If the jamming is the slugs tumbling and not staying upright, only solution I found was to use heavier/taller slugs or light/tall slugs with hollow base or LDC core from griffin slugs.
If you're serious about shooting slugs and don't want to single load them, buy one of these aluminum inserts from Great Britain. Made for slugs, they are a bit narrower, so slugs can't turn on their side. The maker is a good guy, ships fast and they arrive in less than a week. You can find the maker on the Facebook Impact pages. Stoti
I've had better luck with the original magazines...vs. the side shot. The side shot is looser and that doesn't play well with slugs. Even better, the CARM magazine has individual chambers for each pellet. They can't rock over and jam at all. I've got several CARM magazines for the Impact and Priest and am really happy with their performance...especially with slugs.
Eagle Vision is making an all metal magazine that should fix the slug issue...but it will be a couple months till it is out. They do have one on sale that will work with the .22 Impact now...though it wasn't designed for it.
I sent the plastic version of this magazine back because of the slug tipping issue, and paid the extra money for the original machined metal magazine. It works flawlessly now. The plastic unit is a bit off dimensionally, causing the issue.