Measuring OGIVE

[BBarn]

I can certainly relate to where 44 AMP is coming from. For a bolt action:

I take an empty case fired from the rifle and slightly dent the case mouth until it will hold a bullet in place. Then I measure about 10 bullets and choose the longest one. Next I push that bullet in the case about 0.1” or so. Then I blacken the exposed portion of the bullet with a black Sharpie.

Open the bolt and insert the bullet/case into the chamber with a finger. As the bullet/case is pushed fully into the chamber, you can feel the bullet being driven further into the case by the rifling. Close the bolt. Open the bolt and carefully remove the bullet/case, holding the case against the bolt face as long as possible, and carefully removing the bullet/case from the action without disturbing the bullet position. (This is more difficult on actions with plunger ejectors). If the bullet slips out of the case slightly as it's removed from the chamber/action, there will be scratches through the black Sharpie near the case mouth (and you repeat the process, ignoring that particular attempt).

After removing the bullet/case, measure it's overall length and write it down. Repeat at least 2 more times, or until a consistent measurement is reached, one that is close to the longest length noted. Then I use that as a max overall length of that cartridge in that gun when using that bullet.

As I load the cartridges, I shorten the OAL by about 0.030” or so by seating the bullet deeper (as a starting point). (This also assumes that cartridge length will also fit in the magazine). If I wish to increase the overall length, I will do so, but only up to about 0.010” shorter than the maximum OAL length noted earlier.

No fancy tools. Just a fired case, bullets, a Sharpie, and calipers. Other similar ways to do it. Some probably better. Has worked fine for me since I'm content to locate the bullet about 0.010” or more off the rifling. Perhaps not good enough someone trying to shoot the smallest of groups.

 

[Unclenick]

44 AMP,

The ogive tools, like most loading tools, are a convenience. Their purpose is controlling bullet jump to the throat. There is almost always another way to do it or a way to improvise that takes another step or two or a little more coordination, so the tools are not a "must", by any means. Just a convenience. Since a lot of bullets (hollow point match bullets, in particular) have significant length variation (I've measured up to 17 thousandths in the same box of MatchKings in one instance) the ogive location is a more consistent locator and most seating die rams (stem tips) contact the bullet somewhere along the ogive and not from the tip, so it coordinates with them a little better.

As to why one wants to control ogive location, there are two reasons: pressure and accuracy optimization. Ninodesmente, in his other thread, found a bullet with a short ogive that was jamming the lands in his gun even at the bullet factory (Hornady) recommended COL. In order not to see throat proximity elevate pressure he needs to be sure that short ogive location (a Hornady V-max design, btw, so, not a rare oddball) and his short throat have about 0.020"-0.030" clearance (see graph below for why). You can also get to this number by making a split neck gauge and finding the bullet jamming COL and then seating shorter by 0.020"-0.030". Again, there are several special tools on the market that try to make this easier, but you don't have to have them. It's just a matter of what you think your time is worth or what helps keep you from trying your patience or what gives you more peace of mind regarding the accuracy of your control.

Group size is something many people don't realize can be further tuned beyond powder charge alone by controlling seating depth. Under item 3 in this old article, an old sporterized 8 mm Mauser with a badly worn throat is turned into a sub-half moa shooter just by getting jump long enough. In this Berger article, it explains it is actually necessary to find the best jump for some of the VLD bullets to make them shoot well at all. In the 1995 Precision Shooting Reloading Guide, benchrest competitor Dan Hackett reported moving the jump in a 40X in 220 Swift from 0.020" to 0.050" shrank 5-shot 100-yard groups from half an inch to about a fifth of an inch.

If you establish a good jump for your gun with one bullet, it often likes others to jump close to the same amount. The cartridge head-to-ogive measurement tools let you quickly set the jump of a new bullet with a different ogive shape to the same depth as another to use as a starting point to find the best jump for accuracy with the new bullet. Again, the specific tools are not essential, as there are numerous workarounds, but they are a convenience.

Now, do you need any of this to shoot to hunting or even basic high power target accuracy? Usually not. Unless you are using secant ogive VLD bullets the standard designs can usually just be set to their maker's recommended COL and they will shoot quite well. These methods are usually just for those of us driven to shave the last fraction of a moa off our groups by whatever compulsion, usually just because it's fun to get some success in this regard. But occasionally you get a situation like Ninodesmente's where the bullet and chamber just don't fit and there is potential for it to be a safety issue. Probably not a catastrophic risk type of safety issue very often, but more often about avoiding primer piercing and bolt face gas cutting and case head expansion or short brass life.