"A" Preventative Maintenance Program

[Hawkeye]

Diz, You have twisted my arm! my next barrel will be a mid-length. Possibly a RRA unless someone can suggest a better choice.

Lots of better barrels out there.

RRA's are ok, but I'd go with a Sabre or CMMG first. Denny's Operator barrel is another excellent choice.

[toddackerman]

With regards to preventative maintenance, i wanted to make this report.

I have an LMT MRP with about 6400 rounds on the barrel, and 4,000 rounds on the bolt that is in the gun. i also have a back up bolt.

I finally got around to getting a "No-GO" and Field Gauge" to check the wear and subsequent head space of the MRP. Note that I always lube the bolt and barrel lugs with Mad Dog Labs XF-7 Grease to minimize wear.

The result s were that the bolt closed on the "No -Go Gauge" and not o the "Field Gauge". Not even close. I'm aware that the No-Go is primarily for new barrels that are being reamed, but was a little surprised that the bolt closed. Doesn't;t matter.

I will be checking this situation with the Field Gauge every 500 rounds until she closes on that gauge and will report when it does.

Tack

[AR15barrels]

I finally got around to getting a "No-GO" and Field Gauge" to check the wear and subsequent head space of the MRP. Note that I always lube the bolt and barrel lugs with Mad Dog Labs XF-7 Grease to minimize wear.

The result s were that the bolt closed on the "No -Go Gauge" and not o the "Field Gauge". Not even close. I'm aware that the No-Go is primarily for new barrels that are being reamed, but was a little surprised that the bolt closed. Doesn't;t matter.

What's the dimension marked on the "no-go" gauge?

If it's a commercial spec gauge, many 5.56 barrels will close on that "no-go" gauge when they are brand new.
If you look at my Headspace Gauge Info sheet, the actual dimensions on the side of the gauge would be more meaningful than the "no-go" markings.

[toddackerman]

What's the dimension marked on the "no-go" gauge?

If it's a commercial spec gauge, many 5.56 barrels will close on that "no-go" gauge when they are brand new.
If you look at my Headspace Gauge Info sheet, the actual dimensions on the side of the gauge would be more meaningful than the "no-go" markings.

1.4666" Definitely a little ahorter than the No -Go Gauges on your chart. Explains why it would close on it.

Just to make sure...you are 100% confident that if I use the Military Field Gauge from Brownells you recommended (and I bought) that I am GTG until the bolt closes on that Field Gauge???

[AR15barrels]

1.4666" Definitely a little ahorter than the No -Go Gauges on your chart. Explains why it would close on it.

Just to make sure...you are 100% confident that if I use the Military Field Gauge from Brownells you recommended (and I bought) that I am GTG until the bolt closes on that Field Gauge???

You are supposed to be just fine until your chamber will take the 1.4736" gauge.
If you want one more level of security, buy one of the 1.470" gauges which would be very similar to a military "no-go" gauge.

[toddackerman]

You are supposed to be just fine until your chamber will take the 1.4736" gauge.
If you want one more level of security, buy one of the 1.470" gauges which would be very similar to a military "no-go" gauge.

Thanks Randall! Good to know.

One last question...why are the Military Gauges a little bigger than the commercial ones. I can only speculate that the commercial Gauges have a "Lawyer Attached" somewhere looking for a law suit.?

Tack

[AR15barrels]

Thanks Randall! Good to know.

One last question...why are the Military Gauges a little bigger than the commercial ones. I can only speculate that the commercial Gauges have a "Lawyer Attached" somewhere looking for a law suit.?

Tack

Commercial gauges are based on SAAMI guidelines which the military is not bound to follow.
Military chambers are traditionally deeper to allow for ammo to be more out-of-spec and/or so that dirt/debris will not cause reliability problems.

The minimum spec is actually the same (relatively), it's the maximum spec that's longer on military chambers.
This makes the "acceptable range" quite a bit longer as well.
The "acceptable range" of chamber lengths is roughly double the commercial specs so it's easier to make a mil-spec barrel that falls within specs than a commercial barrel.
This ultimately lowers manufacturing costs when you don't need to be as precise.

[toddackerman]

Commercial gauges are based on SAAMI guidelines which the military is not bound to follow.
Military chambers are traditionally deeper to allow for ammo to be more out-of-spec and/or so that dirt/debris will not cause reliability problems.

The minimum spec is actually the same (relatively), it's the maximum spec that's longer on military chambers.
This makes the "acceptable range" quite a bit longer as well.
The "acceptable range" of chamber lengths is roughly double the commercial specs so it's easier to make a mil-spec barrel that falls within specs than a commercial barrel.
This ultimately lowers manufacturing costs when you don't need to be as precise.

Again...Thanks very much!

Tack