Using Cylindrical gage to measure Barrel diameter? accurate or not?

[JohnE]

Hey all, long time reader, first time poster.

I'm getting the tools together to start casting for my .380 and had read about slugging the barrel to get the diameter.

I have access to some cylindrical gages and thought I'd try that route.

I checked both my LCP and my wife's Ktec and the .348 gage slid through the barrel and the .349 gage did not.

But that doesn't seem - to me - to square with the idea that I'll be casting a .356 diameter bullet.

Am I mistaken in that idea, or are cylindrical gages not the way to go with this?

Thanks!

[Storydude]

Gauges are measuring land diameter. You cast to Groove diameter.

[9.3X62AL]

Rather than measuring the "land diameter" of the bore, try using the pin gauges to determine the throat diameter of your barrels. Start about .355", and progress upward from there until you get the "no-go" indication.

For this purpose, the "throat" would be the unrifled portion of your pistol's barrel ahead of the chamber, to the point of rifling origin. I woould predicate my boolit sizing for each pistol on that throat diameter.

Welcome to the asylum, sir!

[JohnE]

Welcome to the asylum, sir!

Thanks very much!

I gave your suggestion a shot and assuming I did this correctly, I found the point just before no-go for the LCP at .359 and for the Kel-Tec at .362

Does that sound at all reasonable, and how does that relate to a bullet mould that should nominally cast at .356?

[mpmarty]

That's about normal and indicative of what degree of accuracy the weapons are manufactured with. Typically a .380 would require from .357 to .359 to work properly the Kel Tec may never be satisfactory unless you cast some .363 boolits ala Makarov style of 9mm.

[lwknight]

All you need is a small hammer like 8 oz and a wooden 5/16 dowel cut no longer than necesary and a soft lead boolit.
Take the gun apart and slug from the chamber. You can put the end of the barrel on a piece of soft wood and drive the slug till it gets to the end.
After that you will have to hold the barrel in your hand to finish up.
Thats why you need a small hammer so that the impact will have more velocity and less kinetin energy.

[MtGun44]

Using a wooden dowel for slugging is asking for a dowel jammed in the barrel. They
split on a long angle and the two pieces wedge incredibly tightly into the barrel. There
have been several threads on how to undo this mess without ruining the barrel.

Use a brass or steel rod. Brass is too soft to harm a steel barrel, and a few wraps of
tap around a steel rod protect the bore.

Bill

[9.3X62AL]

.359" is at the upper end of 'acceptable', .362" is pretty slack. But, these aren't target arms, and their makers "assumed" jacketed bullets being used. So it goes. My 9 x 19 pistols get .357" boolits fed to them, and do pretty well downrange. Both 380 ACP and 9 x 19 can have VERY wide dimensional tolerances in both pistols and the components of the ammo that feeds them.

[theperfessor]

Chamber throat diameters won't necessarily be the same as the groove diameter of the barrel. Which diameter to make bullet sizing decisions on is what makes things interesting...

[lwknight]

Using a wooden dowel for slugging is asking for a dowel jammed in the barrel. They
split on a long angle and the two pieces wedge incredibly tightly into the barrel. There
have been several threads on how to undo this mess without ruining the barrel.

Use a brass or steel rod. Brass is too soft to harm a steel barrel, and a few wraps of
tap around a steel rod protect the bore.

Bill

OK, that is good to know, I guess I have been lucky so far and never split a dowel.
Brass rod it is. I think they have brass round rods at Tractor Supply.

[JohnE]

So, as a practical matter, am I likely to be able to drop a bullet from the Lee mould, load it for a light target round, and use the ammo to practice on 15 yd center of mass targets without much trouble?

Thanks!

[theperfessor]

I would bet you would be fine. In general, a soft lead alloy bullet can be several thousandths of an inch over groove diameter without any problems with reasonable loads. The limiting factor with a too-large bullet would be when it makes the round too fat to chamber.

Load a dummy round and try to drop it in your barrel. If it chambers easily you're probably OK. Start at the lower end and work up as always. Because a .380 case has a very limited volume, bullet depth has a greater effect on pressure than with larger cartridges of similar caliber.

[XWrench3]

i have never had a problem using a wood dowel to drive a boolit through a barrel (even rifles). maybe i am lucky, maybe i am smart. i use straight STP to lube the barrel and boolit with prior to driving it through. if you are trying to push a 50 caliber boolit through a 40 caliber bore, they you are asking for trouble.