M16 bolt carrier groups -- why?

OccasionallyOnTarget

OccasionallyOnTarget

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Another N00b question: I saw a site sponsor is selling M16 bolt carrier groups; how is this different than, say, the bolt carrier groups in an SP1 or LE6920, and why would I want the M16 version?
 
People like the M16 FA bolt carrier groups because they are heavier.

There's not that much weight difference between them, it's only like about 0.3 oz, but using the auto carrier combined with a heavy carbine buffer it really helps to slow down the cycle of a carbine and midlength gas system AR.

A heavier bolt carrier has more mass, which should give the carrier more inertia. This increased inertia is important throughout the bolt cycle; it acts to keep the bolt locked up a little longer to allow the cartridge to cool more before extraction (it will contract and extract more easily this way), and gives the bolt more energy to reliably strip and seat the next round.
 
ctcs said:
People like the M16 FA bolt carrier groups because they are heavier.

There's not that much weight difference between them, it's only like about 0.3 oz, but using the auto carrier combined with a heavy carbine buffer it really helps to slow down the cycle of a carbine and midlength gas system AR.

A heavier bolt carrier has more mass, which should give the carrier more inertia. This increased inertia is important throughout the bolt cycle; it acts to keep the bolt locked up a little longer to allow the cartridge to cool more before extraction (it will contract and extract more easily this way), and gives the bolt more energy to reliably strip and seat the next round.
Click to expand...

I'm learning everyday.
 
^Actually it's less about cartridge temperature than it is chamber pressure, the later you extract on the pressure curve, the better. If anything, you want that brass to be as hot as possible to remove as much heat from the chamber (one of the big downsides of caseless/polymer cased ammunition) as possible.

There is no real downside to having a Full Auto carrier. Having a semi-auto carrier means that by chance you head to the states, you could not throw your upper on an M16 lower and take advantage of the full auto selector. So is it a big deal to Canadians? Not for most. But there is no real reason for anyone to import/manufacture semi-auto bolt carriers in Canada.

Carrier weight: A very heavy carrier + buffer combo can reduce felt recoil (technically it doesn't reduce recoil, merely changes the impulse/force curve), but inertial mass is increased. How is this a bad thing? Well, greater reciprocating mass means you have to fight the gun more when controlling recoil force (Force = Mass x Acceleration). Check out a slow motion video of a full auto AR-15, and watch how the carrier causes the gun to actually dip forward after the actual recoil cycle. This is what people mean when they say the gun is 'bucking' in their hands. And that's why 3-Gun competitors like to use ultra-low mass carriers
 
ctcs said:
People like the M16 FA bolt carrier groups because they are heavier.

There's not that much weight difference between them, it's only like about 0.3 oz, but using the auto carrier combined with a heavy carbine buffer it really helps to slow down the cycle of a carbine and midlength gas system AR.

A heavier bolt carrier has more mass, which should give the carrier more inertia. This increased inertia is important throughout the bolt cycle; it acts to keep the bolt locked up a little longer to allow the cartridge to cool more before extraction (it will contract and extract more easily this way), and gives the bolt more energy to reliably strip and seat the next round.
Click to expand...

Good info ctcs!

I figured people wanted them so that if the laws ever changed they wouldn't have to replace their BCGs. :D
 
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