My quest for a 7.62x39 reamer... neck length, freebore and throat angle?

MiltonBradly

MiltonBradly

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So... I have thus far achieved a rough blank to make my reamer out of...

762x39reamer1.jpg


Now I have to figure out how long to cut the neck, how much freebore and at what angle does one typically cut the throat

I have found references to a 2 1/2 degree taper to the throat on a number of different cartridges so I suspect I can go with that. My Max cartridge drawings show a neck length of 0.2392" so I know I must be over that, but how much over? As for freebore I'm planning this just for shooting mil-surp ammo. Having it go bang and not boom is my prime requirment. Accuracy and velocity are secondary concerns...

Any chance someone could do a chamber cast of there 7.62x39 mil-surp and let me know what a factory chamber runs?

Thanks
MB
 
What material are you making this out of? It appears you will be rough guessing the throat angle so 2` would likely be a good place to try for, plus minus either way. Where the neck transitions into the freebore its usually a 45` and .010" longer than the max case length. The lead length is up to you. You could measure a loaded round to find out the distance from the base of the round to the bearing surface of the seated bullet. Bore a hole in a comparator the same diameter as the barrel, should be .308". Or you could just go with .050"

This must be a learning exercise because there are used 7.62x39 reamers a round.
 
It's O1 drill rod... This is quite a learning exercise for me. I have done my own .22 rimfire reamer but this is the first center fire one I have tried.

The intention is to set back the barrel on a sportied' Enfield and clean up the chamber to be suitable for surplus ammo. From the measurements I have taken off of surplus ammo It looks like 0.050" freebore would be fairly close to the bearing surface so I'll likely go a little longer to ensure a bit of margin on a poorly seated round. 0.010" over case length sounds good but again perhaps I'll add a tiny bit to that for leeway. Since I'm not intending on reloading I'm not too concerned about case life and would prefer to be a bit loose and long. Unfortunately I may not have left enough material for a decent length pilot on my reamer. :redface:

Thanks for the info
MB

P.S. I'm sure I could track down a factory reamer but this serves as a good project to try and practice precision fabrication. As a side bonus I might get a reamer and unique Enfield for little more than $150 out of it too :D
 
Since you need the correct dimensions. This is for a .308 throat Sammi spec'd PTG reamer. Doesn't matter whether you have a .308 or .311 barrel. That's just the grooves as the bore is still .30. Czech bullets mike .309 roughly and cases slip right into that chamber. You may need to add some tolerance on the throat. .310 will do. I'll experiment with Czech surplus and see if I need to open up the throat or not.
If you're using a .303 bore those bullets may rattle somewhat down the bore. I've heard accuracy isn't the best with Lee Enfield barrels.

http://yfrog.com/0wptg762x39mmj

I assume you have all your milling and hardening techniques down. Good luck!
 
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lejarretnoir said:
Since you need the correct dimensions. This is for a .308 throat Sammi spec'd PTG reamer. Doesn't matter whether you have a .308 or .311 barrel. That's just the grooves as the bore is still .30. Czech bullets mike .309 roughly and cases slip right into that chamber. You may need to add some tolerance on the throat. .310 will do. I'll experiment with Czech surplus and see if I need to open up the throat or not.
If you're using a .303 bore those bullets may rattle somewhat down the bore. I've heard accuracy isn't the best with Lee Enfield barrels.

http://yfrog.com/0wptg762x39mmj

I assume you have all your milling and hardening techniques down. Good luck!
Click to expand...

That's Awesome! Thanks!!! I was finding my Czech surplus ran from .3095" at the neck to .311" at the base of the bullet. My hope is that they will perform reasonably well out of an Enfield as .311" 150 Grn. Sierras seem to run reasonably well out of my tanker No4.

I wouldn't say I have my milling and hardening techniques down... More like, Once I finish my attempt at turning the blank I will then attempt to harden and mill/grind my reamer :D

There is a remote possibility that I might have a usable reamer at the end of this experiment ;)

MB
 
I have only played once at making a reamer, I used w1, and just ground it afterward to make a D or shell reamer. It actually works surprisingly well, well enough that I wouldn't bother with cutting flutes.
 
I'll be ordering a couple complete sets of x39 tools from a company I met at SHOT last week.. if you want me to add another set for you I'd be more than happy to.

If you're more interested in making your own, it seems like a great project. I look forward to following your progress.
 
lejarretnoir said:
Since you need the correct dimensions. This is for a .308 throat Sammi spec'd PTG reamer. Doesn't matter whether you have a .308 or .311 barrel. That's just the grooves as the bore is still .30. Czech bullets mike .309 roughly and cases slip right into that chamber. You may need to add some tolerance on the throat. .310 will do. I'll experiment with Czech surplus and see if I need to open up the throat or not.
If you're using a .303 bore those bullets may rattle somewhat down the bore. I've heard accuracy isn't the best with Lee Enfield barrels.

http://yfrog.com/0wptg762x39mmj

I assume you have all your milling and hardening techniques down. Good luck!
Click to expand...

If he is using a 303 brit barrel he will have to match the pilot to the bore diameter so the reamer runs true. No match and odds are the reamer will chatter and ruin the chamber.
 
NeitArms said:
I'll be ordering a couple complete sets of x39 tools from a company I met at SHOT last week.. if you want me to add another set for you I'd be more than happy to.

If you're more interested in making your own, it seems like a great project. I look forward to following your progress.
Click to expand...

Thanks for the offer but I think I'll keep working away at my reamer... It is more a learning as anything else :D
 
10x said:
If he is using a 303 brit barrel he will have to match the pilot to the bore diameter so the reamer runs true. No match and odds are the reamer will chatter and ruin the chamber.
Click to expand...

It is a .303 As such I still have to cast the chamber/bore to see what I have to turn the pilot down to...
 
what are you gonna mill the flutes with?
the article suggets using an end mill but i prefer using a 30 degree toothed cutter the real name evades me now but hopefully you know what i mean, fits on a saw blade arbor.
ive made a few with varying degrees of sucess but not a 7.62x39 so looks good so far.
did you turn between centres?

good luck

ian
 
bluestratus said:
what are you gonna mill the flutes with?
the article suggets using an end mill but i prefer using a 30 degree toothed cutter the real name evades me now but hopefully you know what i mean, fits on a saw blade arbor.
ive made a few with varying degrees of sucess but not a 7.62x39 so looks good so far.
did you turn between centres?

good luck

ian
Click to expand...

Parallel sections were turned in the chuck and live center, the chamber wall taper was between centers and the shounder was done with the compound.

Just curious why you didn't just order a reamer? Or is this this a learning project?
Click to expand...

Mostly a learning project, and the satisfaction of being self sufficient (oh, and cheap too...)

Why not contact a custom endmill-reamer grinding/shaping/sharpening shop and ask'em?
Worst they can say is no.
Click to expand...

Because, they likely wouldn't be as sweet and kind as you all have turned out to be :p:D
 
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