RCBS PRecission Mic

So you guys are going to start using transfers and standards? I am not sure about transfers but verifying? I am the fan of verifying.

F. Guffey
 
The dimension that he referred to is 2.502" +15 thou, not +2 thou.
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The .015" dimension is the one no one wants. I make things that check that. A reloader that is trimming his cases is not helping; when the bullet leaves the case gas is escaping past the bullet, add that one to the problems that reduce the speed of the bullet. I am the fan of the jump start, I want my bullets to hit the refiling a-running.

F. Guffey
 
Reloadron said:
Here is what higgite is getting at:
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Ron's photo shows the PM off by ~.0005". FWIW, my .223 Prec. Mic is on the money, but the .308 PM that I have now, which is a replacement for the first one I had, is off by .0025". Those are results of tests done with go gauges which I had sent to Forster for verification.
 
Higgite:
Ron's photo shows the PM off by ~.0005". FWIW, my .223 Prec. Mic is on the money, but the .308 PM that I have now, which is a replacement for the first one I had, is off by .0025". Those are results of tests done with go gauges which I had sent to Forster for verification.
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Something I should point out in that photo was my camera angle wasn't exactly true to the micrometer reading so the end result is a picture with some parallax error tossed in, so a bit of bad on my part.

What I have done is on the outside of the box I label any error I find to the effect of -.001 or +.002 as an example which tells me to add or subtract accordingly from my gauge reading. Yes, my 308 gauge is one of the better ones of those I have.

Ron
 
I've been down the RCBS Precision Mic path and I haven't used any of the 6 calibers in which I invested for the last 10 years or so. The major problem I had was reproducibility of the initial measurement. Do you gently spin the unit to a stop? Do you turn it gently instead?
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Mine reads the same consistently. I would suggest that it be held vertical and given a little shake to center the case as the mic meets the datum. I just let it stop where it meets the case.

F. Guffey:
When determining the length of the chamber from the datum/shoulder to the bolt face the reloader is instructed to fire a case and then measure the length of the case from the shoulder/datum to the case head. It gets confusing when reloaders claim the case does not fit the chamber until it is shot 5 times and then there are those snap back, jump back and spring back reloaders that make fire forming impossible.
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You commented a while back on another thread that the factory does a much better job of sizing brass. This little tool sure proved that point! My case head to shoulder/datum is all over the place for shot brass except for rounds that were fired with hotter loads.

BTW you seem to have come a long way since the bolt face question. This stuff is not rocket surgery but there is so much to learn I find I learn new things almost on a daily basis
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Thanks to everyone here. Really everyone, thanks! It is actually much like rocket science in many ways. I dabbled in experimental rocketry for a while and this is more useful to me. Rockets cost more, take more time and get me no animals. If I had more money I would be making them still for sure! I made a rocket motor out of a mini-mag flashlight and propelled it with molasses and KNO3. Took 6 months to develop it to be reliable.

You can measure to the datum line, so what? I can neck size with a FL die till the bolt won't close anymore then work the case through the FL die adjusting it several times till it fit's. Whatever that measurement might be, who care's and why? I even re-read the directions again and haven't a clue what is going on. I find the tool useless, if it does give some kind of measurement, I find it of no use at all!
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I did it that way too. But now, with the new tool, I don't have to use trial and error.

If you know the numbers use them so that you don't have to guess. I know that the length of my bolt face to the datum of my chamber is 2.051". My die resizes a case to 2.048" so I use a feeler gauge to find the gap between the shell holder and the die base and wind up with a .007" gap. I adjust the gap to .009" and now I have a headspace of .001" on the brass I resize that was too big. I know the dimension of my chamber so I no longer need to take the bolt apart or even pick up the gun any more.

Really a pretty slick improvement and thanks for sharing that.
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So glad I could give something back! I used a fired partial sized case and cut it off behind the shoulder. Then I unscrewed the metal bullet from the adjustable bullet and wrap the body with 1/16" less than 3 full wraps of masking tape. The neck will very snugly slide over the body with the tape and should be concentric. I spin it around and always get the same readings. When you test your chamber do not leave it too tight or too loose. If it's too loose it will move after you chamber it. If it's too tight it will compress and decompress giving a long reading. Think Goldylocks.

So you guys are going to start using transfers and standards? I am not sure about transfers but verifying? I am the fan of verifying.
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I got lucky! My little gauge is at 0.000 on a go gauge!
 
Interesting. So ogive is not the same from one bullet to the next? I am curious to see what those differences are. I guess that feature was not designed so well. They could have made the test cartridge so that a bullet could be seated into it to test that specific bullet. My existing method of finding the lands is probably more efficient and reliable then.
 
Yes, the case-base-to-ogive feature on the RCBS Precision Mic is worthless. I use the Stoney Point (now Hornady) O.A.L. Guage for that function. Note: even the Sierra MatchKing bullets will have ogive variances of up to 0.010", since they come off of difference machines at the factory, so don't seat your bullets to an OAL of less than 0.010" for the best accuracy.

Don
 
The difference between a RCBS Precision Mic and the Hornady device that clamps on a calipers is precision and consistency. That is not a knock on the Hornady. The Hornady is a practical,economical ,and useful tool.

The RCBS Precision Mic is just a different approach to doing the same job.

Another method is using a bushing gauge,the min/max step,and also measuring over the case in the gauge.
There are preferences and tradeoffs,but its good folks are measuring and controlling.

On the bullet seating feature,agreed that the absolute number may not directly mean too much,but if you simulate the bore dia at the leade with the hole that contacts the bullet,you have a reasonably useful tool to pick up where the ogive will contact the leade. Much more useful,you have a tool to measure an increment of change. "I want .005 deeper" You can measure it.
 
So the difference between the ogive bullet that comes with the tool and the 180SST bullet touching the lands measured with the ogive mic is .113"! I had to check. I will use a 30-30 neck to make an attachment like I did for the shoulder for each bullet I reaload with to determine lands distances.
 
Hunter Customs, sure. I suspect this is the wrong place to engage in this type conversation, but let me just give an overview and you can e-mail me at cdoc42@ptd.net for details:

RCBS Mics: .22-250, 7mm Rem Mag, .270 Win, .223 Remington, .338 Win Mag (only 5 - my error)

RCBS full length die sets: .270 WSM, .17Rem (w/121 cases- 21 once fired; 101 25gr Hornady spire bullets, 7mm STW, .380 auto standard resizer die w/#10 shell holder; .222 Rem
 
Getting repeatable measurements with that dummy ctg that comes with it is extremely frustrating.

I ended up tossing their dummy cartridge and just used a sized case & real bullet. A bullet is short of the lands if it falls out of the chamber when you tip the muzzle up. So start with it seated it out very long, and stuff it into the chamber with your thumb. Seat it deeper in small increments until it drops clear. Then measure.

It's quick, repeatable, and doesn't require a stream of profanity. Plus the seating die is now set for zero jump and adjusting from there is a piece of cake.
 
Yosemite Steve:
So the difference between the ogive bullet that comes with the tool and the 180SST bullet touching the lands measured with the ogive mic is .113"! I had to check. I will use a 30-30 neck to make an attachment like I did for the shoulder for each bullet I reaload with to determine lands distances.
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The problem is not all with the tool. The problem is as Don points out is with the bullets. When used correctly the tool will pretty accurately measure the distance from the breech face or breech block face to where the bore diameter is 0.30" in the case of a 30 caliber rifle. That distance is a hard number for your rifle. In the case of a .30 caliber bullet the bullet ogive is where the bullet has a .300" diameter. The problem is the guys making the bullets can't maintain perfect uniformity bullet to bullet and as Don points out, they can vary by 0.010' within a single box of the same bullet. If all the bullets in the box were the same and exactly like the drawing then the tool would work fine.

Discounting the ogive for a moment I have sitting here a box of Sierra 168 grain HPBT Match bullets. Measuring 5 random bullets here is what I get for overall bullet length. 1.219", 1.208", 1.210", 1.214" and 1.220". Now with the same 5 bullets in the same order we will measure bullet base to ogive, base of the bullet to the end of the 0.300" diameter. 0.581", 0.581", 0.588", 0.581" and 0.586". So while 3 of 5 were consistent at 0.581" we still had a few and one of five was 0.007" out from three of the others. This makes seating our bullets consistently a given distance off the lands, in the case of a .308 rifle with a .30 caliber bore diameter a little difficult. Since I don't have a drawing for a Sierra 30 caliber 168 grain HPBT Match bullet I have no clue what nominal numbers should be. I can say out of 5 random bullets I saw a spread of 0.007" in base to ogive measurement.

Ron
 
My method has been to use a fired case with no primer and put a small dent in the neck with a bur facing the bullet so that it leaves a tiny scratch in the mark on the bullet up to where it stopped pushing in. I triple check and measure until it measures the same three times. I think that if I develop this tool to hold a bullet concentric it will be easier to use. I will make a slip on for each bullet I load and recheck the lands every 100 rounds.
 
Ron, my 180 SST bullets have been seating to the same col within .001 95% of the time. My sierra vullets are all over the place.
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There you go. Finding good consistent bullets is like a Holy Grail thing. :) This is the sort of thing which can take someone who is OCD right over the edge.

Ron
 
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