I have a similar problem with slim-line muffs from any manufacturer.
Foam plugs work well, ebven the simplist disposable ones, provided you fit them correctly. If you just shove 'em in your ear they aren't goig to work well at all.
I've actually been using mechanical valve type ear plugs for shooting a braked .308 outdoors & found them just fine. Indoors, or in a confined range house they won't be enough though. They get a lousy NRR factor because the way they're tested is with continuous noise, so the valve doesn't close. with pulsed sounds, like muzzle blast, they work much better than the NRR would lead you to think.
Norton ear-sonic used to be popular, but I can't find them locally so I'm now using a similar product called "Silencio", they work as wel, but the rubber is much stiffer & nowhere as comfortable to wear. This is supposed to be the newer, better version. For $10.00 give them a try you might be pleasantly surprised.