4, 5 (usually a cut down factory 6 in), 6, 8 3/8 inches.
Model 686 (plus/seven shot). Covers several barrel lengths. Should be visible on the inside of the yoke.
Try e-gunparts.com
Dan Wesson is now operated by CZ USA. Barrel nuts are available for about $15 plus shipping. See the link at the bottom of this page to link to the CZ parts page for Dan Wesson Revolvers:
There are no available records to date a Dan Wesson by serial number. Value depends on the model you have. Watch Gunbroker.com .
The available trimmer lengths for this model are 1mm, 3mm, and 5mm.
The Remington Model 10 slide action has barrel lengths of 26" 28" 30" and 32"
@ 4"
I would start my search at Smith and Wesson first.
22LR
Yes.
4.5 or 6 inches
You will need to ask a gunsmith