.44 mag carbines
I have posted many times about the twist rate used on the majority of .44 mag carbines from most mfgs up until just recently........1-38". My observations and experience with two vintage Ruger .44 semi's, and my Dad's M94, all so twisted, was that accuracy in those rifles was only so-so....3-4 MOA. Well with minute of whitetail and the useful range of the carbine/ctg, but not what many shooters expect from a modern firearm.
Now, MANY fellas report much better results, with their older carbines, but those three examples mentioned, that I have shot personally, with magnifying optics, were only that capable, with 240 gr bullets. I'd add that heavier bullets, the old 265gr and 300 gr jacketed bullets from Hornady, were much worse. In my gas guns, the lighter bullets, 180 and 200 gr, shot best.
Revolvers in .44 mag have traditionally been twisted 1-18" and .44mag revolvers have a stellar reputation for accuracy. Ruger with with 1-20" twist in the new model 96 and 99 carbines in .44 in their limited production lifespan, basically admitting that old .44 slow twist rate could be improved upon. I read the new Marlin/Ruger carbine is twisted 1-20" and should be a good shooter with a variety of bullets.
Regards peep sights, Skinner offers a couple of options, but one might have to experiment with front sight heights to get on target. A simple arrangement is the Lo-Pro, a single stem arrangement, affordable, and it screws right in to a drilled and tapped scope base hole on the receiver. Skinner also offers more elaborate arrangements as well.
The 1-20" Marlin/Ruger has only been released a short while. Anything prior has to be from the much berated Marlin/Rem arrangement, or an earlier true Marlin, both twisted 1-38.