TargetTalk

It's time to clean my .22LR Benelli MP90S which has been keyholing and ejecting inconsistently. I took a look with my borescope before starting and there are some lead flakes and sootiness, which I expect. But I also noticed something odd in the forcing cone area of the chamber - tiny orange flecks of some sort of material. You can see a couple in this photo at 2:00 and 11:00, and the closeup in the central mirror. The chamber itself seems relatively clean, and rounds drop in ok.

Is this shaved brass? Rounds/brass sometimes "bump" the chamber mouth when going into battery but they feed just fine. Or is it perhaps some sort of ignition byproduct? I shoot exclusively SK Pistol Match. The flecks are not dislodged by running a dry patch. A nylon brush knocks them down, but I seem to need a soak and a bronze pass or two to remove them.

After a good scrub, I expect the issues to disappear for a few months as they usually do afterwards. But I'd love some opinions on what the orange debris is, and how I might maintain the pistol to keep it away. Thanks for any ideas!

I suspect it's brass. Occasionally, they don't adjust the crimping die carefully enough. Instead of crimping the mouth of the case, the die is set too low and cuts into the brass. I was shooting Eley Target ammo several years ago, and found brass flakes all over the inside of my Benelli MP90S:
When I examined the ammo, I found the crimp cutting into the brass. I reported it to Eley, and they could have cared less...

Years later, I had the same issue with some Aguila in my MatchGun MG2. I managed to find some unfired rounds that actually showed the brass separating around the crimp:
I've found that BoreTech Rimfire Blend does a good job of getting leading out of the bore. Benellis have shallow rifling, and are susceptible to lead building up enough to cause keyholing. I can usually go 10,000 rounds or more between rimfire blend treatments.

That makes good sense, I'll inspect some boxes/batches of my ammo, thanks.

Agreed on the Rimfire Blend, it lifts the lead beautifully and seems to prevent it from returning. Here's the same chamber view, post-cleaning.