I have used a peep sight on three different firearms starting out with a 760 Remington, you can see the Williams base still on the side of my rifle. The peep sight was a big improvement over the factory semi-buckhorn sight.
Mounting a scope on the Model 760 was an improvement over the peep sight. I replaced the factory rear sight with a folding Lyman sight.
I have a Marlin Model 336 which was sold as a package gun with iron sights and a 4x scope. The iron sight was sighted in long ago and forgot because I prefer the scope.
With my eyes I could not have shoot this group with iron sights. The Marlin is now wearing a 2-7x35 Burris. Top two are factory Remington 150-grain, the bottom two are my Hornady 150-grain Roundnose reloads.
The tough one for me and the jury is still out is not scoping my Jungle Carbine. I am happy with the peep sight for close range shooting. Good commercial scope mounts are made for the rifle, but I want to have a rifle with iron sights for those super nasty heavy rainfall days. Most shots are within one hundred yards and I do okay at that range with a peep. I am writing about one of those days that you are exhausted from being in the rain.
This fall I hunted about a week with the scope equipped 336 Marlin. The light rain and snow came down a couple of days. It was not enough to bother the Burris scope. I was pleased with the scope/Marlin combination. If the conditions deteriorated enough I could have removed the scope from the base of the Weaver mounts and put the scope in my day pack. It did not get that bad.
Last spring I needed low scope rings to mount a scope on a bolt action rifle. High rings are easy to get but the low ones are more difficult. I happen to spot rings and a base for a Marlin 336 at Wal Mart with low rings. I bought the package for a few dollars, kept the rings for my project and passed the Marlin base to a friend.
I have also used a combat shotgun with a peep sight. I recommend it.
When I shoulder a rifle with a peep sight my eye picks up the center of the hole/light, in my mind the peep sight is out of focus and the eye focus on the foresight (front) and the target. Focusing on the peep, the foresight, and the target is a complex process for the eye.
I do not mind using a peep sight on the right rifle. This one has one in the ladder sight, and when it is folded down the user has the use of another peep sight.