RCBS Case Mic and over sizing?

[gunsnjeeps]

So I got a new toy this week, an RCBS .223 Precission Mic and now I have a couple of questions. When I measure an unfired factory round, LC 01, it measures about 2.5 to 3 thousandths under 0. I measured 8, all the same. Fired brass is 3 thousandths over 0. So my question is, my resized brass is 4 to 6 thousandths under 0, am I over sizing or am I the kid with a new toy?

I bought it more to find my depth for 80's than for case measurement but since I have it and was figuring out how to use it this is what I found.

Rifle is a RRA NM AR-15. I've had great scores with the "over sized" brass, so the ammo is not an issue. Just curious.

 

[Fuzzball]

Re: RCBS Case Mic and over sizing?

" Fired brass is <span style="text-decoration: underline">3 thousandths over 0</span>... resized brass is <span style="text-decoration: underline">4 to 6 thousandths under</span> 0, am I over sizing.."

Yes. Your resized cases will have to stretch at least 7-9 thou each time and that's far too much for good case life. There is no reason to set a resized shoulder back further than the fired length for bolt rifles, maybe a couple thou further for autos. That's the best use of that gage (or any doing the same measurement).

Checking factory ammo is simply a curiosity thing, that's not meaningful info to a reloader at all.

 

[MitchAlsup]

Re: RCBS Case Mic and over sizing?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Gunsnjeeps</div><div class="ubbcode-body">So I got a new toy this week, an RCBS .223 Precission Mic and now I have a couple of questions. When I measure an unfired factory round, LC 01, it measures about 2.5 to 3 thousandths under 0. I measured 8, all the same. Fired brass is 3 thousandths over 0. So my question is, my resized brass is 4 to 6 thousandths under 0, am I over sizing or am I the kid with a new toy?</div></div>

Just size the brass down 0.002 to 0.003 from its fired size (0.002 to maximize case life.)

 

[gunsnjeeps]

Re: RCBS Case Mic and over sizing?

I'll have to play with my sizing die or get one of the Redding Competition Shellholder Sets. I'm currently set where the shell holder touches the sizing die using a T-7.

 

[Fuzzball]

Re: RCBS Case Mic and over sizing?

"I'll have to play with my sizing die .."

Well, the expensive comp shell holders make it pretty easy to limit the over-resizing for sure. Thing is, turning a die a full turn changes the shoulder a bit over 71 thou. Turning your sizer <span style="text-decoration: underline">up</span> about 1/10th of a turn will get the 7+ thou of change you need. With your shoulder gage you can work it out pretty quick.

You will soon note that shoulder locations will vary after both firing and sizing by as much as 3 thou, and the more they are fired the more pronounced the variations become. That's because the brass work hardens as it's cycled and that changes the spring-back; we live with it. Just make sure your longest resized lengths are no longer than your longest fired lengths and all will be well.

 

[gunsnjeeps]

Re: RCBS Case Mic and over sizing?

For $70 bucks I figured I'd play with it. Biggest thing is finding the top of the stroke. I've been thinking of a way to add a stop to the linkage but I think I'll just find the top of the stroke. I figured I was oversizing at least by 3 thousandths since I was under the LC length. I'll try the next batch a 2 thousandths under chamber length. Ammo's been good and I have a lot of brass sized and primed so I'll be playing with everything later in the season. Probably when I start loading 80's for my first 1000 yard match, start ammo in May, first Long Range match is in June. It'll be my fist match over 600.

 

[mclevela]

Re: RCBS Case Mic and over sizing?

You can follow Fuzzball's very good advice and work out the shoulder bump by turning the die up, which to be done correctly starts with the size die screwed out farther than needed and gradually screwing it down until the correct should bump it found.

Another alternative is Sinclair sells shims to place under the die for a bit more precise movements.

 

[Dtarget]

Re: RCBS Case Mic and over sizing?

Your results are similar to the measurements I have taken. When I looked into this, I was told to be careful assuming a fired case from a semi-auto is an accurate representation of the chamber.

I try to keep the 5.56 ammo flexible for a variety of rifles so I always size to 0-> -.003. My objective is to make reliable ammo, not get 10 loads from a case.

 

[Tripwire]

Re: RCBS Case Mic and over sizing?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Fuzzball</div><div class="ubbcode-body">That's because the brass work hardens as it's cycled and that changes the spring-back; we live with it. </div></div>

I'll be damned if I live with it....I anneal.

 

[gunsnjeeps]

Re: RCBS Case Mic and over sizing?

I only have the one AR and only gun I have in 5.56/.223. I figure going back so I'm a little over zero and chamber a few before I do too many. I learned my lesson on a misadjusted .308 sizing die and 500 cases. Resized 25 loaded in a body die and he other 475 in my new press.

I haven't annealed anything yet but I have equipment available to me if I bring propane. Annealing is going to get tackled this fall probably. I've preped and primed the brass I need though July or August. Everything I've prepped was once fired. When I prep more it'll also be once fired. I'm assuming I'll size everthing that's on it's second firing then anneal it before I prime and load unless it needs sized after anealing in that case I'll switch steps.

Thanks for the help so far, lots of new knowledge.

 

[Fuzzball]

Re: RCBS Case Mic and over sizing?

"the brass work hardens as it's cycled and that changes the spring-back; we live with it."

"I'll be damned if I live with it....I anneal."


Good for you, you're very bright. But, do you also anneal the shoulder and body? If not, my statement stands as written because the shoulder <span style="text-decoration: underline">is</span> the topic, not the neck.

 

[Tripwire]

Re: RCBS Case Mic and over sizing?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Fuzzball</div><div class="ubbcode-body">"the brass work hardens as it's cycled and that changes the spring-back; we live with it."

"I'll be damned if I live with it....I anneal."


Good for you, you're very bright. But, do you also anneal the shoulder and body? If not, my statement stands as written because the shoulder <span style="text-decoration: underline">is</span> the topic, not the neck. </div></div>

Necks and shoulders both...my statement stands.