Probably a stupid question but does using this tool eliminate the need for a chamber OAL measureing tool?

And to make sure that I am understanding the description, you use the mic to take measurements of fired cases to obtain exact dimensions of a particular rifle's chamber??

quote:

Originally posted by 28sstony:
does using this tool eliminate the need for a chamber OAL measureing tool?

quote:

In short, no. What this gauge will do, if it's the one I think you're talking about, is give you an accurate reading of head space. Seating bullets to a determined length is a different matter involving the throat/ogive relationship.

quote:

And to make sure that I am understanding the description, you use the mic to take measurements of fired cases to obtain exact dimensions of a particular rifle's chamber??

Yes. When making resizing die adjustments, I still use case gauges for my semi-auto guns, and use the "feel" method on bolt guns.

I just found this review:

http://www.centerfirecentral.com/productreviews/precisionmic.htm

You may want to take a look at Stoney Point system using a dial caliper and obtaining very accurate readings and can do so for many calibers with relatively low cost. Believe you can buy all inserts for something less than 30.00 Very accurate as well. Just a suggestion.

I've had one for years and used it just the other night with a new rifle I just purchased and to check on the status of a well used old one.

I haven't really used the headspace function of it as I full length resize all my brass. However, it is useful for determining the boltface to lands measurement which will allow you to seat your bullets knowing where the lands on your rifle actually begin. I take that measurement off the "dummy round" part of the tool using a Davidson seating depth checker. That way I'm measuring from the Ogive and not the tip of the bullet. I use the same checker to measure loaded rounds to adjust my seating die too.

The other night I compared the boltface to lands measurement on one of my rifles I had initially measured quite a number of years ago. I estimated I've shot about 700 rounds through it since then. What I found was my lands have been eroded about ten thousandths of an inch. No big deal really, I had adjusted the bullet seating depth a couple years ago cause accuracy started to drop off slightly. At the time, I didn't know why accuracy was dropping off but a change in seating depth and powder cut my group sizes in half. It's a useful tool.

Here is my take on the RCBS Precision Mic. It is a useful tool, but it has its limits.

There are two measuring tools. The headspace nut screws onto the base with an empty fired brass case installed. This measures what I will call the "case headspace," or the measurement between the base and datum line on the shoulder of the case. This measurement allows you to adjust the seating die so that you can size the shoulder by a minimal amount, avoiding overworking of the brass.

The second measuring tool is the land nut. Similar to above, but this measures a "base to ogive" length of a loaded cartridge. This measurement allows you to adjust the bullet seating depth accurately. Note, however, that this measurement is for an arbitrary point on the ogive of the bullet and will change with different bullets - even different bullets of the same caliber. Therefore, the measurement is valid for that type of bullet, and that type only. You should use this base to ogive measurement instead of an overall length measurement (measured to the bullet tip) because bullets of the same type will vary in length be a few thousandths. (Honest! If you don't believe me, try it yourself. Measure a few hollow point or plastic-tipped bullets to confirm this.)

These two tools alone are worth the price. You can make the same "base to ogive" measurement with the Stoney Point/Hornady case measuring tool, but not the "case headspace" measurement.

The third item in the RCBS kit is a dummy round that you place in the chamber as a substitute for an assembled cartridge in order to measure the base to ogive distance with the "bullet" seated to the lands. This measurement will be close to, but not the same as the measurement for your loaded cartridge. The difference in measurements is due to the difference in the shape of your bullet's ogive compared to the shape of the RCBS dummy bullet. They are not the same, so the RCBS dummy round is not a true reflection of your loaded round.

Having said that, the RDBS presicion mic is quite useful. I use the headspace nut frequently to adjust the sizing die as stated above. The land nut is useful to adjust the bullet seating depth of the seating die. You should use your own dummy cartridge, however, instead of the dummy round supplied by RCBS.

Infantrytrophy,

That's a great synopsis of the functions. However, If I understood your post correctly you stated the ogive on the RCBS dummy round won't be the same measurement as the ogive on your loaded round. The micrometer manual states it will be with the exception of "bore riding designs" whatever those are. As an example, I just measured the point on the RCBS dummy ogive using my calipers and my Davidson's seating depth checker. I then measured the ogive of one of my loaded rounds using the same tools and they are the same. Apparently, Barnes X bullets aren't a "bore riding design".

Bore riding bullets are referring to bullets "shoved" into the lands and grooves of the barrel or at least some refer to them as this. Some VLD, very low drag, bullets perform better set up accordingly. Personally I have found the RCBS device to be not the best for quality precision loads and that is particularly true in determing bullet seating depth with the unit. Again, check out the Stoney Point system and use your calipers to do all of the things the RCBS does, only with a heck of a lot more precision. Headspace, ogive measurements, case resizing data, and very prcisely via the calipers. Good luck.

Hey 28sstony, Unless you just enjoy messing with gadgets, you do not need one to make consistently accurate cartridges. Everything the "Precision Mic" does can be accomplished with a regular Die Set.

quote:

Originally posted by 28sstony:
Probably a stupid question but does using this tool eliminate the need for a chamber OAL measureing tool?

It isn't needed at all. If you have a Bolt Action or Break Barrel Single Shot, you can use good old P-FLR and adjust the Die so the Bolt closes on the Case with a bit of resistance - a slight Crush Fit. No need to measure anything, you set it by feel.

quote:

And to make sure that I am understanding the description, you use the mic to take measurements of fired cases to obtain exact dimensions of a particular rifle's chamber??

This would depend on if the Spent Case is a Snug Fit when chambered in the rifle. If it is a Once Fired Case, the "Precision Mic" will provide you with a measurement which isn't the actual Bolt Face to Chamber Shoulder distance. That is because the Case initially Expanded to fill the Chamber and then it Contracted to a smaller size. So, any measurements taken from a Once Fired Case will be "undersize".

That brings up the question of how many Firings does it take on a Case to get a proper measurement from the "Precision Mic"? Beats me. Depending on the Temper of the Case and the Intensity of the Loads, the answer would not be the same for each situation.
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Oh yes, if you are using a Lever Action or Semi-Auto, then it is best to FLR to reduce chambering difficulties. And no measuring is needed.
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If people enjoy using the "Precision Mic", I'm all for it. But it is not needed to make long lasting Cases and accurate cartridges.

Best of luck to you.

quote:

Originally posted by dsiteman:
Bore riding bullets are referring to bullets "shoved" into the lands and grooves of the barrel or at least some refer to them as this. ...

Hey dsiteman, I've never heard the term used that way, but you might be correct.

Hornady still makes some 2-diameter Bullets. The portion Forward of the Cannelure is Bore Diameter and the portion Aft is Groove Diameter. To me this would be a Bore "Riding" Bullet.

I can't imagine how a 2-diameter Bullet would have any effect on the "Precision Mic" except the Diameter of the Ogive might be small enough that the "Precision Mic" can't get a reading for a specific Caliber.

quote:

I can't imagine how a 2-diameter Bullet would have any effect on the "Precision Mic" except the Diameter of the Ogive might be small enough that the "Precision Mic" can't get a reading for a specific Caliber

HC, I read somewhere once that the angle/lgt of the lead (5* vs 15*?) and various ogive shapes (say VDL vs RN) could cause the contact point to move up or down the ogive or lead. Maybe this is what is being discussed?
Personally I`ve no idea if this is true or even a measurable distance with common tooling, but I thought I`d toss it at you for thought.
BTW, aren`t the 2 diameter bullets built to allow the foreward half to ride the lands with the rear in the groves? What would be the important part of the bullet contact in this case? The rear full diameter that takes the ingraving of the rifleing, or the front section that doesn`t touch the lead and just skims across the rifleing? I don`t know the answer to this either, just opinions.

quote:

Originally posted by Ol` Joe:
...HC, I read somewhere once that the angle/lgt of the lead (5* vs 15*?) and various ogive shapes (say VDL vs RN) could cause the contact point to move up or down the ogive or lead. Maybe this is what is being discussed? Personally I`ve no idea if this is true or even a measurable distance with common tooling, but I thought I`d toss it at you for thought.

You may be 100% correct, I sure don't know cause I've never owned an "RCBS Precision Mic".

quote:

BTW, aren`t the 2 diameter bullets built to allow the foreward half to ride the lands with the rear in the groves?

Yes. And it is an absolutely excellent Design.

quote:

What would be the important part of the bullet contact in this case? The rear full diameter that takes the ingraving of the rifleing, or the front section that doesn`t touch the lead and just skims across the rifleing? I don`t know the answer to this either, just opinions.

They seem to work together to create a situation that is not attainable with most other Designs. The "Ringed Bullets" use a similar Design Concept, but it is applied differently(and they work well too).

I agree the Forward portion rides only in the Bore(or atop the Lands). It does seem to cause the CenterLine of the Bullet to become extremely close to the CenterLine of the Bore. And it retains that CenterLine position as it moves through the Barrel, better than a lot of other Designs.

Having a smaller Contact Patch means "Less Friction" due to Engraving and Drag which allows it to move easer(quicker) for the same amount of Force acting on the Base. This seems counter intutive to the folks that believe the only way to get a Bullet moving Faster is to have a Higher Pressure. In the 2-Diameter Design, it just doesn't take as much "Work" to get it going or to Accelerate it.

This is one of the Reasons people are Warned to "Always Re-Develop a Load when any Component is changed." A Load Developed to a SAFE MAX using a 2-Diameter Hornady has the potential to show HIGHER Pressure Indicators "if" the Bullet is simply swapped to a different brand.

It has always been a great Design and Hornady would be wise to Market the advantages and move to a 2-Diameter Design on more bullets.
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If anyone doubts what I've posted about the 2-Diameter Bullets, and if you have a 30cal rifle of some sort, get a box of 150gr RN Hornady Bullets(Part# 3035). Now work-up to the same amount of Powder as one of your other 150gr Loads and see how the accuracy is and if the velocity is a bit higher with the same amount of Powder. Of course the accuracy is always dependant on the Barrel Harmonic, but you should see relatively small groups as you work-up the Load.

Great Design that we could use more of.

The precision mic is great as a headspace tool. I only have to disassemble the bolt once, in order to establish a proper "feel" measurement.

I've made "adapters" for some wildcats, so I can use the same mic.

Hope the pic works......

I use the Sinclair tool for bullet seating depths.

Friend Of The 17....and 20
Kevin Gullette
[IMG:left]http://outcast.homeunix.org/uploads/17AB-HBHSGauge.jpg [/IMG]

quote:

Originally posted by sep:
Infantrytrophy,

That's a great synopsis of the functions. However, If I understood your post correctly you stated the ogive on the RCBS dummy round won't be the same measurement as the ogive on your loaded round. The micrometer manual states it will be with the exception of "bore riding designs" whatever those are. As an example, I just measured the point on the RCBS dummy ogive using my calipers and my Davidson's seating depth checker. I then measured the ogive of one of my loaded rounds using the same tools and they are the same. Apparently, Barnes X bullets aren't a "bore riding design".

Sep -

Thanks for your comment.

For many "standard" types of bullets, we may be talking about a distinction without a difference in the practical sense.

Keep in mind that we want to keep track of the point on the bullet where it contacts the lands. We want that point to be a certain distance from the lands (.020 short of the lands, touching the lands, or whatever).

The comparators that we are discussing - the Stoney Point/Hornady tool, the land nut part of the RCBS tool, your Davidson tool - measure a point on the ogive forward of the point where the lands contact the bullet. For illustration purposes, let's say that these two points are "x" distance apart for bullet A. For bullet B, this distance might be x +.005 or x -.005 because the ogive shape is different from that of bullet A. On the other hand, the difference might be less, or even insufficient to measure for the usual types of bullets that we use.

Based on your observation we might conclude that the comparator's measurements of your cartridge loaded with the Barnes bullet and the RCBS dummy round are the same because the ogive shape of your bullet and the RCBS dummy bullet are so close that the difference between the measurements is too small to measure. In other words, the RCBS dummy bullet is a good proxy for your bullet and possibly for other commonly used bullets. More tests would be required to confirm this. It would not surprise me if RCBS had designed their dummy bullet ogive to be similar to several commonly-used commercial bullets.

Does this make sense?

In practice, I found that it was easier to make my own dummy round using my own bullet seated in an empty case, then chamber that round "to the lands" than to try and carefully chamber the RCBS round.

In contrast to what others have said, I found the RCBS headspace nut and the land nut to be accurate, reproducible and easy to use.

Hey 28sstony, I forgot to mention the "Precision Mic" is also not needed to properly Seat the Bullets at any depth you desire. The key is being able to have a consistent measurement from the Ogive as infantrytrophy has mentioned.

But once again, you can also accomplish this by Converting OCL to ODL using a Standard Die Set.
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I'm not trying to argue the points with any of the posters, just saying I don't have a "Precision Mic" and get along fine using the old Methods.

The Precision case Mic tool is a useful tool but as mentioned before you can get along without one. If you have several calibers and case sizes you can mix and match to get more overall use. For example if you have a 300 mag and a 7-08 case mic, you can use the 7mm head and bullet to measure lands on a 7 Magnum by mixing the tools. The absolute measurement won't necessarily be the same but what you need is a repeatable distance from the lands.
The most surprising thing I've found out from using the Case Mic is how far off some Virgin Brass is at the shoulders. I measured some Virgin WW 338 Win Mag brass and the shoulders varied from -.020 to -.040! Of course everyone knows that the 338 is supposed to headspace off the Belt but is more accurate when headspaced off the shoulder but I was still amazed at how much variation the shoulders had. It explained why all of a sudden a Very accurate 338 Win Mag I had wasn't shooting quite as well.
For measuring just the distance from the lands I think that the Hornady (Stoney Point) tool is probably a bit easier to use and cheaper overall. When I've measure rifles with both tools I ended up at the same place even when using different bullets.
But even though the Hornady is cheaper in some ways I still like the RCBS tool, especially because it helps with Cartridge headspace. BTW it takes only 1 normal pressure firing for the case to establish it's headspace...........................DJ

I won't tell how I like and use the RCBS Case Mic, Infantrytrophy has said it all. I'll just add that I don't think I would feel comfortable without mine to set size dies and confirm bullet seating to the ogive.

Good write up Infanty!

Infantrytrophy,

I just read the Precision Micrometer instructions again to confirm my long-standing assumption. The RCBS dummy round or "freebore tool" as they call it, measures the point "at which the bearing surface of a bullet will contact the lands of your rifle." That should be consistent from bullet manufacturer to bullet manufacturer even though ogive profiles may differ. I'm really splittin hairs now. ;-)

quote:

Originally posted by sep:
Infantrytrophy,

I just read the Precision Micrometer instructions again to confirm my long-standing assumption. The RCBS dummy round or "freebore tool" as they call it, measures the point "at which the bearing surface of a bullet will contact the lands of your rifle." That should be consistent from bullet manufacturer to bullet manufacturer even though ogive profiles may differ. I'm really splittin hairs now. ;-)

Sep,

Hey, no fair!! You read the instructions! Real men don’t read instructions. Oh well, we can have some fun splittin’ hairs and pickin’ nits.

First, define terms. Glen Zediker, in his book Handloading for Competition, defines the “major diameter†as the first point on the bullet that contacts the lands. The land diameter of the barrel is, of course, smaller than the groove diameter.

When I said that the bullet comparators that we discussed measure a point on the bullet forward of the actual land-contact point (“major diameter†from above), I was correct, at least for the Stoney Point/Hornady OAL gauge. To confirm this, take a loaded cartridge and insert it bullet first into the hole of the bullet comparator insert (of the Stoney Point/Hornady tool). You will see that the bullet stops in the hole well forward of the case mouth, so you have a reference point. For my sample cartridge, a very rough “eyeball†measurement of this distance is .150 in. forward of the case mouth. You can also see that the bullet’s diameter at this point is conspicuously smaller than the bullet’s maximum diameter.

OK, here is where my crow-eating begins. Now, let’s try the same thing with the RCBS land nut. When I insert the bullet of the same cartridge into the hole in the land nut, the bullet goes farther into the hole. (Note: to make this observation you have to use the outside hole of the land nut, not the hole inside the land nut. Hopefully they are the same diameter.) For my sample round, the distance between the case mouth and the hole of the RCBS land nut is about .100. All this means is that the hole in the RCBS land nut is larger than the hole in the Stoney Point/Hornady comparator insert (duh!). You could measure the hole diameter directly, of course. The difference is easier for me to see using the tapered bullet, because I don’t trust my “inside†measurements using the caliper.

The hole diameter of the Stoney Point/Hornady comparator is obviously smaller than the “major diameter†of the bullet and the land diameter of the barrel (should be the same thing). It follows that both of the different points on the bullet (corresponding to the two different comparator hole diameters) cannot be the one “major diameter†of the bullet. The point contacted by the S.P./Hornady comparator can’t be; the point contacted by the RCBS land nut might be (or might not be).

Now, here is the pertinent question: is this larger hole diameter of the RCBS land nut the same as, or smaller than the “major diameter†of the bullet, the point where the bullet contacts the lands? It is obviously closer than the S.P./Hornady tool, but is it the same? If yes, then Sep is right, I eat crow and I was at least partly wrong with reference to the RCBS unit (I was right with reference to the S.P./Hornady unit). If no, then I was right for both units. In any case, it doesn’t really matter. They are both close enough to the major diameter that they can be used to define a reference point for very accurate bullet seating. You seat the bullet, compare the round to the reference, then adjust as necessary.

Another hairsplit is in order here. I emphatically agree that the RCBS freebore tool or dummy round is a perfectly adequate proxy for a standard .223 cartridge. However, when Sep referred to the freebore tool (or dummy round) measuring the major diameter of the bullet, this is not exactly right – it is the base/land nut unit that does the measuring. This distinction is important because it directs our attention to land nut, not the freebore tool or dummy round. Sep has prodded me (thanks, Sep) to open my eyes to the difference between the S.P./Hornady comparator and the RCBS land nut. The RCBS land nut is actually much closer to (if not equal to) the bullet’s actual major diameter than the S.P./Hornady tool’s comparator. I missed the fact that the two comparators measured a different point on the bullet because the bullet’s insertion into the RCBS land nut is hidden from view; the bullet’s insertion into the S.P./Hornady tool’s comparator is visible. The RCBS unit does not give an absolute measurement, but instead gives a reference measurement unique to that tool. The S.P./Hornady tool can give either an absolute measurement or a reference measurement depending on whether you zero or calibrate your caliper with the comparator installed on your caliper.

If you, Sep, or if anyone else can tell us whether the diameter of the hole in the RCBS land nut is actually the same as the major diameter (where the bullet contacts the lands), please let us know. Beware that we may be getting into more hairsplitting. For example: is the land diameter of all .223 barrels the same? I do know that different .308 barrels can differ in their land diameters and groove diameters. Is this true for .223/5.56 barrels as well? If we define the bullet’s major diameter as the first point where it contacts and lands and if the land diameters of different barrels vary, then it follows that the major diameter of a particular bullet will vary, depending on which barrel it is fired in! Can this be right? Have we opened another can of worms?

Well, yes we have. We know that the point in the barrel where the bullet contacts the lands can vary. As more rounds are fired through the barrel, the throat erodes. Sep mentioned this earlier. This means that the lands are worn away and the contact point with the lands recedes farther into the barrel. It stands to reason that the “leade angle†will change as well, as the throat erodes. It then follows that as the angle of the lands that face the approaching bullet changes, the point on the bullet that contacts the lands might change, as well. So, not only can the “major diameter†of a particular bullet be different for different barrels, that same “major diameter†might change over time in the same barrel!

I suspect that these two esoteric considerations are of limited importance. Regarding the different barrels, this is of no practical significance. You are going to determine your reference point “to the lands†for each barrel anyway. Regarding throat erosion, you can re-determine your reference point “to the lands†periodically, depending on how many rounds you fire. A competitive high power across the course target shooter will reassess his/her target rifle each season. A hunter might never have to reassess his hunting rifle because he fires fewer rounds.

Don’t lose sight of the big picture – the whole point is that either of these tools can be used to seat bullets accurately; more accurately than using the COAL, meaning the cartridge overall length to the bullet tip. In addition, don’t forget that the RCBS kit also measures the case headspace, the distance from the case head to the datum line, accurately. This is very useful for adjusting the sizing die for a particular amount of setback of the case shoulder.

OK, Sep, ball’s in your court. Should I start eating some crow now or wait until we get some more answers?

Infantrytrophy,
You're not gonna let this one go are ya! Interestingly enough, earlier today before reading your latest post, I measured the inside diameter of the RCBS tool and my Davidson seating depth checker with my micrometer and they were within one-thousandth of an inch of each other. So, it would appear they both measure the point of the projectile which will first contact the lands of the barrel. As you pointed out in your latest post, as long as we are consistent with our measurements, regardless of the bullets and the barrel lands we'll be able to find and maintain acceptable accuracy. Now, I've gotta figure out why some of my full length resized brass won't chamber in my new rifle...

quote:

Originally posted by sep:
...Now, I've gotta figure out why some of my full length resized brass won't chamber in my new rifle...

Are you Crimping?

quote:

Originally posted by sep:
...Now, I've gotta figure out why some of my full length resized brass won't chamber in my new rifle...

Since you full-length resized, you can assume that the case body diameter and the neck diameter are OK.

Could be …

Bullet seated out too far.
Case neck too long.
Shoulder not “bumped back†when sizing. Was the sizing die backed off from full contact with the shellholder?

Do factory loaded rounds chamber OK?
Is this a factory rifle? Does it have a “custom†chamber?
Any debris or grit in the chamber?
Check the case heads. When I first started reloading, I managed to actually warp a few case heads.
Are primers seated below the case head? High primers might cause failure to chamber. Yep, I’ve done this, too. Have to learn the hard way sometimes ...

Hotcore/Infantrytrophy,

I'm not crimping any rounds. I P-FLR and trimmed the cases to length. At first, I thought my die wasn't setting the shoulder back far enough. So, then I started measuring cases that chambered okay and discoverd that wasn't the problem. I think the chambering problem is the bottom of the case just above the belt. (338 Win Mag) I miked the ones that wouldn't chamber and compared them to those that would and found the problem cases to be anywhere from .002-.005 wider right above the belt than the ones that would chamber easily.

I did some internet research and found a guy named Larry Willis who sells a belted magnum collet resizing die designed to fix the case expansion just above the belt. I ordered one and we'll see if that fixes the problem.

quote:

Originally posted by sep:
... I miked the ones that wouldn't chamber and compared them to those that would and found the problem cases to be anywhere from .002-.005 wider right above the belt than the ones that would chamber easily.

I did some internet research and found a guy named Larry Willis who sells a belted magnum collet resizing die designed to fix the case expansion just above the belt. I ordered one and we'll see if that fixes the problem.

Hey Sep, I hope that fixes it for you. I believe Kraky who posts here has one of those tools.

For whatever the reason, all my Belted Cases do fine in a regular Die. And I had a problem seeing a use for Mr. Willis product when it first came out. But it sounds like that might just fix you up.

Don't take this as being critical of your approach, but I believe I'd have sent my FLR Die back to the manufacturer with a few of those Cases that exhibit a wider Pressure Ring Expansion. They could have fixed it so there was no need for the $100 donation to Mr. Willis.

Anyway, best of luck to you with the new Tool.

Hotcore,

Strange thing is I had this same problem with a set of Redding dies for 338 Win Mag too. Full length resizing isn't rocket science and that's why I'm gonna give the collet die a try. Hopefully, that will fix the problem. If not, I can always take RCBS up on their old offer...forever or for life...whichever comes first.