What's causing this - brass bulge near base

[Bill K]

If it is only 10 or so out of 100 cases that did this. Just side line them and use a small base die to resize them down, all the way, then they also should be fine. But keep them sorted and alone.
If these same cases do it again, then maybe those have a soft area in the brass base. Just something that can occur with brass, even if it is Lapua.

 

[SeabeeKen]

A well known barrel maker over polished the chamber of my 280ai and left a .010 bulge on one side. Perhaps that is what happened to yours

 

[Metal God]

Have the primers been removed in these picks?

Yes , FWIW the out of square cases are once fired LC-14 that were fired from a machinegun . Without getting into the specifics . This specific lot of brass also seems to be a tad softer then usual . Primer pockets get stretched out with mild loads and one out of every ten had loose pockets after there first firing .

 

[Nick Caprinolo]

What rifle was this brass fired from. Is it a bolt action or a semo auto like an AR?

 

[gme]

Yes , FWIW the out of square cases are once fired LC-14 that were fired from a machinegun . Without getting into the specifics . This specific lot of brass also seems to be a tad softer then usual . Primer pockets get stretched out with mild loads and one out of every ten had loose pockets after there first firing .

if that brass came out of an M249 I would consider it junk, I wouldn't even try to make anything useful out of it

 

[Nick Caprinolo]

if that brass came out of an M249 I would consider it junk, I wouldn't even try to make anything useful out of it

It is Lapua brass. I doubt anyone would fire this from an M249.

 

[scyzer]

Based on what I can see, I'm going with "too hot a load during load development". It looks like the case web diameter has grown on those cases. Have you measured the diameter difference, below the ring, between the cases with the ring and those without it?

Just measured - some do measure slightly wider, 1 or so thou

 

[scyzer]

This, or there needs to be more of a bevel on the mouth of the FL die. View attachment 1315097
Standard factory dies.

There's actually a fairly flanged bevel in the die mouth

 

[scyzer]

Bulge or ring?
All cases have a bulge to some degree. Thin side expanding more than the thick side seems to be the most logical explanation.
If it's a ring then your die is making full contact around the case head. That's where the sizing die stops doing it's work. Hot loads might have affected those cases in fewer shots expanding the case head as it transitions from solid to thin. My guess is it will appear on the other cases with use.
Just for the hell of it lay a straight edge on the case in several locations and look for a gap under it.

Ring - there's a lip on transition to the unsized portion

 

[scyzer]

Going to guess that your new dies are Hornady? I have had Hornady FLS too tight for Lapua at that area and leaves that same ring. You might call the die maker and see if they can lap your die a little. BTW, have also seen that on a custom die, especially when I requested that the die be made on the tight side.

Not Hornady - not a super common die this, won't name the manufacturer just yet

 

[scyzer]

Is this the bulge at the extraction grove ?

Optical illusion / iPhone magic - disappeared when I looked for it in those 10 cases

 

[scyzer]

Other points of note:

• It's a bolt gun - gunsmith reamed
• Some loads were definitely pushing pressures in the ladder - though bolt lift was okay and the primers all seemed okay with a bushed firing pin hole
• Will cut open one of the worst cases later when I have time

Thanks for the help all!

 

[Metal God]

if that brass came out of an M249 I would consider it junk, I wouldn't even try to make anything useful out of it

I believe it was and I have prepped it out to a useable state for light plinking loads . It's not lasting long as far as times loadable but I have over 1k of them so time wise they are lasting for several years now .

I do agree they are barely worth keeping but I toss nothing that can work . The SHTF Zombies wont know the difference lol

 

[Old Navy]

Sure would be interested in what head space you have.

 

[boltfluter]

Some of the younger smiths have a bad habit of putting a giant chamfer on the back of the chamber in the name of better feeding. Not good, and in some cases down right dangerous on an unsupported part of the case. Seen this more than once. The edge only needs to be broken in my opinion. If it feeds that bad, something else is wrong!

Paul

 

[WVRJ]

Very good possibility that there's too much clearance from the bolt face to the chamber.Either the barrel wasn't set back as far as it needed to be when the chamber was reamed or there's too much of a chamfer in the chamber.Not really unsafe but not a good condition either.

 

[Uncle Ed]

It could also be cases thinner at the base web area. Below are .303 British cases showing smaller base diameter.

You need gauges to measure case wall thickness.

 

[RegionRat]

Beautiful photos of the issues @Uncle Ed

Some of this is harmless, some if it needs to be watched. Either way, it really helps to get educated.

 

[scyzer]

Hi all.

Just an update - cut the worst offending piece open. The ring is right the base of the brass - doesn't look like there's enough signs of stretching to be too worried.

I'll just cull these pieces to be safe but it looks like it could have just been hot loads stretching the webbing.

Let me know if you have any additional thoughts.

 

[MGYSGT]

Looks like my brass do when I use the small base sizing die. Hasn't hurt anything yet.