Frustrated with RCBS Precision Mics.......

[mattmcg]

So have to vent a bit about the RCBS Precision Mics. Turns out they are anything but precision!

I purchased 3 different versions and measured them against some known dimensions on Forster Go, NoGo, and Field gauges. Turns out one of them was off by -.003", the other -.0015", and the last +.002". I realize that I could simply mark them as such to ensure accurate base to datum lengths but I'm a little pissed that I would have to do that with a product that has "precision" in the damn product title!

Sorry for the rant but if you're going to sell a mic that gives proper headspace dimensions and be off by that much (which is close to the difference between a Go and NoGo gauge), you have no business selling precision equipment.......

 

[memilanuk]

Re: Frustrated with RCBS Precision Mics.......

My understanding of the RCBS Precision Mic, and the Stoney Point (now Hornady LnL and/or Sinclair) comparators is that they were never really intended to give you an absolute reading, but a relative one. In that regard, it does work as intended - you can compare one measured item relative to another, but you can't expect it to give you an absolute reference in and of itself. Accept it for what it really is, a tool to measure your headspace after firing as compared to after sizing, and call it a day. Does it really matter what it reads compared to some arbitrary standard? Not really, other than as a mental safety blanket. Trust me, I wasn't any happier when I figured that out myself. Even the Stoney Point comparators (which I personally find to be a heckuva better value than the Precision Mics) ain't perfect - a radiused hole that matches some theoretical datum line on the case shoulder at a particular diameter. Turns out radiused holes ain't exactly the most precise way to measure a spot like that. But they are fairly consistent and give repeatable readings, and give a fair indication of how much I'm bumping the shoulder on my cases, which is what I really bought them for anyways...

 

[mattmcg]

Re: Frustrated with RCBS Precision Mics.......

meilanuk, yes you make some good points. I guess my dissatisfaction is when you look at the instructions and read about how they calibrate these items to a particular size and provide an absolute dimension, you would expect them to hold to that dimension. Since they include that in their instructions, they sure as hell should not expect an end user to have to be smart about it and actually test it against a known reference to know how off the absolute reading was.

Frankly, I think they could get into a heap of trouble approaching it like this as well. Let's say that I know my 223 Rem chamber measures to GO headspace specs (e.g. 1.4636") as provided by my gunsmith or reputable manufacturer. From there I simply purchase the mic assuming that RCBS has done their job and begin sizing with a mic that shows 0 (the 1.4636" measure provided in the instructions) but that is actually -.003" or worse. Now I'm undersizing my cases consistently using the mic and not knowing it. Finally one day I have a case head separation and have the gun blow up in my face.......

I think the easier solution is for them to clean up their act. Bad business risking the safety of your customer let alone providing an incorrect product.

 

[mattmcg]

Re: Frustrated with RCBS Precision Mics.......

BTW, I also use the new Sinclair bump gages. I really like that product and they do a good job of providing a consistent relative dimension for shoulder bump from a fired case. Works pretty well too minus my dislike of having to balance a case between the base of the caliber and the bump gage insert. The only other negative is that it doesn't reference off the datum point but at the start of the shoulder. That doesn't give you a nice headspace measurement because of its design.

I was hoping the mics would help me speed up the process and ensure a perpendicular measurement at all times (removing the caliper balancing act). The bonus was that it referenced a true datum point and used an absolute measurement from the zero mark. Theoretically it would have made it easy to see if you bumped too far or not enough, don't worry about off angle headspace measurements, and is able to provide an absolute measurement of headspace as well. I guess theory and practice don't match here unfortunately!

I actually thought about buying 10 of each type from Midway to pick and choose to see if I could find 3 that provided an accurate relative measurement. Then again, I appreciate Midway too much to do that to them. Perhaps going to a store could accomplish the same thing if somebody stocks them locally. Hmmm.

Guess I'll go back to the tried and true for the time being.

 

[Fuzzball]

Re: Frustrated with RCBS Precision Mics.......

Sgt. Memilanuk nails it, quite well.

We are reloading/shooting OUR weapon, not SAAMI's, so all we need do is match our ammo to our chamber and go! The RCBS Mic is a very good tool for doing that as well as it needs to be done.

 

[mattmcg]

Re: Frustrated with RCBS Precision Mics.......

After a bit of research, I have an idea that I'm going to explore. Supposedly the top of the "precision" mic is glued on with threadlocker to calibrate it and put it together. In theory I should be able to use a heat gun, remove the numbered portion, and after cleanup reset it to a proper calibration with my go gauges. That would clean things up a bit if I'm successful. I'm sure I'll cook off the white type on the dial but since it is indented, I can put a whiter material there to improve its visibility.

I'll take some pics and post the process when I'm done.

 

[memilanuk]

Re: Frustrated with RCBS Precision Mics.......

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hazardus</div><div class="ubbcode-body">BTW, I also use the new Sinclair bump gages. I really like that product and they do a good job of providing a consistent relative dimension for shoulder bump from a fired case. Works pretty well too minus my dislike of having to balance a case between the base of the caliber and the bump gage insert. The only other negative is that it doesn't reference off the datum point but at the start of the shoulder. That doesn't give you a nice headspace measurement because of its design.</div></div>

Hmmm... I haven't used the Sinclair variant of the Stoney Point bump comparator yet, mainly because I didn't see a reason to replace all my existing ones yet. I did have to order one for a .338LM which should be here in a few days, so I guess I'll see then. I was under the impression that they referenced off the whole shoulder angle, not 'the start of the shoulder'? Isn't that why they are marked and sold by shoulder angle in degrees?


<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">
The bonus was that it referenced a true datum point and used an absolute measurement from the zero mark. </div></div>

...before you take into account production tolerances

For it to be that exact it'd probably have to cost a lot more than it does. That and anymore I think a lot of the 'consumer' grade measuring tools pin their accuracy claims solely on us believing them.

 

[mattmcg]

Re: Frustrated with RCBS Precision Mics.......

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: memilanuk</div><div class="ubbcode-body">
I was under the impression that they referenced off the whole shoulder angle, not 'the start of the shoulder'? Isn't that why they are marked and sold by shoulder angle in degrees?</div></div>
Yes, they do reference off of the entire shoulder angle and end at the shoulder to body junction. So when you reset your calipers with both caliper jaws touching the front and back of the Sinclair gage, you'll get a reading from the base of the case to the body/shoulder junction.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: memilanuk</div><div class="ubbcode-body">...before you take into account production tolerances

For it to be that exact it'd probably have to cost a lot more than it does. That and anymore I think a lot of the 'consumer' grade measuring tools pin their accuracy claims solely on us believing them. </div></div>
Heck, for $45 per precision mic, they aren't cheap! I thought the expense was actually deterministic of a level of precision you would get with them. With their construction, they should be easy to calibrate at the factory which doesn't explain why my 243 Win and 308 Win Precision Mics differ from .002" from each other when reading the same case! The datum point is identical for both case types so they should read the same, even if off by the same amount from a different Go gauge at the factory. To me that just says sloppy manufacturing processes.

 

[DocB]

Re: Frustrated with RCBS Precision Mics.......

Good day,

The RCBS PMs should be accurate and precise in relationship to a standard, since they are measuring headspace; which is a known data point for a particular caliber. Finding out I've bumped the shoulder 0.004" too much after setting the die to the nominal spec for the mic is a real PITA, as well. I load for more than one gun with a particular set of dies.

The reason the .243 and .308 mics have different measurements is they measure to different data points on the case.

HTH,
DocB

 

[mattmcg]

Re: Frustrated with RCBS Precision Mics.......

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DocB</div><div class="ubbcode-body">The reason the .243 and .308 mics have different measurements is they measure to different data points on the case.</div></div>

Sorry DocB but that in incorrect. The 243 Win, 260 Rem, 7mm-08, and 308 Win are all based upon the same parent case (that being 308 Win) and all index to the datum point at exactly the same dimension.

Definitely saves me money on headspace gauges thank god! Here's a quick link for headspace compatibilities.