.40 Range Rod

[haggis]

I have found it difficult to find a range rod for all the various .40 caliber revolvers out there, including .38-40, .40 S&W, and 10mm Auto, so this is a multipart question.

1. Does anybody know where range rods for these calibers are available?
2. Does the same range rod fit all of them? All have .400"-.401" groove diameters, but is the land diameter different between the .38-40 and the .40 auto cartridges? The auto cartridges should be similar, but the lead bullet .38-40 may have deeper grooves.
3. If I have to make my own rod, does anyone know the land diameter for each cartridge and how much smaller the range rod is than that?

With the CAS revival of the .38-40 and the various moon-clipped 10mm's out there, I was surprised that .40 range rods were so difficult to find. Any help would be gratefully appreciated.

Thanks,

Buck

 

[haggis]

I have found it difficult to find a range rod for all the various .40 caliber revolvers out there, including .38-40, .40 S&W, and 10mm Auto, so this is a multipart question.

1. Does anybody know where range rods for these calibers are available?
2. Does the same range rod fit all of them? All have .400"-.401" groove diameters, but is the land diameter different between the .38-40 and the .40 auto cartridges? The auto cartridges should be similar, but the lead bullet .38-40 may have deeper grooves.
3. If I have to make my own rod, does anyone know the land diameter for each cartridge and how much smaller the range rod is than that?

With the CAS revival of the .38-40 and the various moon-clipped 10mm's out there, I was surprised that .40 range rods were so difficult to find. Any help would be gratefully appreciated.

Thanks,

Buck

 

[john traveler]

Sad to say, throughout the long production history of .38-40 revolvers and carbines, bore and groove diameters have been a "sometimes" thing. You will find that they vary by several thousandths from one manufacturer to another, and even from one model produced a generation earlier.

If you intend to grind/turn your own range rod, it should be a slip fit, say 0.0005" smaller in diameter than the barrel bore. The object is to have a rod that barely enters the bore, and clears the chamber throat by the depth of a rifling land.

 

[haggis]

Yeah, John, that's one more thing I have to worry about for the .38-40. If I have a rod made, I'll give the shop the NS and have them make the rod specifically for it.

I know that .38 target guns use 0.0005" under land diameter, but I thought service guns were 0.001".

The range rod for .45ACP is 0.441" for a 0.451" bore. The rod for a service .38 is 0.344" for a bore diameter of 0.357". I thought that the difference between bore and rod for the .45 (0.010") was less than for the .38 (0.013") because the rifling for jacketed bulets is shallower than one designed for lead bullets.

The lands on my S&W 646 in .40 S&W appear to be 0.004"-0.005" (tough measurement with 5 grooves). With my logic above, I would suspect an appropriate rod diameter would be 0.390"-0.391". So far, I haven't gotten anybody to confirm this, including S&W.

Thanks much for your reply,

Buck

 

[john traveler]

Your machine shop contact should be able to get close using a set of plug gages. I would look for one that just drops through with minimum clearance, and start by grinding the rod to 0.002" larger diameter, and then fit-and-grind to get the 0.0005" slip fit.