Thread: How to make a D-type reamer to chamber a barrel

I'm interested in having a miniature martini modified to centrefire and then having a 30 cal barrel chambered in 32 S&W Long or 32 H&R Magnum. 32 S&W L is almost extinct and 32 H&R Magnum is very thin on the ground. I expect I will have to make a reamer. I've read about D-type reamers which can be effective for a few chambers. Has anyone got advice on what would work for this make-your-own reamer project?

would M1 carbine round do same for you...might be more main stream so easier to source.
if straight walled design....it can be done with boring bar...well it can with .45/70 anyway,so if you clever machinist ...

Micky: certainly 30 Carbine is straight walled (as is the 32 S&W L) but it does not have a rim and a martini really needs a reamed cartridge. I wonder how accurate a boring bar would be, particularly in the area of the entry into the bore of the barrel.

so....you talking lead/throat.... well to my simple non engineering mind you garden variety drill bit has what 45 degree angle ,you run correct size in to remove the rifling to required depth...then do chamber with boring bar.... @homebrew.357 feel free to chime in here.

What about 7.62 nagant? Or even 32 acp?

Originally Posted by Micky Duck

so....you talking lead/throat.... well to my simple non engineering mind you garden variety drill bit has what 45 degree angle ,you run correct size in to remove the rifling to required depth...then do chamber with boring bar.... @homebrew.357 feel free to chime in here.

Problem is centering the chamber according to the bore. I understand chamber reamers need a special flexible holder when used in a lathe to allow them to find their own way according to their bore pilot. Sure you can use a boring bar to make a chamber, IF you have the barrel perfectly centered in the 4-jaw chuck. It must be centered according to the bore and not to the outside of the barrel.

There are also plenty, cheap, straight reamers on Ali Express.

Yes, the lead/throat is a concern. Preferably the shape that is kind to the entry of lead bullets. Good ideas re 7.62 Nagant (is that even more obscure than 32S&W) and 32ACP but I need a real rimmed case for the martini, not just a suggestion of rim like the 32ACP.

Making a D reamer is a piece of cake. Start with a piece of 10 or 12mm silver steel and a good accurate drawing. Face and centre drill the rod then extend it from the chuck about 75mm to give you working space and support the centered end with a live centre. Turn a pilot about 25mm long that is a neat running fit in the bore then work your way back turning the leed, case and rim to a very high finish about 0.01mm above the desired finish diameter and bring it to size with a fine file and fine grade (400 then 1000 grit) wet & dry paper and oil. Evenly heat the entire length of the turned portion to a good cherry red and vertically quench in oil (SAE 30 is fine, swirling could cause the hardening to be more on one side and cause warping, hence the vertical plunge). With a good bench grinder a pail of cold water, neatly grind the entire length of the leed, case, and rim to exactly half of the diameter, (D shape) quenching frequently to avoid overheating. A light flick across the ground face with a fine slip stone and the reamer is good to go. I recommend boring or drill the chamber to within 0.5mm of the finished size before reaming. I prefer to grind a square on the end of the shaft and use a tap wrench supported by the live centre on the lathe rather than using power as you would with a proper reamer. Use plenty of good cutting oil and withdraw the reamer and clean the reamer and the bore frequently to avoid swarf picking up and grooving the chamber. Go to whoa in less than a hour!

I liked the comment about the 30 carbine. There will be a lot of the ammo about as its mostly soft point therefore not banned but every firearm that used it (well almost every one) has been banned so would be an interesting idea...

@gundoc: thanks for that very clear info.

Originally Posted by timattalon

I liked the comment about the 30 carbine. There will be a lot of the ammo about as its mostly soft point therefore not banned but every firearm that used it (well almost every one) has been banned so would be an interesting idea...

For sure, I have something like a thousand rounds of SP just parked there looking sad

pretty sure you can buy...or have made...an adaptor to fire it through a .308 or larger .30calibre case.....adaptor is basically a solid .308 case with chamber cut inside rear of it.....
would take awhile to get through your thousand rounds with single shot at a time...but it could be done.

I made a chamber reamer for .357 sig a couple of days ago, and have made a couple of other chamber reamers and several projectile reamers using this technique.

Gundoc has it right, except I tend to cut the reamer in half before hardening. Much easier to do it on the mill when soft than trying to grind when hard.
I mill them very slightly over half and then harden, Once hardened and tempered, I use a fine stone to bring it down to exactly half.
Once you have the thickness sorted, you can do the relief angles behind the cutting edge. Basically you want to use a fine stone to make a small flat (2mm wide) just behind the cutting edge, coming very close to the edge but not touching.
On the back edge that is not cutting, you want to stone the edge off and even round it over a little, I have found this helps to prevent tearing and galling.

The key to D Reamers is having them exactly in half. Im talking within 0.05mm or better if you can do it. Erring slightly thicker than half is better than being a little under.

If you make them correctly, they will hiss a little when cutting and produce chips so fine it looks like a paste.
Run them very slow with lots of good cutting oil and back out regularly to clear chips. They should require almost no pressure to cut, if they do need a lot of pressure to get them cutting, the reamer is likely not perfectly in half.

Those cartridges you mentioned should be pretty easy to make reamers for as they dont have much or any body taper and no bottleneck.

Needless to say, you will need a lathe to make these. Can be done without a mill, but its tricky.

I cant get any photos to upload at the mo, ill try to add some pics later.

@SixtyTen: that helps to clear the process a bit more. Pictures would be good. What about the section of the reamer when it goes from the pilot to the beginning of what will be the leade? And is it possible to make a removable pilot?

A removable pilot is not really required unless you are going to be chambering multiple barrels with variable bore sizes. For a one off job, just sizing the pilot to the barrel on hand is fine. I tend to make a seperate plug before making the reamer, so that I can figure out exactly what pilot size I need, then I dont have to test fit the barrel while trying to make the reamer as I know what size to hit. You could do a removable pilot by just making the pilot section longer with a step down, then you can drill and tap the end of the reamer for a retaining screw, then make the bushing.

I make my pilots quite long and cut the flat section onto the pilot so that I have a place to measure half thickness. I do the same at the other end with a parallel section and cut onto that a ways. I then make a note of those diameters before I start cutting it in half so that I can tell exactly how far I need to go. This will also allow you to see if you are cutting the flat section with a taper and be able to correct it.

I still cant upload photos. Iv played with the settings and poked around, but the photos simply wont upload. Anyone know why this is happening?