C3A1 did not have iron sights and was a scoped gun. However, the National Defense manual clearly shows 2 drilled and tapped holes at the muzzle the end of the barrel althought there are plug screws in place.
If you have an original C3A1 barrel it should be marked "12" for the twist rate. I have not seen any D&T'd C3A1 barrels....doesn't mean that there's not a few out there.
Ron
What you refer to as the National Defense Manual is actually called a CFTO:
Canadian Forces Technical Order
The C3A1 CFTO is: C-71-234-000/MA-000 - this is the first book
MA - Data summary
MB - Operating instructions
MD - Equipment description
MM - 1st line maintenance instructions
MN - 2nd/3rd line maintenance instructions
MX - Illistrated repair parts manual and scale
MY - Parts identification list
The C3A1 barrels never ever had front sight bracket holes drilled. The rifle was never ever designed with iron sights in mind - period! If you have a barrel with the holes, you have a C3 barrel. The above tech drawing is a mishmash of several diagrams. That is an M87 stock, iron sight C3 style barrel and a Canadian C3A1 action body.
I'll have to scan my C3A1 parts diagrams to give you the true parts look. I don't have a scanner so it might be a while. Maybe I can snap a picture of the page. It doesn't have the screw holes you refer to. Maybe you're looking at a C3 CFTO, which did have the bracket holes.
Also, here's a tidbit of info probably most people won't know unless they were a tech - there were 2 lengths of barrel available - 24 & 26" as well as 3 twist rates 1:10, 1:12, 1:14. This all depended on what nato stock # you used to order.
Don't ask me why it was like this - only the LCMM(Life cycle material manager) can answer that. Most techs I knew were not shooters or collector's either. I happen to be one of the exceptions within the trade.
The overall weight of the rifle with the scope was: 15.875 lbs - say 16 pounds for ease of remembering. The rifles weight is on par with what the M40A3 weighs(17 lbs).
I don't want to sound rude or come off as condesending, so please take this with the spirit with which it is intended


- but if you've never worked with this rifle and only have used a book to give an educated guess - please don't offer advice, because you'll only confuse people searching for the correct answers. I'm not the end all answerer to this rifle, I just happen to know what I know from years of using and maintaining this rifle!
All the best, Carl