For metal polishing I typically use sandpaper and polish by hand because I can control things very carefully. I rarely go any more coarse than 400grit. Even that would be reserved for areas that really need significant smoothing.
For inside the trigger return channel where things are really rough, you could roll up a piece of sandpaper that is a little more coarse than 400 to start with and then go up from there.
I've not found it productive to go finer than 1000 but then I don't typically use liquid/paste polish for this kind of operation and it may work a little differently.
For most of my polishing work, I use light pressure and 800-1000 grit paper.
...polish the inside of the Hammer spring...
I'm not big on polishing springs. For one thing they're usually pretty smooth to start with, for another, I'm wary of altering the surface finish of springs because I'm not confident I understand all the ins and outs of how that can affect things.
https://ac.els-cdn.com/S18777058140...t=1523703672_a5cb507c8da3727c4980cd07618ea581
Are these shims sold ready to install or do I need to make them from feeler gauges ?
I have a big collection of washers and other parts that I've collected over the years. I usually pick through it until I find something the right size and close to the right thickness. Making shims from feeler gauge material is pretty smart. I've never thought of that, or done that, but I see no reason it wouldn't work. If you don't want to go to the trouble, you can probably find something at the hardware store that will work. If you can't find something thin enough, you can always sand it down to the proper thickness.
I will confess that I don't like shims because they make the gun harder to reassemble. But sometimes they can make a big improvement.
Would that work in a lever gun ?
I think it will work in any gun--just make sure that the abrasive is non-embedding and that you can get it cleaned out of all the possible nooks and crannies it can find its way into after you've finished. I've never used that approach because I like to know exactly what I'm polishing and exactly how much I'm polishing it.
While I'm here any lube recommendations.
I like (very light) grease for revolver innards since it stays in place a little better and because revolver internals tend to be protected better than autopistol lockwork. You could always use something like Hornady One Shot that leaves a dry residue in place after the propellant/cleaner evaporates. It's supposed to be a very good lube and is very easy to use/apply.
I don't know what Geissele provides with their triggers, but as long as it's not too thick, it's probably not a bad choice.
Of course, many revolvers are lubricated with nothing other than oil and work just fine.
. The problem is that this is CA and the ten day waiting period . It gives you time for buyers remorse . If i change to the 6” this will be the third time I’ve changed my mind During a ten day waiting period . The other two I’m very happy i changed my mind . Both were the same type of firearm but I changed the brand . 