1-10 will do it but I would go 1-9 or 1-8 in case I wanted to try some of the longer bullets like the Hammers they suggest a 1-8" twist. There are probably some other longer heavier bullets too. I don't think the light bullets would melt down at a 1-8 twist but you might want to check with the manufacturer about this first.
I've got a 1-8 twist mullerworks barrel on a 20 practical and it'll spin 39 gr sierra blitzkings apart. The 40 gr. Hornady Vmax won't come apart so that's what I use in it. Lesson learned and I wouldn't do an 8 twist again unless I intended to shoot real heavies in a 20 cal. I've got another 20 practical with an 1-11 twist that shoots the 39 gr Sierras great.
For a 32-35 gr bullet a 12 or 11 twist would work fine. I'd probably prefer an 11 twist because of the ability to shoot the 39 and 40 gr. bullets. In my opinion the 39-40 gr bullets are where it's at in the 20 cals, I don't really see much use for lighter bullets. The 39-40's have good B.C.'s and can be shot at 37-3800 in a 204 ruger, 20 practical or 20 tactical. It pretty much mimics a 22-250 trajectory shooting 55 grainers with a lot less blast and recoil. The 32-35 gr. bullets can be launched at the speed of heat but have poor B.C.'s and won't really reach out where I want them on the prairie dog field.
Truth be told I think a 1-10 twist would be about optimum for the fast 20 cals but for some reason hardly anyone makes 10 twist barrels. I wish one of the good makers would start.
