Hi Dave, Depending on the types of terrain you hunt in determines the length of the barrel with shorter barrels desirable if hunting in heavy cover where a longer barrel will be difficult to maneuver and the shots are at close range. In this type scenario the .300 WIN MAG would not be a good choice. A .308 or 30-06 would be a much better choice. One of the major issues with any rifles performance is having all of the powder in the cartridge burning within the confines of the barrel accelerating the bullet as much as possible. Powder that burns outside of the barrel does nothing to increase the speed of the bullet as it burns harmlessly in the atmosphere. If you hang out at ranges a lot like I do (Rifle and pistol instructor) as the daylight fades and you watch people shooting you will notice muzzle flashes that vary from almost nothing to long flames shooting out of the barrel. What is happening here is that the un-burnt powder leaves the barrel prior to ignition and results in the fire works. You can eliminate or tone down the fireworks by loading the ammo with powder with a burn rate and charge that can be utilized totally within the barrel. This may end up with you shooting somewhat reduced loads but with the powder doing it's job and not burning up uselessly in the atmosphere. As an example my .308 ammo, since I rarely shoot these rifles over 200 yards has the bullet leaving the barrel at around 2500 FPS (Nosler 165 Partitions). The result is that there is virtually no muzzle flash out of either my 20 inch or 22 inch barreled .308's. The reduced powder charge 46.0 gr vs 50.0 gr cuts down the cost of power. Keeping this in mind, think about how this would effect a .300 Mag. Utilizing the same powder the 300 Mag is using between 68 and 72 grains of powder (approximating factory loads would mean approximately 70 grains of powder. If you were to shoot that load out of a 22 inch barrel think about how much unburned powder is going to simply turn into muzzle flash and how much money you are wasting on unused powder with no increase in velocity. I have a Browning AB3 chambered in 300 WM. It has a 26 inch barrel and a 2 inch muzzle brake giving the total barrel length of 28 inches. That extra 6 inches of barrel length allows more if not all of the powder to burn adding velocity to the bullet, adding an additional 600 fps as well as increased energy within the barrel.
If you are going to shoot a magnum, shoot a magnum length barrel no less than 24 inches on up. My AB3 300 WM chronos out at just short of 3200 fps out of the 26 inch barrel, So my advise to you my friend is don't ruin an perfectly good magnum rifle by sticking too short a barrel on it. Without using a chronograph to measure velocity you might be surprised that your 300 WM has no more velocity that a .308 leaving the barrel.
