I have a Husky 4100 30-06. I am attempting to measure for OAL with Sierra 165gr boat-tails.

With the bolt in, I marked a cleaning rod inserted into the barrel. Next, I installed a dummy round with the bullet seated out farther than normal in the chamber and held it in place while remarking the rod.

Measurement ~3.125

This is way short! The load manual calls for ~3.300 If I seat at that depth I have a hard bolt push. With the 3.125 the bolt moves smooth, as it should.

With the bullet seated at 3.125 it is so deep it that the case mouth is on the ogive.

What am I missing here? Can the chamber really be that short?

Have you cleaned the chamber and bore? Could be something stuck in there. Is this a new (to you) rifle? Have you tried a factory round? Are you sure the bore is .308 and not something smaller? Are you sure your bullets are 308 and not something bigger? Might be time for a chamber cast.

Are you taking into account that the tip of the bullet in your dummy round is going into the hole in the end of the cleaning rod?

Just for the heck of it try a different method of measuring COAL.

Run a fired case into the sizing die just enough to resize about 1/8" of the case neck. Seat a bullet long by hand, chamber the dummy round, close the bolt, remove and measure. Repeat to verify.

I will look at both things.

I'll have some time tomorrow to play around.

Good point. I have taken a screw that is the correct thread for the end of the cleaning rod and ground the head flat. Also make sure the firing pin does not protrude from the bolt face when you are getting that measurement. That should give you a true MAX COL.

Nothing like simplicity. I also soot the bullet so I can see if the lands grab the bullet and pull it out a bit upon extraction. This does happen, but if you soot the bullet, you can see exactly how far the bullet was pushed in by the lands, even if it does get pulled out a bit. Works every time and is a pretty damn accurate and easy way to find max OAL (aka lands)...

Yep.

Another thing I've done to get an understanding of the bullet/lands relationship is make a dummy cartridge with a fully sized neck, seat a bullet to max OAL, black it with a sharpie, chamber it, look at rifling marks, then decrease the OAL in .005" increments, and check the rifling marks at each stage.

It gives you an understanding of jamming the bullet, just a kiss/partial contact, and no contact.

That is the method that I use and it works every time.

I tried all the above. Only the Sinclair tool gave me repeatable (within 1-2 thousandths), and only then after recognizing some cases needed more force to chamber.

This was a finicky property to measure for me and the Sinclair tool was what I needed.

I use a variation of fish head's method. I FL size the brass, then cut and deburr two slots at 180 degrees to each other, the length of the neck, with a Dremel tool. With a little fiddling, that gives the right tension to hold the bullet just enough to get the OAL to the lands. As mentioned, I repeat it a couple of times to make sure I'm getting consistent results.

It's a very good method.

I use denton's method.

+1 for denton's method. Just have to remember to re-do the whole COAL measurement whenever I try a different bullet

The Hornady Lock & Load overall length gauge thingy works for me.

I use yet another variation--crushing the neck of a case fired in the rifle very slightly, either with pliers or a vise, just enough to hold the bullet.

That's all I do. Seat the bullet long and jam it home, pull it out and measure. Sometimes a bullet gets caught in the lands, sometimes not.

What I don't want is MORE stuff around, I have enough stuff.

Split case for the initial measurement then set the seater a few thousands long. Chamber the dummy to see land engagement (sharpie), adjust as the load tells you.

...and use a comparator

+1 on the comparator. It's just a lot more repeatable.

I don't know how people go without it. The Hornady one with inserts is the cats azz as far as I'm concerned. They can keep the modified shell chit though. Once size my brass, I'll take one piece and make a cut with a dremel. Then when I've found the COAL I want, it goes in the box and gets used to set the seater for each batch. Each lot of brass stays designated to a box (50 rounds, well 49 actually) with a designated dummy, and all loading data and drops stuck to the inside lid.

Easy peasy.

Like this...

THIS... get that Dremel tool out, does a great job on the slot. Repeat to check results.

3.290"

Finally had time to look at this again.
Used: "Run a fired case into the sizing die just enough to resize about 1/8" of the case neck. Seat a bullet long by hand, chamber the dummy round, close the bolt, remove and measure. Repeat to verify."

Thanks to all.