First post here but ran into a problem while chronoing my old Delta yesterday banging up case mouths and clueless to why. Load was 11gr #9, 220gr Rimrock cast, Winchester primer, once fired PMC brass. Have shot close to 300 of these and never had this happen. Gun wears 24# recoil spring on a full length guide rod. Nothing odd on the chrono, still shooting 1075fps with a 23fps ES. Out of the 27rds, these popped back at me on ejection, rest were flung a good 10' and in perfect shape.

any ideas guys??

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that looks like the slide is hitting them/pushing into frame before fully ejecting... 
extractor holding case to much?

I occ see small dents on case sides as the brass hits the unbeveled ejector port opening upon exit, but not like that.

Sounds like the case is hitting the barrel hood because the slide is moving forward before the case has cleared. Try shooting it without the guide rod or dropping to a lighter weight spring. 

I would suspect that the extractor is not tensioned correctly and holding the brass till the next cartridge pushes it up and over.
On the DE They are bent to a specific arch to set the tension.  This may have changed.  Especially if rounds were dropped into the chamber and sending the slide forward where the extractor has to jump over the extraction rim of the cartridge.  That can bend the extractor enough to change the set tension.
Another issue could be that the slide is not traveling all the way rearward for the casing to be kicked out by the ejector or the ejector could be damaged.

Another vote for extractor tension.

Without the extractor holding the case properly, the ejector cannot properly lever the cartridge out of the action.  As a result, the spend case is still in the action when the slide starts to close.  These rounds got clamped against some part of the action.

Had the issue myself before, though much worse:



I added some tension to the extractor, and the issue was gone.

I get little dents in the sides of my empties with my old DE running a 23# spring and a full length guide rod. It's the slide coming forward so quickly that the case hasn't fully cleared the ejection port and the rear of the ejection port makes contact with the case. I also get little brass marks behind the ejection port on the slide as the cases spin around after that contact. It sends them a little forward.

The fact that your damaged empties were buzzed back at your head and undamaged cases don't sounds like they're making contact with the front of the ejection port or possibly the barrel hood before the slide has travelled fully rearward. If you were getting jams and crushing cases in the ejection port, I would look at extractor tension as many have suggested. Could also be the ejector is just a tiny bit too long and sends slightly longer cases out too early to completely clear the ejection port. Hence the intermittent problem.

Did you measure the length of the damaged cases against any that ejected perfectly?