As most of you may know, a standard m91 has a 28 inch barrel. That is ridiculous. There are several reasons to cut a Mosin barrel down.
First, a 28″ barrel looks funny on a Monte Carlo stock. A barrel that long is also difficult to manoeuver in dense brush, which is where most of my hunting spots are. Third, longer barrels have more “whip” than a shorter, thicker, profiled barrel.
Lets look at that last point in particular.
When a bullet is fired from its’ cartridge through a barrel several things are happening. We call this “internal ballistics”.
The basic idea is that when the projectile leaves the cartridge mouth it passes into the barrel. The barrel has spiraled grooves cut in it, called “rifling”. These grooves grab the bullet and impart a spin to it, so that when it leaves the muzzle, the bullet is spinning, like a football. This spin aids accuracy. While the bullet is still travelling through the barrel, several forces are acting on it. There is the pressure wave of the explosion in the casing, which pushes the bullet forward. Friction is created by means of the interaction between bullet and the rifling, which gives spin. Air resistance is also present, as the volume of air in the barrel must be displaced, but this is really minimal.
The “whip” in a barrel is a result of the friction between the bullet and the rifling. We know that every action has an equal and opposite reaction. As the bullet spins, the barrel will move in an opposing manner. To be sure, the barrel posses more mass than the bullet and will not move as much as the projectile, but it moves nonetheless. After the bullet leaves the muzzle the barrel will return to its original position. A shorter, thicker barrel should whip less that a longer one. With less whip comes a higher degree of probability that the barrel will more consistently return to its true position after firing.
All this to say, a shorter, thicker barrel ought to be more accurate, especially over a longer shooting session.
On account of these reasons I shortened my Mosin barrel.
Some other folks are better equipped than I in regards to tooling and such, so I have had to improvise somewhat. Before ya’ll start throwing the blog-o-bombs, hear me out. I cut my barrel down to 22″ with my angle grinder. After using my files and elbow grease, I switched to sandpaper and buffed the muzzle up.
As I do not have a crowning tool, I made use of my drill, a screw, and toothpaste. It makes a decent crown. A crown does not need to be much deeper than the bottom of the grooves. This method works pretty well, and for pennies on the dollar.
Insert the screw into the drill chuck, with the head sticking out. Put a dab of toothpaste on the screw head, and mill out the crown. Toothpaste acts as a grit paste. Move the drill in a circular motion so as not to wear any part of the crown more than another. It is important to get as even a bevel as possible.
We will cover accuracy and results in the final installment at the end of this series. Suffice it to say, the accuracy of this rifle improved over the course of this build. It doesn’t take expensive tools to do a job, nor to do it well. Time, some expertise, and a good idea of the end goal are worth just as much.
In the next post we will examine the drilling, tapping and mounting of the scope rail…