Just finished loading 50 rounds of .308 WIN with Hornady 180 SP projectiles.

The COAL called for in the Hornady manual is 2.74, but I found a wide variance in the final COAL using the same competition die setting; I set the die until I got the required COAL by increments, then subsequent cartridges would vary by as much as +/-0.005-0.007. It looked like the lead insert was being mashed by the seater.

The projectiles had a cannelure, so I used that as the correct insertion level.

So, my questions is: how to accurately measure COAL with a malleable tip in the projectile.

BTW, this is the first instance of this issue I've had. HP and plastic tipped projectiles did not exhibit this.

COAL is a maximum specification to allow the ammo to fit any magazine box that conforms to SAAMI specs. You will have variances from the lead meplat, and that is perfectly normal.

You need to use a comparator to get a measurement of bullet seating depth independent of the meplat. This acts like a little collar that allows you to get a more consistent measurement, however the effectiveness of this tool depends on how consistent the bullets' ogive are from bullet to bullet.


https://www.midwayusa.com/prod...c-set-with-6-inserts

Link to original video: https://www.youtube.com/watch?v=cX1M3Nk_CkM

You can get a custom seating plug made for your seating die that fits the bullet profile your using. I know Hornady has them for some of their bullets. With these contoured to the bullet you will not do any damage to the bullet. With every die set I get I always remove the seating plug and smooth out the sharp edges, so it doesn't mark the bullet.

Like said you need to measure your bullets at some point were you stay away from the tips. You can make your own up pretty easy. If I have a preference it would be the dia in which the rifling contacts the bullet. This will let you know what your jump to land is once you know your chamber.

Put 0.005" on your calipers, you can barely see it. It is not an issue UNLESS that length puts you into the rifling. It will not affect pressures or accuracy. A bullets nose profile can vary that much.

Before you get all worried, why not first measure the COL of factory rounds and the length of your bullets.
Next, get a custom seater that does NOT touch the meplat and contacts low on the ogive. Note: the micrometer only helps to return to a past setting, provided you made note of it--it doesn't improve the accuracy or precision of the rounds.
Finally, the COL in a manual is their test COL, and that is all it really is.
Your COL (Cartridge Overall Length) is determined by your barrel (chamber and throat dimensions) and your gun (feed ramp) and your magazine (COL that fits magazine and when the magazine lips release the round for feeding) and the PARTICULAR bullet you are using. What worked in a pressure barrel or the lab's gun or in my gun has very little to do with what will work best in your gun. For rifles, I find that the longest COL that fits the magazine and chambers without directly contacting the lede/rifling is almost always the most accurate.
Create two inert dummy rounds (no powder or primer) at max COL (or COL that fits the magazine) and remove enough case mouth flare for rounds to chamber (With handguns, you can achieve this by using a sized case, expand-and-flare it, and remove the flare just until the case "plunks" in the barrel or cylinder).
Feed the inert rounds in and decrease the COL until they chamber completely. This will be your "max" effective COL. For handguns, I prefer to have the case head flush with the barrel hood (or a few mils higher than where the head of an empty case aligns with the barrel, as all cases are too short and I prefer to minimize head space). After this, place the inert rounds in the magazine and be sure they fit the magazine and feed and chamber.
You can also do this for any chambering problems you have. Remove the barrel and drop rounds in until you find one that won't chamber. Take that round and "paint" the bullet and case black with Magic Marker or other marker. Drop this round in the barrel and rotate it back-and-forth.
Remove and inspect the round:
1) Scratches on bullet--COL is too long
2) Scratches on edge of the case mouth--insufficient crimp
3) Scratches just below the case mouth--too much crimp, you're crushing the case
4) Scratches on case at base of bullet--bullet seated crooked due to insufficient case expansion (not case mouth flare) or improper seating stem fit
5) Scratches on case just above extractor groove--case bulge not removed during sizing. May need a bulge buster.

I don't worry about slight tip variations, I measure to the bullet 'olgive'/shoulder.

I compare book numbers, to mag length, then most importantly to the point of rifling contact. One doesn't want a bullet pulled out & stuck in the rifling while out hunting(unloading).

I have a simple tool that measures max COL to rifling contact with any bullet. It's a rod with two locking collars in the stem. Whatever I'm doing I leave a bit of room so the bullet never contacts the rifling.

With certain chambers, book COL is no guarantee the load won't contact the rifling.

I run the bullet in an empty case in the chamber and let the pressure of being chambered press the bullet into the case. Chambering the round allows the firearm to select the cartridge length, and then I work it back slightly. Minima jump into the forcing cone, better accuracy. After that, so long as they can cycle properly and they're accurate, then it's a matter of working up the load to go behind it.