I don’t like plastic dummy rounds, they are expensive and they have light weight which makes them inappropriate for dry fire trainings.
Shotgun dummy rounds should be of the same weight and size as the live rounds. This way, you will have proper skills during dry fire trainings.
There are two best variants to get such dummy rounds for your shotgun. First is to make them yourself. If you have friends which reload shotgun shell you can ask them to make such dummy rounds for you. You just don’t add live primer and gun powder. That way you will have dummy round which has the same weight and size as live rounds.
Or you can buy dummy rounds made by Brownells. They are exactly what you need for dry fire trainings. These shotgun dummy rounds are cheap, so you can get a box of them for your dry trainings.
ATTENTION: Remove all live rounds to a safe place or to another room, so you will not mix live and dummy round. This is extremely important! Train in front of the wall, point your shotgun only into safe direction.
Information about Brownells shotgun dummy rounds:
Manufactured to exact specifications, including diameter and length dimensions, weight and balance of factory loaded ammo, these DUMMIES have the proper functioning characteristics to reliably check magazine feeding, action timing, extraction and ejection of all guns. The only professionally accepted and safe way to check gun functioning; live ammo should never be used except in actual test-firing on the range – after you have checked the gun with DUMMIES. The very reasonable cost per DUMMY is an added incentive to use them regularly. The blackened case makes them distinct, and instantly recognizable as DUMMIES, which makes them ideal – and safe – to use as a sales aid. Especially useful when demonstrating how a particular gun functions or in gun safety instruction classes. They absolutely eliminate the chance of an accidental discharge.
The are available on Brownells: http://tinyurl.com/z9cr98g