The C7 Assault Rifle, M16, & AR15 family (C7A1, C7A2, C7 replacment, and C7 vs M16)

[brihard]

What`s this I hear about "cook offs" ? I`ve yet to fire a C7 and have never heard of such a thing until today. So yeah, what`s a cook off?

It's something that *can* happen but very rarely does.

When you fire a rifle rapidly for a length of time, parts of it will heat up, particularly the chamber and the barrel. Because the C7 fires from a closed bolt, an unfired round will sit in the chamber indefinitely until you either fire it, or clear the weapon. If, hypothetically, your rifle has been fired to the point of being very hot, a round in the chamber could itself heat up to the point where the propellant in the round ignites and the round fires. I've only ever personally had it happen to me once that I can recall, and we had just put a ludicrous amount of ammo downrange very quickly.

 

[daftandbarmy]

It's something that *can* happen but very rarely does.

When you fire a rifle rapidly for a length of time, parts of it will heat up, particularly the chamber and the barrel. Because the C7 fires from a closed bolt, an unfired round will sit in the chamber indefinitely until you either fire it, or clear the weapon. If, hypothetically, your rifle has been fired to the point of being very hot, a round in the chamber could itself heat up to the point where the propellant in the round ignites and the round fires. I've only ever personally had it happen to me once that I can recall, and we had just put a ludicrous amount of ammo downrange very quickly.

Or. more usually, that's what the RCO will do if you screw up on the firing point somehow  ;D

 

[fraserdw]

I still got my C1 bayonet, along with my ration pack can opener, they are my most venerated relics!

 

[MeatheadMick]

A Cooked round occurs much more regularly in a machine gun vice a rifle... I have never had a round cook off in a C7, but have seen cook offs in a C9 a few times, seen a mag explode off of a C9 and had the wonderful experience of having a C6 being a run away gun as well...

 

[Snaketnk]

If you're doing Urban Ops shoots and doing mag dumps, you'll quickly see a couple of cook offs. That's why we leave our bolts to the rear between shoots.

 

[MeatheadMick]

Interesting, and good to know. I've only ever done CQB with blanks and Sim, have been fortunate enough not to experience this. Wonder how the HK416 does in this area. Seen videos of it firing 1000+ rounds and the bolt is still cool.  Would be an excellent replacement for the C7/C8, however I'm sure H&K would not want to sign over their tech to Colt Canada either

 

[KevinB]

Its not the bolt its the chamber, for the most part that causes the conductive heating of the round until it goes off.

C6 and C9's don't cook off - they are open bolt weapons, thus the round does not chamber until its firing, nor is the cartridge sitting on the face of the bolt.  The M-2 .50 could cook off - as the round was sitting in the T slot against the face of the bolt -- leading to the reason for hot barrle unload drills.

Run Away guns with the C6 and C9 are not related to weapon temp - but the bolt not going back far enough to engage the sear and the secondary sear is usually worn.

 

[Snaketnk]

Run Away guns with the C6 and C9 are not related to weapon temp - but the bolt not going back far enough to engage the sear and the secondary sear is usually worn.

Or the pistol grip falling off, with one of the most classic looks you can ever see on someone's face.

 

[KevinB]

Yeah, I guess no sear would be a minor issue too 

 

[uzi]

Interesting, and good to know. I've only ever done CQB with blanks and Sim, have been fortunate enough not to experience this. Wonder how the HK416 does in this area. Seen videos of it firing 1000+ rounds and the bolt is still cool.  Would be an excellent replacement for the C7/C8, however I'm sure H&K would not want to sign over their tech to Colt Canada either

Impossible for the price

 

[KevinB]

Lots of negatives that folks don't understand about piston op rod designs in the M16FOW...

 

[Colin Parkinson]

Was offset torque on the bolt carrier caused by the piston continuing to act on the top of the bolt carrier one of them?

 

[brihard]

Lots of negatives that folks don't understand about piston op rod designs in the M16FOW...

You've piqued my curiosity, Kevin. Care to elaborate?

 

[KevinB]

How long do you have? 
  I think the Hk416 is the best of the piston guns out there -- and its a great gun, but it like all the other piston setups in the M16FOW. 

The M16 was designed in an impingement setup -- the gasses that are vented at the gas port travel down the gas tube and when vented into the carrier the bolt acts as the piston -- the bolt is pressurized against the bolt face while the carrier starts rearward travel.  In the tappet piston systems - there is not pressurization and unlike the DI series guns there is not a slow cushioning of compressed air thru the gas tube first before the gasses -- the piston just impacts carrier and drives it rearward.

With a suppressor - the majority of the fouling comes from the gun unlocking while the barrel is still pressurized -- piston guns with the faster and more violent unlocking often exhibit this worse (believe it or not).

Piston guns are also much more ammunition sensitive thus require adjustable gas systems to cater to different ammo's or unsuppressed/suppressed firings.

 

[Retired AF Guy]

Piston guns are also much more ammunition sensitive thus require adjustable gas systems to cater to different ammo's or unsuppressed/suppressed firings.

FN C1 for example?

 

[KevinB]

One example...

 

[Dissident]

My platoon some C8A3 on order, which should apparently arrive shortly. I'm told the optics they will be paired with are C79A2. Anyone done the math on the shift in POI at the pre-set ranges on the scope dial? I could probably figure it out myself with a bit of work, but figured I'd ask first.

 

[MilEME09]

My platoon some C8A3 on order, which should apparently arrive shortly. I'm told the optics they will be paired with are C79A2. Anyone done the math on the shift in POI at the pre-set ranges on the scope dial? I could probably figure it out myself with a bit of work, but figured I'd ask first.

Any idea if they are production models or for limited testing? last I heard Colt was in prototype stages for the A3, and that the SAM project was lacking funds for all projects. That said the M203 is being shifted to reserve only with the Colt Canada Eagle being brought in for the reg force in the coming years. SAM project is also looking to purchase new C6's within the next five years to replace older ones in the system.

 

[Dissident]

Anyone got the exact sight height over bore of the C7/C79 combo? No luck with google.

 

[Loachman]

Reported in the Ottawa Citizen on 1 June 2014 - but don't anybody even think of posting a link - Colt Canada intends to market semi-automatic C7s and C8s, possibly beginning this summer. No forecast price yet.