Peculiar case stretching

[mp40man]

IMG_2697.jpg

Anyone ever have a case stretch like this?
Some background.
New Starline cases. this is the second firing. Case was annealed once before first firming and again before this second firing. Using a PP bullet. Not new to loading, shooting, paper patching. I am familiar with case stretching, trimming in smokeless modern rounds.
I do not resize the cases for my single shot rifles. I segregate cases for each rifle and index the rounds as they are fired so they go in the same way every time.
Chamber of rifle looks to be fine. Not every case in the 20 I shot did this, only seven out of the 20. The other cases are fine, still com in under the trim length.
No rifling marks evident on the odd cases like you get when the case is starting down the bore like they do when they separate.
There is also no telltale bright ring just above the base like you get when cases are thinking about separating.
Another odd thing about these seven cases. The mouth of the case is smaller now after firing, its almost like the case mouth has developed a lip on the inside (think the opposite of a trumpet).
I swab between shots and make sure the chamber is dry.
I had a few rounds that needed a bit more pressure to seat in the chamber but at the time I thought this may be because the patch may have swelled a bit as it was damp out. Ive experienced that before shooting in rainy days so I didnt pay it too much mind. Could have been a few bullets that dropped a bit fat from the mold too.
All 20 rounds shot well, no weird fliers. So nothing to tip me off that something was amiss until I went to de-prime them and noticed the odd stretching on one side and the weird inside lip.

Anyone else experienced this?
Thanks

[country gent]

Check case wall thickness cases may be thicker on one side than the other.

[martinibelgian]

Check inside case necks for roughness. Also, no need to anneal every time, a soft(er) case is more prone to stretching. Looks like those cases stretched into the lease. Over annealing might also be an issue.

[D B Cooper]

Did you F/L resize before loading?

[45-110]

I am trying to understand your photo, I looks like the case mouth is squished? Did you step on it?

[M-Tecs]

Better pics would be helpful. I first thought the same that it was squished but the more I looked at it I am thinking it's very uneven stretching?

[RandyW]

I have encountered case stretching like yours. I found the cause in my 40-65 rifle was failure on my part to ensure the inside of the case neck was completely free of powder residue. With paper patched bullets, I would have a couple of cases out of every 20 fired to stretch like your photo. I tumble my fired cases with cleaning solution and SS pins. If I don't tumble for about 3 hours, a small amount of powder residue can remain inside the case neck. Once I made sure I tumbled for a full 3 hours and inspected cases to ensure they have no residue, the case stretching problem went away.

[semtav]

I anneal every reloading, but I run Steel wool on a drill mounted brush before and after annealing so the inside of the Case is smooth and clean. I'd go with rough neck before over annealed

[Delkal]

It might just be the lighting but it looks like there is an anneal line where the OP's finger is which is too far back. It also looks like the case mouth close to where the anneal line should be is black and cooked. As mentioned by someone else. If you still have any retry your loads with the original unannealed brass.

OP. How are you annealing your brass? Are you putting them in a pan of water and trying to heat them evenly with a torch? That method never works and always cooks half of the case. I have had much better luck with the cordless drill / Harbor Freight adapter / socket method.

[SiliconeSword]

I can't tell too well but your cases may be too long or some weird headspace/crimp thing or your throat
/chamber is wide or your case diameter is small. I had a similar issue with 350 Legend that headspaces off the neck and I think too long of a case that had too sharp of a crimp. One case was ripped in half and sent down the barrel and another had a stretched side. My thinking is that the overdone crimp and possibly weird barrel fed or partially fed the cartridge itself into the throat a bit where it then got pinched and stretched/torn. I'll add that the brass was annealed, probably more than it should've been. Think I saved the ripped piece somewhere, pretty funny looking

[Castaway]

I’ve experienced it with 32-40 brass. It’s a mystery to me too. I anneal after every 3rd firing, loads are low pressure and with head stamped 32-40 brass. Not one, but entire batch of 20’pieces.

[Bent Ramrod]

I've had everything from annoying minor stretching that nonetheless needs trimming (paper patch loads seem to be much more critical than grease groove as to matching of case and chamber length) to outright case separation like you show. I don't lube the patches with whale oil or substitutes or use a grease wad underneath, relying on wiping to manage the fouling.

Consequently, when the black powder deflagrates and the boolit slugs up to fill all the diameter available, that paper holds onto the inside of the case mouth it's being pressed against like grim death before it starts moving down the bore. The longer the case, the more likely it'll be yanked in half (.40-90SS is a particularly bad offender, but I've had it happen rarely with .45-70 as well). I've seen everything from cases yanked in half and the front end being dragged into (or completely through and out of) the bore to long, straight cases turned into extra-length "bottlenecks" with the leade and rifling imprint on the "bottleneck."

My solution to the problem is a variant on Frank Mayer's old procedure. He would rub some graphite on the bottom end of the patched boolit with his fingers before seating. I use a formula of one tin of Imperial graphite mixed into one can of Motor Mica and use an acid brush to spread the powder around the inside of the case after the wad is seated with the compression required before seating the boolit. This has eliminated the cases being pulled in half and greatly reduced the stretching problem. Also no graphited fingers to have to clean.

I would imagine semtav's steel wool polishing would get you the same results.

[Gunlaker]

Cases often stretch like that when using BP and breech seating with zero compression loads interestingly.

If you are getting a ring near the base I'd check for headspace. I have an 1885 that I had built for shooting PP bullets using Dan T's 45-90 reamer. It was chambered incorrectly and has nearly 0.010" excess headspace. It shoots well but stretches cases.

If a stretched case gets pulled forward far enough it gets pinched by the throat of the rifling and will reduce in diameter.

Chris.

[Kenny Wasserburger]

What is your fouling control method?

I suspect oil or wet chamber.

Kenny Wasserburger

[mp40man]

Thanks to all who took time to respond. I’ll provide some answers to questions not answered in the original post.

Fouling control- when shooting w/o grease cookie I swab with damp patch ( Balistol and water) two times followed and dry my chamber before seating new round. With previous loads using GG bullets I use blow tube. I have used grease cookies with PP loads as well all performing well.

Annealing method- I have used the pan and tip method as well as the socket in drill but now have gone to an annealing machine so they are all done the same. This particular loading was done with annealing machine.

Case cleaning- all cases are de-primed at the bench then put in a container of water for the ride home. When home they are brushed out with more water. Then wet tumbled with case cleaner and SS pins then dried on my wife’s plate heating mat (I don’t tell her about that process obviously) cases are then put back into container marked for this rifle only. All cases are like new after this process. No residual fouling from previous firings.

Sizing- cases are sized when new and never after. All cases are indexed in the chamber to make sure they all go in the same way every time.

Annealing line- there is a definite line where the annealing process stops, cased by the annealing machine use.

Patching- I wet patch, patches are not lubed with anything. Finger seated no crimp. Case mouth tension is minimal. Bullet will fall out of case if upended. This is how I’ve shot all of my previous PP rounds and have had very good results.

Compression- I’m shooting 1.5f Swiss, minimal compression 1/16”, just enough. Fouling is very minimal using this compression.

All of these cases are from the same bag of brass. This is the second load for these cases, both in same rifle.

[craneman]

The only time I've seen brass stretched like that is with a wet chamber. Maybe forgot to dry the chamber with that shot and the chamber was particularly wet?
Todd

[JKR]

I had the same happen once last fall. The case stretched into the chamber throat and partially separated where the annealing ended. Also a PP load. My conclusion at the time was a wet chamber. I wipe with 7-1 water, cutting oil mix followed by dry patch. I’ve fired, I dare say, thousands of similar PP loads and this only happened once. Not completely sure why.

[mp40man]

The only time I've seen brass stretched like that is with a wet chamber. Maybe forgot to dry the chamber with that shot and the chamber was particularly wet?
Todd

Possible but I doubt it. My wiping rod has a slit at chamber length for a dry patch each time. I’ve had a case seep before with a wet chamber so I’m pretty careful about it.

[mp40man]

I had the same happen once last fall. The case stretched into the chamber throat and partially separated where the annealing ended. Also a PP load. My conclusion at the time was a wet chamber. I wipe with 7-1 water, cutting oil mix followed by dry patch. I’ve fired, I dare say, thousands of similar PP loads and this only happened once. Not completely sure why.

Same here , I’ve shot may many PP rounds and this is the first time I’ve had these weird lopsided case stretches. Weird.

[mp40man]

Im going back out this week for another session. I’ll post results either way whether I get more weird stretches or nothing.