Load Development (Part 3)

This is Part 3 of the Load Development Article, if you were bored before, it is not about to get more exciting, except now it's time to load test cartridges.

Loading Test Cartridges

To most people this is what they've been waiting for, a chance to load up some cartridges and head to the range. Depending on your circumstances and how serious you are about your craft, you could go one better than most people, and take a portable reloading bench with you to the range, working out of the back of your pickup making custom cartridges one by one and testing them out. I don't care if you do this, for me at least I think this approach is actually easier on the mind than many others because if a problem comes up you can deal with it right then and there, rather than having to make another trip.

Now it's time to pick some candidate loads. For statistical purposes I typically shoot 3 rounds to establish velocity, and I shoot 10 rounds to establish an average velocity and calculate a standard deviation. 10 rounds allows me to exclude anything that looks like it may be erroneous data, like a bird flying over one of the sky screens, or round not being measured correctly because the chronograph saw the gas and measured it's velocity.

Refining Specifications and Choosing Test Data

Looking back at the last post, here is the spec I decided I was going to load up:

Caliber: .223 Remington
Powder: Varget, H335
Charge Wt. 24-26, 22-24
OAL: 2.235-2.250"
Velocity: 2850-3000FPS

Looking at the load data from the last post, it seems a minimum load will likely not meet the minimum velocity specifications. The book velocities given for Varget were 2784-3010FPS at 24 and 26 grains respectively, doing some basic math that's roughly 113FPS for each grain of powder, so 25gr should be somewhere about 2897, which is perhaps faster that needed for our minimum loading, so lets split that in half again... 24.5gr is somewhere about 2840FPS, which is just a hair slow, so lets use 24.6gr as our first load. For most charges of this size, I will typically do the next several loadings in .3gr increments, typically .1gr does not offer enough change to really be measurable except in large lots, and .3 is a good baseline. Also, I always subtract .1gr from any max loading to account for variations in powder drop when I'm loading progressively.

For the H335 load, it looks like H335 will not achieve the higher velocity Varget will, using the same process, a starting load of 22.7gr was selected. Follow the same procedure to select the rest of the loadings.

Selecting an OAL

OAL is an important variable in loading ammunition, but for auto-loading rifles is much less critical than most might think. However, I out of habit tend to load long, so lets go with a 2.245" OAL, this will make sure none of the ogive is inside the case mouth, allowing us maximum neck tension on the bullet. Under certain conditions, this can be a very major factor (such as with the very long 75gr AMAX which cannot be loaded to a length which satisfies magazine constraints) maximizing neck tension is a necessity for loading good ammo for an autoloader. Too little can cause bullet setback.

Loading Procedure

If you have been reading my blog for any length of time, you probably know what the best practices for loading procedures are, but lets constrain things a little further since it's serious this time:

Process your brass (small base size, trim, wash and tumble)
Seat your selected primers, for AR-15 loads I use CCI-400, #41 Arsenal, or Winchester WSR primers exclusively. Seat these using a bench or hand priming tool being sure primers are minimum of .003" inside the case, and no more than .010" below the base of the cartridge.

Assuming this will be a single stage operation, put your shell holder into the ram, insert a case, and raise the ram. Back the seating plug all the way out of the die, now screw in the seating die until you feel the resistance of the die starting to crimp the case, back off at least 1/2 turn but no more than 1-1/2 turns. Lower ram, now put a charged primed case in the shell holder and place a bullet on top of the case. Raise the ram with one hand while guiding the bullet with the other hand, before the ram is at Top Dead Center, insert the seating punch and begin screwing down. Slowly adjust the seating punch by lowering the ram a little, turn the seating screw, and then seating the bullet slightly farther periodically taking measurements until the seating depth is adjusted to that outlined in our specifications.

Now go ahead and charge and load the rest of the cases.

Next Installment... Getting Data at the range!