How much should brass stretch radially

[wpwarren]

I recently traded a glock I never used for a decent shape savage 99 chambered in .300 savage. The gun was manufactured in 1941 and seems to be in good working order. I took it to the range and test fired it the other day and am curious how much the brass should stretch radially. The ammo I used was factory remington core-lokt 150 gr. First, there is no measurable stretching of the head or the web of the case. However, just above the web, there is a nice smooth (and quite consistent) bulge on all of the brass. It isn't a rounded lump in the brass, just a noticably larger section that tapers gently to the shoulder. I measured 10 of the 20 cases fired and there is between 6/1,000ths to 65/10,000's of an inch of radial stretch (the diameter is that much larger) to the cases when comparing the fired cases to those of the unfired cases. The length of the case is fine. Should I be worried? The rifling and bore look pretty good so I don't think the barrel has been beat on too much.

I have done a bit of research and it seems like some of the savages had slightly oversized chambers. Also, guys report pretty short brass live from savage 99's in .300 savage (3 firings before failure with full length sizing). Because of this I had planned to try to neck size to minimize the amount I was working the body of the case. The brass does rechamber into the gun and ejects without issue.

I am new to reloading and none of my other rifles or handguns cause deformation of the brass like this. Is this dangerous or normal?

 

[Canadian Bushman]

This is not a preferred situation but it is common. Im betting your rifle is headspaced toward the upper end of saami tolerance or this particular batch of brass was headspaced toward the bottom. This is not a "dangerous" situation but it does have some unfortunate side effects.

In an ideal situation the transition from head to body on the brass after firing would be indistinguishable.

I like you have also used neck sizing to circumvent this situation and it is effective.

 

[wpwarren]

Good to know. Thanks for the reply. I am new enough to this to be a bit unsure. Does anyone know how much radial stretch is ok and when I should be concerned?

 

[Canadian Bushman]

Thats gonna be dependant on a few variables like the thickness of the brass, the temper of that batch, the pressure of the current firing and the firings thereafter etc. your current cases strecthed. .006" so thats .003" per side, about the same as a human hair. Id say when you get to .005-.007" a side (.010-.015 per diameter) you are flirting with case failure. Again this is a rough estimate based on what ive seen and the moderate pressure of the 300 savage.

A rifle i currently reload for streches about .002-.003 per side and i start seeing rings indicating web fatigue around 5-6 firings. When i recklessly fl sized i experienced a case head seperation at 6 firings.

 

[wpwarren]

That makes perfect sense. I know that ductility for brass can vary greatly from batch to batch.

So on that note. 2 more questions about brass. Why do people avoid annealing the body of the case? Also, can I get a full length die machined to only bump the body diameter back a couple 1000ths to avoid over-working the brass.

 

[Canadian Bushman]

People avoid annealing the body because if it were annealed it would become too soft to properly contain the pressure of the ignition and almost certainly rupture possibly damaging rifle or even the shooter.

Yes in fact you can get a die to bump the body in just a few thou., they are called body dies and a number of manufacturers make them. I personally use a redding neck die set that included a body die with it. I dont use it much because my little rifles dont stretch brass enough but to need a bump every 6 to 8 firings.