Is the bolt not headspacing correctly something that occurs frequently among quality parts makers such as Daniel Defense or BCM?
Printable View
Is the bolt not headspacing correctly something that occurs frequently among quality parts makers such as Daniel Defense or BCM?
Actually, I've never even heard of a new bolt not headspacing correctly in a new upper.
Never, ever.
That doesn't mean it doesn't happen, and maybe someone else can add input.
My understanding is that a properly made bolt (dimensionally correct) will always headspace correctly in a barrel which was setup correctly.
IE: It's the barrel to extension relationship alone which determines headspace if the bolt is dimensionally correct.
I'll defer to the hardcore armorers on how often barrels are not setup correctly or bad bolts are released. My experience has been all but the fly by night bottom feeders get this right. I can't see DD letting a dimensionally incorrect bolt past QC.
Of the 8 uppers (mostly BCM and LMT) I've purchased or built, none of them closed on a USGI field gauge. The same can be said for the 2 uppers that my cousin sourced from DTI and Armalite that I checked for his piece of mind. Iraqgunz or Grant would be the ones to ask about this.
I have never had it happen with a new quality weapon. I assisted an armorer on another contract in Iraq doing some checks of the new Colt M4's that they received to replace their previous weapons.
Not one of those failed. As a matter of fact the only issue I recall was one loose FSB.
None of the AR's that I have put together either for myself or others has failed to pass either. If you are using KNOWN QUALITY manufacturers that chances are probably slim to none. Since I have the gages, I check everything regardless.
Thanks for the info
Like everyone else above, I've not seen it.
Apparently none of you have toured OLYMPIC ARMS? :jester:
Assuming both the bolt and barrel are new here, this should not be an issue. On mil spec parts you can easily put a gun through 5K rounds before even having to worry about head space being an issue. I would check your gauge ensure it is still within tolerance, or borrow someone else's just to double check. .001 th of an inch is the difference between success and failure here, I'd want to be sure before I called the company and gave em an ear full.
A rifle bought assembled should have the HS set properly. That means that it will take a GO gage, that dimension is far more important than the NOGO dimension. A lot of rifles that turn unreliable when hot have short (sub GO) HS or tight chambers.
It is the responsibility of the assembler to check and/or correct the HS.
The GO check isn't an issue will USGI rifles as those are checked at the factory and, at least once, prior to acceptance.
I recently took The Defensive Edge Armorers course. There was an officer in there that had what most consider a "top tier" rifle. His rifle failed the 5.56 headspace test although it was marked 5.56. First I ever seen it.
Failed which part of the test? Was the HS long or short? Well used rifles will eventually go FIELD but usually the accuracy drops off before this becomes a safety concern. Also depends on the FIELD gage used. USGI chambers are allowed more length from the start. That helps with interchanging bolts.
A gunsmith or armorer should have three gages: GO, NO-GO, and FIELD-REJECT.
If a bolt does not close on a GO gage then the chamber is too short.
If a bolt closes on a NO-GO gage you are very close to or at maximum headspace tolerance. Your precision may start heading for the toilet and you may start seeing severe case wall stretching/thinning and/or case head separations.
If your bolt closes on a FIELD REJECT gage your stuff is way past maximum and the weapon is UNSAFE TO FIRE.
We have seen barrels where the bolt will not even fit in the extension.
That means the breech is .010 too close to the face of the barrel extension lugs. There is a huge difference in bolts, CMT/stag have a.153 dimension from the back of the lugs to the face of the bolt, some LMT bolts have a .147 dimension from the same points so that is .006 difference. If you get a deep chamber(.006 deep is in spec) and a LMT bolt along with ammo that is .008 undersize(which is still in spec) you have a combined tolerance stack of .020 which is enough to allow the primers to back out for sure and with thin cases it could be enough to expand the case to look like a belted magnum after shot, combine that with a little excess pressure and you could have case rupture. It is unlikely that you will find one too tight where the ammo does not fit in the chamber because most ammo is under the size of a "go" gauge.
"Constructor" runs AR Performance (actually it seems like his wife, Donna, runs it, but he is the guy in the shop.)
http://www.ar15performance.com/
Depends on the gun, I have 5 gages just for ARs. SAWs use still another set and match guns another. The GO dimension is similar on all, the "fail" points differ. Self loaders need more room than do bolt guns and autos more room still.
Most military chambered rifles will take a civilian NOGO gage but not the FIELD as the length of the USGI NOGO gage is closer to the civilian FIELD than it is to the civilian NOGO.
Deeper HS usually means greater reliability up to the point that accuracy starts to suffer.
I've seen one carbine that didn't have accuracy issues that had case head separations regularly. The owner had reliability issues due to the tight chamber so I opened up the chamber to just shy of the civilian NOGO length. His reloads started to pop about one in 20 fired. Only his reloads separated no other brands or other's reloads. He was using SAW brass that had he had reloaded many times for his reloads. With the very tight chamber the thin brass was supported enough to just bulge.
constructor is on the mark. I've seen extensions with the index pin hole drilled out of time so that the feed ramps were anywhere but 6 o'clock and barrels that had been mis-machined so that the bolt bound up between the extension and the breech face. If it can be done poorly it's been done on an AR.
The HS dimension on the bolt is 0.156" +/- 0.003", bolt lugs should be 0.278" +/- 0.002"
If your AR/M series works then don't worry about HS folks.
If you're building them then you'd better be checking it and an unfired cartridge isn't a reasonable alternative as cases expand on firing.
If you're burning through rounds and are prone to worry about such things then buy a 1.4730" - 0.0002" FIELD gage or a 1.4736" FIELD and be happy.