Hello everyone. First time on the boards, been using the great knowledge here over the past month to try and and build a new upper and have come to a point where input would be greatly appreciated.
I already own a complete rifle (functioning fine) from manufacturer X and planned on using the lower, BCG and bolt in the new upper build.
From manufacturer Y I ordered a new barrel, upper receiver, gas parts etc.
Went to check head space and these are the results
Gauge dimensions are
GO 1.4636
NOGO 1.4666
FIELD 1.4736
With old bolt disassembled (extractor/ejector removed)
New barrel passed GO (closed and rotated into battery without pressure)
New barrel FAILED NO GO " " “”
New barrel FAILED FIELD " “”“”“”“”
Went back and ordered a new bolt from manufacturer Y (same company as barrel)
With new bolt disassembled
New barrel passed GO (closed)
New barrel FAILED NO GO (closed)
New barrel passed FIELD (would not close)
New Bolt in old barrel
Passes go (closes)
passes no go (would not close)
passes field (would not close)
So even with a new bolt and barrel it failed the NO GO gauge.
I know it is probably safe to shoot but should this be expected out of a new bolt/barrel combo? Is the barrel out of spec? What would be the best way to proceed? Thanks in advance.
You should read some of the threads in regards to headspace. Since you don’t mention manufacturer its all guesswork but basically I think you are using .223 gages and in addition all military weapons are gaged with a Field only.
Any specific thread you can refer me to?
Why is manufacturer relevant thought that was a no-no? both barrels marked 5.56, are the gauge specs off? Two separate gunsmiths checked bolt/barrel combinations and came to the same conclusion that it was a little sloppy.
As I said I know the rifle is safe, it passes the field gauge test, but should I be expecting tighter tolerances out of a higher end new bolt/barrel? If it fails no-go now that simply means less life out of the combo does it not?
Could it be possible that the old barrel marked 5.56 actually has a .223 chamber and that is why the 1.4666 no-go stops the bolt correctly and not in the new barrel?
Iraqgunz is correct,Not that he’s ever wrong,you are using a 223 no go gauge. A 5.56 Forster Nato gauge set is min 1.4636 and max is 1.4736 Field.
If you go to Forster and ask for 5.56 Nato Headspace gauge set this is what they sell
Knowing the manufacturer is important because everyone marks their barrels ‘5.56’ but not all of them are actually 5.56 dimensions. However, it’s my opinion that it doesn’t matter whether a gauge is a “.223” or a “5.56” gauge. IG will disagree because while overseas he had weapons fail a “.223” gauge but pass with a genuine field gauge. Personally, I think that happened because the “.223” gauge was ground too short; not just because it was a “.223” gauge. I tend to suspect how accurately the commercially available gauges are ground. Your numbers for go, no-go, and field are correct but I wouldn’t be surprised if your gauges are more than a few ten-thousandths off from those numbers.
Yes and/or no…
If we are talking about commercial 223 REM gauges marked NoGo it’s anyones guess what the length is even supposed to be made to. Gauges marked with the actual length will measure exactly the same marked 223 or 5.56, given equal quality manufacturing.
SAAMI headspace is 1.4636 to 1.4736, though firearms are rarely made to be on the high limit. So commercial NoGo gauges are usually less than 1.4736.
Military M4/ M16 acceptance spec (complete, new rifles) is 1.4646 to 1.4706, while only the Field gauge is needed for armorer level barrel replacement. So you have more than the 1.4666 as acceptable for a new “mil-spec” rifle.
Note for the “Field gauge only” crowd: I expect military spare barrels and bolts to be in tolerance and actually inspected to assure it more than most commercial parts.