Neck chamber dimension

[300bee]

Hello all, first time asking a question,
i have a newly built 308 norma mag, Question is, the sammi neck dimension is .340, but my fired brass outside dimension measures .344. is this too much neck clearance? i probably wouldnt be looking at anything except im getting smoke down to the junction of neck and shoulder. not down onto the shoulder per say but almost.
i have 30 rounds down the barrel. i went and measured my 4 other rifles fired brass, and they come within 1 thou of book neck outside dimensions. not 4 thousands. so my question is , did the reamer have too large a neck ? take it easy im still leaning the custom rig game! thanks!!

 

[ShtrRdy]

If what you're asking about is the 300 Norma Magnum then the SAAMI spec shows the neck portion of the chamber to be a little over 0.340".

 

[300bee]

no 308 norma mag, but reguardless, is 4 thousanths over too much?

 

[msgriff]

Where are you finding SAAMI drawings for a 308 Norma Mag? Here are some C.I.P. 308 Norma Mag drawings:
C.I.P. pdf

 

[300bee]

the drawings i have is in my verry old sierra book and my hornady manual
reguardless i guess im not asking the question right. to simplify,, if the regular neck dimension is .340,, is actual chamber neck dimension around .344 too loose of a fit?

 

[Edds]

The spec for a 308 Norma Mag chamber neck is for it to be tapered, 8.75 mm at the front and 8.80 at the rear.

The spec for the neck diameter of the cartridge is 8.65 mm.

If your loaded rounds measure 3.40" and your fired cases measure .344", that is perfect.

 

[300bee]

EDDS,, thank you verry much!
I just measured my loaded ammo, and it measures. 337. So that puts it at .009 over. Is that OK.? It's norma brass

 

[Edds]

Yes it is OK.

If I had a choice, I would choose less. But what choice do you have? When you size your brass to reload, you are going to be squeezing it down to at least .334" so you might want to consider annealing your brass every 2-3 loadings.

 

[300bee]

thanks verry much Edds!!!