Gunsmithing The No-Go Gauge Went

[Nimrodmar10]

Today I changed out a barrel on a Impact Precision 737R with a new Proof Stainless 6 GT barrel. After torqueing the barrel to the action to 75 ft. lbs. I put a
Manson Go gauge in the chamber and closed the bolt. No problem. I then put the No-Go gauge in and the bolt closed easily. Problem! I put a .0015" piece of Scotch tape on the back of the No-Go gauge and the bolt would not close. I didn't force it, but there was resistance on the bolt handle. I then took the Go gauge and put 2 layers of Scotch tape (.003") on it. The bolt closed easily. When I added a third layer of Scotch tape (.0045") the bolt again would not close. I'm taking this to mean that I have approximately .004" of excess headspace.
I'm new to swapping prefit shouldered barrels. My question is, is this a problem?
I have not fired the barrel yet, but am thinking about it. I can call the gunshop where I purchased the barrel, but since it's Saturday, I guessing I won't be able to call Proof until Monday. What should I do, shoot it or return it?
TIA
Nimrodmar10

 

[AleksanderSuave]

You can email proof for support and possibly get your answer quicker than waiting for monday to call.

I wouldnt rush to shoot it, but thats just me.

 

[cwinner]

Technically you don't have a problem.

Sounds like your measurements have confirmed it's safe to me. Remember, go : no-go gauges are for chambering to +/- .004"ish.

If the action will close on a field gauge +.006" then you have a problem:

https://thecmp.org/headspace/#:~:text=If%20the%20bolt%20DOES%20close,to%20check%20absolute%20maximum%20headspace.

It's not ideal but headspace is a relative measurement, brass life me be a bit less but if you resize properly and don't switch brass between rifles you will be fine.

Here's a suggested list in order of how I would address:

1: shoot the gun
2: try a different brand of gauges, or even another set of Manson gauges.... you may be surprised by the results!
3: send your action to a gunsmith to fit your new barrel and action while the barrel is still indicated in the machine.
4: throw a fit and demand that proof "fix" their mistake! Send it back to them with the instructions to shorten the headspace .002" ish (measure a human hair just for fun) and stomp your feet about the quality control that allowed such a barrel to be produced and fall just outside a range of stacked tolerances for a price point never before seen in the precision rifle industry.

 

[Maurygold]

^ don't listen to that guy. step 1 is to reach out to proof not to fucking shoot the gun

 

[cwinner]

You're absolutely right...... not sure what I was thinking..... the simple fact that the Op posted this question instead of doing a search and reading the dozens of similar threads leads me to believe they don't have the experience to be making the determination how to proceed.

Emailing proof to ask if you should shoot a barrel that closed on a no-go gauge is like emailing your local district attorney to ask if you can legally drive 56 in a 55 mph zone......he should go ahead and pull it off and box it up cause it's going back!

Sorry for the distraction......now back to your regularly scheduled programming

 

[loveha]

You can google field vs no-go till you are dizzy. While a field is safe, it's not optimal if you reload. Think about the stretch your brass will get with all that extra space. If you don't reload, I would not worry about it, but still contact Proof and see if you can get it exchanged for a tighter tolerance.
You are also not the first person I have seen on the forum with a Proof barrel that takes a field gauge to pass.
Actually, glancing down at the Similar Threads section, see one thread just from last year.

Proof prefit headspace issue?

So I just spun on a 6 dasher prefit from Proof onto a Lone Peak Fuzion. The go gauge passes, but the no go closes with zero resistance. Everything is new, clean, and the bolt fully disassembled. Gauges are from Manson and the barrel was torqued on at 80 ft/lbs as recommended by the guys at...

www.snipershide.com

https://bulletin.accurateshooter.com/2017/02/understanding-headspace-what-you-need-to-know/

An excerpt from Brownells out of that article.
"A firearm that closes on a NO-GO gauge and does not close on a FIELD gauge may not give good accuracy and may have very short cartridge case life from the ammunition re-loader’s standpoint."

It is threads like these that keep me from ever wanting to mess with Proof prefits. Rather buy a blank and send to a smith like LRI, Keystone Accuracy, PVA etc.

 

[Cascade Hemi]

I've seen far worse, I'd shoot it. Just bump the shoulders minimally like always and enjoy the slightly extra case capacity.

 

[Herb Stoner]

I’ve never had this issue with Proof prefits so I’d contact them. I’d expect better than “field” tolerances even on a prefit.

As noted, it’s likely not that big of an issue. As far as brass life you’ll stretch an extra thou or two on initial firing only but if you are bumping the shoulder based on that chamber going forward it shouldn’t impact brass life.

Extra headspace might show up with factory ammo but now you’re getting into other variable with factory cartridges.

 

[ma smith]

-4 thou is enough to be a problem.

So you need to deal with it. whether you fix it or say fuck it and shoot it. You still need to deal with it, even if its just buying new gauses, and modifying your reloading process, doing alot of extra QC and measurments as you shoot out the barrel, etc.

Probably makes sense to call proof and talk to them. Even on your own dime, $40 2-way shipping for a replacement is cheaper than $60 for new gauges. Just don't be a pain in their ass I bet they'll give you some options.

 

[Cascade Hemi]

-4 thou is enough to be a problem.

So you need to deal with it. whether you fix it or say fuck it and shoot it. You still need to deal with it, even if its just buying new gauses, and modifying your reloading process, doing alot of extra QC and measurments as you shoot out the barrel, etc.

Probably makes sense to call proof and talk to them. Even on your own dime, $40 2-way shipping for a replacement is cheaper than $60 for new gauges. Just don't be a pain in their ass I bet they'll give you some options.

What kind of problem are you anticipating? 4 thousandth isn't enough for case head separation. It's common to see AR brass grow 15 thousandth depending on how small the new brass is sized and how large the chamber is cut. 30 Thousandth is when things get spicy and even then it probably won't be on the first firing of the brass.

In an ideal world the HS would be a thousandth over minimum. However, in the prefit world you're only bargaining for somewhere between a field gage and a minimum gage.

 

[Wade]

Edited: I'd try another set of gauges first if you can borrow them.

 

[Cascade Hemi]

Today I changed out a barrel on a Impact Precision 737R with a new Proof Stainless 6 GT barrel. After torqueing the barrel to the action to 75 ft. lbs. I put a
Manson Go gauge in the chamber and closed the bolt. No problem. I then put the No-Go gauge in and the bolt closed easily. Problem! I put a .0015" piece of Scotch tape on the back of the No-Go gauge and the bolt would not close. I didn't force it, but there was resistance on the bolt handle. I then took the Go gauge and put 2 layers of Scotch tape (.003") on it. The bolt closed easily. When I added a third layer of Scotch tape (.0045") the bolt again would not close. I'm taking this to mean that I have approximately .004" of excess headspace.
I'm new to swapping prefit shouldered barrels. My question is, is this a problem?
I have not fired the barrel yet, but am thinking about it. I can call the gunshop where I purchased the barrel, but since it's Saturday, I guessing I won't be able to call Proof until Monday. What should I do, shoot it or return it?
TIA
Nimrodmar10

6GT's HS is 1.364" - .007". That means max headspace per SAAMI is 1.364" measured at the datum line (.375"). The Go gage should measure 1.357" and No-Go should measure 1.361". If you chambers measures smaller than 1.364" (which it sounds like it does) it is within SAAMI specification. Again, prefit only means it will meet maximum specification.

https://saami.org/wp-content/uploads/2024/04/6mm-GT-Public-Introduction-Rev-2024-03-30.pdf

 

[spife7980]

.001 over no-go is nothing to worry about. Shoot it.

 

[Nimrodmar10]

6GT's HS is 1.364" - .007". That means max headspace per SAAMI is 1.364" measured at the datum line (.375"). The Go gage should measure 1.357" and No-Go should measure 1.361". If you chambers measures smaller than 1.364" (which it sounds like it does) it is within SAAMI specification. Again, prefit only means it will meet maximum specification.

https://saami.org/wp-content/uploads/2024/04/6mm-GT-Public-Introduction-Rev-2024-03-30.pdf

That may be my problem. My Manson Go gauge measures 1.3555". The Manson No-Go gauge measures 1.3585". The Scotch tape I used measures. 0015". With one layer on the No-Go gauge, the bolt would not close. So my chamber measures ~1.360" max.
Thanks for the help. I'll contact Manson Reamers tomorrow for reference, and I'll contact Proof for confirmation.
I intend to start breaking in the barrel tomorrow, along with a new 22 Creedmoor.
It's built on an Impact Precision 737R also, with a Stuteville Precision 20" Bartlien Carbon Fiber barrel, a Triggertech Diamond Trigger. It's on a loaner stock right now, but I intend to put it on a MDT Carbon Fiber stock.

 

[diggler1833]

To put this into perspective a little for the OP:

Decades ago, I didn't have headspace comparators for anything. The die manufacturer's instructions were to raise the ram & shell holder to the die, and then lower the ram and tighten the die down another 1/8 - 1/4 turn...so that's what I did, typically trying to split that 1/8 and 1/4 turn.

To my surprise years ago when I started measuring all of this stuff - I found that this was sizing my brass about .008 back from what my fired brass datum line was (in almost all cases). The fact that I'm able to sit here and type this is proof that I never blew my face off. Actually, I never had a single case head separation either. Brass life however, is a completely different story.

Closing on a no-go, but not after adding a single piece of scotch tape isn't ideal...but your face too will survive. You just need to make sure that (if you don't already) segregate that batch of brass to that rifle and note your shoulder bump.

If you still feel uncomfortable, you are more than within your right to reach out to who did the work to ask for help in correcting the issue.

 

[Cynical]

That may be my problem. My Manson Go gauge measures 1.3555". The Manson No-Go gauge measures 1.3585". The Scotch tape I used measures. 0015". With one layer on the No-Go gauge, the bolt would not close. So my chamber measures ~1.360" max.
Thanks for the help. I'll contact Manson Reamers tomorrow for reference, and I'll contact Proof for confirmation.
I intend to start breaking in the barrel tomorrow, along with a new 22 Creedmoor.
It's built on an Impact Precision 737R also, with a Stuteville Precision 20" Bartlien Carbon Fiber barrel, a Triggertech Diamond Trigger. It's on a loaner stock right now, but I intend to put it on a MDT Carbon Fiber stock.

Man I would have stuck with another Stuteville barrel. The support if you need it is just a few posts up in this thread, that @Wade guy knows a thing or three.

https://impactprecisionshooting.com/collections/barrels-impact-precision/products/6mm-gt-26-m24

 

[earthquake]

Wait, you’re supposed to gauge shouldered prefits? I thought they were perfect. In 10 years I’ve never gauged one from Proof, or PVA etc. I run TL3’s though, if that makes any difference…but probably not?