Since you seem to want to stay with a caliber you currently load for, I would suggest the Ruger American Gen ll in either 6CM or 6.5 CM. If you go with the 6.5 CM you can get the Ranch version with a shorter barrel if that hel[ps him. Not a lot of money and great resale value if he isn't into...
I don't have any experience but check out the All Things Rimfire section under Vudoo Rifles. I believe there is a picture from Rob01 with one on his Vudoo. I currently use an NX8 and it works well for me.
I'm running a 28" barrel and only seeing 2910.
63.7 4831SC
ADG Brass
F215M
Obviously less powder than dankcincy. No pressure signs further up but accuracy seem to change. Stayed with 63.7.
I tried the rapid z 1000 with a 308 rifle. At 1000 yds it was very hard to use the bottom of the reticle. Traded it for an ATACR Mil- R reticle awhile back and still use it. Not a fan.