Took my newMossberg 4X4to the range today and shot over 2 boxes throuh it. I was shooting right at 1in to 1 1/2 in groups when first started but toward the end when barrel was hot, I couldn't get better than 3 in. Why does the rifle not shoot as accurate when barrel gets hot?

When you fire a shot the barrel vibrates a little. As the barrel gets hotter it expands and the vibration frequency changes and that has an impact on accuracy even with floating barrel.

Thanks...I knew that id did, just wanted o understand why. What exactly does a floating barrel do. what riflrs have them?

My Savage has a floating barrel. It means the barrel does not touch (is not attached) to the stock.

A floating bbl...floats in the stock. There's no contact with any part of the gun except where it attatches to the action. It's not always best as some will shoot best with some stock pressure.

Also as the barrel gets hotter,it reveals stress where it wasn't completely stress relieved. Proper stress relief is somewhat lengthy,labor intinsive,and takes skill-whatever method you use. At the price you pay for mossberg you can't expect to have a perfect fully stress relieved barrel. Getting a barrel too hot is the WORST thing you can do and is EASIEST way to ruin a barrel.

Thanks...I've learned something

There are 2 main advantages to free floated barrel. The first is because a barrel does vibrate when bullet is travling down bore,it can vibrate uninhibited thus naturally. The second is with solid wood stocks,if the stock warps(and all solid wood stocks warp to varying degrees),it won't touch or put pressure on barrel to affect poi or vibration. In a few instances usually with lighter contour barrels,it's preferable to have a pressure point at or near muzzle end of forearm to damper vibration in a consistant controlled manner. The only way to tell for sure which YOUR barrel performs best is to fire group,put temp spacer very close to and forward to front action screw to temp free float barrel,fire group,then put spacer(matchbook layers work fine for temp only)at front of forend under barrel to put pressure on barrel,then fire group. Only after you know for sure which it prefers should you permanently bed rifle accordingly.

Yes overheating a barrel greatly increases the rate of throat erosion,and shortens barrel life considerably.