M14 Forum

william neal

I just bought my first M1A Scout. I shot it without optics and had an inch and a half group with 168 grain ballistic silvertips. I put on an Ultimac forward rail and the rail is not touching the receiver or stock. But now the barrel band is loose and flops around. The gas cylinder is tight. The groups went to 3-4 inches.

Could the slack in the barrel band be the reason the groups got bigger? And should I shim the gas cylinder to take the slack out of the barrel band?r

Any comments on the Ultimac forward rail are welcome. I want to put a 2.5 power Leupold Scout scope on it for deer hunting.

Seventh Fleet

Yes you need to shim it. Here's you a Youtube video showing how it's done. You can get shims from Fulton, Browells and several other places on the net.



7th

bd111

Got any photos of the problem area? It's worth taking a look at because that Ultimak mounting rig gets good reviews from Garand shooters who use it.

wetdog1911

Thanks for the vid 7th!

Never occured to me to cut the shim. Saves buying all the tools to remove/replace the FS.

Wet

adrbe

Two things that weren't covered in the video:

1.) Check the gas port alignment after shimming. You want to be sure the gas port in the barrel aligns with the gas port in the gas cylinder. To do this, remove the gas piston and insert a thin toothpick into the gas relief port on the bottom side of the gas cylinder. If your gas ports are aligned, the toothpick will protrude into the barrel. You'll probably need to shine a light into the barrel to see. A small allen wrench will also work.

2.) It is possible to over shim a gas cylinder, which will result in too much pressure on the gas cylinder which can degrade accuracy -- or worse, improper port alignment. You only want to shim it enough so that it gets tight somewhere around 5 o'clock/11 o'clock (depending on your perspective).