Need help with Sig P240

[Joe350]

Hi.
Recently I've got this beautiful pistol Sig Hammerli P240 .38 sp WC, but it's giving me some troubles. It shoots very tight groups, but every once in a while empty shell stays in a bore.
I thought that problem was little of oil I've put in the bore, so next time I went shooting, I've cleaned bore and barrel dry. But it happened again.
When I inspected empty shells, almost all of them had one side black with smoke, some more, some less.
I use original Sellier&Bellot 38spWC ammo.
Can anyone tell me, what is the cause of this?
Thank you.

[Tycho]

Black case sounds like gas pressure is too low. Is the S&B a slow ammo, or might your batch of ammo be pretty old?

[JamesH]

Does the slide go back and leave the case in the bore?

If so its a rough chamber or extractor problem.

[Joe350]

Thank you for replies.
S&B ammo is new, regular 148 grn WC, chamber is like a mirror, extractor problem - hopefully not.
But today I've tried Magtech 148gr LWC and they worked fine. I measured case shells and S&B are little smaller. They don't seem to have as much punch as Magtech also ( low gas pressure?)
So I will probably have to start using Magtech.
If you have more ideas, please, write it, so I will know what to watch out for in the future.

[Rover]

I often see the case blackened on one side when shooting low pressure loads in my revolver. Since it's laying on the bottom of the chamber, there is more clearance at the top.

I don't worry about it.

[jipe]

Not sure that Magtech cheap unreliable ammo is what I would use in such a beatifull, rare and relatively fragile pistol as a P240 !

Why don't you reload and make your own ammo ?

If a side of the case is black, it means that the case was not enough/well expanded by the shot. It can come from a too soft load, too small brass, too hard brass.

[Spencer]

...It can come from a too soft load, too small brass, too hard brass.

for reloads, add:
- insufficient crimp
- undersize inside sizing die (learnt this the hard way when one of my inside sizing dies wore down)
- undersize projectiles (unlikely in a P240)
- HBWC projectile too hard to expand properly