.308 neck wall thickness

[bob_wuzza]

First a bit of context:
Fiocchi, G.F.L. and Hornady match brass from factory ammo
all fired through my norinco M305
Just reloaded the same brass for a 4th time, had to trim to length 0.005 or so every time I reloaded.
IMR4895 38-40 grains ( was playing around with loads, suggested starting load in Lyman manual is 40)
Hornady 150 gr BTSP
I'm using a Lee 4 hole turret with lee dies.

So I just finished rolling 14 rounds and started measuring the finished rounds for fun.
The neck measurement on all 14 and 5 left over from reload #2 are 0.335".
According to Lyman and Sierra it should be 0.343"

Something else to note is all the brass that fires from my m305 has ( what I'm assuming is ) carbon build up around the outer neck......

It cycles my rifle and prints fairly, but is it normal?

 

[bob_wuzza]

After typing all of this out I measured some Winchester and Hornady factory ammo and their case neck diameter is also 0.333-0.335.

 

[just having some fun]

Assuming your bullets are .308 and case neck is .010 x2 you could have a min neck of .328
Most brass will be thicker so you are good to go unless they will not chamber

I would not trim unless sized length is over 2.015 -- then trim to 2.005 or so

I am getting 4 firings before i trim ( headspace is tight on my rifle) and i don't over size brass

 

[bob_wuzza]

Assuming your bullets are .308 and case neck is .010 x2 you could have a min neck of .328
Most brass will be thicker so you are good to go unless they will not chamber

I would not trim unless sized length is over 2.015 -- then trim to 2.005 or so

I am getting 4 firings before i trim ( headspace is tight on my rifle) and i don't over size brass

I always just trimmed to 2.015 I'll go shorter next time so I don't have to trim every time. Thanks

 

[OldDude]

So I just finished rolling 14 rounds and started measuring the finished rounds for fun.
The neck measurement on all 14 and 5 left over from reload #2 are 0.335".
According to Lyman and Sierra it should be 0.343"

Something else to note is all the brass that fires from my m305 has ( what I'm assuming is ) carbon build up around the outer neck......

It cycles my rifle and prints fairly, but is it normal?

The dimensions shown on the drawings in the Lyman and Sierra manuals would be the maximum allowable. The trim-to length of a bottleneck rifle casing is usually 0.010 under maximum casing length....

I don't trim my cases every time, but I do measure them for any that are over max. Just set your calipers to the max length, lock the slide down, and check that the cases fit into the caliper. If they fit, they are under max.....

Stan

 

[Trevor60]

the .343 number would be fired chamber dia.
.335 to .338 is loaded round dia .308 + neck thickness (.015 x 2) .030 +.308 = .338 now with .002 neck tension it is .336

My lapua brass measures .015
Norma brass measures .0135

measure some fired case dia and you will see they read .343 - .346 (more is better in a semi)

as an example .335 load neck dia and chamber dia of .343 gives you clearance of .008 that is good clearance for a semi

Trevor

 

[chrismc]

Mine are neck turned to .0125 - so that, x 2, + .308, = .333 loaded round.

 

[cartwheel]

yup- .343 is chamber diameter so this would be the OD on the neck after firing... and it sounds like you have a dirty chamber.

 

[bob_wuzza]

Thanks for all the info guys!

I'm assuming the solution for the dirty chamber is cleaning it?

If I remember correctly even the first rounds after cleaning were dirty... I'll do some extensive cleaning and check back