Odd dimpling on once fired casings

[Rob]

I have a Marlin 1889 Lever gun chambered in 38-40 Winchester.  This particular gun was manufactured in 1890.

When I shoot it, the brass comes out with a dimple near the neck.  The photo below shows it (I have reloaded the brass, but this case has been fired once already.)

The dimple does not show up if you cycle ammo thru the chamber without firing.  It only shows after firing.

In my mind, it looks a lot like the hydraulic dimples you get reloading when you have excess lube on the brass when runs thru the resizing die.

I have it at a gunsmith right now for another issue (looks like a worn sear).  He has inspected the chamber with a scope and is not seeing anything that would cause this.  He does not know what is causing it and is pinging some of his resources to get their take.  I am curious if anyone else has seen something like this.  Again, the dimple only appears when after a cartridge is fired and the chamber has been scoped and shows clear/clean.  I should note that it happens on every single round fired regardless if the brass is factory fresh previously fired.

[Henrydog]

I don't have an answer, but I am tagging a long for a lesson.  Does it do it if you just cycle shells through the action without firing or just after firing?

[elkslayer069]

I know it’s a marlin but you might ask the same question on the Winchester collectors forum. https://winchestercollector.org/forum/ Lots of knowledge on there. Good luck.

[BULLBLASTER]

Is there usually black soot in the dimple?
It looks like the neck didnt seal in the chamber and gas blew back and made it.
Ive seen it from light underpressure loads.

[Rob]

Only happens when firing.

These are light loads-given the age of the gun that is all I want to shoot.

The dimple is always the same shape.

At one time i slowly ejected to see what side of the chamber it was happening.  I cant recall and the gun is in the shop so I cannt retest, but i dont think it was on the extractor side.  That was my theory as to cause.

Not sealing is an interesting thoery...

[ghosthunter]

Can you try one factory cartridge and see if the same thing happens?

[Rob]

Can you try one factory cartridge and see if the same thing happens?

I have shot about 90 factory loads and every one dimples.

Every spent shell has the exact same shaped dimple in the same location. 

Shells I load and eject without firing come out without the dimple.

[Fidelk]

Seems like the shell case is impacting on something metal just after the moment of firing (and only after firing). Is the ammo loose in there and is bullet length correct? These are my guesses?   

[wadu1]

Bazar, tagging along with a positive outcome.

[jrebel]

If you don’t figure it out and you get the gun back….mark the case with a sharpie and index the mark 12oclock in the chamber.  Then see where the dimple is in relation to your indexed round.   Do this with a couple rounds and see if it occurred in the exact same spot.  Then you have a map and starting point that could help identify the problem. 

[Platensek-po]

Have you fired any of the dimpled cases again? Does it dimple twice? Cause issues with the round chambering or case splitting? This is very interesting.

[elkslayer069]

If you don’t figure it out and you get the gun back….mark the case with a sharpie and index the mark 12oclock in the chamber.  Then see where the dimple is in relation to your indexed round.   Do this with a couple rounds and see if it occurred in the exact same spot.  Then you have a map and starting point that could help identify the problem.

That’s what i was thinking as well.

[Rob]

I did a single shot with an index mark.  Even have the shell!  But i have forgotten where i indexed at!!  I think it was top of chamber and if so then it would be the bottom of the chamber leaving the mark.  I will fire it 2-3 times when I get it back.

It happens with every shot-i have reloads with multiple dimples.

One unique thing about this cartridge is that it has super thin walls.  It would dimple easier than other chamberings.

Might be interesting to reload a shell without powder and primer and see if a dry fire dimples it.  I somehow doubt it will but I think I will try that.

[JDHasty]

I put a link to this thread out for these guys to weigh in.  https://castboolits.gunloads.com/showthread.php?463175-What-do-you-figure-caused-this-case-neck-crease

It’s getting some action, but nothing definitive so far.  There is a tremendous amount of knowledge on that site.  If I were a betting man my money would be on either someone there will have an answer or nobody knows. 

The only time I’ve gotten anything resembling that without it being a lube dent is when sizing 30 carbine cases down to 17 caliber. 

[JimmyHoffa]

Is there usually black soot in the dimple?
It looks like the neck didnt seal in the chamber and gas blew back and made it.
Ive seen it from light underpressure loads.

Sounds like a possible cause.
Also, I think even with standard pressure if the gun starts to loosen up, similar things can happen. The lock up can feel tight when not under pressure. But the various components can wear or stretch, especially in a 130 year old gun. Then when firing, either bolt shifts back or barrel forward. With that much taper and being headspaced off the rim, seems quite possible.

[BULLBLASTER]

Is there usually black soot in the dimple?
It looks like the neck didnt seal in the chamber and gas blew back and made it.
Ive seen it from light underpressure loads.

Sounds like a possible cause.
Also, I think even with standard pressure if the gun starts to loosen up, similar things can happen. The lock up can feel tight when not under pressure. But the various components can wear or stretch, especially in a 130 year old gun. Then when firing, either bolt shifts back or barrel forward. With that much taper and being headspaced off the rim, seems quite possible.

Thats a good point. Or possibly some irregularity in the neck of the chamber prohibiting a seal?
I think that is a pretty low pressure round already.

[Rob]

I will chat with the smith about the low pressure dimpling that was mentioned on this thread and the castboolits thread (thanks for cross posting.)  that seems the most likely cause.

Not sure if there is excessive soot - I can check when I get it back.

I took a photo of six shells with the dimple - they all look identical to me.  The far right cartridge has been fired 2x out of the gun and you can see the remnant of the first dent which has fireformed about 50% out after the follow up shot.

[Rob]

Would "failure to seal due to a low pressure charge" put a consistent dimple of the same size, location and depth on the brass?

[JimmyHoffa]

Would "failure to seal due to a low pressure charge" put a consistent dimple of the same size, location and depth on the brass?

If the brass is the same structurally and all the other conditions close, I'd imagine so. Kind of like how sausages all seem to split in the same place when grilled.

[mountainman]

Is there usually black soot in the dimple?
It looks like the neck didnt seal in the chamber and gas blew back and made it.
Ive seen it from light underpressure loads.

This👍

[JDHasty]

I would be inclined to look further into post #17 on this thread.  It impresses me as a possibility.   

https://castboolits.gunloads.com/showthread.php?463175-What-do-you-figure-caused-this-case-neck-crease

[chukardogs]

Have you made a cast of the chamber? Just because the chamber looks clean doesn't mean there isn't an imperceptible high spot or depression in the surface. It doesn't have to be obvious to cause an issue when you're dealing with material movement of the cases. This may seem or actually be silly but unless it would be unsafe, I would try putting a filler of some kind (possibly a cotton wad) in the case. If the powder charge is small enough to leave a significant amount of empty space in the case, as the pressure builds on the material, it could be uneven enough to cause a concentrated load to be unevenly applied around the case. Have you measured the thickness of the neck around the case opening. If the case neck material thickness is consistently thinner 180 degrees from the dimples, I think you will have found your issue. Another way to know if this is your issue would be the case length. If the case is consistently longer (even a couple thousands) inline with the dimple, this means the case material growth when fired is uneven because of an uneven pressure build in the case. Just an idea....

[chukardogs]

What powder are you using for the loads causing the dimples?

[chukardogs]

Looking at the reload data, there's a huge difference in volume cc's between titegroup (.42) and  IMR trail boss (.98)
Throw in the fact that titegroup is a faster burning powder than the IMR trail boss. Just a change in powder may fix the issue you're experiencing. Good luck

[Rob]

the rifle is still with the smith and he is making a new sear for it as it is quite worn.  Once I get it back (probably Feb - I am not in a huge hurry), I can test stuff out a bit more.

I would be inclined to look further into post #17 on this thread.  It impresses me as a possibility.   

https://castboolits.gunloads.com/showthread.php?463175-What-do-you-figure-caused-this-case-neck-crease

I can say it chambers easy.  Only creates the dimple after firing, and the dimple goes into the case, not outward for what it is worth.

[chukardogs]

The dimple has to go inward. When material grows, it takes the path easiest traveled. Just a FWIW, If you look at your cases total volume cc capacity, it's 2.33. The volume of .42 cc's of titegroup is less than 1/5th of your capacity. This means when the gun is level, there's a very good chance that you have no powder in direct contact with the primer. Compare that with the IMR trail boss, being just a little under one half of the cases total volume capacity in cc's, I can't believe that just based on simple physics, that fact alone has wouldn't cause some pressure issues within the case at the point of ignition.

[Rob]

What powder are you using for the loads causing the dimples?

I reload with 15 grains of I-4227 with 180 grain LRN.  I would need to go back and find my data source but this was on the very low end of the scale - a starting load.  I want to say the range of charges was 14ish to 18ish.

The Black Hills factory ammo were cowboy action loads, but of course I have no idea what powder or charge they were shooting. 

A cast of the chamber might be interesting

[Rob]

The dimple has to go inward. When material grows, it takes the path easiest traveled. Just a FWIW, If you look at your cases total volume cc capacity, it's 2.33. The volume of .42 cc's of titegroup is less than 1/5th of your capacity. This means when the gun is level, there's a very good chance that you have no powder in direct contact with the primer. Compare that with the IMR trail boss, being just a little under one half of the cases total volume capacity in cc's, I can't believe that just based on simple physics, that fact alone has wouldn't cause some pressure issues within the case at the point of ignition.

I suppose I was thinking if there was a chamber issue where there was a crater in the chamber somewhere, that might create a dimple going outwards.  But these dimples look like the hydrolic dimples you see when there is too much lube on the case - the shape seems to "flow" which I think might give credence theory of the brass not sealing off the chamber which was allowing gas to flow past and create the dimples (as was mentioned earlier by a couple folks)

[chukardogs]

They make products specifically for this issue. Plastic shot buffer, dacron fiber pad, etc... If you don't find a distinct residue pattern on the outside of the case from this escaping gas, I'd have to look at other possibilities. I had a buddy that reloaded a bunch of 25-06 shells without trimming length. This caused each case to run into the end of the chamber during expansion from the pressure to crack down the full length of the neck area. Every one of these cracked cases had a distinct black residue along the entire length of the crack. If the case doesn't have enough room to grow in length during the firing, something gotta give. Good luck

[wadu1]

Any update on this @Rob? It's been a interesting follow along.

[Rob]

Well....  not a satisfying update I am afraid.  But a little interesting I suppose.

Short story is that I have not shot it again since I got it back from the smith a couple weeks ago.  As I noted earlier, the trigger became "floppy" after the last time I shot it.  I took it in expecting it to be a spring issue.  The smith completely disassembled and cleaned it out (said it was very dirty inside - likely it had been 100 years since it was last cleaned this well...)

He diagnosed the floppy trigger as a worn sear.  He searched all his sources and contacts and was unable to find a replacement sear.  He is able to manufacture parts so he tried 2x to make one.  He was unable to replicate the spring tension so the trigger was impossible to pull.  He outsourced it to another fabrication place he uses from time to time and they had a similar issue - although the trigger would pull now, it had a 25 pound pull pressure!

He did fire it with some factory brass and said he thought the dimpling was a bit lighter than before.  I looked at the brass and the dimples did look a tiny bit shallower - perhaps 10% shallower than the original dimples.  I am not sure I would call it a step-change from prior but it was marginally better.

I will say, I really like this smith.  He spent HOURS diagnosing, cleaning, researching, fabbing parts and testing.  Because he could not fix the issue, he did not charge me a dime.  I immediately dropped off two other rifles that I wanted some work done on.  Contact info for anyone interested:
Pollock Precision Gunsmithing
Evan Pollock
pollockprecisiongunsmithing.com (208) 889-8380
Sagle Idaho

So unless I can find someone who can look it over and fix/replace the sear, this firearm will sit in the safe.  And still no solid theory's on why it dimples.

[elkslayer069]

Have you tried Old Arms of Idaho yet for parts? I think you can get on a wait list for parts too if its something they don’t have and they get one in.

[Rob]

I have not but I will look them up.  Thanks!

[JDHasty]

PM me.  I can probably put you in touch with someone who will know who has a lot of experience with these old Marlins.