Dry Fire laser cartridges with or without O-rings

I have been dry firing my Sig P320RX and M&P Shield. I have a iSight 9mm laser trainer cartridge, but the O-rings have gotten torn up. The M&P is VERY tight getting the cartridge in. Looking on Amazon and eBay, I see trainer lasers with and without o-rings. I am wanting to buy another cartridge and would prefer one without O-rings if they work just as well. The more expensive ones have o-rings so I assume they serve a valid purpose (like preventing or dampening vibration). Any have experience with both types or advise?

The Oring allows for a tight fit into the chamber without metal to metal contact. Not that a brass insert would damage the chamber. But chambers are cut different.

McMaster-Carr is your friend. Pop one of the o rings off and do your best to measure. Order a few with a similar ID and various thickness to find one you like.