Gauging AR BCG's

[lostchild]

Very cool.
I’d love 30 minutes alone in his gauge room.

Well, there's a kink I haven't heard before.
Care to elaborate ? (keep it R rated or less, please)

 

[cmshoot]

Well, there's a kink I haven't heard before.
Care to elaborate ? (keep it R rated or less, please)

Chad Albrecht of SOTAR has gauges for pretty much every part and parcel of the M16/M4/AR15.

 

[cmshoot]

Spreadsheet updated in original post.

Up to 116 BCG’s.

Tall Pine it’s now alphabetized, thanks to some help from a friend.

 

[Tall Pine]

Looks great. You can visually see patterns. Example is the Anderson bcg

 

[greg vess]

I've had the full set of SOTAR gauges for gauging AR BCG's for a while now. I've been gauging BCG's that I come across, and recording the results in a spreadsheet for my own personal knowledge.

I gauge every BCG that we sell before it leaves the shop.

On the cutaway, color-coded BCG below, here's what the colors mean:
- purple: gas key
- orange: gas key screws
- yellow: path of the gas as it flows from the gas tube into the gas key, through the gas key, and down into the bolt carrier
- green: bolt carrier
- red: Primary Bore, the first part of the carrier bore that the bolt enters
- white: Secondary Bore, the second part of the carrier bore that the bolt enters, this is the section where the gas rings compress and seal
- blue: Tertiary Bore, the third part of the carrier bore, where the tail of the bolt goes through

On the chart below, Green is good to go. Yellow is inefficient on handling gas. Red is worse than Yellow, and I consider it to be a failure of that part in handling gas.

The Primary and Secondary bores have 2 Green gauges, and 2 Yellow. G1 is tighter than G2. Y1 is tighter than Y2. So, Y2 is more inefficient than Y1.

The Secondary bores have 2 Red gauges, so R2 is worse than R1.

"Bolt Tail" is measuring the OD of the bolt tail.

"Gas Key Bore" is measuring the ID of the gas key where the gas tube enters, shown as yellow on the cutaway.

"Key Align" is measuring whether or not the gas key is centered and aligned with the hole in the receiver where the gas tube passes through.

"Extractor" is measuring the extractor groove.

I've gauged 96 so far. I consider that to be a small sample size, but I've noticed some trends.

All FailZero BCG's that I've gauged, whether they're new or used, nitride or NiB, have had multiple inefficiencies, if not downright failures.

Microbest and AO Precision have been the most consistently well-gauged BCG’s.

All NiB BCG's I have gauged have shown inefficiencies, if not failures.

All nitride BCG's I have gauged, except for the single one I gauged from an HM Defense rifle, have showed inefficiencies and/or failures.

I offer BCG gauging as a service here at TruPrep for $25. Only takes me a few minutes. I need your BCG to be at least moderately clean when you bring it in. If I have to clean the pertinent parts of the BCG first, it'll cost ya extra.

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So how many BCG's have you come across that are actually just screwed beyond help?

 

[greg vess]

So I guess in the future all builds will demand a Microsbest BCG.

 

[Asbestos]

I can barely do a spreadsheet. I’m an Armorer, not an accountant.

All that post needs is a “Dammit Jim…”

 

[Tall Pine]

So I guess in the future all builds will demand a Microsbest BCG.

Many many folks do consider them to have the best BCG around....phosphate and chrome lined version that is. Some say they were the oem supplier to Colt back when the Colt BCG (and the 6920 rifle) was the mil-spec gold standard.

 

[cmshoot]

Many many folks do consider them to have the best BCG around....phosphate and chrome lined version that is. Some say they were the oem supplier to Colt back when the Colt BCG (and the 6920 rifle) was the mil-spec gold standard.

Microbest is still the OEM contractor for companies like BCM, SOLGW, and Centurion Arms.

 

[cmshoot]

So how many BCG's have you come across that are actually just screwed beyond help?

Anything with red gauged areas in anything except the gas key (install a new gas key) or the extractor groove (install a new extractor) can't be repaired.

If the bolt tail is undersized and in the red or yellow, you can replace the bolt, but that is getting into a more costly "repair", as the bolt costs more than the carrier.