GLOOB said:
And how often have to gotten better accuracy by increasing OAL?
I personally don't think it matters much in a handgun, unless you are shooting off a bench.
Testing max OAL is good to avoid problems. But it your gun's max OAL is way longer than normal, there's no reason to purposely make your ammo out of spec unless you're ACTUALLY getting better accuracy and reliability.
Right. Ultimately, holes on target speak volumes regardless what we rationalize.
In theory, the sooner the bearing surface of the bullet engages the rifling, less high pressure gas leaks around the bullet and faster the chamber pressure starts to build. This would result in more consistent chamber pressures and more consistent muzzle velocities which affects shot group accuracy.
At least in theory.
In practice, I am more concerned with reliable feeding/chambering from the magazine than the absolute longest "Ideal OAL" as you cannot obtain those "super accurate and tight" shot groups if the rounds won't chamber fully. Right?
And if reloading process/component variations produce enough OAL variations to allow the bullet to hit the rifling when chambered, pressure spike could occur on initial powder ignition.
Once I determine the
Max OAL (the longest OAL the chamber/rifling will allow without hitting the start of rifling) for a particular bullet, I focus more on the
Ideal OAL (the longest OAL the pistol/barrel/magazine combination will reliably feed when the slide is manually released) before I start my powder work up. I could be wrong, but to a certain extent, adjustments to the powder charge may make up for the slightly increase in high pressure gas leakage from shorter Ideal OAL (If anyone has any test experience, I would love to hear them and we are talking about semi-auto pistol only).
As the powder work up is conducted from a designated start charge (if I am using a shorter OAL than published, I will decrease my start charge, say by .2-.3 gr), consistency in chamber pressures should be expressed as accuracy trend in shot groups. It's been my observation that for most powders, accuracy tends to increase as powder charge increases. For some powders, especially for faster burning powders (W231/HP-38 and faster), accuracy is achieved even at start-to-mid range load data and plateau or increase more gradually. Sometimes, depending on barrel diameter/rifling type/leade length and bullet type, accuracy starts to degrade, especially for lead bullets.
For lead bullets, proper bullet-to-barrel fit is very important and I believe the longer Ideal OAL plays a key role in generating the initial pressure build up to deform the bullet base to seal the bullet to the barrel (obturation) to produce accuracy and minimize/prevent gas cutting/bullet base erosion and leading.
Glen Fryxell's ebook has an excellent chapter on lead bullets/powder selection/leading -
http://www.lasc.us/Fryxell_Book_Chapter_7_Leading.htm
Many years ago Elmer Keith used to write about the "balance point" of a given powder; the range of pressures at which that powder delivered smooth uniform ballistics. Basically this boiled down to fast powders for light target loads (e.g. Bullseye, W231, HP-38, AA #2) ...
... Match the powder to the pressure curve. The use of fast powders for higher than normal pressures with plain-based bullets can cause bad leading, due to the very rapid pressure rise time early in the P-T curve leading to high pressure faster than the bullet alloy can obturate in response to the pressure, and as a result severe gas cutting can result. The other issue here is that the slow pistol powders reach their pressure peak when the bullet is an inch or two in front of the forcing cone, when the bullet is fully supported and contained by the barrel ...
The take-home lesson here is to not use fast powders for magnum pressure levels in the first place! Just match the powder to the pressure curve.
