When I switched to 15 inch end feed shuttles, I found it was easy to "submarine" the shuttle while throwing it on a somewhat wide warp. So, I added extensions to the shuttl race on each side. This is for my 40" B5 Macomber loom.
Here is the race extension for the left. The part with the metal pins sits against the vertical part of the beater.
Here is another picture, showing how the pins sit in the vertical piece. The little piece that swivels allows me to clamp this to the side of the beater to drill some holes (partial holes, not all the way through) in the vertical piece of the beater, and so I'm able to to get it in exactly the right place, not too high and not too low.
And here it is installed. It's held on by the piece of texsolv and the fact that the pins are in exactly the right place.
The piece on the end has two layers of leather glued on for the shuttle to hit, should it go that far when I throw the shuttle. You can't really see this leather in this picture, but you can see it in the first picture.
The nice thing about this design is that I can remove the side pieces easily by simply pulling the arrow peg out of the texsolv.