Semi-Auto handloading.

[G19Kev]

So, I'm starting to pickup where I left off over a year ago with learning how to precision handload for my AR-10. Basically all the material out there is for bolt rifles. Part of that process is figuring out bullet seating depth that works best for your rifle, right?... I'm confused how you incorporate that process when handloading for semi-autos because the magazine length obviously restricts that, and you're already setting way back off the lands, and then you have to worry about pressure right, in an autoloader if your oal is longer than load data says? If anyone can point me in the right direction, I'd appreciate it, thanks.

 

[FuhQ]

I measure out my chambers with a particular bullet I plan on using. After measuring it several times (usually 5-10 measurements), I take an average of the numbers. Then I write that average number down. Then I measure the inside of my magazines, and come up with an alternate number. I compare the 2, and figure out my jump, while still being able to feed from the magazine.

In some instances, like with my 6.5 Grendel, I can load just 0.020" off the lands (which is a nice short jump minimizing wiggle) and still fit into my C-Products Defense magazines. So I worked my numbers, figured out my COAL to maintain that 0.020" jump, and then I set my die to that COAL, and I did load testing from there. I kept my seating depth static, and used ladder-testing of powder charges to find my best and most consistent accuracy node.

 

[diggler1833]

I focus on COL/COAL instead of CBTO since I'm almost always dealing with magazine limitations on length in my ARs.

My end goal for my AR platforms is consistent sub-MOA accuracy for five shot groups. I'm content with a rifle that I can count on for a .8 MOA group since I'm usually just using it for critter control or informal shooting enjoyment. If you're trying to see if you can get your large frame AR to shoot 1/4 minute groups, then you might want to overlook my process.

Very generically, I'll still conduct some seating depth tests with secant ogive bullets - usually starting at max mag length, and working back in .010 increments for .050. No guarantee that you're going to hit the magic depth in jumps that large, but you'll find one that stands out. From there it is charge weight testing to find the accuracy and velocity node that I'm looking for. If I really want to, I'll include a third step where I fine tune seating depth in .003 increments.

I usually don't mess with depth testing tangent ogive bullets unless I just want to see how well a bullet will shoot when loaded at the cannelure (for crimping). Otherwise I keep them to mag length generally.

I have yet to run into pressure issues when working up a load like normal. Maybe I don't start quite as close to max, but ARs are usually pretty good at producing the effects on brass necessary to detect pressure (swipes and burrs in addition to normal primer signs) before you start blowing primers.