Sizing kit for the .40 S&W

[dearslayer]

Hello again folks. I recently purchased the Lee mold for the noted caliber. I have the 6 cavity TL401-175-WC .So I finally took the leap ( was a little nervous about it getting stuck etc ) and slugged the barrel on the .40. measured .3965. so now that I know that measurement which sizing kit should I order if I'm powder coating? In the attached photo would I need the .401 sizing kit?

[dearslayer]

Photos attached. Am I measuring correctly?292767292768292769

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[ryanmattes]

What pistol is that for? .3965 seems small.

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[dearslayer]

What pistol is that for? .3965 seems small.

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It's a Para Ordnance 16/40 limited made in Canada.

[Dusty Bannister]

Since the numbers seem a little small for the 40, I have to wonder if you have an even or odd number of lands and grooves. If odd number, you are measuring the high side on one side of the bullet and the low side on the other so your reading an error. I believe you have an accurate measuring device but I prefer to use a micrometer and then "roll" the bullet between the anvils in order to get the largest diameter reading. Others might take a thin shim strip and hold that tight around the slug and measure that and then subtract 2 times the shim thickness. There is probably a sticky on that method.

You also need to be absolutely certain that the slug starts out larger than the largest diameter possible with that caliber. The groove is often in excess of .401". If the slug is a little undersized, set the slug on a flat steel surface and bump the nose of the bullet with a heavy hammer to expand the slug larger than "as cast". The slug should display clear indications of contact on the entire circumference of the exterior. Soft lead, well lubricated, is much easier to drive through with a brass rod. If using a wood dowel, you may need to locate another sticky discussing how to remove a splintered wood dowel from a barrel. Here are a few methods of slugging that might give a better picture of the process for slugging a barrel that you might have missed.

https://castboolits.gunloads.com/showthread.php?123417-Slugging-the-barrel&highlight=slugging%20barrel

[GBertolet]

Micrometers are often better than calipers for measuring diameters. If you have a micrometer, or can borrow one, try measuring again. Dusty Banister has good info on how to slug a barrel. Try his method, and see what you get.

[Larry Gibson]

Don't over think it.

Get the .401 sizer kit. Follow lee's instructions with the LLA. Apply thin coats (bullet should have just a golden hue after lubing) and let dry thoroughly. Go shooting and enjoy.

[45-70 Chevroner]

Larry knows what he is taking about. My thoughts were the same.

[dearslayer]

Since the numbers seem a little small for the 40, I have to wonder if you have an even or odd number of lands and grooves. If odd number, you are measuring the high side on one side of the bullet and the low side on the other so your reading an error. I believe you have an accurate measuring device but I prefer to use a micrometer and then "roll" the bullet between the anvils in order to get the largest diameter reading. Others might take a thin shim strip and hold that tight around the slug and measure that and then subtract 2 times the shim thickness. There is probably a sticky on that method.

You also need to be absolutely certain that the slug starts out larger than the largest diameter possible with that caliber. The groove is often in excess of .401". If the slug is a little undersized, set the slug on a flat steel surface and bump the nose of the bullet with a heavy hammer to expand the slug larger than "as cast". The slug should display clear indications of contact on the entire circumference of the exterior. Soft lead, well lubricated, is much easier to drive through with a brass rod. If using a wood dowel, you may need to locate another sticky discussing how to remove a splintered wood dowel from a barrel. Here are a few methods of slugging that might give a better picture of the process for slugging a barrel that you might have missed.

https://castboolits.gunloads.com/showthread.php?123417-Slugging-the-barrel&highlight=slugging%20barrel
I'll check that slug a Little closer in a little bit to see if I'm measuring it correctly from high point to high point. I guess while I'm at it I should re-slug the barrel again?. I remember it being a tight fit going in to the point where it got to the edge of the muzzle a small ring of lead curled up from the slug and broke off indicating that it was tight going in. One thing you did mention about lubing it which I did not. So if I remelt some lead to make another slug and do it again I should lube it?

[justindad]

Calipers aren’t reliable for the precision needed here. Need micrometers.

[dearslayer]

Calipers aren’t reliable for the precision needed here. Need micrometers.I don't have micrometers but I'm gonna look into getting some.

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[David2011]

Calipers aren’t reliable for the precision needed here. Need micrometers.

I see this comment every time there’s a discussion about measuring. If a mic and calipers show the same dimension, how are calipers less accurate? For the sake of this discussion I went to the shop and measured a steel rod. Good mic, measured to tenths, 0.3943”. Very old US made mic, to thousandths, 0.394”. Dial caliper, interpolated to tenths, 0.3943”; 0.394 without interpolation but the needle was clearly over 0.394. Both of my dial calipers are accurate to .001.

Digital calipers are a separate discussion. I use them only for less stringent requirements like brass and loaded cartridge overall length where I’m happy with 0.002 accuracy.

[Dusty Bannister]

My statement in post #5 establishes my preference for the micrometer instead of the caliper. Once set, the micrometer does not change adjustment as when rolling a slug to find the largest diameter. A caliper depends upon how tightly the two pieces of the caliper fit together and any looseness in that fit can allow for an error in reading. Use what you are comfortable with.

[justindad]

I see this comment every time there’s a discussion about measuring. If a mic and calipers show the same dimension, how are calipers less accurate? For the sake of this discussion I went to the shop and measured a steel rod. Good mic, measured to tenths, 0.3943”. Very old US made mic, to thousandths, 0.394”. Dial caliper, interpolated to tenths, 0.3943”; 0.394 without interpolation but the needle was clearly over 0.394. Both of my dial calipers are accurate to .001.

Digital calipers are a separate discussion. I use them only for less stringent requirements like brass and loaded cartridge overall length where I’m happy with 0.002 accuracy.

If you are capable & experienced with dial calipers of good quality, I’ll buy that you can get the precision needed here. In this case, seeing a .40 barrel slug to 0.397” with digital calipers makes me suspicious of the measurement system.
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I’ve been using calipers and mics in an engineering capacity for 20 years… almost regularly. My calipers and mics are calibrated annually, and my calipers are the same as what the pic shows in the OP. I trust those things within 0.003”, and I have seen my mics & calipers disagree in this range.
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There’s a general rule of thumb in quality systems that the precision of the measuring device should be 1/10th of the discrimination needed. I’m generally fine with precision being 1/4 of discrimination. These digital calipers don’t meet either of those standards.