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Posted: 9/8/2014 10:48:21 PM EDT
| I'm starting my first from scratch build and seem to have an issue. Bought a 8.5" Noveske barrel with headspace bolt for this pistol build and...I watched video on how to check headspace on both unmounted and mounted barrels and even though noveske has a solid reputation I wanted to be safe and check it. Well, the go gauge turns really easy (Uninstalled barrel), can almost do it without putting a punch through the bolt for leverage. The no go gauge will turn if I push in and turn with a punch. Do I have excessive headspace? |
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You are applying too much force to turn the bolt. It normally rotates by the action of the cam pin following its slot in the carrier. Using a punch as a lever may be applying enough force to crush the headspace gauge into the chamber.
Turn it by hand and it should not fully rotate into battery. If checking with the barrel mounted in its upper receiver, finger pressure to close the bolt. Do not let it slam forward or be driven by the action spring. 
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Did the video tell you to use a tool to apply leverage? Also have you removed the ejector and the extractor from the bolt? eta Okay, I just watched the video on youtube that did exactly as you described. I was always taught and the instructions that come with the gauges tell you to always to remove the ejector and extractor. Who made your gauges? Did you buy the barrel new or used? |
| I watched a couple and the Uninstalled barrel one they said to use a punch to aid in turning the bolt. I guess this is the disadvantage to youtube ha but it at least maybe I'm good to go? I suppose I'll double check when it's installed as well, just didn't want to do all that first then test it when I could do it disassembled |
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Are there measurements printed on both your Go and No-Go Gauge? If so, what are they? If not, do you have any paperwork that lists the measurements? To verify the length of headspace the gauge is machined to that should hopefully also be printed on the side of the gauge, Measure from the bolt-face side of the gauge to the side with the 0.330" datum line. The SAAMI 223 REM Maximum Cartridge / Minimum Chamber Blueprints shows where the 0.330" datum line lies on the cartridge.
Military Specifications set the minimum headspace for a new barrel that has been high pressure tested (HPT) at 1.4646" (Go Gauge). As for the maximum headspace for a new barrel that has been high pressure tested (HPT), it is set at 1.4706" (No-Go Gauge). The Colt II Field Gauge is 1.4736" (which is the maximum length a chamber can be before barrel life is considered used up, or the barrel is deemed unsafe). SAAMI sets the minimum headspace at 1.4636" (Go Gauge). The SAAMI No-Go Gauge measurement I have found is 1.4666" (which is the longest a cartridge can be from the bolt-face to the 0.330" datum line. The maximum headspace is set at 1.4736" (which is the maximum length a chamber can be before barrel life is considered used up, or the barrel is deemed unsafe). Also, to find out whether the potential headspace problem is with the bolt or barrel, the bolt should measure from the bolt-face to the rear of the bolt's lugs 0.156 -.003. The barrel should measure from the inside edge of the barrel extension's lug to the 0.330" datum line 1.6206". Which would make the headspace between 1.4646" to 1.4676". 
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| Gauges have no measurements on them. With extractor and ejector removed, bolt rotates on go gauge easily with what I would say is quite a bit of play. No go gauge I cannot rotate by hand but will rotate if a SMALL amount of leverage is used, by this I mean I'm not using a punch or anything, I can rotate it by sticking a spent .17 hmr casing in the bolt to turn it. So it seems that if these checks are done exclusively by hand I'm good but if you're supposed to use ANY leverage to test if it will go into battery than I have an issue... |
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I've found my Noveske 300blk barrel has very close head space, as does my 556. As a matter of fact both are .001 close to interference (per saami specs). Measured from my Hornady head space gauges on fired brass.
You'll find the accuracy is pretty good. If you're worried, get a LE Wilson 300 BLK case gauge and measure your fired brass. If it stays between the grooves you have close head space if it creeps out the gauge it's got clearance. Excessive head space is .007 based on SAAMI IIRC of the top of my head. |
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