• Quick Shot Challenge: What’s the dumbest shooting myth you’ve heard?

    Drop it in the replies for the chance to win a free shirt!

    Join the contest

RCBS Precision Mic.....(One more time)

jeo556

jeo556

Sergeant
Full Member
Minuteman
Nov 3, 2009
406
5
Pittsburgh Pennsylvania
#1
Okay, So I've used the search function to look up past threads regarding the RCBS precision mic and it seems to me that there is a tremendous amount of incorrect(that is if I'm not mistaken) info floating around.

So I'm here to converse about the RCBS precision mic with those of you that have used it successfully in order to determine if I'm correct in some of my assumptions.

<span style="font-weight: bold">Lets talk about the seating depth portion of the mic.</span>
(Because this seems to be where all the mis-information is.)

So I've read that the "plastic" bullet insert that comes with the mic is useless because it has a "profile" that does not mimic a traditional bullet.

I have to disagree with this completely. And here is my explanation.......

The lands of a barrel have a certain measurement(diameter). And somewhere on the ogive(of a bulet of the same caliber) that measurement exsists. So regardless if the "plasic bullet" has stubby profile and a VLD berger has a lond & sleek profile, the precision mic is only measuring the distance to where a ogive has the intended diameter. Of course the OAL of the round with a VLD is going to be longer than a stubby bullet but the distance to the ogive will be the same. Isn't that all that really matters when trying to load a round within a certain distance to the lands. That is as long as the loaded round fits into the magazine of course.

So if my above assumtion is correct, using the seating depth portion of the precisioin mic I'm going to be provided with a <span style="font-weight: bold">ARBITRARY</span> measurement to the ogive. This measurement will only be useful when comparing other rounds in the mic.

Now, I set my seating die and seat a bullet. Take that bullet and put it into the precision mic in place of the "plastic bullet assembly". Now if this matches the measurement taken before I now have a round that, regardless of bullet type or OAL, is touching the lands. Correct?

Record the ARBITRARY measurement from the precision mic and from there I can load <span style="font-style: italic">into</span> and <span style="font-style: italic">off of</span> the lands rather easily.

Altohugh I agree that the actual measurement of the precision mic is ARBITRARY, I'm going to assume that the increments are correct. Does anyone have any expierence to refute this assumption?

I'm looking for some back and forth here so any comments and advice or expierences are welcome.

<span style="color: #FF0000">Edit: My above reasoning is based on the assumption that the Precision Mic has a inside diameter the same as the rifling in a barrel. </span>


 
#2
Re: RCBS Precision Mic.....(One more time)

I've used the Prec Mic in several calibers, and the seating depth tool will get you close. You can't get a better tool to find the lands than an actual round loaded long with your bullet of choice, and chamber check it to see where it touches. If it touches or the bolt won't close, then seat the bullet a little deeper and re-check. When you can close the bolt, and there are very faint rifling marks (not deep scratches or heavy marks) left on the bullet, then you are touching the lands.

I like using the Prec Mic for measuring a loaded round to the same seating depth each time. Alot of HP bullets have inconsistent tips, so measuring from the ogive ensures consistant seating depths.

For what it's worth, I don't use the Mickey Mouse cartridge thing-a-ma-jigger to find the lands. A loaded round with your actual bullet is a much easier tool.
 
#3
Re: RCBS Precision Mic.....(One more time)

I have one and can't figure it out. I just take a sized case stretch the neck a bit push the actual round I'm using in gently place in chamber push bolt closed gently measure remove measure repeat repeat. That seems to get me close enough, that mic seats different bcause the ogive is at a different point I believe than an actual round? Seating depth may change when you change style of round or am I incorrect.
 
#4
Re: RCBS Precision Mic.....(One more time)

I understand the process that you guys are using to determine a seating depth and I appreciate your input, but I'm trying to determine if my reasoning is correct so that I can use the precision mic for measurement.

Refering back to my original post and comparing it to what you describe I'm still wondering what the difference is.

The only difference that I can see is that with the method that you two are using, you technically get a seating depth to the lands and because you are using the same projectile a corresponding OAL.

With the "plastic bullet assembply" I'm still getting the distance to the lands but I'm obviously going to have a different OAL than with the actual bullets that I'm loading for. Like I mentioned in my OP, once I have my measurement to the lands I can play with the seating depth. As long as my seating depth isn't associated with a OAL that is too long for my magazine I should be good......Right?

In other words using yout method you would get a distance to the lands and the OAL all in one because your projectile has the same profile. Using the "plastic bullet assembly" I only get a distance to lands. Only after I then use that measurement with the actual projectile can I determine a OAL.
 
#5
Re: RCBS Precision Mic.....(One more time)

Here is a link to my post when I sorta went through the same process you did when I was trying to learn ogive and how to utilize the RCBS MIC
http://www.snipershide.com/forum/ubbthre...562#Post2047562
it might help it helped me.

i believe your on the right track. Keep in mind I gave up on my MIC and use the poor mans method of finding the 1st contact, and back off a bit on the die and see how it goes. The ogive is where the 1st contact occurs and touches the bullet,so OAL doesnt matter except in my method the OAL measurement read using my actual brass and bullet method gives me an OAL to set my dies to start out at and back off a few thousandths at a time. I never actually have the ogive measurement just an OAL based on ogive contact. but it doesnt matter because its my actual bullet and brass and all you need to know is where to set up your OAL on your dies in relation to where it contacts the lands ie the ogive so you can back off a bit ? Using the plastic bullet wont help because the OAL for it wont matter or be the same ogive for say your 175SMK round that your about to load? Try your method with the plastic bullet and then try it with actual unloaded brass and a bullet measure both to see what you get.I bet they are different. My analogy is its like sticking two different footballs in a mailbox at different times. At some point they get stuck between the top bottom or sides, its OAL in the box doesnt matter the tip of the balls dont matter, and they will fit a little differently. OAL can matter if you get too long for mag purposes of course. At least thats how I think about OAL and OGIVE they will be different from say 175 SMK to a 155 Scenar, to a 220 SMK, to the lil plastic bullet in the MIC.
KEEP IN MIND THERE ISNT ONE MEASUREMENT YOU CAN GET WITH THE MIC THAT SAYS WHERE ALL BULLETS TOUCH YOUR LANDS AT, That number will change and its different from model of round to model as I stated above.
 
#6
Re: RCBS Precision Mic.....(One more time)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: woodspider</div><div class="ubbcode-body">
KEEP IN MIND THERE ISNT ONE MEASUREMENT YOU CAN GET WITH THE MIC THAT SAYS WHERE ALL BULLETS TOUCH YOUR LANDS AT, That number will change and its different from model of round to model as I stated above. </div></div>


this.
 
#8
Re: RCBS Precision Mic.....(One more time)

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">KEEP IN MIND THERE ISNT ONE MEASUREMENT YOU CAN GET WITH THE MIC THAT SAYS WHERE ALL BULLETS TOUCH YOUR LANDS AT, That number will change and its different from model of round to model as I stated above.

</div></div>

This is what I'm trying to wrap my head around and I think that you are mistaken.

Here me out. The plastic bullet assembly is strictly measuring the distance from the bolt face to the lands in the barrel. And the mic gives a arbitrary measurement, lets call it a datum point to use later when seating actual bullets.

Now when actually seating bullets I'm going to take this datum point and compare it to loaded rounds. Regardless of the type of bullet that I use the measurement from the bolt face to the lands is going to be the same. The OAL is going to change.

Now if you are loading multiple types of bullets to the same OAL then the precision mic is going to give you a different measurement because the different bullets will have different profiles. I wish that there were some way to illustrate this with a drawing......

Am I right? Wrong? I thought that I had this figured out but you guys are starting to make me wonder.

 
#9
Re: RCBS Precision Mic.....(One more time)

I think that the misunderstanding is that you are working from an OAL back. Like I mentioned earlier, if you load a specific bullet to a specified OAL then it will have a different measurement(using the precision mic) than any other bullet(because of differing profiles).

On the other hand, if you use the precision mic to establish a measurment from the bolt face to the lands, then you can load any bullet so that the ogive is set to hit the lands dead balls.

Am I a moron or something????
 
#10
Re: RCBS Precision Mic.....(One more time)

"So I've read that the "plastic" bullet insert that comes with the mic is useless because it has a "profile" that does not mimic a traditional bullet. I have to disagree with this completely. And here is my explanation......."

Two things.

First, I and a lot of others find it useless because it's made to work with a controlled round feed rifle and I don't have one of those any longer. For push feed rifles that dummy bullet/freebore tool is largely useless because it tends to set the "bullet" back before the extractor snaps onto the case rim.

Second, it wouldn't matter about the bullet shape IF the seating thimble actually measured the ogive at bore diameter but that's not true, at least not for any of my Precision Case Mics; not a lot of difference but there is some. So the actual shape of the individual bullet's ogive does make for small differences in the seating readings from the freebore tool, enough to destroy any high precision to the measurements.

I prefer to find the max seating lenght to the lands with a loose bullet and marking a cleaning rod. I can easily get within a couple-three thou with that method and that's close enough. Then it's easy to use the Mic's bullet thimble to set my seater for whatever jump I want and KNOW what I'm doing.
 
#11
Re: RCBS Precision Mic.....(One more time)

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">First, I and a lot of others find it useless because it's made to work with a controlled round feed rifle and I don't have one of those any longer. For push feed rifles that dummy bullet/freebore tool is largely useless because it tends to set the "bullet" back before the extractor snaps onto the case rim.

</div></div>

I never even considered this as I've only used one for my Ruger, which is obviously a controlled feed action. Your point is well taken.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Second, it wouldn't matter about the bullet shape IF the seating thimble actually measured the ogive at bore diameter but that's not true, at least not for any of my Precision Case Mics; not a lot of difference but there is some. So the actual shape of the individual bullet's ogive does make for small differences in the seating readings from the freebore tool, enough to destroy any high precision to the measurements. </div></div>

So you're saying that I'm correct in theory, IF the thimble had the same diameter of the land in the barrel? If completely agree that it the thimble doesn't match the barrel then it throws all my reasoning out the window....

Do you know for certain that the thimble doesn't match the dimension of the barrel?

I feel like I've figured this out but with all the feedback I'm starting to think that I'm just missing something.
 
#12
Re: RCBS Precision Mic.....(One more time)

When I used the plastic bullet with my remington, I just loaded the bullet into the ejector by hand. Compress the spring and feed it into the chamber. That being said, a normal piece of brass with a split neck works better. You will get the same measurement no matter what projectile you use. I don;t know if the measuring device is accurate in thousanths, but it is repeatable. As long as you use it as your point of reference you will get accurate results. I use both tools, headspace and length for 308 and 223. It works if you understand it's limitations and how to use it. This tool has nothing to do with OAL period.
YMMV-Rob
 
#13
Re: RCBS Precision Mic.....(One more time)

"Do you know for certain that the thimble doesn't match the dimension of the barrel?"

I can only speak to the ones I have and they (4) are all slightly smaller than bore diameter by a couple of thou, ie, my .30 cal thimble is actually .298". Not a lot of difference but it could easily allow a couple of thou difference in different bullet ogive profiles.

Actually, my rifles are all factory arms and I NEVER find best seating at the lands, always from 20 thou off to as much as 5x that much. Given that I also find windows of good seating to be 5-10 thou wide I use the lands contact point as a reference for my loading records but I no longer agonize over the last few thou of "OAL" precision or consistancy for seating. Only if I'm on the ragged edge of the good seating will 2-3 thou of variation in the wrong direction push a round into "flyer" country.
 
#14
Re: RCBS Precision Mic.....(One more time)

I believe the OP is on the right track.

I don't remember how many I have, but, I've used the .223 the most, in ARs, and boltguns without any issues, but, I can't get the .308 to work in my DPMS. Maybe one of these days I'll try to take the extractor out of the bolt.
 
#15
Re: RCBS Precision Mic.....(One more time)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jeo556</div><div class="ubbcode-body">I think that the misunderstanding is that you are working from an OAL back. Like I mentioned earlier, if you load a specific bullet to a specified OAL then it will have a different measurement(using the precision mic) than any other bullet(because of differing profiles).

On the other hand, if you use the precision mic to establish a measurment from the bolt face to the lands, then you can load any bullet so that the ogive is set to hit the lands dead balls.

Am I a moron or something???? </div></div>

1st your here asking questions so no you are no moron we all seek advice thats a sign of intelligence. 2nd im no expert as I am learnig as I go to. Now here is my thoughts/opinions.

Measuring from Bolt Face to lands in a gun is a waste in my opinion and worthless to do? what are you measuring the 1st piece of cut metal from the reamers or whatever tools cut the chamber and lands and grooves? What does that matter I dont get it. You could stick a piece of dry pasta in your barrel and it would never contact the lands right. so why does it matter where it all starts at? Changing OAL is done after you figure out where the bullet your working up actually touches the lands. In my opinion all that needs answerred is WHERE DOES THIS PARTICULAR BULLET PROFILE OR BULLET ACTUALLY BEGIN TO TOUCH MY LANDS? Because diff bullets will touch the lands at different points on your lands, thats just how it is, they dont all hit at the same point, unless they are all the same bullet like say 175 SMK or some other bullet.Then you decide to seat at lands , jammed , or began backing off for some jump, wahtever you decide. Different stlyes of bullet will begin to actually touch your lands at different spaces on the bullet. Thats the ogive correct? So figuring out where they lands are with the plastic mic bullet is useless I would think? Or am I mistaken someone correct me if my logic here is wrong please.
Ok answer this question and it might give me a better idea as to your understanding; If we loaded 10 different bullet styles say 175 SMK to 208 Amax to 155 scenars whatever but they are all different styles ok? We load them all to the exact OAL from boltface into the barrel, now do you believe they would all contact the lands at the same place just because they are all the same OAL? If you do then theres your problem. Thats not reality same style bullets at same OAL WILL touch lands at same exact spot, different bullets loaded to the same OAL will have differing Ogives, the search is for where the Ogive is for any given rifle then decide where to seat in relation to it the ogive.
 
#17
Re: RCBS Precision Mic.....(One more time)

Joe,

I believe you're correct. The shape of the bullet nose has little to do with anything in terms of distance to the lands, as that measurement is taken from the bolt face to the lands. The Precision Mic does that. Different shaped bullets that are all seated to touch the lands are going to have different OALs because of the shape of the nose but the measurement from the bolt face to where the bullet contacts the lands remains the same. In the end, it's really no different than using a bullet comparator with a caliper.

FWIW, the only complaint that I have with my precision mic is that in my custom throated .308, it wouldn't measure SHORT enough to be useful.

John
 
#18
Re: RCBS Precision Mic.....(One more time)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: woodspider</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jeo556</div><div class="ubbcode-body">I think that the misunderstanding is that you are working from an OAL back. Like I mentioned earlier, if you load a specific bullet to a specified OAL then it will have a different measurement(using the precision mic) than any other bullet(because of differing profiles).

On the other hand, if you use the precision mic to establish a measurment from the bolt face to the lands, then you can load any bullet so that the ogive is set to hit the lands dead balls.

Am I a moron or something???? </div></div>

1st your here asking questions so no you are no moron we all seek advice thats a sign of intelligence. 2nd im no expert as I am learnig as I go to. Now here is my thoughts/opinions.

Measuring from Bolt Face to lands in a gun is a waste in my opinion and worthless to do? what are you measuring the 1st piece of cut metal from the reamers or whatever tools cut the chamber and lands and grooves? What does that matter I dont get it. You could stick a piece of dry pasta in your barrel and it would never contact the lands right. so why does it matter where it all starts at? Changing OAL is done after you figure out where the bullet your working up actually touches the lands. In my opinion all that needs answerred is WHERE DOES THIS PARTICULAR BULLET PROFILE OR BULLET ACTUALLY BEGIN TO TOUCH MY LANDS? Because diff bullets will touch the lands at different points on your lands, thats just how it is, they dont all hit at the same point, unless they are all the same bullet like say 175 SMK or some other bullet.Then you decide to seat at lands , jammed , or began backing off for some jump, wahtever you decide. Different stlyes of bullet will begin to actually touch your lands at different spaces on the bullet. Thats the ogive correct? So figuring out where they lands are with the plastic mic bullet is useless I would think? Or am I mistaken someone correct me if my logic here is wrong please.
Ok answer this question and it might give me a better idea as to your understanding; If we loaded 10 different bullet styles say 175 SMK to 208 Amax to 155 scenars whatever but they are all different styles ok? We load them all to the exact OAL from boltface into the barrel, now do you believe they would all contact the lands at the same place just because they are all the same OAL? If you do then theres your problem. Thats not reality same style bullets at same OAL WILL touch lands at same exact spot, different bullets loaded to the same OAL will have differing Ogives, the search is for where the Ogive is for any given rifle then decide where to seat in relation to it the ogive. </div></div>

Woodspider,
You don't understand how the Precision Mic works. Let me see if I can explain it clearly enough to understand (I am only going to describe the bullet seating half of the set since that is what is in question):

1. You close your bolt on a 'dummy round' that is part of the set which compresses to length dictated by where that 'dummy round' contacts your lands.

2. You use the mic to determine a (purely arbitrary) measurement from the base of that dummy round to the place on the 'bullet' where the diameter of the bullet is the diameter accross the lands. I say 'purely arbitrary' because it is not an actual measurement of that distance, but a measurement taken off of a scale. Instead of something like 2.310", you get a reading like +.126.

3. Now, you seat your bullet (any damn bullet) in your case. Start with a shallow seat and check the measurement with the Precision Mic. Lets say your initial measurement with the mic is something like +.157. Now keep adjusting your seater die down incrementally until you end up with a seated bullet that the mic measures as +.126. At that point, you have a bullet that is seated so that it will just touch the lands (in theory), and it doesn't matter what bullet you start with. If you want the bullet .02" off the lands, then shoot for a measurement of +.106. If you want a bullet that is seated so that is jammed by .01", then shoot for a reading of +.137.

Using this tool, OAL is only an important or useful measurement if you are magazine length constrained.

The OP's logic is correct. That said, here are a couple of caveats:

1. No two barrels are alike. Not every barrel has precisely the same land diameter. Measuring this would be useful.

2. Again, no two barrels are alike. Not every barrel has the same lead angle that the intial rifling is cut at. If that angle is shallow, some bullets will contact the lead of the lands before the land reaches its maximum height (where the actual land diameter exisits). Bullets with tangent ogives are most likely to have this problem.

In any event, the Precision Mic is a very useful tool that will get you pretty darn close.
 
#19
Re: RCBS Precision Mic.....(One more time)

I never took into consideration that different barrels would have different lead angels. This would affect the accuracy of the Precision Mic but like you mentioned it would probably get you a good starting point.

Thanks for all the input guys. I appreciate the help and comments.

Take care.
 
You must log in or register to reply here.

Similar threads

N_Turs
Dillon 650 Setup Confirmation/Advice
Replies
66
Views
800
ubet
ubet
T
Seating Depth / Lands Measurement Way Off?
Replies
9
Views
543
_Thor_
T
W
Bullet jump on 5.56x45 when slammed into battery
Replies
21
Views
839
918v
918v
mark5pt56
Bushings and expander mandrel? .223 to start
Replies
8
Views
344
mark5pt56
mark5pt56
barnesuser28
Berger 105 Hybrid Target VS Hornady 105 Aeromatch: PART 1 - Dimensional Consistency
Replies
30
Views
4K
Chrsclnngr
Chrsclnngr
Top Bottom
Back
Home
Forums
Merch
Alerts