RCBS precision mic

[jkgts1]

I have a quick question. I have used this for my 308s and figured out how to use it. My question in do I need to full length size the brass after each firing? Thanks

[ocabj]

One of the functions of the RCBS precision mic is to get a headspace reading that you can use to adjust your FL die so can set the die to size down the shoulder the minimal amount as possible.

Bumping the shoulder back down to .002" from the fired headspace length is an accepted number.

[jkgts1]

Yes, and I have set my dies per the instructions, and I have run the brass through the dies. I have since loaded and fired the rounds. Now when I reload the same brass the second time do I need to FL size it again? That was my question, sorry if it was not clear.

[rksimple]

Setting the die per instructions doesn't mean much. The purpose of having the precision mic is so you can measure how much you're bumping the shoulder. You can adjust your die to bump the shoulder a couple thousandths (all you need) or make it not touch the shoulder at all. Are you shooting them in a semi? If so, fl sizing by bumping the shoulder a couple thousandths is necessary every time. If its in a boltgun, you can just neck size if you want. Feeding and chambering are easier with a couple thousandths headspace though. If you just arbitrarily set the die as per instructions, you could be oversizing. This will result in more case stretching, less case life, and more potential issues.

[jkgts1]

It for a bolt gun. Thanks for the replies.

[ocabj]

Yes, and I have set my dies per the instructions, and I have run the brass through the dies. I have since loaded and fired the rounds. Now when I reload the same brass the second time do I need to FL size it again? That was my question, sorry if it was not clear.

Well, I think you're misunderstanding the point of the RCBS Precision Mic with respect to headspace.

If you're not going to use a FL die to resize the brass (thereby setting the shoulder back), why use the Precision Mic to check headspace at all?

But if you are asking if you should FL size your brass (independent of the fact that you own a Precision Mic), well, there isn't a simple answer. You can get away with neck-only sizing your brass in a bolt gun, but eventually, after numerous neck-only sizing, you'll need to use a FL die to set the shoulder back.

This has been covered many times in previous posts about full length vs neck only.

Also, it is apparent after reading tutorials on reloading (which cover the fundamentals of what happens with a cartridge is fired), why FL sizing will be a necessity at some point in time.

The best answer is to use your Precision Mic to set your FL die to resize your brass for that specific gun/chamber such that the shoulder is set back .002" from it's fired headspace length.

[xrMike]

Setting the die per instructions doesn't mean much.

I found that out with my RCBS mic too. Setting my Lee FL sizing die per instructions bumps the shoulder back waaaay further than necessary.

[westcoastr]

your gun is going to dictate if you have to full length resize. if rounds are difficult to feed and close the bolt then FL. also you might not be able to use these reloads in other guns of the same caliber if they have smaller chambers

those precision mics are the cats meow...but a word of caution, since they index off of the bottom of the head, a bent rim, say from a semi-auto, or from some other rough handling, will give you longer reading.

everybody should have one of these things, otherwise you are just guessing