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This blog is simply intented to share information. It is in no way a loading manual. I'm not an expert blogger or author so there will be typos. If you don't recognize these typos and blindly use ridiculous charges it is your own fault.

Use common sense. Double check all information in this blog with other manuals. Work up your own loads. I'm not responsible for your mistakes, even if you're making the same mistakes as me.
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Using RCBS Mic and setting die

Posted 10-16-2012 at 11:46 PM by mroels

So I'm just getting into reloading. Finished reading a lot. Got the Lee hand press cheap to see if this was something I'd get into...although I haven't been this exited about anything shooting related I a while. I really wanna see every step so I figured the hand press would be perfect. For now I don't want to experiment too much, just want to learn about a whole new aspect to shooting. I'm really just looking to recreate the factory .223 ammo I'm shooting pmc-55gr and BHA 69gr, and I'm not even really talking about performance just safety and reliability. I'm shooting RRA AR-15 platforms with Wylde Chambers. Once a I have a couple hundred of rounds under my belt I'll start playing with velocities & accuracy etc. For now just middle of the road loads, of course I'll try some different loads to inspect the effect on casings and rifle, but am not planning to go near maximum loads yet.

I've been using the rcbs mic gauge to figure out how far back to set the neck when FL sizing. Factory pmc and BHA are reading -3 unfired, 0.003" under ANSI minimum. Fired I'm getting a reading between +1 +2. So my understanding is that the headspace in my rifle is probably around +0.004" above the ANSI minimum, considering brass shrinking back down a little again, well within the limits. I also understand that factory ammo is sized under the minimum for reliable loading. What I'm wondering is what should I push the shoulder to? In my quest to just replicate factory cases Im setting back to the -3 reading. However as I was adjusting the die I got a few cases right at the 0 reading, or right at the ANSI min, would these be ok or am I gonna have feeding issues? It's only 3 cases so I don't care about tossing them but just curious. I understand that the closer i set to the chambers actual headspace the more accurate the reloads should be but at what point will autoloaders stop feeding nicely? Or is that really more an OAL issue?

Also as I was adjusting the dies I went a bit too far and ended up with a couple of cases around -0.005" under ANSI minimum. Again I'm happy toss a few cases for safety as part of the learning curve but I do want to learn something from it. I understand that a case going from -0.005" expanding to +0.002" is going stress the brass a lot and shorted life of casings. But how far under min can you set the shoulders before absolutely having to toss them?

Hope I made sense and at least show a little understanding of what's going on.

Thanks for all info!


Bump to 0.000 and that's plenty for the fired cases that show +0.001 or +0.002. You don't want to replicate factory ammo dimensions, after all, when you can size for your chamber instead!

Let's assume you are loading for an AR. Feeding success for these is both an OAL and a headspace issue, but you'll see OAL problems as soon as you load rounds into a magazine; things appreciably over 2.26 aren't going to fit. You'll only see headspace problems when you close your bolt on a round, and it's hard to say that you'd actually "see" such a thing since I don't think there isn't any positive sign of full bolt closure and lug lockup on an AR. Somebody can correct me on that point - for example, if it's possible to know by pressing on the forward assist whether things are actually all the way locked up.

I don't have any advice about oversized brass. Given this is .223, and they are only worth pennies, I would just keep them in a box of tester brass for calibrating your annealing process one day, etc.


I've only been reloading about 6 months, got about 1k rounds under my belt, so take my opinion with a grain of salt. But I too had a little bit of difficulty understanding the RCBS mic and where to seat the shoulder. The annoying thing is that the RCBS manual doesn't really explain what the values on the mic mean. Or specifically what it means to your reloads. But for the AR platform just set shoulder back to ANSI minimum or so that a resized case reads 0 on the mic.

What I noticed was that:
Unfired factory ammo - PMC/ BHA/ AE - consistently measured at -0.03 or -0.003" below ANSI minimum, presumably to allow for consistent loading in a wide variety of weapons systems.

My once fired brass measured at +0.02-+0.03 with a couple of odd ones at -0.01

The way it was explained to me this meant that my chamber is probably +0.003" to +0.005" above ANSI minimum, but that after expansion the brass shrinks back a little again.

I set the die to bump the shoulder right back to ANSI minimum. Although I was told I'd be ok setting back to +0.02 if I really wanted to size closer to my chamber's specs.

I have noticed that multiple fired cases don't expand as much so the shoulder doesn't need to be set back as much.

btw make sure to use the mic before applying resizing lube, while you don't lube the shoulders i've noticed that it does affect the measurements.

I haven't played to much with OAL, i've noticed that most of my favorite factory match grade ammo brands are all at 2.20". Also from what i've read and noticed trying to use RCBS mic to measure ogive is difficult. The little bullet thing they give you doesn't like it when the bolt is closed too hard or too soft, i'm getting very inconsistent readings.
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