Strange dent in fired case

[dskogman]

I had a strange dent in a fired case today:

I’ve had it once before and thought it was from bumping the shoulder too far although this time that was not the case. It is close to a max load in a 300 WSM with H4350. It was cooler today which may have contributed. The neck tension was also lower than I normally run but not that light (20-30 lbs).
I found this on a previous thread which indicated that it was caused by low pressure.
http://forum.accurateshooter.com/threads/strange-dents-in-fired-cases.3770985/
Thoughts?

 

[KMart]

The only time it has happened to me, it was on the low end of a starting load.....low pressure.

 

[rardoin]

Doug, do you think you could have had some powder bridging in the funnel that lead to an undercharge?

 

[Metal God]

Tagged to follow . I’d like to understand what could cause this . Hmm could it be some how gas/preasure getting past the neck and shoulder then gets trapped by the expanding case . While pressure drops in all other areas that trapped gas/pressure collapses the case in the area it was trapped ? Or maybe the gas gets trapped while case is expanding and collapses it while pressures rise .

 

[dskogman]

Doug, do you think you could have had some powder bridging in the funnel that lead to an undercharge?

Muzzle velocity was good on lab radar and the shot went high.

 

[KMart]

I have no idea what happened for sure, but here is a What IF.
If the case necks are somewhat hard and/or thick necks, coupled with a bullet that is not seated deep enough to give the neck time to expand properly, you could have gotten blow by causing this.

Just thinking out loud.

 

[mikegaiz]

I had this problem back a few years in a 300 WSM with H350. It had everyone (top loaders, shooters and smiths) I know in a quandary for at least two months. I tried everything and every component. Come to fine out, it was me. I had switched to a lighter bullet (185) shooting in a chamber cut for a heavier one (210). I was seating the bullet out in to the lands and did not have enough bullet seated depth into the case for the case to expand and seal before the bullet moved and released the case sealing pressure. Had the barrel re chambered for a lighter (shorter) bullet and never had it again.
Hope this helps.....

 

[dskogman]

I had this problem back a few years in a 300 WSM with H350. It had everyone (top loaders, shooters and smiths) I know in a quandary for at least two months. I tried everything and every component. Come to fine out, it was me. I had switched to a lighter bullet (185) shooting in a chamber cut for a heavier one (210). I was seating the bullet out in to the lands and did not have enough bullet seated depth into the case for the case to expand and seal before the bullet moved and released the case sealing pressure. Had the barrel re chambered for a lighter (shorter) bullet and never had it again.
Hope this helps.....

Now that you mention it I did have this issue running a short bullet in a long throat a while back. In this case I’m thinking the same thing happened with not enough neck tension. I run a pretty long throat anyway so the light neck tension didn’t generate enough pressure to seal the case.

 

[Dusty Stevens]

Not enough pressure or time to seal the neck so the pressure tried to come back

 

[Metal God]

I like Dusty’s idea but we all seem to have the same basic understanding of what likely happened. My only hesitation would be that the OP says it’s a stout max charge or whatever wording he used . Which may lend the explanation more towards the light bullet hold idea .

 

[davidjoe]

Doug, I get those dents after a bullet sticks in the chamber and a stray grain of powder escapes removal.

Usually a grain will prevent bolt closure but sometimes a “full length” (EC proper) resized case will permit bolt closure, especially for fine powder or a smaller grain.

The dent is always gigantic compared to the grain that caused it.

It’s a very repeatable phenomenon. You could place a small grain on a greasy case shoulder to hold it in place, fire the shell and get that exact dent every time.

Usually you know it will happen because there had been a power spill and the bolt closed tighter than normal.

 

[tommeboy]

Low pressure.

 

[MagnumManiac]

I have seen this twice, one in a 25 Pronghorn (25-300WSM) which happened with every powder until we started using 257 Weatherby start loads as our max and reduced the charges 5%. The other was with a new 7RUM we tried loading without ANY DATA available, first few rounds came out with those dents and soot all the way the extraction groove...scary pucker time!
Once we increased the charges in both instances, the dents went away.
It is from low pressure, the neck doesn’t seal and gas gets past causing the dent.

Cheers.

 

[243winxb]

neck tension was also lower than I normally run

running a short bullet in a long throat

Correct these problems.

Primer fires, bullet moves to soon, neck not expanded, bullet contacts rifling, secondary pressure spike , blow back.

A mag primer should be used. The H4350 burn rate is fast enough, not an issue. More bullet shank in contact with the case neck may help? Shorter COL.

My general rule.
The bullets front should contact the rifling before the bullet shank exits the case neck. Less blow by past the bullets. Longer barrel life.

 

[Canadian bushman]

If you get a dent like that after firing its usually caused by a “Secondary explosion effect”


Low neck tension with a big jump on a cool day might do it, but usually its from an undercharge with slow powders.

 

[mikegaiz]

Not enough pressure or time to seal the neck so the pressure tried to come back

I think that is what I said?

 

[bozo699]

Doug, I get those dents after a bullet sticks in the chamber and a stray grain of powder escapes removal.

Usually a grain will prevent bolt closure but sometimes a “full length” (EC proper) resized case will permit bolt closure, especially for fine powder or a smaller grain.

The dent is always gigantic compared to the grain that caused it.

It’s a very repeatable phenomenon. You could place a small grain on a greasy case shoulder to hold it in place, fire the shell and get that exact dent every time.

Usually you know it will happen because there had been a power spill and the bolt closed tighter than normal.

I’ve seen this before as well.
Wayne

 

[Uncle Ed]

If think your case looks strange with its little dent, then you never want to shoot old surplus Pakistani .303 British click.............................................bang ammo.

This is what happens when shooting a mad minute and opening the bolt before the "BANG". (hang fire)

 

[Uncle Ed]

I’ve seen this before as well.
Wayne

In your case Wayne your dents are from over lubing your cases.

 

[Metal God]

Ed, are you sure that wasn’t a kernel of powder stuck between the case and the chamber LOL