Stupid barrel question.

[std7mag]

I've been looking online at barrels.
After the cartridge i'm seeing a (XXX) after it.
Example would be 7BR(.312)

What does the number in the parentheses refer to?

Thank You!

 

[DaveTooley]

Neck diameter

 

[Stan Taylor]

That's probably the neck diameter of the reamer they used.

 

[watercam]

Neck diameter in the chamber. Subtract the diameter of the loaded round and you will have your clearance. Should be at least .003" I believe.

 

[std7mag]

Ok, so i would need to load a dummy round and measure before i ordered?

I don't have a neck turner or inside reamer.
I'm not opposed to getting either.
Just putting it out there.

 

[INTJ]

I guess a dummy round goes with a stupid barrel.......

A .312 neck means neck brass could be .014" thick and it will just fit the chamber of with a .284 diameter bullet. I think that would require turning for most brands of brass to get the desired .003 -.004" clearance on a 7mm. I suspect that is a common size as most would want to turn the necks a little.

Often when you seat a bullet the dimensions measure .001 less than the measurements of all the components.

So yes, seat a bullet in a case from the lot of brass you will be using, measure the neck diameter, and then order a reamer with the amount of clearance you want.

 

[ebb]

K&M makes neck turners all the time. If I can figure out how to use one anybody can.

 

[Dusty Stevens]

If you use 6br brass that starts out at .014 or under a .312 is a no-turn

 

[hoz53]

Ok, so i would need to load a dummy round and measure before i ordered?

I don't have a neck turner or inside reamer.
I'm not opposed to getting either.
Just putting it out there.

order what? anyway in other words you dont need to make a dummy round just measure the case neck thickness of brass you want to use. In this case .014 per side would be your clearance from bullet to chamber so youd prob want to get cases with not over .012 case neck walls if you dont want to turn them. That would leave you .002 clearance per side. Now some people use alot less clearance than this so you could buy thicker case wall brass and turn it if thats what you wanna do. you do need a little clearance for case neck to expand.

 

[jds holler]

My formula:

Lapua neck-brass thickness x2 + bullet diameter +.003 = desired neck diameter. jd

 

[hoz53]

My formula:

Lapua neck-brass thickness x2 + bullet diameter +.003 = desired neck diameter. jd

that would work if youd ever clean your gun

 

[std7mag]

Thank you all!

Looks like i need to call Peterson Cartridge first.

 

[jds holler]

that would work if youd ever clean your gun

I'm workin with the theory that a good carbon ring keeps the cartridge well centered in the chamber. jd

 

[hoz53]

I'm workin with the theory that a good carbon ring keeps the cartridge well centered in the chamber. jd

Well mabie in ur necka the woods

 

[Dusty Stevens]

Thank you all!

Looks like i need to call Peterson Cartridge first.

Every lot will be different so its better to go ahead and get set up to turn from the start. Skim turn every piece that matters and once your tool is set up the next box you get, run it over those and theyll be the same as the last box. Keep it simple- doesnt seem that is the simple way but it really is.