need help with barrel choke project

I have some 7 barrels I need reamed and tapped for chokes. less expensive to get the tooling and access to lathe however it turns out the lathe has a .010 wobble in the chuck while I have access to other lathes not all of them have the distance between centers and I havent checked them all for wobble in the chuck.

using manson tru choke reamer and tap. not sure how to go about this.
got a floating reamer holder but the reamer doesnt fit.

piloted reamer and tap

2 barrels are ribbed though dont doubt I could get the ribbing between the chuck jaws.

manson recommends making a plug for chamber end putting that in a chuck then making a clamp to hold in your left hand while the reamer is put in a collet. recommended speed 55rpm.
unfortunately dont have access to palmgren which seems to make the job easier.

appreciate any idea's or help

One thing you might consider is chucking a piece of scrap and making a pot chuck to hold the barrel. The bored hole will be on center even if the scrap is not.