AR15 New Build and Possible Headspace Issue??

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Chuck R.

Chuck R.

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Jan 23, 2005
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Leavenworth, KS
Hi,

Working on a new build and I’ve got a possible headspace issue with a new RCA Low Mass Competition Bolt Carrier Group and a new Larue Tactical Predatar Barrel. I tried the bolt in the barrel and checked it with a set of Clymer .223 gauges. The bolt closed and turned freely with both the go and no-go gauges inserted. Tried a Colt 6920 bolt and it would not close on the no-go gauge (as it should). This has me just a bit nervous.

For both the RCA bolt and the Colt Bolt I removed both the ejector and extractor before checking. Tests were conducted with the barrel mounted, and later removed, same results.

The Clymer NG gauge is 1.666”. According to the Q&A section on Brownell’s the Clymer .223 G/NG gauges will work for a Wylde chamber (Larue) and 5.56.

What do you think the issue is??

Thanks,

Chuck
 
  • Headspace gauges are available in three different lengths, listed below, from shortest to longest:
  • Go Gauge: Go Gauges match the minimum chamber dimensions allowable under SAAMI specifications. In order to accept SAAMI maximum ammunition, the rifle must be able to chamber the correct go gauge.
  • No-Go Gauge: No-Go Gauges are sized to the maximum recommended headspace dimensions. If a rifle will chamber the no-go gauge, it may still be within specifications, or this could indicate excessive headspace. To determine if the rifle is safe to shoot, the chamber must be checked with the field gauge.
  • Field Gauge: Field Gauges correspond to the maximum safe headspace dimension. If a rifle will chamber a field gauge, it should be inspected and repaired by a competent gunsmith prior to use.
I seem to remember my Colt M16A1 use a different gauge, just because Colt was different?? I used this gauge. full.jpg
 
Looks like the Colt provides a tighter headspace .

Looks like a Field Gauge is needed to check the RCA Low Mass Competition Bolt's headspace.

I'm not a gunsmith, so get more opinions.
 
You are doing it correctly from your above description unless you are forcing the bolt closed--finger pressure only.

What can happen is tolerance stacking with the bolt being a bit short and the barrel being a bit long--result is excess headspace and failing the go gage. My suspicion with your other bolt passing the nogo with that barrel is that the RCA one is too short.

One way to avoid that is to buy the bolt and barrel from the same source and tell them you want proper headspace from the pairing. They have the barrels and bolts to fit you up with a rifle that has proper headspace.

On a new barrel/bolt combo, I would be uncomfortable with going to a field gage for a bolt/barrel combo to pass--I would probably try to return the bolt (or the barrel if you wish) and either exchange it for a new one or swap to match the bolt/barrel brand.

Wish you luck.
 
Guys, I've watched the Brownell's tech videos a couple times just to ensure I'm doing it right!

I've fired off an email to the RCA guys to see what they have to say, and I'll test another bolt or 2 on Monday when I get back to the office. When I checked the breachface depths between the 2 bolts I have:

Colt: .1245"
RCA: .1270"

So the RCAS breachface is cut deeper. Once I get a reply from RCA I'll look at the next step which is hitting a gunsmith and checking it with a field gauge.

Thanks,

Chuck
 
Chuck R. said:
When I checked the breachface depths between the 2 bolts I have:

Colt: .1245"
RCA: .1270"

So the RCAS breachface is cut deeper.
Click to expand...

That is one part of measuring your bolt. Since lockup to the barrel extension occurs on the back face of the bolt lugs you also need to measure the lug front to back dimension and subtract the bolt face depth measurement to get the distance from the back face of the bolt lug to the bolt face. Compare those dimensions bolt to bolt.
 
BBBBill said:
That is one part of measuring your bolt. Since lockup to the barrel extension occurs on the back face of the bolt lugs you also need to measure the lug front to back dimension and subtract the bolt face depth measurement to get the distance from the back face of the bolt lug to the bolt face. Compare those dimensions bolt to bolt.
Click to expand...

Checked it out as per your suggestion. Believe its on of those stacking of tolerances deals. The RCA bolt also had slightly shorter bolt lugs, so that combined with the deeper breach face probably explains it. I also checked the bolt using my Colt LE6920 barrel/chamber, again it closed on the No-Go, while the Colt bolt did not.

Looks like I'm in standby mode until I hear back from RCA.

Thanks for the suggestions,

Chuck
 
Chuck R. said:
When I checked the breachface depths between the 2 bolts I have:

Colt: .1245"
RCA: .1270"

So the RCAS breachface is cut deeper.
Click to expand...
Chuck R. said:
Checked it out as per your suggestion. Believe its on of those stacking of tolerances deals. The RCA bolt also had slightly shorter bolt lugs, so that combined with the deeper breach face probably explains it.
Click to expand...

thumbs-up-hand-gesture-smiley-emoticon.gif Yep. Your headspace will be .0025" (difference in bolt face depths) plus the difference in lug dimensions greater with the RCA bolt than with the Colt bolt. That can be a significant difference depending on the specifics of the chamber in question.

Side note - When/where were you in the 11th ACR?
 
Quick Update......Spoke with RCA on Monday, new bolt arrived THURs along with return label, it does not close on the No-Go gauge. Very fast & courteous response from "Jeff" at Rubber City Armory. Upper is now re-assembled and I'll test fire this weekend.

BBBBill, 11th is a very good unit with a long/proud history (not as long as the 2nd/3rd ACRs which is while I believe they're now OPFOR).

Chuck
 
I'm a bit late to the party but this serves as a testament that it's always a good idea to check headspace anytime components are swapped. Glad it was taken care of.
 
Chuck R. said:
Quick Update......Spoke with RCA on Monday, new bolt arrived THURs along with return label, it does not close on the No-Go gauge. Very fast & courteous response from "Jeff" at Rubber City Armory. Upper is now re-assembled and I'll test fire this weekend.

BBBBill, 11th is a very good unit with a long/proud history (not as long as the 2nd/3rd ACRs which is while I believe they're now OPFOR).

Chuck
Click to expand...
Good for you and good on Rubber City Armory. I try to check out companies that give good service.
 
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