BCG technical spec question?

[Clint]

Not that I'm doubting you; do you have a schematic / engineer drawing depicting the measurements or another source? I ask only because I like to build reference libraries. Looked forever for his request and the only data I found is what appeared to be a "to scale" drawing which included no measurements. Could have set up a proportion but got lazy. Thanks.

The bore offset at the gas block is .625, as shown in the FSB drawing.

The gas tube offset bend
is .156", as shown on the rifle gas tube drawing.

.625" + .156" = .781"


This combination can also be arrived at from the bolt carrier and key, as shown in the bolt carrier group print set.

Carrier bore to flat .420"

Gas Key base to gas tube bore .361"

.420 + .361 = .781"

[lysander]

The bore offset at the gas block is .625, as shown in the FSB drawing.

The gas tube offset bend
is .156", as shown on the rifle gas tube drawing.

.625" + .156" = .781"


This combination can also be arrived at from the bolt carrier and key, as shown in the bolt carrier group print set.

Carrier bore to flat .420"

Gas Key base to gas tube bore .361"

.420 + .361 = .781"

It can also be arrived at by looking at the print for the upper receiver, DWG # 9349063, Rev E, Area E6, or DWG #8448524, Rev E, Sheet 2, Area D2.

The 0.781" dimension has, however, a +/- 0.005" tolerance on both the carrier/key combination and the receiver, so there is the possibility of a 0.010"+ interference with the gas tube and the carrier. The gas tube not being straight and/or parallel will exacerbate the interference.

But, that's why they gave the gas tube a chamfer on the end, a perfect alignment/no-interference fit may not be possible without minor tweaking of the gas tube . . .

[bamashooter]

It can also be arrived at by looking at the print for the upper receiver, DWG # 9349063, Rev E, Area E6, or DWG #8448524, Rev E, Sheet 2, Area D2.

The 0.781" dimension has, however, a +/- 0.005" tolerance on both the carrier/key combination and the receiver, so there is the possibility of a 0.010"+ interference with the gas tube and the carrier. The gas tube not being straight and/or parallel will exacerbate the interference.

But, that's why they gave the gas tube a chamfer on the end, a perfect alignment/no-interference fit may not be possible without minor tweaking of the gas tube . . .

Thanks. Is there a link to the prints in a graphics format or .pdf? Thanks.

[opngrnd]

My calipers give me .787", leaving me to believe the key is slightly higher than it should be. Combining that with a gas key hole that seems a hair "snugger" then it perhaps should be, I'll replace the key and see where I end up before adjusting the gas tube. I ordered Ned Christiansen's gas tube bender, since it's relatively cheap and looks like it'll be useful both now and in the future. Kind of enjoying the learning process.