Firing my P220 Compact, this afternoon. After an uneventful box of FMJ white box Winchesters, I loaded some old, Federal .45 hollow points. Upon discharge, approximately four of the twenty-some Federal rounds produced noticeable sparks and I felt gas/powder particles strike my cheek and forehead. Fortunately, I was wearing glasses. The pistol was clean, before my shooting session began and I found nothing unusual when inspecting it, afterward. The experience was unpleasant. I would not want it to occur in a self defense situation. What would likely cause this "back blast" in a semi auto?

Check the recoil spring for damage or coil binding?

Does the brass show any physical damage or ruptures?

Definitely sounds like an ammo issue, not the gun...do you know how the older ammo was stored, and is there a possibility is was somehow contaminated?

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Originally posted by Samps:
I would not want it to occur in a self defense situation.

As mentioned, check the gun, but my first suspicion would be that the ammunition is responsible. Recommendation? Try something new and different.

Got a feeling that you know the old ammo was the problem. Blow back like you described requires bullet not cleared from the muzzle while breech / ejection open, the case at the time was also backed away from barrel.
My guess would be the old bullet has corrosion or not clean, it could have stuck inside and caused bigger problem. Think along line the machinic step, you will know.
You did mention P220 had no issue with that white box of ammo, therefore, to fill your wish of "not wanting it to occur in a self defense situation", all you need to do is to practice regularly and cycle your ammo - keep fresh ammo in your weapon.

These were some old, Hydra Shok rounds stored in the bottom of an ammo drawer for probably 8--10 years. Aside from tarnish on their jackets, the rounds looked normal. I'll go with the trend and blame the ammo. I did not attempt to retrieve the brass, lost on my muddy range. I've experienced this with revolvers, but never a semi auto. Your answers make good sense. Thanks, all.

I had some Federal "Ultra Target and Range" 9mm 115gr ammo that was shooting sparks. It was fairly new, less than 1 year old, fired in my 2 P365s

Could you tell if your sparks occurred at the ejection port or from the muzzle? Mine seemed right in front of my face and the particles were hot. I'm sure the whole mess had blown back from the breech. I think corrosion was my culprit.

I picked up a case of Federal Gold Medal .45 semi wad cutters for bullseye. I'm getting a lot of trash out of the combustion, similar to what you're explaining, including some crusty metal-looking flakes on my hands. It's just the ammo.

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I did not attempt to retrieve the brass, lost on my muddy range

Too bad. The only time I ever had anything like that was with badly burnt through cases.