That will be interesting for sure...DPMS barrels do not have good QC so it could easily be that as well.
NEA BCG issues
- Thread starter jdman
- Start date
That will be interesting for sure...DPMS barrels do not have good QC so it could easily be that as well.
Bob Greenleaf, while a design engineer at Savage, tested a .30-06 M110. He kept firing the rifle, with the barrel being unscrewed between shots, until the rifle could not be fired because the firing pin could not indent the primer. No cases separated. All ammuniton was fresh factory.
jdman has noticed an apparent situation of what could be too tight headspace; excess headspace is not an issue and is irrelevant.
Headspace is basically not adjustable in the AR system. Manufacturers must assume that their products will be used as is. Could there be a mismatch between the bolt and this particular barrel? Sure. Could it be the barrel and not the bolt? Sure. Could it be the bolt and not the barrel? Sure.
Problems are rare? Is this because industry wide tolerance control is effective, or is it because headspace just doesn't matter?
An AR bolt carrier does slam shut; it things are a bit tight, the round is no doubt adjusted to fit as the bolt closes.
Perhaps jdman should just assemble the rifle, and shoot it, and just forget that he gauged the assembly.
I wonder what would be observed if every mix and match assembly was actually gauged, rather than folks just relying on the manufacturers? Manufacturers guage every assembled rifle they ship. At least I assume that they do.
jdman has noticed an apparent situation of what could be too tight headspace; excess headspace is not an issue and is irrelevant.
Headspace is basically not adjustable in the AR system. Manufacturers must assume that their products will be used as is. Could there be a mismatch between the bolt and this particular barrel? Sure. Could it be the barrel and not the bolt? Sure. Could it be the bolt and not the barrel? Sure.
Problems are rare? Is this because industry wide tolerance control is effective, or is it because headspace just doesn't matter?
An AR bolt carrier does slam shut; it things are a bit tight, the round is no doubt adjusted to fit as the bolt closes.
Perhaps jdman should just assemble the rifle, and shoot it, and just forget that he gauged the assembly.
I wonder what would be observed if every mix and match assembly was actually gauged, rather than folks just relying on the manufacturers? Manufacturers guage every assembled rifle they ship. At least I assume that they do.
My bad - yes, you remove the ejector pin. I mis-spoke. I take the extractor out as well since it is easy to do.
Also, I'm going to assume it rotated nearly all the way into battery. If so, it likely would seat to spec when either proof fired (if a factory gun) or after a range session.
Most ammo is well under SAAMI maximum - in all liklihood without the gauge you never would have known it was off.
Also, I'm going to assume it rotated nearly all the way into battery. If so, it likely would seat to spec when either proof fired (if a factory gun) or after a range session.
Most ammo is well under SAAMI maximum - in all liklihood without the gauge you never would have known it was off.
Many headspace gauges have a slot milled in the base so you don't always have to remove the ejector pin.
If it rotated it would have gone into battery otherwise the bolt carrier would not have gone far enough forward to allow the firing pin to hit anyways.
Having seen various blueprints for the ar15, the tolerances for things like the bolt and barrel extension are typically +-.001" or less so properly spec'ed parts are in fact plug and play.
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If it rotated it would have gone into battery otherwise the bolt carrier would not have gone far enough forward to allow the firing pin to hit anyways.
Having seen various blueprints for the ar15, the tolerances for things like the bolt and barrel extension are typically +-.001" or less so properly spec'ed parts are in fact plug and play.
An interesting point for sure. Not that I would tell anyone they SHOULDN'T spec out their guns...of course it's worth doing just for the sake of interest.
But it does beg the question...if you spec out a gun with an NEA part and find something is off, potentially the NEA part but possibly not, then what? What is your baseline for data? How many other guns have been subjected to that scrutiny, and is the problem a foregone conclusion?
For example, there are probably thousands of Bushmaster and DPMS rifles floating around in Canada, which could well be out of spec. But no one is checking them and their flaws are consequently unreported - and unnoticed during use.
Now we have a situatioin which there is a problem with a gun with an NEA part, and the conclusion is automatically "NEA ####ed up" despite the fact that from the information posted there is no way to know whether that is the case.
I believe pretty strongly in research for the sake of research. I applaud anyone who specs their guns, because more knowledge is, in my opinion, better than less knowledge.
But it is important to remember what exactly the significance of the information you glean is. In this case it's extremely hard to say. We don't have a known good barrel, or even known good guages. We do have a barrel from a manufacturer that is notorious for stamping .223 guns "5.56 mm NATO" that is failing to interact correctly with a BCG.
More information is needed before conclusions can be drawn.
Headspac is not just affected by barrel extension, the upper receiver extension tolerance and the amount of torque applied to the barrel nut affect headspace as well.
In general, if you cobble parts together to make an upper, it is not unreasonable to check headspace. The problem with failing the guage is that you do not know how undersized/oversized the headspace is. Most people will just shoot the thing and see if there are pressure signs, but that is kinda like squeezing the trigger to see if the safety is on.
Have I ever heard ka-boom due to bad headspacing with AR - not yet. Given the architecture of AR, it is probably very very rare for an AR to have dangerously out of whack headspace due to manufacturing errors. However, bad headspacing does affect accuracy and generate all kinds of pressure signs, like excessive brass shavings.
In general, if you cobble parts together to make an upper, it is not unreasonable to check headspace. The problem with failing the guage is that you do not know how undersized/oversized the headspace is. Most people will just shoot the thing and see if there are pressure signs, but that is kinda like squeezing the trigger to see if the safety is on.
Have I ever heard ka-boom due to bad headspacing with AR - not yet. Given the architecture of AR, it is probably very very rare for an AR to have dangerously out of whack headspace due to manufacturing errors. However, bad headspacing does affect accuracy and generate all kinds of pressure signs, like excessive brass shavings.
A bolt will close on a Go gauge when the spring loaded plunger ejector is still in the bolt. This is not good practice, though, because feel of the gauge is lost. FYI.
GT - headspace is set by the relationship between the bolt, the locking abutments in the barrel extension, and the chamber (in particular the portion of the chamber's shoulder where the gauge makes contact). Barrel nut, bolt carrier shouldn't affect headspace.
The upper receiver and barrel nut torque have nothing to do with headspace. Barrel extension torque could affect headspace if the chamber was reamed before the extension was installed but that's not generally the best way to ream a barrel.
The aluminum threads would fail long before you could ever tighten the barrel nut enough to distort the barrel extension.
I agree with the rest of your post.
The reason it is ALWAYS recommended to remove ejector to test headspace is this:
Lets say you are using a no go gauge (on no go field gauge), you DO NOT want it to chamber...well lets say you test it and it barely chambers, you know your have to much headspace...now lets go back in time a few minutes and pretend that you did not take the time remove the ejector and that little bit of extra tension kept it from chambering falsely leading you to believe you were good to go since it did not chamber...this would be a false reading.
And with a go gauge, same thing that extra tension could keep it from chambering because you have very tight headspace (but still in spec) and you might think, oh s**t, my go gauge would not chamber I must have a problem, when in fact with the ejector removed it would have chambered...
Unless the plunger ejector cannot be pressed back into the boltface all the way, its presence will not prevent the bolt from closing - or not closing - on Go or No Go gauges. The pressure alone will not prevent closing the bolt on the gauge.
Its presence will make it difficult to get a good "feel" of the gauge's fit.
Use of these gauges requires a light touch. Ham handed use prevents this light touch. This is particularly important with No Go and Field gauges. In a bolt action rifle, the powerful camming force can close a bolt on a No Go gauge, even though the gauge is making contact, bolt face to shoulder. With the plunger ejector removed, it is easy to feel the contact; with the ejector installed, not so much. If the No Go can be felt, that is all that is needed to say that the rifle passed the |No Go test. In a rifle like an AR, which does not have powerful camming on final bolt rotation, a light touch is very important. Removing the ejector is important. But not for the reason you are suggesting.
Mystic Precision
CGN Ultra frequent flyer
- Location
- Summerland, BC
Most new cars do not come in crates of parts you assemble in your garage...
Jerry
Dude, it's an AR.
Maybe I'm a little jaded since we had some one come into the store a week or two ago. Seems they were getting a custom AR made by a "precision" rifle maker.
He was told to buy a bolt head, then send it to the builder so the builder could make a custom bolt carrier group that would match up with the barrel and bolt head.
I didn't hear how much this un neccesary service was going to cost.
If the "precision" maker was doing a one-off barrel, fitting the barrel extension and chambering, it would make sense to have the bolt that was going to be used, when finalizing the breeching. Custom bolt carrier group? OKaaay......
Hope laddie knows what he is getting, and what he is paying for.
Hope laddie knows what he is getting, and what he is paying for.
Mystic Precision
CGN Ultra frequent flyer
- Location
- Summerland, BC
having fitted bolts to a match barrel is common practise and required by some of the top US AR match barrel makers.
so it depends if you want a USGI spec AR which is designed to run over a wide range of parts and service.
Or a true match rifle with the same intent as a precision bolt rifle.
AR has many personalities these days.
I am working on a Service Rifle capable AR and it will have a fitted bolt.
As for the BCG..... well....
Jerry
