The Firing Line Forums - View Single Post - Would somebody explain about barrel resonance?

riddleofsteel · December 4, 2001, 10:23 PM

Your guitar string analogy id true for a true free-floated barrel. Putting a fore end shim in is somewhat akin to fretting the string at some point on the neck but not exactly. In a true free-floated barrel, no matter how thick, there is a signwave type vibration in a three dimensional pattern and a slight wobble. Fore end shims and adjustable fore end tensioners (ala old remington 40X rifles) tend to dampen those vibrations but they still exist. I once shimmed the free-floated factory barrel on an old Mauser at the shooting range with a makeshift aluminum shim made from part of a soft drink can. When you fired it the rifle it rang like a little gong as the barrel vibrated against the shim despite four pounds of upward pressure. Later I replaced the aluminum shim with one made from a block of plexiglass.
Best procedure seems to be to stabilize the action in the stock by bedding and free float the barrel. Shoot it and see how it acts. If you are not satisfied start shimming the barrel with heavy paper or thin paste board shims until you find an upward pressure that shoots well. Remove the shims and use a micrometer to measure the thickness. Cut a shim(s) out of plastic or some other stable and non porous material and slip it into the same location between the barrel and fore end. Shoot for groups and adjust the tension as needed.

As far as a new stock a Fajaen Rhinehart wood or an H&S Precision or McMillian synthetic is hard to beat.

December 4, 2001, 10:23 PM	#16
riddleofsteel Senior Member Join Date: January 18, 2000 Location: above ground Posts: 1,558	Your guitar string analogy id true for a true free-floated barrel. Putting a fore end shim in is somewhat akin to fretting the string at some point on the neck but not exactly. In a true free-floated barrel, no matter how thick, there is a signwave type vibration in a three dimensional pattern and a slight wobble. Fore end shims and adjustable fore end tensioners (ala old remington 40X rifles) tend to dampen those vibrations but they still exist. I once shimmed the free-floated factory barrel on an old Mauser at the shooting range with a makeshift aluminum shim made from part of a soft drink can. When you fired it the rifle it rang like a little gong as the barrel vibrated against the shim despite four pounds of upward pressure. Later I replaced the aluminum shim with one made from a block of plexiglass. Best procedure seems to be to stabilize the action in the stock by bedding and free float the barrel. Shoot it and see how it acts. If you are not satisfied start shimming the barrel with heavy paper or thin paste board shims until you find an upward pressure that shoots well. Remove the shims and use a micrometer to measure the thickness. Cut a shim(s) out of plastic or some other stable and non porous material and slip it into the same location between the barrel and fore end. Shoot for groups and adjust the tension as needed. As far as a new stock a Fajaen Rhinehart wood or an H&S Precision or McMillian synthetic is hard to beat. __________________ For him there was always the discipline of steel.