Previously, there was a discussion on the Stoney Point comparator. Another use is sorting bullets. Its common when seating bullets to find variations in both the LOL and COL lengths. It your trying to get every bit of accuracy out of 'ol Betsy or your favorite varmint rig, sorting bullets may help.
Lets say you want to seat .010" off the lands, so you measure the depth of the chamber with a modified case with your favorite bullet. You take that reading, seat a bullet 10 off and load 100 rounds with that setting. All the same right? Well, mabye not. Two things may affect that measurement. First is the casehead runout and second, the ogive placement on the bullet. All bullets are not created equal even from the most respected makers. Mass produced bullets can vary quite a bit and short of buying only the best quality, like Fowler's,BIBs,etc, the average guy picks up Hornady,Nosler,Sierra and so on. Contrary to what is said, bullets from different machines are (sometimes) mixed in the same box and lot. If one machine is out of adjustment or the dies worn, variations in bullet dimensions will occure. To make the matters worse, setting 10 machines up exactly the same is almost impossible. This may be one of the reasons we get flyers or shoot good groups one day and shotgun patterns the next.
Using the tool to check and sort bullets from the base to ogive may help keeping the shots in one spot.

In the picture below are a group of 6mm bullets from a well known manufacturer,same box, same lot. The variation,from a low of .436" up to one at .445", .007" difference in the bullet bearing surface.
Recently I received 400 68 grain flat based 6mm "Custom" swaged bullets from someone trying to make accurate BR slugs. The base to ogive varied from .351" to .382". I think his process needs a bit more work.
I like experimenting, so most of my seaters have been modified to contact close on the bullet ogive to help eliminate COL lengths due to variations forward of the ogive.

Well, I just wanted to pass this info on. I'm sure some already know this stuff, but for those that didn't, mabye it will be of some help.
By the way, a even more accurate method is to use two comparators for boat tail bullets, one on the ogive and the other on the base.

Bill

Hello BillPa,

You really hit the nail on the head with that one. Dimensionally all bullets are definitely not the same. I do find most are fairly concentric to the ogive, but the OAL leaves something to be desired. That's always been a problem, even among the custom bullet makers. I'll use custom bullets in .224 and .243 occasionally and all other things being equal they are a cut above, well worth the extra money. Just one mans opinion. Best wishes.

Cal - Montreal

Howdy. Good stuff BIll. keep the good info coming

Billpa- Thanks for the info, I had no idea there was that much difference (I'm new to reloading).

Thank you foe the info.

I think the only part that's really vital to our accuracy is the length to the ogive. I don't worry much about the overall length too much because anything beyond the ogive is just sitting out there and touching nothing. Just one mans opinion though. Best wishes.

Cal - Montreal

This is where items like the RCBS Case Mic come into their own. They only measure to the ogive. That's the only important measurement. The actual length of the bullet doesn't mean much in front of the ogive since it just sits out there touching nothing. The Stoney Point OAL guages don't tell us a lot. Much better are some of the ones sold by Sinclair, Hart and others. Really, it doesn't always benefit the reloader to seat out to the lands since some loads prefer to be shorter and have to jump to the lands.
An exact science this area isn't. Best wishes.

Cal - Montreal

I hate to ask dumb question, but what do you mean by "ogive" ?

The ogive is the sloping portion of the bullet that determines where it first touches the rifling. The point it will first touch the rifling is that point where the ogive tapers to the diameter of the bore. That is why the OAL of a cartridge is not as important as the distance from the head space point (the shoulder in a rimless cartridge) to that point on the ogive that will first touch the rifling. As Cal has said....the part of the bullet beyond that contact point just sits in the barrel and makes no difference in bullet seating depth. The bullet could be 1/10 longer than the one before it with no consequence as long as the point on the ogive to the head space point is the same.

If I'm not mistaken, the Lee "dead length" bullet seating die seats the bullet from the point on the ogive described in the previous post. Therefore, as long as you have the die adjusted to the OAL that was determined from your gun, it should seat all the bullets to that point. To find the die adjustment, I take a fired and unsized case, and start a bullet into the neck hand tight. Ink the bullet in good shape (some folks smoke it ), then chamber the round SLOWLY in small fits and starts until the action seats the bullet as it contacts the lands. Then slowly extract the round. If the bullet is in the case, good. If not lightly tap it out from the muzzle end using a suitably sized wooden dowel. Stick it back into the neck to where the ink is rubbed off. Now you have a "dummy round that just touches the rifling. Place the dummy into your press and screw the bullet seating stem down till it just makes contact with the dummy bullet. Remove the round and calculate how much to more to screw the seating stem down (based on what thread pitch you have) to obtain the amount you want off the lands.

Blaine