I have no headspace gauge or other such complicated tools, but I want to experiment with trying different overall lengths of my 22-250s in an attempt to improve accuracy of my Thompson Center Pro Hunter. So I was thinking....
I resized and de primed a case, drilled through the bottom of the primer pocket and threaded the hole using a tap/die set. Thus I am able to screw a small bolt through the bottom of the case and push a seated bullet back out of the case. This is a handy little tool to use when adjusting a seating die, by the way.*
Now, here is my proposition. Suppose a person were to loosley seat a bullet in the case throat of this handy little tool, knowing it was not seated deeply enough. Suppose they chambered this round and closed the breech of their Pro Hunter.
When the round is removed from the chamber would it be possible to measure it's length and have a reasonably accurate idea of what overall case length will produce a round that places the bullet directly ON tthe lands of the riffling?
Would said person then be able to experiment with various lengths of cases, using their findings from the aforesaid process as a baseline? Or it this not a viable option?
I think it would be a good idea to do this several times and get an average length. I also am aware that seating a bullet ON the lands creates pressure issues, necessitating that one decrease the powder used and re-work their load data.
All this aside, I think this idea may work. I understand that using a professionally made headspace gauge/tool would be easier and more accurate, as o-gives vary from bullet to bullet. One of these days I plan to purchase one of these tools, and several others as cash flow allows. But will this work for now?
I would appreciate any good thoughts and input. I will accept useful criticism. If, however you plan to post simply to ridicule, don't waste my time or yours.

*The idea to create this "handy little tool" should be credited to Larry Medler, past Michigan state champion in the 600yard silhouette shooting competition.

In a T/C , a loose fiting bullet in the case should be pushed back by the rifling. Results showing maximum COL.

You have your terms profoundly confused. "Headspace" is the distance from the face of the bolt to whatever feature on the case serves as the "stopping point" for the case (holds the case against the bolt face when the bolt is in battery). This may be the rim on a rimmed cartridge, but most often is the shoulder on a bottlenecked rifle case.

When a bottlenecked case is too short from its base to its shoulder (or the chamber is too long for it), then an instance of "excessive headspace" exists.

You seem to be seeking the optimal OVERALL LENGTH of the loaded cartridge, which has to do with the leade, or freebore, and the shape of the bullet.

Actually you are confusing Headspace with the
distance to the datum line. Headspace is the
distance between the breech face and the head of the case period. You can't have headspace without a case in the chamber.

Many thanks to 243, who had something useful to contribute. I like this idea even better! Again, thank you.

quote:

Originally posted by 243winxb:
In a T/C , a loose fiting bullet in the case should be pushed back by the rifling. Results showing maximum COL.

Need clarification. I tried this method of bullet seating depth on my gun. I get a small ring where the ink rubs off on the bullet from where I assume the bullet and the lands touch. This is ABOVE where the case neck is. Do I lower the bullet into the case where this line is rubbed off or do I just lower the bullet into the neck where the neck scraped off the ink...make sense?

quote:

I get a small ring where the ink rubs off on the bullet from where I assume the bullet and the lands touch.

Correct. This is your maximum COL,This COL must fit your magazing & feed correctly. Hunting rifles should have the COL adjusted shorter/bullet seated deeper by at least .010" More is Ok also, as some bullet may never contact the rifling.

quote:

Originally posted by 243winxb:

quote:

I get a small ring where the ink rubs off on the bullet from where I assume the bullet and the lands touch.

Correct. This is your maximum COL,This COL must fit your magazing & feed correctly. Hunting rifles should have the COL adjusted shorter/bullet seated deeper by at least .010" More is Ok also, as some bullet may never contact the rifling.

Great that helps a lot. So I need to measure up to that line and then seat deeper by a minimum of 0.010", correct? This is measuring off of the ogive and not the tip? I don't have an ogive measuring tool, just calipers...

When I checked mine using this method, I come up with a max COL of 3.050 (.260 rem) I can't hardly seat any longer than 2.890. Is this excessive free bore? The rifle is a Ruger M77 with an E.R. Shaw barrel and does not group very well.
Any thoughts?

quote:

This is measuring off of the ogive and not the tip?

Measure off the tip, because you dont have an ogive measuring tool

quote:

Originally posted by Johnp034:
When I checked mine using this method, I come up with a max COL of 3.050 (.260 rem) I can't hardly seat any longer than 2.890. Is this excessive free bore? The rifle is a Ruger M77 with an E.R. Shaw barrel and does not group very well.
Any thoughts?

Excessive free bore,no is my guess. The rife has to be chambered to accept the longest, heavest bullets for the caliber. Its possible to jump bullets and still have accuracy. Don't make the mistake of thinking you need to have you bullets seated into the rifling. Check the standard free bore measurement. http://www.saami.org/PubResour.../260%20Remington.pdf

Measuring off the tip of the bullet is full of problems because bullets are NOT always uniform in length...you can have up to 0.020" difference.

You can get away with doing it that way IF you use the same bullet FOR ALL MEASUREMENTS...

At one time way in the distant past I had all kinds/brands/weights of bullets all cataloged and measured and used as "standards"...I thought I was doing something new and exciting until one of my mentors took me under his wing and showed me the easy ways, made me a few gauges out of 1" round stock cut to exactly 1" long...for 22-6mm-25 and 30cal, let me make a couple of measuring tools(same as Sinclairs tools) using his lathe/mill THEN showed me what I hadn't learned yet. All that stuff can be found on the net today and isn't "secret knowledge" anymore.

The same thing can happen if you use the ogive althougth ogive usually don't have more than 0.005" variation.

MAKE YOUR OWN OGIVE MEASURING TOOL...just drill a hole smaller than the bullet dia in a piece of brass, steel, etc...measure the total OAL of the "tool" and subtract that number from the total OAL with the bullet inserted into the tool...then subtract that number from the seated bullet OAL...that will be the base to ogive measurement...THAT NUMBER IS ALL THAT IS REQUIRED...SEAT THE BULLET 0.010" SHORTER AND YOU HAVE A BEGINNING POINT TO START.

Look in the Sinclair catalog or Midway...and see just what the tool looks like....it's use should be self explanatory.

The easiest way is to buy a set of Hornady headspace/bullet OAL gauges or one of the "Hex nut" headspace guages from Sinclair...and make/buy one of the tools for measuring seating OAL's from Sinclair.

Probably the best thing you can do is order a Sinclair catalog and a hex nut, go to some of the varminting forums and just read what is going on and learn the correct terminology for all this stuff.

"Lurking" on forums can give you lots of good information, but also just as much BS...the object is to learn HOW to separate the two, keep the good stuff and forget the other.

Your idea is OK, has been used in slightly different forms for probably 100 years, but there are simpler ways to do it.

Break out your caliper and mic and start measuring bullet lengths, ogives, OD's...make/buy a gauge and measure case shoulder to base, case OAL and all the rest of the case dimensions so you can start to understand just what it is you want to do.

Checking out the varminting and benchrest forums will also give you an understanding of just WHAT is really important and what is just wasting time.

Dennis Bellm is the place to go for information on the T/C and how to best set up your dies and adjust headspace...I knew him when I was taking over P.O. Ackley's buisiness WAY back in SLC. I've used his pins and trigger springs in all my T/C's. He explains the problems with T/C's accuracy and how to "fix" them plus will fix your T/C if you want.

Luck

I find the COL by pinching the fired case neck with plyers. Place bullet in case mouth at the longest setting. Insert dummy round into rifle. Extract dummy while holding case with fingers so the ejector does not push it against the side of the receiver. Do this many times till you get the same COL measurement. For hunting, set the bullet at least .010" deeper or till dummy round fits the magazine.