On the AR15.com forums there is some discussion about the Canadian version of the M16 family of weapons. A poster by the name of RebelRouser posted this info in a thread about the C7 rifle.
I apologize for not answering sooner. I‘m afraid I have been avoiding the alligators chewing on my ankles to take care of the ones feeding higher up.
To answer your questions as presented:
The effective range published does not have much to do with the barrel but is an infantry doctrine distance to do with the whole system including the man, sights, weapon ammunition and expected employment. So when you see effective range, it is almost always a subjective assessment of the system capability derived by the user instructor (CTC) and rifle requirements office (DLR), usually before the weapon is even bought. In the case of the C7 it included iron sights and was extended (I think) when the C79 sight and the C7A1 came along. The reference to the rifles origins (M16A1E1) is in reference to the sight option first chosen by the CF. The heavy front profile, 1 turn in 7inch barrel is definitely M16A2. As is the cartridge deflector, handguards and many other changes.
Now lets talk barrels:
The C7 barrel is not the same as any M16 barrel except for the exterior profile which is M16A2. The Material is to a formula developed here in Diemaco (under Gov‘t contract) so that the entire bore and chamber configuration can be integrally formed in one operation on a rotary hammer forge. This process produces a barrel that is much stronger than the US M16A2 barrel. The bore dimensions were developed to fire C77 ammunition, (Chamber, bullet lead, diameters) the bore has dimensional reduction as the bullet moves forward (squeeze) to increase life and accuracy. The bore is plated with harder chrome than the M16. This allows greater wear life (2 to 3 times M16) and lets us machine C9 barrels from the same barrel blank. The SFW was recently tested and purchased by the UK special forces and won in competition against the Swiss SIG series rifles and the H&K G36 rifle. This barrel is now in use by the Special Forces in five countries and the US Navy Seals have expressed interest in putting them in the M4 Carbines that they have.
We have just completed a C8 Carbine upgrade program for Canada which is a new barrel with an improved chamber and stronger extractor spring assembly and a weaker ejector spring. These are the same internal configuration as our very successful SFW barrel.
The C7 rifle and C8 Carbine is made under license with a Tech Data Package provided by Colt to the Canadian Gov‘t. Diemaco reviewed the design and made about 150 changes to the drawing package before Canadian production. These are to numerous to mention her but include things like materials and processes as well as a different barrel configuration and manufacturing processes.
The improved handguard we designed here after CWO John Ginn kept beating the Colt version off the weapon on the parade square. You probably can‘t tell from the outside but if the you take the handguard off, you will notice two types. The improved version has two large ribs under the heat shield and three interlocking ribs on either edge as well as different material. These were introduced late in the program so they had to be interchangable and be a good match with the old handguard.
Another change you may notice is the small diameter front sight post that we developed when soldiers complained that the US large square one actually obscured the target at ranges of 300 and greater.
I hope this helps you with the discussion and thank you for your interest in the C7.
Product Engineering Dept.
Diemaco a division of Heroux- Devtek
Please note: Any opinions expressed or implied in this email are personal are not necessarily those of Heroux Devtek or Diemaco