Mr Kern -
? To start with, you've got to realize that each auto-pistol maker makes their barrel and chamber slightly different from everyone else. That affects ammo feeding, types of ammo, etc that the gun can shoot.... and to a great deal the accuracy that results from shooting said ammo. All these barrels meet SAAMI specs and yet most all are radically different. The following cartoon will try to graphically explain...
? Secondly, when bullet makers tell us, use XYZ length as an OAL what they are saying is, "This is what we used and the results we got." They are
NOT saying this is the "perfect OAL", or that their OAL will work in
every gun, or that they think this is some kind of whiz-bang, never-fail, always-feed-correctly dimension. Far from it. If you'll read your manual you'll discover that this ammo testing takes place in "test barrels". This is a huge block of steel, bolted to a table top, with all sorts of meters and gauges hanging off of it. It is a "gun", but it is
NOT a pistol, and it is MOST DEFINITELY
not auto loading. It's a single shot hunk of steel, such as pictured below.
So anyone who thinks that the Hornady, Speer, or Hodgdon manual is suggesting that you use a certain OAL because it will feed well in your pistol is way, way off base. They never said that. They only said "It worked for us, now go make it work for you."
? Now certainly, those manual writers chose an OAL that will fit "popular pistols" and work out good for a lot of people. The problem is, they didn't tell us which popular pistol they chose. The second problem is, the most popular pistol out there has such huge dimensions on their chambers that you can almost shoot 50 BMG in their 9mm model.
? At the opposite end of the spectrum is the CZ and Springfield XD models. These are made in eastern Europe where they still respect fine pistols and craftsmanship. One of the ways CZ achieves such incredible accuracy is by shortening the "freebore"; that part of the bore in front of the chamber that has no rifling. This section is also known as the "leade". This is not usually an issue with RN bullets, and generally everyone is happy.
However when we use a bullet like the
Hornady XTP that brings the major diameter well out in front of the cartridge case mouth, this diameter can stick out far enough to strike the rifling. That is, the short freebore means we have to use a shorter OAL than most reloading manuals show. This because most reloading manuals are NOT written with the CZ and the Springfield XD series in mind. Follow? Luckily for us, as per above, there is nothing "sacred" about OAL on an auto cartridge and we can remedy this.
? So when you start this adventure of "what OAL should I use", I can only say that
it's a bit like driving. That is, if you stay between the boundaries, then you'll be fairly safe. So where are the boundaries? One is the
MAXIMUM usable OAL (as discussed in the post above), which can be arrived at with the telescoping "test cartridge".
The other boundary is the
MINIMUM safe OAL which is published load data with the shortest OAL you can find. There are also concerns about good cartridge feeding and maximum bullet seating depth when using extremely short OALs. But generally speaking, novice reloaders shouldn't use an OAL shorter than given in published load information.
? So we have our OAL picked out, the next thing we need is a powder load to match that OAL. In any gun the one thing we're fighting is chamber pressure. We definitely want to keep it in the safe range. Two main things make up chamber pressure: volume under the bullet (a function of OAL), and amount of powder. For the same bullet with the same bullet speed, the rule is: as the OAL gets shorter we reduce the powder. This handy chart shows generally what's going on....
?
We always want to start with a published load. ALWAYS. Every load you fire should be based on something published. There are too many authoritative sources available through the internet to use a load from an "internet buddy". This is why reloaders generally build a library, to have numerous published sources they can depend upon.
? So let's say our chosen OAL is 1.247" for a 190gr jacketed bullet and we find a load on-line at the Hodgdon web site with an OAL of 1.235" for a 190gr jacketed bullet. We can use it because the bullet construction and the bullet weights match. We can also use the load because they have quoted a shorter OAL. If we use the
shorter load but stay at the
longer cartridge length, then our pressure will be lower. That's right from the chart. Follow? You can always go for a longer OAL (within reason) on a published load; never shorter without reducing the powder.
My
personal preference would be to load at 1.240". In that way a) my pressure is a tad lower, b) my bullet is .007" further from the rifling, and c) 1.240" is a number that's much easier to read on a caliper. That's killing 3 files with one swat, so to speak. In actuality, it's being smart and thinking safe.
In reloading you always want to err toward safety. ? So what happens if the shortest publish load you can find is not short enough? For very small changes in OAL, you can proportion the load. This will call for some 6th grade Algegra, which if you are not up to it can lead to a very big mistake. I think it best to take those on a case-by-case basis. In other words, we'll cross that bridge IF we get there.
? Then comes the 5-10 rounds starting at the lowest possible load. Depending on the load spread, you might want to work your way upward in 0.1gr or 0.2gr increments. This is all the usual stuff you would do with any load.
? AND AS ALWAYS... you are making notes in your reloading notebook so you can come back to this load, know where you got the load, how it shoots, etc, etc should you be lucky enough to go on vacation for 2 weeks. So write it down!
Hope this helps!
