Written by Sierra Bullets Ballistic Technician Paul Box
We all know that it takes many things in the making of an accuracy load. We have to have a good barrel. It has to be fitted to the action proper. A good chambering job. The bedding of the rifle’s action has to be good, on and on, but even the best built rifle will not shoot to its’ potential with bad brass. Below are some of the steps I recommend to prep new brass.
When I get a new lot of 100 cases, the first thing I do is weigh them. If I’ve never worked with this caliber before I will weigh 20 cases and write the weights down as I go along. Then I add the weights of all 20 up and divide by 20 to get an average. If this is a cartridge in the 22-250 thru the ’06 size, then I use 1.0 gr. above and 1.0 gr. below the average case weight and keep everything in this 2.0 gr. bracket. Cases in the 300 Win Mag size I go 1.4 grs. above and below the average and smaller cases like a .223 I use .7 of a gr. above and below. If you want to use tighter tolerances than this, that is fine, but I’ve found that very well built varmint guns will shoot down in the high .2’s and low .3’s with this method.
Deburr the Flash Hole
The next thing I do is deburr the flash hole. American made brass has a flash hole that has been punched and typically has a burr on the inside. Norma and Lapua have drilled flash holes and usually don’t have any burr or only a very slight one. I still deburr these as well and give them a slight chamfer at the same time. I’ve never been able to prove this, but I’ve always thought this little chamfer would more evenly spread the flash from the primer into the powder column and improve ignition. Besides, it makes me feel warm and fuzzy.
Uniform the Primer Pockets
Next I uniform the primer pockets. Brass that have a punched flash hole will be the worst, but they all will be concave in shape. A uniforming tool will cut them flat on the bottom and allow a primer to be seated perfectly flat giving all the energy from the firing pin to set the primer off rather than final seat it the last .001-.002″.
Measure the Case Necks
Next I measure the case necks and compare the difference between the thick and thin side. What I’m looking for is a difference of .001″ or less. Cases that are between.001 and .002″ are set aside to be neck turned. The more uniform the case necks are, the easier it is for your seating die to seat a bullet in better alignment with the case body.
Brass that has been prepped through these steps will give your rifle the best chance to deliver the accuracy it is capable of.