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[blvedere]

Recently purchased a 30 cal 308 McGowen barrel on line. I have been having trouble making it shoot the way I want, 600 yards. Had a chamber cast made and found that the chamber neck was 0.348" and my loaded round was 0.333". Other than over working my brass do you, as I do, think this is effecting my load development. I have my own answers just want some other feedback. Thanks

 

[Zero333]

I don't have SAAMI max chamber specs for the 308 but I measured a couple of different 308 cases, fired in a SAAMI chamber and unfired.

Winchester brass

Fired = 3.344" 3.3445"
Unfired (loaded) = 3.335

Lapua brass

Fired = 3.3445" - 3.345"
Unfired/loaded = 3.338"

somewhere around there... I just quickly measured and did my best to remember the numbers

 

[XBBR Shooter]

SAAMI Max neck (loaded cartridge) - 0.3435"

SAAMI Max chamber neck (mouth) - 0.3442" to 0.3462"

SAAMI Max chamber neck (base of neck) 0.3462" to 0.3482" (Neck has slight taper)

 

[jonbearman]

What kind of bullets are you using and what does the bearing surface measure?

 

[fguffey]

Recently purchased a 30 cal 308 McGowen barrel on line. I have been having trouble making it shoot the way I want, 600 yards. Had a chamber cast made and found that the chamber neck was 0.348" and my loaded round was 0.333". Other than over working my brass do you, as I do, think this is effecting my load development. I have my own answers just want some other feedback. Thanks

http://mcgowenbarrel.com/

Again, I would expect the .348" chamber neck diameter in a military surplus barrel. I never find my self being stuck with something that does not work. I have tightened the case neck in chambers that were considered loose. The last one I reduce the clearance between the loaded neck diameter and chamber neck by .007" by increasing the diameter of the case neck. I formed 30/06 LC cases to 7.62 NATO cases. When finished the clearance was .003".

F. Guffey