Unexpected Results using RCBS Precision Mic

[Patriot007]

It is not OCD! To be correct, it is CDO so it is alphabetical order!

LOL, AGREED!!!

 

[jimbires]

I'm very grateful for all the thoughtful comments. I got out my Hornady Comparator and using a light touch on the RCBS Precision Mic, I ran the numbers again, and the results were much more consistent. On my reloads (I only have three unfired ones left so the sample size is small). The Hornady comparator said the datum length went from 1.621 unfired to 1.623 fired. The RCBS Mic said the length went from -.002 to -.003, which is counter-intuitive, but may be measurement error. On the Hornady American Whitetail factory loads (I measured about 10 of these all from the same lot, and the readings were consistent) the Hornady Comparator said the datum length stayed the same at 1.623. The RCBS Mic said the length went from -.002 to -.001", so that's going in the right direction, I guess. The directions said to add the fired measurement to the SAAMI minimum (1.630") to get the chamber headspace. In this case, my chamber is apparently .001" smaller than SAAMI minimum. I've ordered a Forster Go Gauge to see if it will chamber. If the Go Gauge won't go, should I send the rifle back to Ruger or just work around it? Thanks everybody.

I'm going to say there is nothing wrong with the rifle . new brass never fully expands on the first fire . please just take a few cases and neck size only . fire / neck size , fire / neck size these a couple more times until they get tight to chamber . when the neck sized brass gets tight to chamber they are fully expanded . now you can set up your dies on these cases . you can measure your case length between each reloading cycle and watch the growth .

 

[Patriot007]

In this case, my chamber is apparently .001" smaller than SAAMI minimum. I've ordered a Forster Go Gauge to see if it will chamber.

I love the thought of a small tight chamber. But, getting brass fire formed for it, can be a pain in the be gaining. You may even have to get a custom sizing die. Matched with slow burning powder to reduce Pressure, could equal some thing really good, down range.

 

[cajun]

I'm going to say you are overthinking this. I find the hornady tool works fine. What you want is a comparator or reference to measure your fired brass. Then you can bump that brass back .001-.002. Who cares what new brass measures or factory brass. Unless your chamber is way out of spec you should not have issues. I have never had a fired case measure shorter than a sized or new case.

 

[xsn10s]

I'm not sure what's happening but I think if you have any unfired ammo left try blackening it with a marker or something to see where the PM is contacting the ammo. And then do the same on the fired brass and see where the contact point is on there.

 

[xsn10s]

I'm wondering what lube you're using on the FL resize and if you lube the inside of the necks. Could be "stretching" the neck/ shoulder area out when pulling the button through.

 

[cajun]

Put it this way factory ammo or new brass is usually undersized so it will fit in any chamber. I find it hard to believe fired brass is actually going to shrink in size.

 

[Patriot007]

I'm going to say you are overthinking this. I find the hornady tool works fine. What you want is a comparator or reference to measure your fired brass. Then you can bump that brass back .001-.002. Who cares what new brass measures or factory brass. Unless your chamber is way out of spec you should not have issues. I have never had a fired case measure shorter than a sized or new case.

Hey cajun, I hope your warm, where ever your at. You lost me on your last sentence. Do you mean you have never had a case come out shorter, than it was before you fired it??? If so, I got a story for you that just happened to me, last week, with some brand new Lapua brass. I knew better, but I took the advice of a couple of my SensorTube reloading pals. Lets just say, it sounded good, but the out come was not expected. Lets just say for now, "Physics prevailed."

 

[cajun]

Yes,I have never fired a round and had the headspace measurement with the hornady tool come out shorter than before said brass was fired.

 

[DartonJager]

I'm wondering what lube you're using on the FL resize and if you lube the inside of the necks. Could be "stretching" the neck/ shoulder area out when pulling the button through.

Had something kind of similar happened to me with a set of RCBS dies for my 35 Remington. My brass was ending up either not any shorter once I FLRS or 0.001-0.0015" longer. Literally about flipped out about this. Then I noticed how much harder (I'm talking really a lot harder) it was on the up stroke to FLRS my brass than the 300wsm I just did the previous evening. Was using Hornady Unique resizing lube absolutely great stuff.
Pulled the mandrel out of my RCBS die and with RCBS on the phone, measured the sizing button and sure enough (the amount escapes me now) it was to large. To RCBS's credit they had a new FLRS die on it's way to me they promised the same day. Once I got the new die I went to measure the old button against the new one but couldn't find it anywhere to save my life. I since came across a great deal on a set of Redding dies in 35 REM at Marlin Owners Forum and bought them and that's what I've used ever since.

 

[Patriot007]

Yes,I have never fired a round and had the headspace measurement with the hornady tool come out shorter than before said brass was fired.

Got it,, Head space. Now I understand. Thank you. The one thing that did come out right on the cases I screwed the pooch on, was the head space. LOL,, Like I said. Deep down,, I KNEW BETTER,, before I did it.

 

[7MAGMIKE1]

I don't mean to hijack your thread but I also use the RCBS Precision Mic with confusing results on 7mm Rem Mag. Without a cartridge case in the mic If I zero the lead nut it comes .025 short of exact zero on the body. If I run the lead nut to zero it runs to -.025 on the body. The headspace nut comes up at 0/0 on the body. None of my other mics (.308, 6.5 Creedmore) do this. Is this just a quirky thing on the belted magnum cases. Anyone else have issues like this?

 

[DrSteve]

I don't mean to hijack your thread but I also use the RCBS Precision Mic with confusing results on 7mm Rem Mag. Without a cartridge case in the mic If I zero the lead nut it comes .025 short of exact zero on the body. If I run the lead nut to zero it runs to -.025 on the body. The headspace nut comes up at 0/0 on the body. None of my other mics (.308, 6.5 Creedmore) do this. Is this just a quirky thing on the belted magnum cases. Anyone else have issues like this?

I think they measure headspace differently on belted magnums, but not sure how the Mic does it.

 

[DrSteve]

I do have a small update. I got the 7mm-08 Go Gauge and I'm able to chamber it, but it chambers with a little cam action on the bolt like all the other ammo I've tried. I did not take the extractor out of the bolt (because I'm afraid I won't get it back together), so that might be throwing off the feel.