Help finding out barrel twist

[LongRangeNewb]

Ok I got a rifle from my grandpa that was home made and was wondering how to find out what the twist is. The only thing that is stamped on the barrel is .308 HGW. I found the guy that put the gun together and he doesn't know the twist either. All he said was the barrel is a mg42 spare barrel from WW2. I would like to know the twist so I can make longer shots. If anyone can help I would very much appreciate it. Thanks

 

[Broz]

Clean it and after you get a patch going through it smoothly use a tight patch on a jag with a rod with a ball bearing handle. insert the rod a few inches into the bore. Mark the rod, with a pencil or sharpie by the handle on top and also at a point like at the beginning of the action. Now push the rod allowing it to rotate with the rifling and watch the top mark to make one full turn. Then put a second mark at the place you picked like the beginning of the action as soon as it has made one full turn. Remove the rod and measure between the action marks to find how many inches it traveled durring one full turn. I would do it 3 or 4 time to be accurate as possible.

Jeff