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Discussion in 'Gunsmithing' started by captain cox, Jan 17, 2011.
What are people using? 300 rum?
300 Rum GO is the one for the Edge. For a NO GO use one layer of scotch tape on the base of your GO guage.
Buy a NO-GO gage, too,,,,,, and do it right!
"Do it right" with a NO GO guage? I operate at a bit tighter tolerance on a rifle set up for accuracy. Most NO GO guages are .004" to .010" over their respective GO guage. A piece of scotch tape is .002". This leaves my headspace with the tape method at nuts on to .001".
Here is some old hack doing it the wrong way like I do.
YouTube - Barrel Chambering & Headspacing
Scotch tape is 'repeatable'? There are better ways to work close to min. tolerances than tape. Your liability insurer wouldn't like the tape 'method' at all!
I think you are on the loosing end of this argument.
I think I recognize Gordy Gritter doing it that exact way in the video posted. If it is good enough for a 1000yard bench rest rifle shooter and gunsmith to do it that way, it is good enough for my rifle build.
Sorry, not into 'hero' worship. As a general rule of 'practice' in my shop I cut SAMMI tolerances in half for headspacing. I'll continue to trust my Starrett depth mic' and my ability to use it rather than a piece of Scoth Tape, to know where I'm at within that tolerance. I've got a couple of rolls in the office, couldn't find a NIST certification anywhere! By the way, I've built quit a few competition rifles in my day, too.
I am glad for you.
And I am not into hero worship either.
Build your rifle any way you want.
Captain, Dave at PTG sells the .338 Edge GO & NO-GO gauges. Thats where I just got them and my reamer. Well worth the investment.
Shortgrass, you must not understand the scotch tape method for a NO GO. I don't even own a NO GO gauge, they're useless and too far on the other side of the tolerance range. If you chamber to what your headspace measurement calls for and check it with your depth mics, I'm sure you then screw the action on and try a GO gauge to make sure the bolt closes. If it closes fine and your at 0 headspace according to your depth mic, remove the GO gauge, clean off the base of it and attach 1 layer of scotch tape. Trim the excess off with a razor blade. You've know taken your GO Gauge and made it .002" longer. The normal NO GO Gauge is any where from .004" - .007" longer, you've just tightened up your tolerance range. Try the gauge now and the bolt should not close. This now tells you your headspce measurement is anywhere from 0 - plus .001" Try it once I'm sure you'll find it handy.
Anyone have one I could borrow or rent?
Pacific Tool and Gauge has them for $27.
Oh! I understand,Kevin! Tape wouldn't 'fly' in any job shop where I've ever worked. Wouldn't 'fly in the bearing plant where I made jigs and fixtures for the inspection department or assembly department, either. Dead 'nuts' measurment is what counts there. Ya' , I'm considered old and cranky. It's not like I'm new at this, I started making 'chips' in '74. Graduated from high school on Sunday afternoon, started work in a job shop Monday morning standing in front of a Warner & Sweasy #3 turrent lathe. Fully versed, not just turrent lathes, ABMs (multipule spindle automatic bar machines- Acme/Gridleys), shapers, horizontal & vertical mills, and making or sharpening the tooling for any of these. Everybody has their own way of doing things, and thats fine. I'll stick to my gages and micrometers, if you don't mind, I get exact 'numbers' that way.
In your experience you must be familiar with tolerance stacking. When building a rifle to measure head space with micrometers you must measure:
1: The distance from the bolt face to the receiver face.
2: The thickness of the recoil lug if so equipped.
3: The distance from your Go Gauge above the barrel tenon shoulder.
4: Guess the amount of crush when the receiver pulls up tight on the barrel with the recoil lug in place.
Here the four measurements plus or minus a few ten thousandths are added together. One of the dimensions is a guess. You are good but the sum is potentially off by a thousandths or two. Pretty close.
If it passes your half of the SAMMI head space tolerance estimate. You carefully put it together and drop in your gauges. Go drops in fine. No Go doesn't quite close. You must be good. The rifle is deemed within spec and out the door it goes. How do you really know the true head space on that rifle? It falls somewhere within the two gauges is all you really know. Your belted magnum rifle chamber could be as much as .0039” over minimum. No way to really know. We do know it is in range.
The hypothetical customer has a set of minimum spec dies for his precision rifle you just built him and is full length sizing. Unknowingly working his brass time after time. 5 loadings later he experiences a head separation. No harm is done but the rifle is out of commission due to a headless brass stuck in his chamber and he is a continent away on the hunt of a lifetime.
Now lets try something new.
Fresh faced new gunsmith using the crazy new fangled way with his mics to get him close and uses only a Go Gauge and some scotch tape to measure his actual head space.
He measures the same way carefully recording all the measurements as he fits the barrel. The barrel is clocked up perfect. The bolt nose to barrel clearance is just right and now the new guy is doing the final reaming to set the actual head space. The reamer is removed. The chamber is dry. The recoil lug is in place and action is cinched up hand tight. No question of the final assembled dimension as all the tolerances have the slack removed now.
Here it comes just the same as you have done for years. The Go Gauge in place. The bolt handle drops with no effort. We expected that. Then he does the unexpected. In fact the No Gauge is no where to be seen. He reaches for that roll of Scotch tape and applies one thickness to the end of his go gauge effectively adding .002” to the Go Gauge. WTF you think. The kid drops it in the chamber and the bolt handle drops. Another thickness of tape goes on. Now .004” over the Go Gauge. He is not happy at all and states he must redo it. You offer to rescue him. Out comes the No Go Gauge and the handle just binds the same as it did on your build. You breath a sigh of relief. The rifle is in spec and the new kid gets a passing grade.
Oh but wait. Thanks to the tape the kid knows this chamber is right at the outside of the head space tolerance. He really wanted only the bare Go Gauge to clear. He knows he is at least .003” over his target. Dam. The kid says he overshot. Off comes the receiver and out comes the cutters to set that barrel back another turn. All clocked up right on our mark. Takes that Go Gauge measurement and goes in .003” less than last time. Receiver back on. Go Gauge drops in nicely. Oh no not the fricken tape again. One .002” thickness of tape added to the Go Gauge. Ahh success! The handle binds up and will not drop on the Go Gauge and his .002” addition. He knows the head space is somewhere between .0001” and .0019” of the target he set for himself. Very nice. Out the door it goes with the peace of mind knowing he has just set up another minimum head space chamber.
The customer now finds his full length die just makes the brass fit with the slightest effort to close. He is not working the brass hardly at all. Brass life averages 20 times before the necks give it up. The gun is a trouble free marvel of precision. The results speak for themselves.
The New Guy.
This just explains the tape. I also use a dial indicater and measue the bolt thrust clearance to read the actual clearance on the assembly with the Go Gauge in place.