The importance of bullet-to-barrel alignment and fit: Part 3

by Tom Gaylord
Writing as B.B. Pelletier

Part 1
Part 2

This report covers:

• Balls
• Patched balls
• Results of patching
• Conical lead bullets
• Pellet head
• An experiment
• Pellet skirt
• Summary

Before I begin, I am enroute today to the Sig factory, here in America. They are bringing in a number of writers to show us their airguns and see their factory. I will take lots of pictures and tell you all about it when I return.

But I will not be able to attend to the blog the way that I normally do. I ask those readers who have been here awhile to help the new readers, just like you always do. I will be back in my office in Texas on Friday and things will hopefully return to normal.

Today I will finish the discussion of bullet-to-barrel fit and alignment. I will begin with bullets and then transition to pellets.

Balls

I will start with lead bullets, because they are fundamental to the fit discussion. Before around 1850, the word bullet meant a round ball. Conical bullets did exist before that time but they were very specialized and hadn’t come into the limelight yet.

Fitting a round ball to a rifled barrel can mean fitting the naked ball to the rifling and ramming the ball down the bore to the powder charge. This effort invariably deformed the bullet from the friction of the rifling. The ball had to be pushed aggressively. The ramrod was iron to take the force of repeated blows, and the top of the soft lead bullet mushroomed flat from being struck. But mutilated noses don’t affect accuracy much, so the rifled ball was far more accurate than a ball fired from a smoothbore. The only problem was it took much longer to load such a bullet, and, as the bore became progressively fouled, the inside of the barrel got so dirty that it had to be cleaned before another bullet could be loaded. All of this slowed down the rifle in operation, making it a secondary weapon on the battlefield.

Patched balls

The patch was invented sometime after the year 1700. A ball (bullet) that was much smaller than the bore was covered with a leather, parchment or fabric patch that tightened the fit within the bore. The patch engaged the rifling, spinning the ball that was inside, yet the patch came off the ball easily when it exited the muzzle. The meant much faster loading, plus patches could be reduced in thickness as the bore fouled, giving more shots before the weapon had to be cleaned. As time passed, riflemen who were not in combat learned to clean the bore as they shot, making it possible to shoot patched balls indefinitely.

The thickness of the patch was the big issue, rather than the diameter of the ball, since the patch was a sabot (container) for the ball in the bore. That continues even today. Muzzleloading shooters must learn which patch material works best with which ball size in their rifle. And, when they can’t get the size balls they like to use, they can always substitute a smaller ball with a thicker patch.

Results of patching

Patch material, alone, can tighten a 5-shot group from 10 inches to 2 inches at 50 yards. So a muzzleloading enthusiast will find a certain ball they like — be it a swaged ball they buy commercially or one that they cast, and then they will try to lay in a lifetime supply of the right patch material. I discussed this to some length when I showed you Part 3 of the Nelson Lewis combination gun. I never finished my testing of that gun because, as some of you might recall, I blew up the gun. It was later repaired and I did shoot it again, but I thought I had better not subject a fine old collectible to constant use like that.

I did switch over to a modern .32 caliber muzzleloader, but that was to test swaged bullets against round balls. I never did enough shooting with that gun to get the patch material finalized, and it looked like the swaged balls were going to be much more accurate. But that was another test I never finished. Let me tell you about one I did finish and what results I had

When I was in the Army at Ft. Knox in the 1970s, I shot an original Green River muzzleloader that was probably made around 1850. It was too short to call a plains rifle and had a barrel that was too fat to call a hunting rifle. What I think I had was a target rifle whose muzzle had been damaged and about a foot of barrel had been cut off. The barrel was only about 28 inches long on this .45 caliber rifle. It weighed about 9 pounds as it was and probably 12-13 pounds before the barrel was shortened. The rifling inside barrel was heavily worn from the patches over the 125 years of its life, but there was still enough rifling to do the job. Cloth patches wear out a soft steel rifle barrel much faster than naked lead because they contain abrasive particles!

I fiddled with that rifle for a year, testing different cast balls and patches until I finally found the right combination. At 50 yards I could put five balls into an inch. The charge was somewhere around 50 grains of FFg powder, plus a grain of powder loaded inside the drum that held the nipple, to enhance ignition. It took me about 2 minutes to load the rifle each time, but when the hammer fell, I knew exactly where the bullet was going. I had found an ideal (patched) bullet-to-barrel fit. I had to sell that rifle to pay bills when my first wife divorced me, and I wasn’t a picture-taker in those days, so all that’s left is the story.

Conical lead bullets

I could go on ad nauseum with stories about conical bullets, because shooting has been my life for more than half a century. But why don’t I just cut to the chase and show you what it looks like when you get the right bullet fit.

Ten .45-caliber bullets ripped through the target at 15 yards. Group measures 2.271-inches between centers.

That’s not such a bad group, is it? I bet you would be happy to shoot one like it. Oh, maybe it’s not up to the standards of all our readers, but most of you would be happy. So, the question on everyone’s mind is — what gun did that? Was it a tuned 1911? Or perhaps an S&W model 25 with target hammer, target trigger and target sights? Not even close.

The gun that shot that target was a battered World War I Webley Mark VI revolver whose cylinder has been shaved to allow the use of American .45 ACP cartridges — as long as they are on moon clips! Yep, it’s a 1916 war bunny that’s been fooled with!

But the bullets I shot were SIZED 0.455-inches, to match the larger 0.455 caliber Webley bore. Ain’t it nice when the stuff I tell you really works?

Yep — this tired old Webley Mark VI that was made in 1916 and then modified to accept .45 ACP cartridges in moon clips shot that target. And the BULLETS FIT THE BORE!

There will be whole lot more on this Webley in the future, so this isn’t your last look by a long shot.

Nuff said! Let’s turn to pellets. This won’t take long.

Pellet head

The size of the pellet head determines whether the pellet rides the bore straight or on a slight angle to the axis of the bore. A pellet whose head is too small will be slightly cocked in the bore and will exit that way. The spin from the rifling and the drag from the skirt in the air will straighten the pellet in flight once it leaves the muzzle, but there may also be a slight bit of instability (wobble) introduced at that time.

An experiment

Those who are curious might try this. Throw a throwing dart at a dartboard tail-first. You will see the dart swap ends in flight and hit the board point-first. This will happen in as little as 7 feet 9.25-inches of flight! The dart is weighted and aerodynamically designed with a high-drag tail to always fly point-first. Diabolo pellets work the same way.

But no dart champion ever threw a dart that way in a match they wanted to win! They hold the dart carefully the same way every time and their arm moves in the same way each time for consistency. And so it must be in a pellet rifle for the best accuracy. The pellet head is what guides the pellet as it leaves the muzzle, so the size is critical.

The diabolo pellet is designed to fly nose-forward.

Pellet skirt

The pellet’s skirt seals the back of the bore so all the air (or gas, in the case of a CO2 gun) pushes on the pellet. Pneumatic guns are extremely gentle to pellets and do not deform the soft lead skirts at firing. There may be 3,000 psi inside their reservoirs, but the valve releases the air slowly at a much lower pressure. So, when shooting pneumatics and especially PCPs, look for pellets with larger skirts.

Spring guns generate a much smaller amount of compressed air, but they do it so violently that they blow the pellet skirt into the walls of the barrel. The power of the spring gun will determine whether this is something you have to consider, but with powerful springers, it always is. A skirt that’s blown out too much will affect the pellet in flight, reducing its accuracy potential.

Summary

Bullet/pellet fit and alignment to the bore is very important to its performance. In this short series I have shown how this works, but I have left many avenues unexplained.

This 3-part series has been very short and to the point. Some of you may not understand everything — especially today. Ask your questions and we will go from there.

Tom Gaylord (B.B. Pelletier)

Tom Gaylord, also known as B.B. Pelletier, provides expert insights to airgunners all over the world on behalf of Pyramyd AIR. He has earned the title The Godfather of Airguns™ for his contributions to the industry, spending many years with AirForce Airguns and starting magazines dedicated to the sport such as Airgun Illustrated.

See Full Bio