I'd be pretty surprised if any of these failed to shoot from a 4" barrel ASSUMING YOU PUT POWDER IN EVERY CASE. You could always say that, but for a first time reloader, I'll ask whether you double-checked powder before seating bullets into the cases?
With four grains of powder and an electronic scale, you could weigh every round and be *pretty* sure they had powder, although four grains is about the lightest I'd believe that. I've gone through and weighed every round in a box where I wasn't *absolutely* certain that I'd checked each and every case twice for powder with my little flashlight before I went and fetched the bullets to the bench. I'd probably set aside and pull any that were more than about 1.5 grains below the average. If using mixed headstamp brass, you would need to first sort them all by headstamp and just compare to the average for that headstamp, since brass weight between brands will vary.
If they all do really have 4.0 +/- 0.2 grains of powder, I'd shoot them in slow fire at a distance that you can reliably see the holes and be SURE you stop and see a new hole with every shot. Seven yards would be safe unless you have terrible vision. If at a range where you only get to go out every 30 minutes to change targets, put up little aiming points every 6" to 8" on your fresh target backer or staple up fresh 8 x 11 sheets of paper every ceasefire and only shoot one cylinder at each. Unless you ONLY like to shoot rapid DA fire, this would be way more fun than pulling all the bullets and starting over, and it's a good opportunity to shoot a lot of careful groups.
If I'd weighed them all and then got through the first box or two with no squibs, I'd probably relax and shoot the rest without being so cautious, but that's just me. I'm not saying it's a good idea.
