7.92x57 (8mm Mauser) SMK reamer

[sharp.shooter.ser]

I am working on a new long range rig, which will be chambered in 8 mm. I got most of the stuff already (action, barrel, trigger etc) but now I have to cut a chamber. I wish to make it "superb" for the brass and bullet I intend to use - that PPU brass, and SMK 200 gr. I have the means to get the custom reamer made locally, but I actually have no clue what to ask for I have to provide the drawing with exact dimensions (or at least precisely explain what I need). I tried to find something similar online, but no luck - it seems no one is/was trying to do this, so I have to "chart it" Could you fellas point me in the right direction

 

[ImBIllT]

SAMMI minimum chamber dimensions for everything except the neck and freebore.

To spec your neck go 003"-.004" over loaded loaded round neck dimension. You should notice that most chambers have slightly tapered necks. Most brass does too. Measure both ends of your loaded neck. Measure plenty of ammo from multiple lots. I'm not sure if PPU is very consistent. You don't want to end up getting lots of brass that is thicker than you planned on. For better consistency consider Lapua brass. They do make 8x57. Make that determination before you spec your reamer. I'm not sure how close most "no-turn" necks are, but lots of guys shooting tight neck guns are turning their brass to .002"-.004" clearance. If someone who actually uses no-turn neck chambers suggests a different clearance, go with their suggestion.

To determine freebore, load a few dummy rounds to have the bullet you are going to shoot seated in the case about the way that you want. Use a comparator to measure your cartridge base to ogive length. Subtract your SAMMI minimum chamber length from that number(don't use your brass length. Your brass should be shorter than your chamber) the number that remains should be the freebore required to get your bullet just touching the lands. This measurement is approximate unless your comparator is set up with the same angle as the lead angle of your reamer, but it will be fairly close either way. Adjust your freebore to reflect desired seating( .015 jam, touching, .080" jumped...whatever). I think most people jump SMK's, but people experienced with that exact bullet may be hard to find. The difference in free bore between your measured length and adjustment for your seating preferences will be minor, so don't stress over that. The important part is to seat the bullets the depth that you want it, measure CBTO and subtract your minimum chamber length.


http://saami.org/specifications_and...ns/download/Z299-4_ANSI-SAAMI_CFR.pdf#page=13

 

[sharp.shooter.ser]

Thank you for your detailed response, and ideas. PPU brass is the one that is mostly available here, since PPU is a domestic factory (maybe 40 miles from where I live). I am aware that their brass is not that consistent in neck area, but I do plan on to shave them, to 0.014 or 0.015. So, reamer should cut the neck dimension to 0.323+0.015+0.015 = 0.353 (at the top of the neck, and plus 0.015 at the bottom).

As for freebore, I had great results with SMK with 3.15 OAL in a different rifle (but that one had a generous neck clearance, and 0.008 jump to lands), but I am not sure how to measure what you tried to explain to me (or do I have all the info I need to adjust the blueprint to my desires).

 

[hakerman]

this sound like a fun project, and the .323 is very interesting caliber choice

 

[sharp.shooter.ser]

after reading it two more times (English isnt my native language) I believe I understood what you wanted to say. Thank you kindly!

 

[ImBIllT]

after reading it two more times (English isnt my native language) I believe I understood what you wanted to say. Thank you kindly!

You want a larger neck diameter than bullet(.323") plus both sides of the neck. If you turn to .015", then your loaded round would be .353". I would recommend a chamber reamer with a 004"-.006" neck diameter. That is still a "tight-neck".

 

[Kurz]

sharp.shooter.ser,

Please check your PM.

Thanks!