Is cylinder/barrel gap measured with hammer down or cocked?

[Anontex2]

Thanks for input, pards!

[Anontex2]

...and how do I move the barrel forward?  It's as tight as Dick's hatband!  I saw a wooden wedge mentioned on here and am trying to fashion one from a Hickory hammer handle.

[Sir Charles deMouton-Black]

Is there is a Capnball Rammer attached?  If so turn the cylinder so the ram comes down between two chambers and slowly lever it down.

If no rammer;  get a dowel, or piece of broomstick a bit longer than the barrel.  Place it beside the barrel, holding both with your left, or off side and tap the dowel against the cylinder with a mallet - carefully!  Have a soft landing ready for the frame etc as it drops away from the barrel.

[Long Johns Wolf]

Let me throw my 2 cents into the ring.
If you follow Sir Charles's "ram method" You may want to consider putting a piece of wood or similar between the rammer and the cylinder. Otherwise you might end up with a nasty mark on the face of the cylinder.
If I have a pistol where the barrel really sticks to the frame and where the afore mentioned method does not work I try something else before moving to Sir Charles's 2nd suggestion: hammering the area where the barrel meets the frame with my hammer with the plastic or wooden head. It takes some time but eventually the lets go of the frame. Of course being right handed, I hold the pistol by the barrel, muzzle pointing to the ceiling.
Long Johns Wolf

[Coffinmaker]

Barrel to cylinder gap should be measured with the hammer back.  The gap should be measured with an automotive type feeler gage and the correct gap is about .008, +/- .001
It sounds like you have added new barrels.  Barrels MUST be fit to the individual gun.  Each barrel requires it's own wedge.  Each barrel should be numbered to the specific gun is is fit to.  No two guns are exactly alike.
There is no bushing between the cylinder and barrel boss on an 1851 so the cylinder "floats" and will move forward with the pressure from the hand as the gun is cocked.  It should not move forward more than a couple of thousands and firing moves it back.
Adjusting the barrel cylinder gap is not done with the wedge.  The wedge is intended to fit thru the barrel until the spring catch clips on the far side of the barrel.  If the gap is too tight, metal is removed from the breach of the barrel with a facing tool, or if your real brave, a sharp bastard file and a steady hand.  The breach must be as square as posable.  After establishing the gap, polish the breach of the barrel and you may need to re-cut the forcing cone.

Coffinmaker