of 2 cases bouncing off the topstrap and jamming the next shot. Don't think that was ammo-related, though - as CCI was one of them.
Anyhow... CCI Std Vel is the recommended ammo for this gun, should always work. I'd stay away from high-vel, unless you change out to an appropriate recoil spring. No use beating the gun up.
Aguila was a no-go in my last 41, and I think anything subsonic wouldn't cycle it. Maybe give the Aguila Rifle Match a try, though. Higher velocity, and has been very accurate in past guns. I'll probably be trying some in the future.