In another thread there's been a discussion about what the tolorences of headspace gauges were and the differences between them.

First let me say that the locking lugs on all but one popular action (P-14/17/Rem M-30) do NOT advance foward on closing. In other words, once the corners of the locking lugs and the lug recesses engage the bolt face doesn't move further foward.

Many times I hear shooters talk about their rifle won’t take a NO-GO gauge, which is .003 to .008 longer than a GO gauge, so they assume it has no excess headspace and use that as a basis for shooting a surplus rifle or even using hot loads. That’s a DANGEROUS assumption on some actions.........especially old Mausers.

To understand it you must understand how an action “sets back” the locking lugs.

Mausers and some Mauser-based actions have a split lug on the left side for the ejector to stick through. Over pressure loads, wet or oily cases, and excess headspace, all can allow the lug to hit the recess with enough force to deform the lug recess. Over time this constant hammering will cause a “wrinkle” to develop at the split lug's point of impact. The steel flows into the slot like dirt in tire tread, just not as far or as fast. This wrikle is slightly higher than the surrounding metal.

When the bolt rotates into position this “wrinkle” must be ridden over by the lug. The bolt starts out rotating in one plane but has to move forward to over-ride the wrinkle.

A NO-GO gauge will many times hang up the bolt when it hits the wrinkle. It feels like the gauge is too long......which is exactly what we expect in a safely headspaced rifle........That's a false reading of reality.

The alternative method of headspace checking and measuring uses only the GO gauge. The GO represents the base-line of the minimum chamber that will still chamber the largest cartride allowed by SAMMI specifications.

I prefer to remove all removable parts off and out of the bolt and allow it to rotate fully into position with a GO gauge in place. Then, using an indicator, the amount of slop fore and aft con be measured. The amount of movement represents the true headspace at the position the bolt is actually in when fired. .

For this reason I’ve never bought or owned a NO-GO gauge. They really don’t tell the truth.

I hope this helps save a nice old action from further abuse. With minimum headspace these actions will last another hundred years and beyond. Once the bolt is allowed to hammer the recesses, headspace increases rapidly and the destruction of the action will follow if allowed to continue.



This is (was) a VERY nice 1912 Steyr action that was barreled to 284 Winchester by someone nearly perfect in his ineptitude.

I got the action from the customer that complained of feeding difficulty and a very sticky bolt lift.

The feed rails had been ground away and ruined and the fine old case hardened action has been beaten into .012 headspace and effectively put out of it's misery.

Thanks Jack nice read.

Ditto. Two thumbs up!

Good stuff. This kind of info does not come by everyday. Thanks for sharing it with us.

Mr. Belk, excellent and thoughtful post. I agree 150%.

Axel

JBelk ,
sorry I dont pretend to understand the stated details,but I am not a gunsmith and devoid of knowing the finer details.Your concept though is of interest to me- as a user for the mentioned contraption. I would therefore appreciate if you could step through the measuring sequence from a laymans vantage point.
1 Yo place a GO-gauge into the chamber and presumably check whether the bolt closes.If so the chamber is not too short- I so interprete.
2 Next to check for a too long chamber == increased headspace you check for " a little bit of slop" rather than using the NOGO gauge.
Please elaborate on the technique for "slop" measurement.
thank you
sheephunter

Jack,
Great thread as usual. I have an interesting tale for you I will relay tomorrow.

Jack

I agree your methods are sound.

A clear first rate explanation and very good photo and example.

I also check for lugs being set back, but have approached it from a little differant angle. Usually by visual inspection with a mirror and light source and or my bore scope. Also if the customer describes any symptoms of set back and I can not see any problem I will set up with a dial indicator as you described. I had one 98 Mauser come in with enough lug set back that you could put a cleaning rod down the bore touching the bolt face, rotate the bolt and actually feel the lugs drop in and climb out with your fingers on the cleaning rod.

I think were both headed for the same destination just taking a little differant route.