Reloading for a match chamber

[wyosniper]

Ok I am by means a novice when it comes to reloading, I have basically full length resized everything I ever loaded. I am having a m40 rifle built and it has a match chamber I was told I am gonna need some small base dies and match brass. I may need to also neck turn my cases also, does someone have a match chamber in 308 that can give me some input, I didn't realize there was a difference in the brass either, and thanks

 

[spife7980]

Who told you this info? To know for sure one would need measurements of the chamber and the brass to be used. Match chambers are usually tighter, yes. But how much tighter depends on the reamer used. Depending on what the neck is cut to you may need to turn necks.

Figure out the brand of brass you intend to use and then figure out how thick the necks are. Your loaded round, bullet diameter plus the brass neck thicknessx2 (to account for each side), EX a 308 round plus brass with a neck thickness of .014 would be .308+.014+.014=.336 total cartridge neck diameter and then add .003-.004 to allow for the brass to expand and release the bullet. So you would be wanting a chamber neck cut to .3395 (336+.0035)
If your chamber neck was cut to .337 that would mean your loaded round (.336) would be only .001 smaller which could lead to issues. You would then want to turn neck to get the couple thousandths more clearance to allow for hassle free function. All of this depends on the thickness of the brass though. Some brass might be .015 thick, some might only be .012 so it depends on what choices you made in reamer and brass selection.

For the opposite end of the case, the part that relates to the small baseness of a die, you would need to know your chamber and reloading die info. I wouldnt imagine that a match chamber would be soo tight as to require that die to be used but if your smith told you I imagine he would know. To be sure though you would want to the diameters and how they match up similarly as above only maybe less room desired for clearance in that area.


This is a match chamber, notice the neck is .342 meaning that this particular reamer would mean that neck turning would not be necessary with brass .014 thick. If the brass was.017 thick that would give a loaded round a total diameter of .342 and would be an exact fit into the chamber. But it also wouldnt ever let go of the bullet and I doubt you would actually ever be able to get it chambered, much less extracted. You would want to turn the necks down a couple thousandths to give it a little room to expand. [IMG2=JSON]{"data-align":"none","data-size":"full","src":"http:\/\/img.photobucket.com\/albums\/v232\/hateca\/308jpg.jpg"}[/IMG2]


This saami chamber would be just fine with the .017 thick brass as the .342 total diameter would be .002 less than the .3442 that the chamber would be cut to.
[IMG2=JSON]{"data-align":"none","data-size":"full","src":"http:\/\/gohunting.dk\/wp-content\/uploads\/2014\/09\/308data.jpg"}[/IMG2]

So its entirely dependent on what exactly you get. To see if small base is required you would need to compare the base. The match chamber in the first image has a .4732 diameter and the second saami spec chamber has .4738. If a normal reloading die can only squeeze the case walls at the case head down to .4733 you would be able to chamber it in the second saami chamber but as you can tell you would still be .001 over the match chambers dimensions and a small base die would indeed be required.

So before you go buying all this equipment lets take a proper first step and get a reamer print from the smith for your particular chamber.

 

[jim10801]

For what it is worth, Forster makes a 'Regular', a National Match, and a Small Base full length sizing dies.