C.O.A.L. vs B.T.O.

[Whiskey59]

I maybe way over thinking this but here it goes. Loading Speer 90 gr. TNT, book says 1.190 C.O.A.L. Now the bullets are supposed to be 0.900 inches long and as we all know length varies due to tip variation. Ok, so I will measure base to ogive. Measuring bullet base to ogive varies as much as 0.005 inch. I even found 2 bullets that measured at .900 but had different bullet base to ogive measurements. How can I get cartridge B.T.O. consistent if I can't find a reliable starting point? Rifle is an AR 20 inch 5R barrel.

[Klem]

You are expecting too much.

Base-to-ogive varies also, but reportedly not as a much as base to tip. Some careful shooters separate their bullets by weight into a few similar batches. You can do the same by length if you want, although I doubt you will notice any difference on target. Definitely more effort than it's worth if you are shooting an AR.

[FLshooter]

[grayfox]

In particular my lead-tips, like the sierra gameking, will vary in length +/- 0.005", but will cloverleaf at 100 yds with my 243.
In an AR the performance (+/- 0.005) is even less obvious, as Klem and FLs have pointed out. The shooter (in this case, me) is the largest source of error.

[imaguy3]

When someone is saying base to ogive, don't confuse cartridge base with bullet base.

The ogive is where the bullet first contacts the lands, the amount of jump b/t the bullet ogive and lands is what I worry about. I worry about cartridge base to ogive measurement being the same, meaning my jump to the lands is the same every time.

When I load my rounds, maybe it's overkill... but I will do the first bullet seating approximately 0.010 longer than I want. I measure it, and then adjust my microjust stem to get it exactly where I want it. This results in every single round I have being the exact same cartridge base to ogive measurement down to 0.001

https://www.hornady.com/reloading/precision-measuring/precision-tools-and-gauges/lock-n-load-bullet-comparator#!/

https://www.amazon.com/Hornady-044090-Microjust-Seating-Stem/dp/B000GU9VU4

You don't need to worry about small differences in bullet base to ogive...

[65newloader]

I agree. Been going through mine the last couple of days. I have ELD-Ms, Sierra MatchKings, SSTs, and LH Controlled chaos. I try to get all of the CBTO the same per bullet. The COAL is just a reference and has really no meaning except if it will fit in the mag(longest thing I could fit in the mag was an ELDM out to 2.305"... the tip just cleared and still have almost .030" jump). Going to modify one 10 rnd mag to except the a longer round and play with the jump and see what happens. It may not yield much, but experimenting is half the fun.

[1Shot]

Yes measurement is to be from base of case to ogive of bullet for closest consistent length. But in my 40 years of handloading everything from precision bench rest rifles down to vintage war rifles 5 thousands difference in ogive to lands 99% of the time will not make any difference in accuracy. I have been involved in some very high class bench rest shooting matches where everyone on the line is SUPER ANIAL about EVERYTHING in their whole set up. The difference in accuracy on target difference between all of them is wind, trigger control and repetitive placement of rifle to the exact place on the rest between shots. Wind is the biggest factor. With a slam bang action of an AR having to load from a magazine where the bullet ogive is usually a mile off the lands shooting from who knows what kind of rest it is a wonder that we can hit the side of a barn. LOL Trigger time will make for more accurate shooting than spending time beating one's head against the wall trying to make every round measure out to be exact in my experience.