I sometimes think I should apply to become a wizard when I consider all the information about handloads I've been asked to conjure up.
Published cartridge overall lengths for handloads are guidelines. Only you can determine if your rifle requires a different length for safety and top accuracy.
I sometimes think I should apply to become a wizard when I consider all the information about handloads I've been asked to conjure up. There are some things a ballistician can determine with absolute certainty and others that the reloader must find using his own intelligence, firearms, and equipment. Let's consider a few questions I've heard more than once.
"Tell me what cartridge overall length gives the best accuracy with my 394 Donnerklapper carbine."
Oh! To have a nickel for every€¦! The caller tells me the make and model of rifle plus the bullet and fully expects an answer to the nearest thousandth of an inch.
The reloading data developer puts safety first; seating the bullet so it clears the standard industry chamber. We did not want jacketed bullets touching the rifling and set most 0.015 inch off the lands — fine for hunting accuracy and safety. If we properly tested every load for accuracy at multiple lengths in some sporting rifle, a reloading manual would feature 20 to 40 cartridges and be updated every 10 years.
You may find that a cartridge overall length (COAL) we recommend may not be the "sweet spot" for accuracy in an individual rifle. Even in factory rifles, there can be variation in throating. If the rifle is a custom job, the throat profile can depend on the gunsmith's choice. A length we've determined as safe in a chamber and throat built to industry standards may be too long in a custom or foreign rifle.
Learn this if nothing else: A published COAL is a guideline, not gospel. It is safe based on the lab's best judgment and adherence to standards, but may not be right for your rifle.
Determining the proper COAL for your rifle is your job, and it's a regular part of the reloading process. There are plenty of instructions in the various reloading manuals.
Can your efforts in this area gain you accuracy? Likely yes. I have a Remington 700 Classic in .250 Savage that shot two brands of factory ammo into 2.75 and 3.00 inches at 100 yards. I found that rifle's throat allowed me to safely seat bullets a bit longer, and my handloads shot under an inch. That was bench and range time well spent.
"What is the most accurate propellant?"
I can tell you what propellant gives the highest velocity in our test gun, but not whether it's accurate in yours. The lab determines that the pressures are within the safe range for a cartridge and that the resulting velocity is appropriate to the task. With the large number of propellants and bullets to test, there is not time to do valid accuracy testing (minimum of four, five-shot groups) and still publish a book with a wide selection of cartridges. And if that testing were done, it could be meaningless.
One of our engineers built a new accuracy mount system for the Speer test tunnel. The 1.5-inch-diameter test barrel was clamped into a recoil sled with a total error of 0.060 inch at 100 yards. The hardware was anchored to a huge buried block of concrete. The engineer ran a number of tests, in-cluding one that involved different propellants. The techs loaded 10 .22-250 Remington cartridges with a 52-grain hollowpoint, each with a different propellant representing our maximum published charge weight for that propellant and bullet. Then they fired the 10 cartridges from the test stand into one 100-yard group. It measured a little over six-tenths inch. They repeated the test to strengthen the statistics — same result. The groups showed a little vertical stringing due to the velocity differences; the horizontal spread was around three-tenths.
This was a best-case scenario, and I agree that an individual sporting rifle can have bedding and/or vibration issues that can make it show a propellant preference. However, I don't have your rifle. Also, recall the column I did on statistics; sample size is everything. If we all fired more shots in testing, we'd likely find that some of our pet loads are not really housebroken. Been there, done that, but I think I'm a better reloader for knowing.
The raw data we generate and the way we analyze it accurately tells if a particular propellant/bullet combo has low variation in pressure and velocity and if its behavior over the useful range of pressure in one cartridge is linear and consistent. We strive to publish the propellants that work the best in these areas. You need to find the accuracy load.
"How much pressure change will I get when I change primers?"
Every so often someone does a study that keeps all components but the primer constant and gets a lab to test the ammo for pressure. This is great, but the bottom line is that this establishes the relation of primer types in the cartridge tested, but those relations may not apply in another cartridge.
I would like to have a massive set of reloading data tested under standard conditions with every permutation possible using today's array of components. Were I 30 years younger with an unlimited budget and a place for a personal "super lab," this would be a great project. In the world where I worked, I could not justify working with bullets and primers that did not bear our company name. I had to be accountable for the company resources I used.
Also, the testing and analysis that goes to developing load data is expensive. I figured that every bullet down an expensive pressure barrel cost me a buck in barrel wear alone. Add to that the tech's time, my time, the graphic designer's labor, and the rather alarming costs of printing and distribution, and the average reloading manual on your shelf represents a significant investment by the company that compiles it.
You cannot abdicate your role in reloading; you are an essential part of the process and more than just the labor source. In this age of fast information distribution and instant gratification, reloading is "old school" and you should embrace the time it takes to do some of the testing. You know your rifle better than any reloading manual author in the world.