I believe 'pt' stands for patent, as in Colt patent firearms
are you sure it's not BP for black powder ??? it means barrel bushing, the pistol is a transition between colt 1911 commercial and series 70. your pistol was probably made in 1969.
Usually caliber and/or serial numbers.
ctg = cartridge
http://remingtonsociety.com/rsa/questions/barrelcodes
Depends on what they are. Could be choke markings, proof mark, etc..
IF ITS OLDER IT MAY BE THE SERIAL # , IF ITS NOT IT MAY BE AN INVENTORY # The Serial # is 310571
While the original length is not indicated on the barrel, the barrel weight is. Example: 1Kg012 which would mean 1012 grams. An accurate scale would help you identify. If the barrel weighs less than the stamped number then the barrel has been altered.
Could be an inspection number.
what does LXG stamped on gold mean
Is it just stamped on one peice of the gun? I have a 5100 12g and each section (Stock, forestock and barrel) are stamped with a number (8WGK) to identify that they go together, kind of like a serial number.
WhAt does a pendant stamped NVC mean
Well, it depends on what you mean. The caliber is "determined" at time of production based on whatever caliber the manufacturer wants it to be. The caliber can be determined later by looking on the barrel. The caliber will almost always be stamped somewhere on the barrel.