OzFclass

Gday Guys,

Just got my Norma Brass for a new 7 saum brass. Intend to build a dummy round for the gunsmith to calculate free bore. Was thinking about getting my first bushing type FLD, but reading online says to insert a projectile first to get correct bushing. I can see some of the brass is a little dinged around the neck. Do I need to /should I run these through and expanding mandrel first and then seat a projectile to measure the bushing size?

Surely not all the necks are dinged up ... my recent shipment of the same Norma brass wasnt ... just find one that isnt, yeah ? ... or if your worried, just run them all through a 282 / 283 mandrel ... you would likely still get the same result if you didnt expand.
If your also getting a Bushing Die for your first time ... I would recommend getting a couple of different size bushings. -0.002", -0.003", -0.004" etc ... just to give flexibility in your neck tension etc.


I would typically run all mine through an expander to iron out the dings, but also to lighten the tension, as factory new cases often are a bit on the tight side.
I also expand to neck turn, but thats a different topic.

Maybe a follow on question, my gunsmiths reamer states 7RSAUM .312 NK .90 freebore. So when ordering bushings can I simply do a bit of math to figure out desired bushing size.

Norma wall thickness average 0.016.
Projectile .284
Reamer NK .312

.312 - .284 = .028 /2 = wall thickness .14 so I would need to neck turn to this diameter
.312 - .003 = .309 Size Bushing allowing for spring back approx .002 neck tension

JezL wrote:Surely not all the necks are dinged up ... my recent shipment of the same Norma brass wasnt ... just find one that isnt, yeah ? ... or if your worried, just run them all through a 282 / 283 mandrel ... you would likely still get the same result if you didnt expand.
If your also getting a Bushing Die for your first time ... I would recommend getting a couple of different size bushings. -0.002", -0.003", -0.004" etc ... just to give flexibility in your neck tension etc.


I would typically run all mine through an expander to iron out the dings, but also to lighten the tension, as factory new cases often are a bit on the tight side.
I also expand to neck turn, but thats a different topic.

Not all the necks were dinged up but maybe 1 in 5 were. I normally wouldn’t worry as they would come out when I seat the first bullets but with a possible need to neck turn (see above) I am a little more concerned.

Hmmm ... unless im reading your comment wrong ... I dont think you are accounting for Chamber Clearance.

I run a 313 NK ... my Neck walls are 0.0125" ... this gives me 4-5 thou of chamber clearance.

If you have a 312 NK Chamber .. I would assume you need your brass to be 12.5 - 12 thou ... pending your preferred chamber clearance. I would want 4 thou clearance as a MINIMUM.

Lets say you want 0.005" chamber clearance ... This is purely what I would do ... not what you HAVE to do.

.312 - 0.005 = .307 loaded round
.307 - .284 = 0.023/2 = 0.0115" Neck wall thickness.

Bushing sizes of 305, 304, 303 would then be my choice

JezL wrote:Hmmm ... unless im reading your comment wrong ... I dont think you are accounting for Chamber Clearance.

I run a 313 NK ... my Neck walls are 0.0125" ... this gives me 4-5 thou of chamber clearance.

If you have a 312 NK Chamber .. I would assume you need your brass to be 12.5 - 12 thou ... pending your preferred chamber clearance. I would want 4 thou clearance as a MINIMUM.

Lets say you want 0.005" chamber clearance ... This is purely what I would do ... not what you HAVE to do.

.312 - 0.005 = .307 loaded round
.307 - .284 = 0.023/2 = 0.0115" Neck wall thickness.

Bushing sizes of 305, 304, 303 would then be my choice

I was not accounting for chamber clearance, thank you so much for reminding me. Will grab those bushings for now.

No worries! Happy to help.

Also dont take my preference for Chamber Clearance ... Everyone has there own preference with clearance.
For the 7mm's ... its typically 4-6 thou clearance is preferable from what I see and hear.