I was thinking (yes I know dangerous) I have rifle with a 411 bore. I have purchased some 410 cal bulets for it. So all other things equal. Less friction yield higher speeds or blow by reduced speeds. Thoughts? Experiences?

Presuming you are talking jacketed bullets, it will make little to no difference. Unless it is a mouse fart load, the bullet will be 411 when it comes out of the barrel and probably already was a few micro seconds after entering the barrel. Even solid shank bullets will bump up some. If you're talking cast, you screwed up. Where did you get the 411 barrel?

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If you're talking cast, you screwed up. Where did you get the 411 barrel?

Nope jacketed. The barrel is a douglas purchased and short chambered using my reamer by IDT

You might want to slug the barrel. If you order a 411 barrel from Douglas, they will send you a barrel but I can prety much guarantee that it slugs .4100 +or- .0001. I've slugged about a dozen of them.

Jacketed lead core bullets will obturate to seal the bore even if they are a few thousands small. Although accuracy may suffer a little, as the bullet may enter the bore out of alignment.

.450" bullets through my 45colt (.452" grove Dia) revolver and velocity was comprable to a .452" bullet of the same weight. Only problem was accuracy went down. Not by much, but enough to want to go back to .451-.452 bullets.