Headspacing on CMP SG and RG carbines?

[ramit]

What has your experience been with the headspacing of a SG and or RG carbines?

[Carbineitis]

All of mine have passed the Go - No-Go test using Clymer gauges..

[J.R.2009]

Ditto on the Go-NoGo on the rackers and SG's. I check ALL of mine when I tear down the bolts for cleaning. Have yet to find one that didn't check out OK. Have even swapped out bolts between them and still have not found one that didn't head-space fine.
J.R.

[ramit]

This racker inland I just received is to be a little project to make a repro m1a1 out of.

MW 3.1
TE just 3

changed the stock to repro m1a1.
repro flipper rear sight.
front bb replaced w/ repro typ1.

While doing that , been waiting on a set of gauges.
They finally came in.

The bolt easily closes on the No-Go gauge, no pain, no forcing.
I thought , ooppss...
tried the field gauge, and it wont close on that....the lug still has a bit to go before it'll round the shoulder of the receiver and go in.

So I said, geez, and took out my other carbines.

1 SG CMP (received it this past fall)

And 2 others, one a SG+, and a minty original as issued inland from Orion 7.

Checked those three...

The SG cmp, just the same as the racker. closes on the no-go , but not on the field gauge.

My Orion 7 carbines, only close on the Go gauge, and wont close on the no-go (and obviously ) not on the field gauge.

I haven't shot the racker yet.

I've shot the SG CMP NPM a bunch of times, inspected the brass, and all looked good.

I've read that this may be acceptable and due to wear that it can still be safe if closing on a no-go, but wont be safe when closing on a field gauge - then it's just too worn ??

[jeeperbob]

Originally Posted by ramit

This racker inland I just received is to be a little project to make a repro m1a1 out of.

MW 3.1
TE just 3

changed the stock to repro m1a1.
repro flipper rear sight.
front bb replaced w/ repro typ1.

While doing that , been waiting on a set of gauges.
They finally came in.

The bolt easily closes on the No-Go gauge, no pain, no forcing.
I thought , ooppss...
tried the field gauge, and it wont close on that....the lug still has a bit to go before it'll round the shoulder of the receiver and go in.

So I said, geez, and took out my other carbines.

1 SG CMP (received it this past fall)

And 2 others, one a SG+, and a minty original as issued inland from Orion 7.

Checked those three...

The SG cmp, just the same as the racker. closes on the no-go , but not on the field gauge.

My Orion 7 carbines, only close on the Go gauge, and wont close on the no-go (and obviously ) not on the field gauge.

I haven't shot the racker yet.

I've shot the SG CMP NPM a bunch of times, inspected the brass, and all looked good.

I've read that this may be acceptable and due to wear that it can still be safe if closing on a no-go, but wont be safe when closing on a field gauge - then it's just too worn ??

How are you checking TE? What brand gauges are you using and where did you get them? Have you tried calibrating the gauges to verify they are in spec? Some gauges require dissembly of bolt. USGI do not require that. I do not mean to infer or sound like you don't know what you are doing, just asking the obvious questions. US Military specs for headspace on this rifle is 1.290 min & 1.302 max. I use USGI gauges that I have checked the specs on all 10 carbines I have and all close on go (1.290) and don't close on no go (1.302). Should I have one that fails no go it comes out of service, just the way we did it in the military and look at rebarrel. As far as extending service by use of a so called "field" gauges, if that gauge exceeds 1.302 I will not buy off. My life and eyesight are worth more than the cost of a measly barrel. Of note, all carbines I bought from CMP were service grade. I did buy a rack grade CMP carbine from a private individual that must have been graded rack because of wood because the specs were equal to service grade as well as finish on metal. The wood was better than some SG carbines.

[ramit]

Thanks jeeperbob....

No problem, I am a "newbee" at this and not sure of the margins...


Brand new Forster Headspace gauge set , Go , No-Go, and Field.
They clear the ejector, very easy no interference fit with assy bolt.
I place the gauge into the chamber, and slowly bring the bolt forward till it rests on the gauge.

TE gauge, brand new...
http://www.brownells.com/.aspx/sid=5...e_Throat_Gauge

CMP ME gauge, brand new.

Break out the digital calibers...
Go : marked 1.290" = measured: 1.290"
No-Go: marked 1.296" measured: 1.296"
Field : marked 1.299" measured: 1.299"

Ah, I see some noticeable differences here in the gauge sizes compared to yours.
My field gauge is shorter than your no-go gauge....

I under stand these meet SAAMI.
I thought I read somewhere that SAAMI is tighter than mil?
And that the go and no-go are used for rebarreling... making my field gauge, really a no-go gauge...... based on the sizes we are discussing..

Again, thanks for the questions and discussion, this is very much apperciated... only way to move ahead and figure it out...

[ramit]

What size does the CMP use?
I understand they just us a No-Go gauge....
I'm thinking now, if they use the USGI as you do, this is why it passed for them, and "failed" for me.
But also explains why the casings looked fine...

[jeeperbob]

You should be within tolerances if closing on 1.296 but not on 1.299 with TE of 3. I could'nt see why it would fail with only 3 on TE. Probably more chamber wear on the RG vs your Orion 7 rifle. It will probably be quite awhile before you reach 1.302. At that point I would see what it gauges with other bolts. A newer one without wear may actually be fractionally longer and still extend the life of the bbl. I thought I read that they use go & no go gauges which if are like yours, are well within specs. They would have to check min headspace to insure it is not short chambered and again they are putting these things together from a box of bolts and some may be newer than others with less wear.

[ramit]

Yes.

My SG CMP is 2.0 TE. Muzzle about close to 1. And again, closes on my Foster no-go, but not the field, as does the Racker.

The 2 from Orion 7, TE, one just under 2, the other close to 1 (correct original minty inland). Neither close on my no-go.

Thanks for the discussion on the numbers, and the USGI gauges.
It starts to make sense why they passed CMP, if they are using USGI no-go gauges.

I've found two articles now that say the Military specs are a bit looser compared to the SAAMI specs, and one that may fail SAAMI, could still pass USGI.
BUT , none has published numbers..............
So your numbers help me make some sense of it.
Now just to try and confirm what the CMP really uses...

[rlexx]

My Forster Field gage is 1.299". All 13 of mine pass headpsace - 11 are CMP SG/RGs - two are barreled receivers from CMP that I bought Underwood *U* round bolts (one in wrap and one used). Most of the right lugs of the bolts touch the top of the receiver - I have a couple where the lug is over the lug recess of the receiver but are far from completely closing.