I've heard about people floating the barrel on their Mosins to make them more accurate. Since there is nothing special about my M91/30 I've been thinking about it. Does floating the barrel really make that much of a difference on a rifle?
I'm not trying to be ambiguous here; it really just depends on your particular rifle.
It all boils down to barrel harmonics. When you fire, the barrel vibrates. If we look at this like a sine wave, the bullet would optimally leave the barrel when the sine wave hit the "zero" mark. All sorts of things factor into this equation, but mostly pressure points along the barrel affect how it vibrates.
Free floating eliminates most of those variables, leaving you to work with the barrel alone.
However, barrels heat up. As they heat, they warp and stop shooting to center. They shoot more in a circle.
This is what my M44 did as it heated with the barrel floated. Notice the pronounced circular pattern.
Granted, in the above target, I should have used on type of ammo, but it didn't seem to matter at that point. I had shimmed the action, leaving the barrel free-floated.
I found that the barrel likes to be shimmed .010" to .020", most of the time with the shim placed about an inch back of the bottom of the stock.
I bought aluminum for this, and afterward measured a Sprite can's Al thickness. I could have kicked myself. It's right around .020".
If you shim the action (one under the rear screw, and one right in front of the recoil lug), add another shim to the barrel.
I found that my barrel likes to be sandwiched between the top hand guard and shims in front as I described, and with the action shimmed. This seems to take the torque off the action and lets the barrel free float between the contact with the upper guard and the receiver.
These two pictures illustrate what it did in its final form. The circles are still there, but quite a bit smaller, and I was firing faster. The flyers likely came from the fact that I was using milsurp Czech 148gr, and that I was standing, resting the rifle on a ladder and using open sights.
If I were you, if you're serious about this, start by putting an old business card under the front of the barrel about 1" back from front, and see where that takes you.
I'll be sure to try this in the next week or so. From what I've heard though I was under the impression that floating the barrel was cutting off the wood just after the handgrip in the fore-stock. Leaving nothing but barrel for over a foot. I'm not doing anything that drastic though, I'll stick to coke cans and business cards for now.
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