How do you find COAL/CBTO

[Wolfdog91]

Split case method here, either that or take a prepped piece of fire formed and should bumped brass for the rifle seat a bullet long and keep seating it till it chambers with no resistance
What about y'all ?


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[waco]

I’ve been very satisfied with this.
https://www.hornady.com/modified-cases#!/

[Dusty Bannister]

Cleaning rod/dowel method of finding cartridge OAL

This is what I use for my guns to determine the max OAL and this eliminates any question of the crimp, incorrect case prep, or other operator induced error.

This method works well on rifles and single shot pistols as well as Semi-autos. You can use a flat tipped cleaning rod, or flat tipped dowel rod. You will also need a sharp pointed pencil, a short dowel and a bullet sized but clean, of the type you are going to load.

For Rifles
Make sure the chamber is empty. Close the bolt, and be sure the firing pin is retracted into the bolt. Insert the dowel or cleaning rod and hold it against the face of the bolt. Mark the rod at the face of the muzzle. Remove rod, open bolt and remove it from the action. Insert the bullet into the breech and hold it snug into the rifling. While in that position insert the dowel or rod again, and with it firm against the nose of the bullet, mark the rod at the face of the muzzle.

The distance between the center of those two marks is the max cartridge OAL for that rifle, with that bullet sized to that diameter.

For Semi-autos
Remove the barrel from the slide and make sure it is clean and free of leading or other debris in the barrel and chamber. The dowel or cleaning rod needs to be longer than the barrel. Hold the barrel, muzzle up, and place the barrel hood on a flat surface like a table top. Insert the dowel or rod from the muzzle and mark the rod exactly flush with the muzzle. Remove the rod and insert the bullet you intend to use into the chamber and lightly press and hold it in place with the short dowel. Place the assy muzzle up on the flat surface. Insert the rod/dowel into the muzzle so it rests on the nose of the bullet and again mark the rod exactly flush with the muzzle. Remove and set the barrel aside. The distance on the center of the two lines is the cartridge OAL. Seat a dummy round to this length, or slightly shorter and begin to apply the taper crimp until the dummy passes the plunk test. This is the optimim cartridge OAL length for this bullet in this gun.

You may need to adjust the seater to shorten the OAL if this does not feed from the magazine, but generally this will be a great fit. Remember, if you seat and crimp in one step, you might force a slight ridge ahead of the case mouth and that will screw up your seating.
Dusty

[Hick]

I like the split case method-- always worked for me. You did a much nicer job of making the split case-- I just use a hacksaw.

[Hannibal]

I also like the Hornady tool. Used to be called a Stoney Point.

You don't need to purchase the modified cases *if* you have a lathe. You can purchase a 14/28 tap and.use your own fired cases.

Otherwise you'll need to buy them from Hornady.

Remember that whatever tool or measurement method you use it is a COMPARATOR. They do not give precise measurements.

Took me a while to wrap my head around that.

[charlie b]

I start with a too long seated bullet and mark it with a sharpie. Chamber it (stripped bolt). At first it won't go in, but, will leave marks where it is touching. Then I reset the seat die to be a bit closer. Repeat until it is where I want it. I mark when it no longer touches and measure the CBTO and OAL.

[cwtebay]

I started before the Hornady option was there. I split a case as you have, place my bullet of choice in the mouth, carefully chamber it, measure the COAL. I do that at least 10 times and record the measurement. The average minus my choice of set back is my starting COAL.

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[Texas by God]

I always just bit the fired case mouth into a slight oval, then started the bullet in the neck and pushed it home. Then carefully removed it and measured OAL.
My brother would do the same, except use a plain base bullet started backwards- it would stop on the throat to indicate OAL.
Nowadays I just seat to a little below magazine length and go from there.
If I had any precision single shot rifles, I’d use the Hornady tool - that I have but never use.


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[M-Tecs]

I also like the Hornady tool. Used to be called a Stoney Point.

You don't need to purchase the modified cases *if* you have a lathe. You can purchase a 14/28 tap and.use your own fired cases.

Otherwise you'll need to buy them from Hornady.

Remember that whatever tool or measurement method you use it is a COMPARATOR. They do not give precise measurements.

Took me a while to wrap my head around that.

Stoney point and Hornady use 5/16 x 36

https://bulletin.accurateshooter.com...y-o-a-l-gauge/

https://www.amazon.com/gp/product/B0...T2UEIIAS3G5PNZ

[popper]

Just ordered the hornady comparator that goes on the calipers. Loaded a bunch and some wouldn't chamber. All other case measurements were fine. Only thing left is ogive is funky (or my seating die), no other way to verify. I tried making a kluged one but not accurate enough.

[Hannibal]

Stoney point and Hornady use 5/16 x 32

https://bulletin.accurateshooter.com...y-o-a-l-gauge/

You are probably correct. I knew it was an oddball and 1/4-28 isn't really odd enough. I can't lay my eyes on my tap at the moment.

[MostlyLeverGuns]

For simply loading and shooting single shots, loading 'max' COAL, based on chamber, throat and rifling can be useful, BUT if loading into the magazine, the COAL must fit in the magazine AND function through the action. Even if a cartridge chambers without problems and shoots accurately, the COAL should allow the UNFIRED cartridge to be ejected, sometimes the cartridges that fit the magazine and function through the action into the chamber are still too long to eject when not fired, do not ask how I know this. Bullet diameter in the throat and where it bumps the rifling also come into play. Usually a little accuracy can be gained with cast boolits bumping the rifling, but there are other considerations.

[JonB_in_Glencoe]

I also like the Hornady tool. Used to be called a Stoney Point.

I also had a Stoney point.
I didn't like it...or it didn't like me?
I sold it (I kinda think M-Tecs bought it???)

My current technique is to load dummy rounds, differing COAL and crimped so the castboolit can't move.
I like to examine witness marks on the boolit, that tells me more than where the boolit stops.
Also, in leverguns, it tells me what will cycle through the action, and what won't.

[Hannibal]

I agree with what you say. I'd add that if you are unfortunate enough to have a long freebore slightly oversized in a repeater or semi-auto you've a decision to make.

You can focus on reliability. You can focus on accuracy. Or you can settle for mediocrity somewhere in the middle.

[JonB_in_Glencoe]

I agree with what you say. I'd add that if you are unfortunate enough to have a long freebore slightly oversized in a repeater or semi-auto you've a decision to make.

You can focus on reliability. You can focus on accuracy. Or you can settle for mediocrity somewhere in the middle.

I would be focusing on buying a better mold design for that particular gun, LOL.

[Hannibal]

I would be focusing on buying a better mold design for that particular gun, LOL.

Rabbit hole, in my opinion.

And that opinion is worth exactly what you paid for it.

[Bigslug]

Used the Stoney Point / Hornaday method a lot. Probably the most ideal.

Go forward to contact certainly works

Have a few for which the magazine length said "Nuts to whatever your throat says! I say the round needs to be shorter!"

[JonB_in_Glencoe]

Rabbit hole, in my opinion.

Yeah, but a mold rabbit hole is lots cheaper than a gun rabbit hole, LOL

[Bazoo]

I start with a too long seated bullet and mark it with a sharpie. Chamber it (stripped bolt). At first it won't go in, but, will leave marks where it is touching. Then I reset the seat die to be a bit closer. Repeat until it is where I want it. I mark when it no longer touches and measure the CBTO and OAL.

Pretty much how I do it too.

[MostlyLeverGuns]

Measuring all that 'stuff' is nice, and interesting, but actually shooting answers many questions and messes with many theories. USUALLY the fattest bullet that chambers reliably gets you to the most accurate bullet so you can enjoy improving shooting skills rather than tinkering with different loads though the tinkering can be fun. You can always buy a box of quality jacketed bullets, pick a standard 'accuracy' load and then try to match that with cast boolits. Accuracy WITHOUT reliability or reliability WITHOUT accuracy are both a waste of time and materials.