The bore slugs at .375 after passing through the threaded area of the bore. The cylinder slugs at .368. Do I need to ream the cylinder or just wait till I see what it shoots like?
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I find it difficult to believe the cylinder chamber is .007 SMALLER than barrel bore diameter (land to land).
The ball would be like a bowling ball down a gutter.
No matter how BIG a ball you pressed into the cylinder chamber it is still only going to be .368 when it leaves (using your dimension).
Land to land in the bore should be about .360 (thus 36 caliber) and the groove to groove (presuming 2 grooves are exactly 180 degrees opposite) would be .370 to .372 on average. Again using your figure of .368 chamber diameter.
The properly machined forcing cone will "roll" back the excess diameter of the ball as it enters the barrel, creating a small ring. It is this ring that then fills in the gap of the grooves.
The older pietta 44's only had 5 lands and grooves.
Thus two grooves were never exactly 180 d apart.
Thus in measuring the barrel bore you took the land to land diameter, added in the depth of ONE groove.
The new 44's now have 6 grooves, so it is possible they could have two exactly 180 d apart.
But looking at them, you can see they are definitely shallower than the old.
I don't know if they also went to 6 land and groove on the .36 cal.
You need a spherical tipped bore gauge or a split ball gauge to properly measure your chamber and land to land bore diameter.
Measure in a couple different areas of the chamber to confirm uniformity.