Making chamber reamer for wildcat

45flaco · September 23, 2020, 10:57 PM

Hey guys. About to make a chamber reamer for a wildcat.
Wondering about the clearance. In other words, if my cartridge has a base diameter of 0.513", do I cut +0.005" on the diameter for the chamber? For a chamber diameter of 0.518" at the base? If this was steel on steel, that would be a very nice slip fit. But I don't know what the tolerances are on chambers. I've made D-reamers before, but all were for low powered cartridges, mostly in blowback carbines, and had tons of slop.
This is going to be running a bit hotter, so I'm hoping to have a good chamber.
And no, I don't want to have a reamer made. I don't particularly need this wildcat, I'm just building something for the experience. Buying the parts won't teach me anything.
Also, if any of you have made a 458 straightwall case from 7mm rem mag brass, about 2.3-2.5" OAL, I'd like to hear about it. Something like a very short 458 win mag, but with a long throat for heavy bullets. Hoping for a nicely suppressible PDW cartridge, to run on fast powder and short barrels. I figure that 65k PSI should get stuff to 1000 fps really fast, then the actual muzzle pressure will be low, compared to something using a slower powder and lower peak pressure in the same length barrel.

Gotta be honest, I'm probably retarded, but it's fun.

Jim Watson · September 23, 2020, 11:34 PM

Look at the SAAMI specifications for the clearance in a cartridge similar to your wildcat.

Before sources of .45- 2.4 to 2 7/8" revved up, BPCR shooters were using belted cases.

45flaco · September 24, 2020, 07:57 AM

Awesome to hear that someone has tried something similar, I guess I'm not insane.
Just checked, for the 458 win mag, it lists the chamber diameter at the base right in front of the belt as 0.5146", and that area on a new case is 0.513"

Unless I'm missing something, this means it has 0.0016" on the diameter. That seems kind of tight. For the neck clearance, it has 0.483", which is 0.002" of clearance.

Does this seem right?
Thanks

Jim Watson · September 24, 2020, 09:54 AM

CAVEAT, I am not a gunsmith. I am not even "mechanically inclined."

But I will point out that the SAAMI book specs are for a minimum chamber and a maximum cartridge, so clearances will normally be greater.

Also, if you get it too tight, you can always grind a new reamer and open it up. Hard to unream a sloppy chamber.

45flaco · September 24, 2020, 07:19 PM

Yep. I agree on it's better to take two cuts, than to start over.
I figure I'll give it a try in a scrap block of mild steel first, rather than repeatedly ruining and cutting a barrel down.
Although, this cartridge is big enough I might be able to do it with a boring bar when I get annoyed with the D reamer.

September 23, 2020, 10:57 PM	#1
45flaco Senior Member Join Date: November 19, 2017 Posts: 134	Making chamber reamer for wildcat Hey guys. About to make a chamber reamer for a wildcat. Wondering about the clearance. In other words, if my cartridge has a base diameter of 0.513", do I cut +0.005" on the diameter for the chamber? For a chamber diameter of 0.518" at the base? If this was steel on steel, that would be a very nice slip fit. But I don't know what the tolerances are on chambers. I've made D-reamers before, but all were for low powered cartridges, mostly in blowback carbines, and had tons of slop. This is going to be running a bit hotter, so I'm hoping to have a good chamber. And no, I don't want to have a reamer made. I don't particularly need this wildcat, I'm just building something for the experience. Buying the parts won't teach me anything. Also, if any of you have made a 458 straightwall case from 7mm rem mag brass, about 2.3-2.5" OAL, I'd like to hear about it. Something like a very short 458 win mag, but with a long throat for heavy bullets. Hoping for a nicely suppressible PDW cartridge, to run on fast powder and short barrels. I figure that 65k PSI should get stuff to 1000 fps really fast, then the actual muzzle pressure will be low, compared to something using a slower powder and lower peak pressure in the same length barrel. Gotta be honest, I'm probably retarded, but it's fun.

September 23, 2020, 11:34 PM	#2
Jim Watson Senior Member Join Date: October 25, 2001 Location: Alabama Posts: 18,541	Look at the SAAMI specifications for the clearance in a cartridge similar to your wildcat. Before sources of .45- 2.4 to 2 7/8" revved up, BPCR shooters were using belted cases.

September 24, 2020, 07:57 AM	#3
45flaco Senior Member Join Date: November 19, 2017 Posts: 134	Awesome to hear that someone has tried something similar, I guess I'm not insane. Just checked, for the 458 win mag, it lists the chamber diameter at the base right in front of the belt as 0.5146", and that area on a new case is 0.513" Unless I'm missing something, this means it has 0.0016" on the diameter. That seems kind of tight. For the neck clearance, it has 0.483", which is 0.002" of clearance. Does this seem right? Thanks

September 24, 2020, 09:54 AM	#4
Jim Watson Senior Member Join Date: October 25, 2001 Location: Alabama Posts: 18,541	CAVEAT, I am not a gunsmith. I am not even "mechanically inclined." But I will point out that the SAAMI book specs are for a minimum chamber and a maximum cartridge, so clearances will normally be greater. Also, if you get it too tight, you can always grind a new reamer and open it up. Hard to unream a sloppy chamber.

September 24, 2020, 07:19 PM	#5
45flaco Senior Member Join Date: November 19, 2017 Posts: 134	Yep. I agree on it's better to take two cuts, than to start over. I figure I'll give it a try in a scrap block of mild steel first, rather than repeatedly ruining and cutting a barrel down. Although, this cartridge is big enough I might be able to do it with a boring bar when I get annoyed with the D reamer.