I bought an HRA today that I am just thrilled with.  It has a serial number of 56364XX and a barrel that dates 4-55.  The finish is all original and it still has cosmoline everywhere.  The stock leaves something to be desired but I think that with a little TLC and it will be fine. The barrel inside is excellent...the rifling is bright and there is no evidence of pitting at all.   I do not have any gauges to check muzzle wear. All of the parts are HRA with the possibility of one that isn't and I need to figure that out.

The gas cylinder has very worn finish and the gas plug has a "P" and a hex on it.  I know from my research on Battlerifle.com that the gas plug is not correct. The front sight post has the excellent finish like the barrel and receiver but the gas cylinder finish is about as worn as my other two S/A's.

The forward handguard is also suspect.  The metal on the front is in pretty poor condition..dinged up.  The wood on this part has also been repaired at some point in its life.  All of the rest of the stock metal is like new condition.

I suspect that somebody at the gun dealer or before him had another rifle that needed some parts and swapped them out.

The first question is there a way to determine if this is the original and/or correct date on the barrel for this receiver?

The second question is that I replace the gas cylinder with another, what am I looking for in its replacement to make it era correct?  Or is there a way to figure out if this is actually the correct gas cylinder and somebody just swapped the gas plug?  

I have two CMP rifles and the plan if to acquire some more but this was just too good a deal to pass on.