Bolt carrier weights

[9mm_shooter]

Weighed on a MS-600 digital pocket scale (reliable to 0.1 gram accuracy) - all units in grams:

Bolt

FailZero m16/4 Full Auto Bolt Carrier Group (EXO) = 330.2 g complete BCG (270.3g carrier only)
LMT MRP Piston = 344.0 g complete BCG (285.2 g carrier only)
BCM = 329.2 g complete BCG (269.6 g carrier only)

[Robb Jensen]

I do have, what I think is, a Colt semi carrier with no bottom. "half circle".?? But am unsure as to maker and didn't weight it.

Colt made these in an unshrouded FP version and a shrouded FP version.

[Iraqgunz]

Been seeing a lot of this monstrosities popping up lately.

Colt made these in an unshrouded FP version and a shrouded FP version.

[Gunrunner]

Progressive Machine & Tool Titanium carrier - 5.1 ounces



Smith Enterprises Aluminum carrier - 3.85 ounces

[spdldr]

I get the impression from this thread that some folks are seeking a lighter weight bolt carrier. If so, this is contrary to good design engineering for best reliability. One reason the AK system is so reliable is that the carrier on a proportional basis is so much heavier than the bolt head. Greater mass of the carrier is very important for reliability as it increases the probability of a full bolt stroke due to higher inertia. Instead of increasing the weight of the buffer in the M4, as is now commonly done to assist in reliable function, it would be best to increase the weight of the carrier. That is neither practical nor easy, so instead as a matter of convenience the buffer weight is increased. At least the cycle is then slowed and the bolt then feeds a fresh round with greater certainty due to the heavier buffer.

[Gunrunner]

I get the impression from this thread that some folks are seeking a lighter weight bolt carrier. If so, this is contrary to good design engineering for best reliability. One reason the AK system is so reliable is that the carrier on a proportional basis is so much heavier than the bolt head. Greater mass of the carrier is very important for reliability as it increases the probability of a full bolt stroke due to higher inertia. Instead of increasing the weight of the buffer in the M4, as is now commonly done to assist in reliable function, it would be best to increase the weight of the carrier. That is neither practical nor easy, so instead as a matter of convenience the buffer weight is increased. At least the cycle is then slowed and the bolt then feeds a fresh round with greater certainty due to the heavier buffer.

I have to STRONGLY disagree! I have been running lightweight carriers for almost 40 years with no issues. Also, on the AR the carrier and buffer operate as a if they were a single integrated unit.

[tom12.7]

This is actually a much more complicated subject than most want to know. Without going into proprietary details and direct specifics, there is a balance that happens when changing total reciprocating weights, total reciprocating weight Vs actual buffering weight, chamber pressure during initial unlocking, gas port size and location for a given length, and at least 11 other variables that I can come up with when someone else who could see with the spreadsheet i'm thinking of could see much more.
Basically, going beyond the normal balance of weights for a 20" rifle gas, you reduce the band of operating range for many of the given variables. Leave the low mass systems for their specific application.

[stwings]

I get the impression from this thread that some folks are seeking a lighter weight bolt carrier. If so, this is contrary to good design engineering for best reliability. One reason the AK system is so reliable is that the carrier on a proportional basis is so much heavier than the bolt head. Greater mass of the carrier is very important for reliability as it increases the probability of a full bolt stroke due to higher inertia. Instead of increasing the weight of the buffer in the M4, as is now commonly done to assist in reliable function, it would be best to increase the weight of the carrier. That is neither practical nor easy, so instead as a matter of convenience the buffer weight is increased. At least the cycle is then slowed and the bolt then feeds a fresh round with greater certainty due to the heavier buffer.

I tend to agree with you. I know the serious three gunners run as light a BCG as they can get, but those guns are specifically tuned for such performance. For combat/field use where reliability is paramount I think what you say holds true.

[exkc135driver]

...
Instead of increasing the weight of the buffer in the M4, as is now commonly done to assist in reliable function, it would be best to increase the weight of the carrier. That is neither practical nor easy, so instead as a matter of convenience the buffer weight is increased.
...

The Tubb Carrier Weight System has been available at least since 2004. It consists of a flange that fits into the rear of the bolt carrier and two weights, one steel and one tungsten, either of which fits into the flange to increase the weight of the bolt carrier group. The rifle does have to be assembled and disassembled slightly differently, though.

[spdldr]

The Tubb Carrier Weight System has been available at least since 2004. It consists of a flange that fits into the rear of the bolt carrier and two weights, one steel and one tungsten, either of which fits into the flange to increase the weight of the bolt carrier group. The rifle does have to be assembled and disassembled slightly differently, though.

The above system works exactly the same as increasing the buffer weight, in that it is one directional only. It increases the resistance to initial movement, therefore retarding the opening of the bolt during the firing cycle. The inertia of the added weights does not increase the "pull" of the carrier on the bolt head in the event of factors resisting the rearward movement of the carrier, such as dirt or inadequate lubrication. Now if there was a cross pin holding the weights in the carrier, that would actually increase the carrier weight and corresponding inertia for both directions in the cycle.

Tom12.7 has it right in every way, as it is indeed a complicated subject. When one messes with a proven design, unforeseen consequences very often pop up and make things worse than they were in the first place.