+1 on go guage and scotch tape I’ve done dozens this way. A go guage isn’t a huge investment and easy to get rid of you don’t need. Headspace isn’t something to fuck around with.
Lets do a little experiment. I take a cartridge out of the box and fire it through a gun known to have a qualified HS dimension. Now, I size that case only I'm a goof and I have my die set way to close to the shell holder. Pick a number, it doesn't matter.
Later I pull the barrel and reinstall it. I use that case to set it back up. It may work fine, but the HS is now too tight because I used a case that was shoulder bumped too far. If I attempt to run OEM brass through it again, I'll likely have a problem.
Now, the inverse.
My gun was fuggered up from the start but I don't know it. The HS is too deep. I pull the barrel for whatever reason and now decide to stick it back on. I use one of those fired cases again as my gauge, and as you suggested, use a piece of tape to serve as the clearance.
The scotch tape I have in my office measures .0035" in thickness. With most HS gauges the difference between GO and NO GO is .004".
That would be issue number #1.
#2:
The HS value was already too long in this scenario, but we don't know it. I use my fired case as the gauge and add the tape. We know now that were at minium, +.0035" from the minimum accepted value. Not ideal, but not a deal breaker for sure. The issue is, we started with a chamber that was already too deep. -Then we added .0035" to whatever that is.
In the real world you can shoot this and in almost every circumstance it'll be fine. No "smile, wait for flash" episodes where your racing to the hospital to reattach your face. In this case, The Devil waits to rear its ugly face after you've gained some false confidence. (cause he's a dick like that)
The issue comes later as you attempt to size the brass. Firing it robbed material from the web feature on the case. It used that portion of the case to make it longer so that it could fill up the vacant area.
The details of how this works:
Case is sitting in chamber. Striker contacts primer, case begins to scoot forward until its stopped by either the throat or the shoulder. Primer is detonated and case begins to expand from the rise in pressure. Case body is now locked against chamber wall because it has "stiction" and quite a bit of square footage for contact. The head of the case is not seated against the bolt face. Pressure continues to rise...
Now its high enough so that the brass yields. It deforms like plastic. It stretches to fill the empty void. The web is where this stretching takes place because its not supported by anything. It literally hangs in space on the ass end of the barrel. Pressure is determined to find something for it to push against. The case head is searching for the face of the bolt. As a consequence, the web feature cross section is now thinner. -BUT, we don't know this. (yet)
Were done for the day, we go home, and we start prepping brass for the next outing. You set your dies up off the original setup, but its too short. -Again, you don't realize this. (yet, its coming...) So you bang away on shoulders, finish it up, and go back the following free moment to shoot.
Roulette wheel time. Maaaybe you get lucky and it works, maybe you start popping case heads like pimples. The brass will at some point give up the goods and show you the mistake you made in judgement. Its usually within 3 firings. Sometimes you get lucky and get 4.
When it fails, the head of the case splits from the case body. It makes a mess, fire checks the shit out of stuff, and usually murders the extractor. You get a face full of garbage and hopefully it ends there. I know of two instances where folks ended up in the ER with one of those poor souls being prepped for surgery.
$40 or so bucks on a HS gauge solves all of this. Anyone of us will spend at least that much this week on shitty drive through lunches.
Take it seriously and save your face, your gun, your sanity.
C.
