I was messing with my bro's bow the other day and it got me thinking. What holds the bolt in the rail on a crossbow besides the nock on the string? What I am meaning is, his bow has a Whisker Biscut on it and it holds the arrow in place. I like that feature alot. No worries about your arrow coming off the rest and despite what some say, it doesnt effect accuracy to the point of being noticed.

Both of my bows, of different brands, have a arrow retention tab. It's a flat metal spring the holds the arrow in place with enough force that I can turn the bow upsidedown horizontally and down vertically without losing the bolt. Does your's not?

The bolt clip (that piece of metal that holds the bolt on the rail) was developed because castle defenders in medieval times had a minor issue with their bolts falling out of their crossbows when they leaned over the battlements to shoot at the people on the ground. I would imagine it was a tad demoralizing to see a whole line of crossbowmen loose their bolts over the side of the walls when the command "AIM" got shouted.
Wyvern

when I first got into crossbows one of my first concerns was that the retention arm didnt seem capapable of securing the arrow well enough to the rail to keep the arrow in position during alot of the mobile hunting that I do,however it didnt take long tosee that it does a more than capable job

I suggested mounting a whisker rest to the front of the crossbow in one of my very first posts, and even though I now know that it isnt really necessary I stillwonder if it would help...

I've noticed that theres a pretty loud, noticablevibration that comes from the arrowagainst rail when the bow is jarred(sometimes even slightly), or if something snags the end of the arrow for a second and then lets go(brush), I can even get it by banging the bottom of the bow with my hand when its loaded, besides the fact that its somewhat irritating when it happens when your trying to sneakaround, its also an unnatural and alarmingnoise in the woods and I wonder if mounting a whisker rest would eliminate it