Brass Rail Tension

[Joey Recker]

How do I check the tension for center pins in a brass rail?

I'm working on a 1907 M. Schulz upright.  It has a brass rail.  Most of
the hammers are sluggish.  No sign of vertigris etc...  

I've started re-pinning the hammer butts (had to rebush a few that have
come apart during the process). I'm familiar with checking the tension
on items with wood flanges.  But on the brass rail I'm having to install
the hammer, check the tension, re-pin, re-bush, ream or burnish,
re-install, try again, etc...   After many tries, many of them just
don't seem to be getting any better.  Any tricks of the trade?

I'm having a hard time with this one.  (But, like daddy said,  "If it
was easy, everyone would do it!").

Any suggestions?

Joey Recker