Why not use the ID caliper teeth for groove width?

[Robanada]

Hi guys, first post for me.

I want to slug my Makarov barrel (expecting ~0.365"), and I'm going to go get some egg sinkers that are about the right size, little bigger. I also need a micrometer or caliper. I was looking at some calipers that have tolerances of 0.0005". I think this will be acceptable tolerance for measuring the width with sufficient accuracy, no? Most calipers come with two sets of teeth- some for measuring outer diameter, and some for measuring inner diameter. Is there a reason that I have to slug the barrel and measure the outer diameter of the slug? Why can't I just use the ID teeth on the caliper to measure the inside of the barrel, if I'm careful to measure the grooves instead of the lands? It seems a lot easier than hammering away at my pistol (it's a fixed barrel, by the way, so that'll be difficult in and of itself). It seems like this would be common practice if it were a better method, so there must be some drawback I'm not seeing. Does anyone know what it is?

[462]

The barrel is round. A caliper's inside jaws are flat.

[Treeman]

Even when you have knife edge jaws and the grooves are spaced to allow measuring across you still have the possible issue ofvarying diameters over the length of the barrel ...... but I find slugging mostly unnecessary. Simply shoot the fattest bullets that will chamber. Swaging down a cast bullet is less an issue than trying to bump one up with chamber pressure. Some folk worry about increased pressure from oversized bullets but unless they are hugely oversize and harder than the hubs of hell you and your gun will never notice.

[R.M.]

It's a caliper, they're not that accurate, inside or out, especially in the hands of the inexperienced.

[uscra112]

It's a caliper, they're not that accurate, inside or out, especially in the hands of the inexperienced.

Even in the hands of the experienced, they're only good to about a thou at best, and rarely that. Even to measure a good slug, they're not accurate enough. Only a proper micrometer will do that reliably. Just because the readout says half a thou doesn't mean it really is that accurate.

[Ajax]

When i first started I used a caliper to measure my slugs. At the behest of some of the moderators in chat I bought a micrometer and found that the measurements I took with the calipers were off by about .003. It amazed me there could be that much of a error on calipers whose tolerance was suppose to be to .0005. I highly recommend micrometers to all beginners now.


Andy

[Robanada]

Alright, thanks for all of the input guys. I want to get into casting mostly because of the ammo shortage (and I think it'll be really rewarding to be connected so intimately with every step in the shooting process), and so I'm trying to keep my overall costs down (the startup costs alone could buy me several cases of ammo, even at today's prices!). I don't have calipers or a micrometer, and I'd prefer just to buy one tool if I can get away with it. I wanted the calipers to size brass (I'm going to be needing to shave 1mm off 19mm long parabellum rounds), but I guess I can use a micrometer for that, too. I was thinking that the jaws on the calipers would be a lot faster than using the micrometer for measuring hundreds of cases, as opposed to measuring a slug once (or twice).

I was originally thinking of these calipers because the extra few bucks for a digital readout would be worth it to me not to use vernier:
http://www.amazon.com/Inch-Digital-C...6537164&sr=1-6

I guess I could swing another 10 bucks for this guy:
http://www.amazon.com/Anytime-Premiu...rds=micrometer

Are there any objections? Anything wrong with a $20 micrometer versus a $100 one?

[Ajax]

I would go a few dollars more and get this one much easier to real

http://www.amazon.com/Anytime-DIGITA...ometer+digital

Andy

[6bg6ga]

As a former inspector I would go with a name brand over the cheap one. You would be surprised how many people do not know how to properly read a micrometer and think that you tighten the hell out of it on what your measuring. I favor old school micrometers without a digital readout. Calipers will measure the length of a shell case accurately enough but will not measure the diameter of a bullet close enough.

Check garage sales especially those having a husbands tools on sale after the husband has passed away. Lots of good buys there and usually name brand tools.

[alamogunr]

As a former inspector I would go with a name brand over the cheap one. You would be surprised how many people do not know how to properly read a micrometer and think that you tighten the hell out of it on what your measuring. I favor old school micrometers without a digital readout. Calipers will measure the length of a shell case accurately enough but will not measure the diameter of a bullet close enough.

Check garage sales especially those having a husbands tools on sale after the husband has passed away. Lots of good buys there and usually name brand tools.

+1 It's not a C clamp.

This was discussed a couple of days ago.

http://castboolits.gunloads.com/show...97#post2178797

Look at post 21.

[MtGun44]

If you are keeping costs down, use the biggest slug that will chamber properly
and you will probably be OK. Slugging a barrel is a good thing but not absolutely
necessary.

Bill

[918v]

Instead of measuring the bore and groove diameter, consider this: you should be sizing to fit the throat. The throat is always the same or larger than the groove diameter. The throat is alot easier to measure. Just take a boolit, smack the nose with a hammer to increase the diameter to about .370", make a dummy round, pound it into the chamber and the throat will engrave itself on the bullet nose. Measure the engraved throat. There you go.

[mold maker]

When acquiring egg sinkers to drive through a bore, watch carefully for steel sinkers. Not many lead sinkers available anymore.
Talk about a way to ruin your day!!!!

[918v]

http://www.taurusarmed.net/forums/bu...et-mold-2.html

Go to post #18

Look at the chamber schematic.

It shows a CIP spec chamber has a tapering freebore starting at .368" at the case mouth and ending at .365" at the beginning of the leade. If your chamber is a perfect copy, you'll need at least a .367" boolit.

[country gent]

Another draw back to measuring ID with calipers is they dont get the whole length of the barrel just 1/8 - 1/4" at the muzzle. The lead slugs can be pushed in a inch from each end then one passed thru completely this will show tightest spot, or any taper or choke and in which direction it is.

[Robanada]

Thanks for the pointers, guys.

Instead of measuring the bore and groove diameter, consider this: you should be sizing to fit the throat. The throat is always the same or larger than the groove diameter. The throat is alot easier to measure. Just take a boolit, smack the nose with a hammer to increase the diameter to about .370", make a dummy round, pound it into the chamber and the throat will engrave itself on the bullet nose. Measure the engraved throat. There you go.

Huh. Not a bad idea. So what happens if the throat is a lot bigger than the groove diameter? Do you just shave off a bunch of lead each time you fire?
The problem for me, going in from the chamber side anyway, is that the makarov has a fixed barrel, so even cleaning it from the chamber side is kind of a pain- the hammer and everything tends to get in the way.

When acquiring egg sinkers to drive through a bore, watch carefully for steel sinkers. Not many lead sinkers available anymore.
Talk about a way to ruin your day!!!!

Ooh good tip- I didn't even think about that!

http://www.taurusarmed.net/forums/bu...et-mold-2.html

Go to post #18

Look at the chamber schematic.

It shows a CIP spec chamber has a tapering freebore starting at .368" at the case mouth and ending at .365" at the beginning of the leade. If your chamber is a perfect copy, you'll need at least a .367" boolit.

Thanks for this- I saw the thread, and I've seen this schematic, but I don't have much experience in this whole thing so I didn't notice the tapering freebore. How are you getting .367" out of .368-.365"? Would you get gas cutting from the point where it's .368" until it reaches .366"?

[smokeywolf]

6bg6ga has it right. Find yourself a name brand micrometer; older Starrett, Brown & Sharpe, or Mitutoyo. Better to stick with mechanical digital or non-digital. Get a standard to check calibration occasionally. Clean your measuring faces by gently closing your mike down on a piece of paper and dragging the paper through/across the measuring faces.

smokeywolf

[cwheel]

First off, ditch the metric system, don't buy a micrometer or calaper that in metric. Loading books list sizes in thousands, not MM. Some calipers do both, and that's a good thing. I also agree with Smokywolf, go to ebay and buy a good Starrett, Brown and Sharpe, Lufkin, or Mitutoyo 1" micrometer. Go to ebay and search for Starrett 230 and look at the ones with the red or black hard case, looks like it is in a glasses case. ( black case is older, but still a great tool ) Lots of these sell in the $25-50 range. Make sure the little spanner wrench is with it to set the zero. Finaly a good 6" digital cal is very handy for setting OAL's in your seating die, to trim cases as well, a must have as well. Don't count on any caliper to measure something closer than .002, it might read to .0005 but not that accurate, that is what a micrometer is for. You shouldn't have to spend much money on these.
Chris

[zuke]

I use a set if Mitutoyo point mic's I bought specifically for that purpose.

[918v]

So what happens if the throat is a lot bigger than the groove diameter? Do you just shave off a bunch of lead each time you fire?

Thanks for this- I saw the thread, and I've seen this schematic, but I don't have much experience in this whole thing so I didn't notice the tapering freebore. How are you getting .367" out of .368-.365"? Would you get gas cutting from the point where it's .368" until it reaches .366"?

In a loaded round, at least some of the bullet shank is already in the throat while the slide is in battery, so there is no shaving going on.

I'm thinking .367" because .368" won't chamber freely. A .367" bullet will chamber freely and bump up if you use a soft enough alloy. Think of the .45 ACP. It typically has a .453" throat and we use .452" bullets. There isn't any leading cuz the bullet bumps up to seal the throat upon ignition. The round chambers freely and there isn't any lead shaving cuz part of the bullet rests in the throat while in battery. The Mak is just a smaller .45 ACP.