Confused after slugging bore

[AggiePharmD]

I just finished slugging my 30-40 Krag barrel. I started with a bullet sinker with a OF greater than .308 (at least .350). After the "slug" came out the chamber end I used my caliper to measure lands and grooves. My measurements were .299 and .302.

I can't figure my problem. Somewhere I screwed up? I was expecting at least .308.

Note: This was my first attempt at slugging a bore.

[btroj]

Use a micrometer, not a caliper.

[Digital Dan]

Which measurements? The grooves in your slug represent the lands in the barrel, or the BORE. The high surfaces, or major diameter represent the GROOVE depth of your barrel.

The measurements you have above may represent the bore dimension of your barrel but I'd have to doubt they represent both bore and groove. Per chance does your barrel have an odd number of grooves?

[mannyCA]

Odd number of grooves are impossible to measure without specialized equipment.
Save yourself the heartache and cast/size/paper patch for .311 :-)

[AggiePharmD]

Thanks guys. I don't have a micrometer unfortunately. I tried again with a 1903 with the same result as my military Krag so it is something I'm doing.

So as not to become discouraged and completely drop the idea of beginning to cast, I think I'll size my Krag bullets to .311 and my '03/A3 bullets to .310 unless .311 would be fine for those as well.

[AggiePharmD]

The barrel has an even number of lands/grooves. I have no doubt my measurements are incorrect. It is just irritating to me because I can't get it right.

[petroid]

take a factory jacketed bullet of known diameter and measure it with your calipers to verify they are accurate. then measure both the bore and groove diameter of the slug. and measure along the length of the slug not across it. if you arent square across the grooves they will read small

[Pb2au]

Welcome to the site Aggie.
Keep an eye on craigslist/flea bay,/ China freight for a micrometer to buy. You can scoop one up for modest money. Starret, mitutoyo, brown and sharp are some names to look for. The china freight comment was tongue in cheek, as they aren't known for super precsion tools.
Anyway,
Find a micrometer and fire up google to learn how to read it. It will take but a short period of time. Pretty soon you will always find it in your hand while at the bench.
Oh, and go buy a copy of Lymans cast bullet manual. Great reference tool.
Good luck

[Pb2au]

Oh, Krags are awesome. I just picked one up. I'm trying to find a job where I can just sit around and shoot a Krag and load ammo for the same.

[cbrick]

The barrel has an even number of lands/grooves. I have no doubt my measurements are incorrect. It is just irritating to me because I can't get it right.

Welcome to CastBoolits Aggie,

Not to worry about getting it right, I doubt very many people did on their first go round. As was mentioned a caliper, a good one, is only designed to be accurate to .001" so plus or minus that's .002" possible error. Just the wrong tool for the job.

Odds are that .310" or .311" will work fine. The sure way to know is to load'em up and shoot'em.

Rick

[btroj]

Rick is right. Try some at .310 and .311 and see what they do.

Don't sweat the difficulties measuring. It is a skill that needs time and work to develop. As a pharmD you have different skills. Now if you were a BS pharm you could measure them just fine....

[AggiePharmD]

Rick is right. Try some at .310 and .311 and see what they do.

Don't sweat the difficulties measuring. It is a skill that needs time and work to develop. As a pharmD you have different skills. Now if you were a BS pharm you could measure them just fine....

I was expecting an Aggie joke before a pharmacy you joke but hey it was funny! I count by 5s all day.

[btroj]

Me too. Have been for about 23 years.

[largom]

Nothing wrong with .310 or .311 boolits. Unless your mold drops very large boolits just lube as cast. I shoot .312 in my 30 Cal. guns.

Larry

[AggiePharmD]

Me too. Have been for about 23 years.

Just 7 for me but they've been long.

[mikeym1a]

My rebarreled Chilean Mauser, in 308, measures .299 on the lands and .308 on the grooves. I got a .301 sizer from buckshot, and plan to paper patch. I have a .309 sizer from lee, already. Just have to find some 12# paper. Ordered some 45gsm paper from amazon. According to a comparitor chart I found online, 12# bond is equal to 45gsm, so, I'll find out when it comes in. Your measurements are close to mine. You have to hold the slug really still, and make sure you instrument is touching the center on both sides to get an accurate reading. A tiny desk vise would be helpful. If I can find one I can afford, I intend to get one. mikey

[montana_charlie]

The barrel has an even number of lands/grooves. I have no doubt my measurements are incorrect. It is just irritating to me because I can't get it right.
Are your calipers made of plastic or steel?
Are your calipers vernier, dial, or digital/electronic?
Is there a means that allows you to zero the reading?
If you close the jaws on a quarter-inch drill bit, do the calipers read .250 inches?

CM

[Mk42gunner]

Thanks guys. I don't have a micrometer unfortunately. I tried again with a 1903 with the same result as my military Krag so it is something I'm doing.

So as not to become discouraged and completely drop the idea of beginning to cast, I think I'll size my Krag bullets to .311 and my '03/A3 bullets to .310 unless .311 would be fine for those as well.

Odds are that 0.311" will be fine in the 03-A3 as well as the Krag. .311" is my go to sizing diameter for 30 caliber rifles, and I only change size if it doesn't group decently with the first set of loads. So far I haven't had to go down in size at all.

Robert

[TMenezes]

Don't sweat the slug size as long as your cast slugs are bigger than your bore diameter. Lead is a wonderfully soft metal that molds to your bore size. Just don't cast super hard slugs that are too small and you will be fine. Best/easiest way to get into loading cast is with a low pressure straight wall pistol case like 38 Special, 44 special, or 45 colt. But you'll do fine with what you have.

[AggiePharmD]

Don't sweat the slug size as long as your cast slugs are bigger than your bore diameter. Lead is a wonderfully soft metal that molds to your bore size. Just don't cast super hard slugs that are too small and you will be fine. Best/easiest way to get into loading cast is with a low pressure straight wall pistol case like 38 Special, 44 special, or 45 colt. But you'll do fine with what you have.

I've been loading for the 38, 41 and 45 Colt and learned some valuable lesson concerning leading. First it is a PITA to remove and second BHN issues. Never cast my own though.