New brass growth

[NCHillbilly]

Shot my rpr in 300wm today for the first time. Came home this evening and decided to examine the fired brass. I didn't have any loads that were particularly hot. Iwas function testing/scope zeroing/load testing, so I was single feeding, taking my time.

Anyway, after using my fired cases to set my adjustable case gauge, I measured the base to datum, then measured some of my new, unfired brass (same brand), and found that my fired cases had grown .015"-.016"! I know new cases grow upon first firing, but that seems a bit much. My new brass has NOT been sized, only checked in case gauge to assure chambering, and the necks hit with a turning mandrel to assure roundness. Am I concerned for no reason? This is my first magnum bolt gun, so I want to make sure everything is as it should be

 

[Snuby642]

That is x2 what I have ever seen in smaller rounds.

 

[NCHillbilly]

That is x2 what I have ever seen in smaller rounds.

Same with me.I'm used to 5.56 and 308 fired out of a gas gun, and most of that brass was once fired, so I'm in unusual territory. Honestly, if it was an issue, not sure that I could correct it with load equipment. Seems it would have to be a machining issue with the barrel, if, in fact it is excessive.

 

[Steel head]

That’s a lot and in my opinion a recipe for disaster in a standard non belted case.

If your true belted case headspace(boltface to forward edge of belt) is tight and doing its job holding the brass against the boltface upon firing your growth shouldn’t be a problem because just the shoulder got blown forward instead of stretching the body of the case.

 

[NCHillbilly]

All of the growth is in front of the belt.

 

[lash]

There’s really no reason to be concerned. It’s not a whole lot different than fire forming a wildcat cartridge. As long as you understand your new headspace from here on out and don’t push those shoulders back down upon sizing, you should be fine.

 

[Snuby642]

Once fired is expanded so not a good base line.

My notes are across town but remember a fiew mesurements roughly.

Nato 223 rounds are the shortest shoulders I have seen commercially about .008 thousands below go gauge.

2 brands of new brass I purchased were 6-7 under.

My brass and range brass is normally right at go gauge fired.

I don't want to quote specs without my hands on them but .016 below your chamber seems like--

A possible measurement error
Brass not in spec
A chamber out of spec

Look up the saami specs online.

Details of your adjustable case gauge?
I have never seen an adjustable one.

 

[NCHillbilly]

Yeah, for the first time I'm keeping as much detail as possible with regards to headspace, bto lengths with different bullets, round counts, the whole nine yards. Told my wife I was writing a diary for the weapon.

Once fired is expanded so not a good base line.

My notes are across town but remember a fiew mesurements roughly.

Nato 223 rounds are the shortest shoulders I have seen commercially about .008 thousands below go gauge.

2 brands of new brass I purchased were 6-7 under.

My brass and range brass is normally right at go gauge fired.

I don't want to quote specs without my hands on them but .016 below your chamber seems like--

A possible measurement error
Brass not in spec
A chamber out of spec

Look up the saami specs online.

Details of your adjustable case gauge?
I have never seen an adjustable one.

I'm pretty sure it's not a measurement issue. I measured the once-fired cases three times, and the new cases three times (measured 6 total cases). The case gauge is an L.E. Wilson unit. The reason their belted mag gauges are adjustable (according to them) is because there is much variance in the factory chambers FORWARD of the belt, so you use your fired case from your gun to set the gauge. Of course this would have to be changed if using for a different weapon. If I can find a link , I'll post it, but I know a few of the major reloading equipment suppliers carry them. I have and use them for everything I shoot.

 

[NCHillbilly]

The only once fired brass I have for the 300wm is brass from ammo that I fired in that rifle. Most of my gas gun brass is once-fired military brass.

 

[FLIGHT762]

Your 300 W/M is a belted magnum. New, factory brass for 300 W/M is sometimes as short as you found. After your 1st firing, set your F/L die to bump the shoulder the normal -.002"-.003" back. You'll be fine.

My guess is some of the people giving advice has never loaded for the 300 Win. Mag.

 

[Alabusa]

I have seen that much change in my 300WM using Nosler brass. I am now on the 5th firing without issue.

I full length size bumping the shoulder .002.

 

[NCHillbilly]

Here's the link:

L.E. Wilson Adjustable Case Gage 300 Winchester Magnum

L.E. Wilson Adjustable Case Gauge 300 Winchester Magnum Technical Information: Material: Steel Precision Machining -This is a two-piece, adjustable cylinder-type gauge for checking fired and resized cartridge cases for cone-to-head and overall length -Used to compare cartridges against...

www.midsouthshooterssupply.com

 

[NCHillbilly]

Full disclosure, I have no financial stake in the company listed. This gauge can be purchased from numerous suppliers. Also, thanks to everyone for the help, I just wanted to be sure I didn't have a serious issue. I was hoping not because I'm loving this rifle.

 

[Snuby642]

Nice

 

[Powder_Burns]

Belted mags headspace on the belt and so the chamber specs for the shoulder and throat can vary a lot from one chamber to the next. Monitor your brass at the web of the case head as this is where the flow of brass causes case head separation. Neck size, bump your shoulder back and carry on.

 

[BCMulx]

So, I'm going through my first firing on my 300 WM now, still dealing with virgin brass so maybe I should go measure some too.

For what it's worth: I've had it recommended not to bump the shoulder back until potentially 2-3 firings as the brass is still growing. You want the bolt to start to close a little tight first. But, that's worth what you paid for it ...

 

[Powder_Burns]

I bumped every two firings, once the brass has been bumped 3 times I retire the case. Case head separation with 74gr of h4831 sucks.