I'm checking headspace on a Proof Research 7mm Rem Mag with a JGS 300 Mag #0002 go gauge. The bolt does not close. I called Proof Research. They say I am using the wrong gauge. JGS's interchangeability chart says that the #0002 gauge works on "300 Mag's" and "7mm Mag". Am I using the wrong gauge?
Go Gauge Compatibility
- Thread starter bill123
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I know my go gauge for belted mags works for all, including Weatherby mags. Not sure why proof would be saying something different.
Forster description
Use to check all standard belted Mags with .535″ O.D.: 257 Wby., 257 STW, 264 Win., 6.5 STW, 6.5 Rem. Mag, 270 Wby., 275 H&H, 7mm Rem. Mag, 7mm Wby Mag, 300 H&H, 300 Wby., 300 Win. Mag, 30-338 Win. Mag, 308 Norma Mag, 338 Win. Mag, 8mm Rem. Mag, 340 Wby., 350 Rem. Mag, 358 STA, 375 H&H, 416 Rem., & 458 Win. Mag.
Forster description
Use to check all standard belted Mags with .535″ O.D.: 257 Wby., 257 STW, 264 Win., 6.5 STW, 6.5 Rem. Mag, 270 Wby., 275 H&H, 7mm Rem. Mag, 7mm Wby Mag, 300 H&H, 300 Wby., 300 Win. Mag, 30-338 Win. Mag, 308 Norma Mag, 338 Win. Mag, 8mm Rem. Mag, 340 Wby., 350 Rem. Mag, 358 STA, 375 H&H, 416 Rem., & 458 Win. Mag.
That's the chart that I checked. PTG's chart says the same thing. Just making sure I'm not mis-reading something. I just assume that Proof would be correct.
I use tape stacked on the end of a go gauge to get a no go reading.
Have you checked the end of your gauge to make sure there isn't any tape? Sure you have but have to ask
Good question. It's a new gauge but I always check anyway. Sometimes it's hard to see the tape.
sable tireur
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You can check the 'GO' gauge you're using by measuring from the front of the belt to the rear of the gauge. It should measure 0.220" for a 'GO' gauge.
It's possible that your gauge was mismarked...
It's possible that your gauge was mismarked...
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Thanks. I did measure. My gauge is .221", so .0005" over maximum spec. I would still think the bolt would close.You can check the 'GO' gauge you're using by measuring from the front of the belt to the rear of the gauge. It should measure 0.220" for a 'GO' gauge.
It's possible that your gauge was mismarked...
sable tireur
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It will close IF the belted area of the chamber is 0.220" as well. If the belted cut is shallower, it will not close.
Don't know what process they use, could be the chamber wasn't cut deep enough- or the tenon was cut a tad too long. Either or both will result in what you've got. Rifle will need to go back, but curious-are you getting any handle fall at all?
In my perfect world (sometimes achieved), the handle will fall almost full travel but then requires light resistance to fully close the bolt.
Surprising lack of QC for a high-end product IMO.
In my perfect world (sometimes achieved), the handle will fall almost full travel but then requires light resistance to fully close the bolt.
Surprising lack of QC for a high-end product IMO.
I spoke with JGS. They confirmed that I am using the correct go gauge. I get no handle fall at all. Proof said they test fired the gun and my bore scoping confirmed that there is fouling in the bore. My customer is returning the gun for inspection. Proof is paying for expedited shipping.
Curious to hear from other rifle builders. Would you have returned the rifle to Proof? I was hesitant to remove the barrel & ream the chamber long enough that the bolt closed on the go gauge. I was concerned that my reamer wouldn't match Proof's reamer exactly. Valid concern?
Thanks for everyone's input.
Curious to hear from other rifle builders. Would you have returned the rifle to Proof? I was hesitant to remove the barrel & ream the chamber long enough that the bolt closed on the go gauge. I was concerned that my reamer wouldn't match Proof's reamer exactly. Valid concern?
Thanks for everyone's input.
sable tireur
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Good for Proof to cover the shipping back for inspection. That's what we expect from top of the line companies.
My first call would have been to Proof after I measured and checked everything I could. Your concerns are valid considering you're not a gunsmith and really don't have all the data needed to confirm or reject their contention that the chamber is correct. Letting them handle the inspection is correct. You paid them for their services and they seem to be standing behind their work.
Good luck with the process!
This is a head scratcher to me. With cartridges that headspace off the shoulder datum it's possible that factory ammo could still chamber with slightly short headspace because factory brass is often undersized. I don't see how that could happen with a belted case- and in this case with zero handle fall, headspace is significantly short based on the confirmed dimension of the gage.
You wouldn't have wanted to run a reamer in (no difference assuming they use a SAAMI spec reamer) as it might not be short chambered. I could be wrong (someone correct me if I am...), but I'm assuming they run the reamer in to a specific depth based on their receiver's ring to boltface dimension and tenon length. If the tenon is a few thousandths too long, the chamber could be perfect depth and you'd have the same end result- insufficient headspace.
