Quick Question

The differanct is about the thickness of 2 peaces of masking tape. If you don't have a No-go gage you can use a standard round for the Go gage & apply 2 thicknesses of masking tape to the end of a round for your No-go

The differanct is about the thickness of 2 peaces of masking tape. If you don't have a No-go gage you can use a standard round for the Go gage & apply 2 thicknesses of masking tape to the end of a round for your No-go

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Wrong. have you ever measured masking tape????? it varies from brand to brand and fom grade to grade with in brands. there are some masking taapes that are .010 thick. do a search some were here I gave the variouis differance of tape I had in the shop. adding two layers of masking tape that are close to .008 thick on a round that is close to the long side of the spectrum is a sure way to get excessive head space not to mention tape compreses.

the differance on most 7.62x39 guage sets is about .005 depending on if there CIP or SAMMI or of country of manufacture.

I have used hand loads on wildcats were I controll the brass and its all the same and then i have used a .002 steel shim (feeler guage piece)

Plus, without special equipment you can't simply measure the length of a gauge. The specs call for a length to a datum line, which on this and most caliber gauges is an imaginary line somewhere on the "shoulder" of the gauge. The OAL could even be the same on a GO and NOGO, the datum length is what determines tolerance, not OAL.

sjohnson said:

Plus, without special equipment you can't simply measure the length of a gauge. The specs call for a length to a datum line, which on this and most caliber gauges is an imaginary line somewhere on the "shoulder" of the gauge. The OAL could even be the same on a GO and NOGO, the datum length is what determines tolerance, not OAL.

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True, but if you know the difference between the length of go and no go gages even at the datum line you can use the difference to figure out how much OAL length to add to a go gage to make it mimic a no go gage and you don't have to measure from the datum reference line. If you know the specs and your rifle uses a 1.00 inch spec go gage and a 1.05" no go gage you know you have .05" difference. The go gage you have is 1.45" long OAL. Make it 1.50" long with whatever tape you have and you have in essence made a no go gage.


SAAMI specs ( worthless IMHO ) for a 7.62x39 AK are (measured from the datum line.)

GO - 1.252"
NO GO - 1.257"

CIP gages are the standard for AK's though and every attempt should be made to secure real Russian or E German gages for AK's before settling with SAAMI.

Agreed, but the OP didn't ask for datum line length, he asked about measuring length. My point was meant to show that measuring gauge length isn't germane, the published datum length is.

I'm sure someone has the datum lengths for the 5.45. I don't.

chipmechanic hit the nail on the head. I'm just trying to make a Go gauge into a NoGo. Looks like it should be .005-.006 longer. Thanks for all the help gentlemen, appreciated.

add a piece of feeler guage that is the correct thickness to the go guage with a dab of grease. I dont have go guages for several caliburs i just add about .003 to the go go guage on a target build. I also verify that the bolt closes on the ammo Im building the gun for. I reload 90% of what i shoot so i fit the gun to my ammo.

Yes I was just going to say use a feeler gauge with a go gauge since tape is "squishy" and really won't be as accurate as you would think. Would grease cause the reading to go off? These things need to be spotless-clean to get a good reading when you're talking about .001". I would clean the chamber and bolt GOOD and degrease them. Also be sure you make the measurements appropriate to your gauge - in other words some gauges work with the extractor, some don't.

I just answered the almost identical info posted here on the headspace question. A slight smear of grease will keep a shim in place with no problems in measuring accuracy. Do it all the time to keep thread wires in place for measuring "Pitch Diameter" when cutting threads on the lathe.