There is No Magic Bullet, Part II
There is No Magic Bullet, Part 2
By Lee Shaver
If you load your bullets as I often do with grease grooves exposed, you need to remember that if you load that cartridge into a hot barrel and leave it sit for very long that the lube will begin to melt and run down to the bottom side of the bullet and puddle up in the bottom of the barrel in the rifling grooves. When the cartridge is fired that bullet will once again bump up, but not bump up properly on the lower side where the puddle of lube is and will be out of balance and will shoot out of your group.
Many times the cartridge case mouths differ in thickness from one side of the mouth to the other. It won’t be much; maybe a couple thousandths of an inch at most. Keep in mind that since the bullet swells up against the case until the case touches the chamber walls, if the case wall varies then the bullet will swell out more on one side than the other. This will once again affect the balance of the bullet. This is a very minor effect, but still it exists.
On the other hand, every once in a while I have seen rifles that had the chambers off center by a few thousandths of an inch and while that seems bad, it really affects the accuracy of the bullet very little even though it will affect the balance. The trick is that it is affecting the balance in exactly the same way each shot, so the bullet will fly off in the same direction each time. It is still not a desirable situation, but may well not be worth the effort to repair for the accuracy improvement you may not receive.
One more thing—the end of the chamber should have no sharp corners in it. Remember that bullet is pressed out tight against the surface of the case mouth, free bore, throat, and bore with several thousand pounds of pressure per square inch as it slips out of the case mouth, across the gap and into the bore of the rifle. You don’t want any sharp corners on the throat or free bore to scrape lead from the bullet. You want it to glide smoothly across with as little damage as possible.
Here is a good place to discuss the case separations I mentioned that can happen with black powder cartridge loads once in a while. With the bullet pressing out onto the inner surface of the case mouth with several thousand pounds per square inch pressure, it tends to grab the case and tries to pull it along with the bullet.
Normally the case is pressed tightly enough against the chamber wall that it will not move, (remember how the case will stay put and not push to the rear to reset the primer), but if there is anything that prevents the case mouth from holding the chamber wall tightly such as a layer of oil or bullet lubricant, the case can move forward with the bullet. Here again I wrote an entire paper on it some years ago, but to keep it simple – the case holds onto the chamber, the bullet holds onto the case. If anything happens to add tension to the joint of the bullet touching the case, or removes tension from the case touching the chamber, and the difference adds up to more than the tensile strength of the brass, the brass will move with the bullet, and at times follow the bullet up the barrel a ways by either stretching the case or breaking it.
If you have a problem with cases stretching forwards or breaking, the answer is simple. You either decrease the tension inside or increase it outside. To increase it outside, you make sure the chamber and outside of the case are dry and clean with no oil, lube, or water from a blow tube that can prevent the case from getting hold of the chamber. To decrease it inside, you make sure the case mouths are not rough inside, the bullet has some lube on it with no dry lead showing that can stick to the case and in some cases a little change like using a different wad material or powder granulation can help.
Now that we have the bullet safely out of the case and transitioned smoothly into the bore, you would think that we were home free; but it doesn’t work that way I’m afraid. We do have the most treacherous part of the journey down the barrel out of the way, but we have about three feet of bad road to travel down before we can assume our bullet has been delivered on its way in a balanced flight. This most treacherous part we have just finished discussing is why muzzle loaders were always thought to be more accurate than breech loaders in the old days. Some of the long range shooters of old shot their breech loading match rifles by sliding the bullet in from the muzzle, and later Harry Pope and others were strong proponents of the idea especially among the Schuetzen shooters. By doing so, they simply bypassed the whole mess of getting a soft lead bullet out of the case and into the bore, and only had to deal with getting the bullet down the barrel without damage.
If the bore were perfectly smooth, clean, consistent, and lubricated from here to the muzzle, the story would be about over; but therein lie the problems. Surface finish of the bore, consistency of the bore diameter, and rifling dimensions all make a difference; as does lubrication and fouling management. Each one deserves a little discussion.
I’m going to start with the actual size and shape of the bore. There have been a number of designs for rifled bores over the years. We seem to have settled on one to two designs, but there have been many over the years that worked just fine. There have also been a number of processes developed to manufacture rifled bores, all of which can be used to create a high quality bore or a bad one. The important question for this article is what works best as far as accuracy is concerned.
The answer is simple. The secret to a great barrel is consistency; consistency of diameter, groove depth, groove width, consistency of twist rate, and even the surface finish. The absolute best barrels I have used have all been lapped for consistency and smoothness.
The actual land and groove design matters little. Some barrels have square cut grooves, while others have sloped or rounded lands to help prevent fouling build up. Some have a straight twist while others have a gain twist, or increasing twist to the rifling. About everything you can imagine has been thoroughly tested in the last hundred and fifty years or so. Everything from deep sharp rifling, to shallow rounded ones, and even oval bores were developed and proved to work just fine as long as they are well made and consistent.
The actual depth of the grooves also matters very little. It was once common to have rifling no more than about .0015” deep in the latter half of the 1800s. By that time it had been proven that even heavy bullets could be spun and stabilized with rifling of .001” depth or less. I once read of a barrel maker that, in effect, put a piece of sandpaper on a rod and forced it through a smooth bored barrel as he twisted it and made extremely shallow scratches that would stabilize a bullet for a few shots. This was done just to prove that it didn’t take much to spin the bullet, and I assume that it either wore slick or fouled full in short order.
The actual diameter of the bore and groove dimensions of the barrel also matter very little. I have already explained how a soft lead bullet will swell up to fit where it is setting when the powder ignites and then squishes back down to go into the bore, and how the bullet needs to be fitted to the chamber, etc., instead of to the groove diameter of the barrel. So the actual diameters could not make a difference. I wish I had a dollar for every time someone told me what their carefully measured bore and groove diameters were on their rifles and then asked me if they should use a .457” or a .458” diameter bullet. Or better yet, the guys that have spent two years on the internet trying to figure out why they shoot groups the size of a basketball at 100 yards, and the internet experts finally come up with the idea that the riflings were just too shallow and allowing the bullet to strip and not catch the rifling. In the words of old man Scrooge… “Humbug.” Bullet stripping may be theoretically possible, but it is very unlikely in any barrel with soft lead bullets. The only situation most of us would every run into where a bullet could strip would be when the riflings are full of fouling, and the bullet simply glides over the rifling on the caked up fouling in the barrel. It certainly does not matter if the groove diameter is .456, .457, .459, or even larger. Just fit the bullet as explained earlier and you will never know the difference.
Like I said before, what does matter when it comes to barrel quality is that no matter what size or shape it is, it needs to be that size and shape all the way through the barrel. Generally speaking, the more precisely it is the same, the better it will shoot. Tight spots, loose spots, and rough spots can and will cause problems.
At first thought it would appear that a tight spot would cause the bullet to be loose in the bore at some point just beyond that tight spot. In reality the soft bullet will obturate up to fit the bore and, yes, it will squeeze through a tight spot and be minutely smaller. But at this point it depends on a lot of things as to whether the bullet remains undersized or not. The obturation of the bullet is possible for several inches up the bore until the bullet gets up to speed enough that the “G” forces working on it are no longer enough to obturate it to fit the bore. That will depend on the hardness of the bullet, the charge and type of powder you are using, etc. But with the softest bullets and the heaviest powder charges, it may be possible for about 10 inches up the bore. So in reality, the tight spots near the breech may cause the bullet to squeeze smaller and then it may obturate back up to fit the bore in the loose spot, only to be squeezed back down as it enters the next tight spot.
At some point though, the bullet will no longer obturate quickly or not at all and the bullet will be minutely loose in the bore. In my experience, bad tight spots will cause a barrel to shoot badly from the beginning, while lesser tight spots will often times allow fouling to being building up on the bore just forward of the tight spot. This holds true with black powder, small bore and to some extent high power rifles as well. Tight spots are why some barrel manufacturers air gauge their barrels to sort out the good ones from the not so good ones. Other manufacturers only sell the best barrels and find that they do not need to air gauge that bore.
I need to mention that jacketed bullets and smokeless powder will often times work well in a barrel that will not shoot well with black powder and lead bullets at all. That said, if you purchase a rifle that was manufactured with factory loaded ammo in mind and you decide to shoot black powder and lead bullets in it, do not be surprised if it does not work well. Black powder and lead bullets just require a higher quality barrel to shoot better than your average hunting rifle.
I recently inspected a .22 rim fire barrel that did not shoot well even though it was new and from a company known for great barrels. I bore scoped it to inspect for rough spots and found none, so I then shoved a .22 bullet through the bore to get a feel for the tight and loose spots in it and found a series of tight spots in it that were worse near the breech. We fire lapped the barrel with only eight shots and it went from shooting over three minutes of angle to under one. Sometimes it takes much more than that to get them shooting well and fire lapping is something that you can use to mess up a barrel quickly. So please don’t just go running off to fire lap your barrel without knowing how to do it. Many barrels have been ruined that way.
When checking for tight spots in a black powder cartridge barrel such as a 45-70, I push a .454” lead round ball through the barrel with a cleaning rod and it works the same as the .22 bullet pushed through the .22 barrel in the example above. I prefer to hand lap the larger barrels we see on the black powder cartridge rifles instead of fire lapping them as in the .22.
When I check a barrel for surface irregularities, I use a bore scope that allows me to look at the surface of the bore as if it were under a microscope. When I bore scope for rough spots I am looking for scratches and pitting. Keep in mind that very few barrels are ever perfect, especially after they have been in use for a while. Most have some very tiny pitting or tool marks left over from manufacturing the barrel. Most of these won’t make much difference because they will get lost in the lubricant layer on the bore. But if they get large enough that the lube won’t fill them up as the bullet goes by then you will develop a problem at that spot.
A perfect example of this would be if the person that chambered the barrel used a solid pilot reamer and did not keep it clean, but pulled it out to clear the chips, and then pushed it back into the barrel and chips got over the cutting edges. This can cause a series of scratches across the top of the lands just forward of the chamber for the first inch or more. These scratches are almost always deep enough to cause fouling and leading problems because they simply work like a file on the bullet as it passes and create roughness where fouling can build up quickly. Very minor surface irregularities are often not a problem because the bullet lubricant simply lays down a protective layer that is thicker than the irregularities are deep.
Now that I am on the subject of bullet lubricant, I might as well elaborate on that a bit. Bullet lube simply has one heck of a job to do. It must have the ability to be applied to the surface of the bore at the speed of a bullet under great pressures without fail, and lay down a layer of lubricant that is thick enough to allow the bullet to slide across the surface of the bore without allowing the bullet to touch the steel. When the surface irregularities are deeper than this layer of lube is thick, you will run into problems.
A good lube will apply a thin layer of lube evenly to protect the barrel not only from the touch of the lead bullet but also to protect the bore from the flame and heat of the burning powder that is coming down the barrel behind the bullet. The lube I have been using for years was tested many years ago by firing, then catching and inspecting bullets; starting with a clean lightly oiled bore and continuing on with the use of a blow tube between shots.
The first bullet out of the barrel measured .4582”, which just happened to be the same size as a bullet driven in to the bore and taken out for measurement. The second bullet measured .4575”, and the third and remaining bullets measured .4567”. This suggests that after two shots, the bullet lube was not able to build up any thicker, and was wiped away by the next bullet each time. This leaves a working layer of approximately ¾ of a thousandth of an inch on the surface of the bore to protect the bore from the heat and flames of the burning black powder.
Lubrication is simple really. If bare lead touches bare steel, it will begin the leading processing of the barrel. If you take a clean cast bullet and rub it on a clean dry surface like it was a piece of chalk, you will get the idea of how easy it is for lead to be applied to the surface of the bore. At higher speeds and pressures, it is almost like applying solder to the barrel.
If the lubricant layer left behind the bullet cannot stand the flame and heat of the burning powder then the burning powder residue will be applied to bare steel and can stick there and begin the process of fouling a barrel. On the other hand, if the fouling lies on top of a layer of lubricant, then it is easily swept away by the next bullet as it passes.
I mentioned in a previous article about how little lead in the bore it takes to move a shot quite a distance on the target because of how it affects the balance of the bullet. In reality, we seldom see a shot go that far off with the first sign of leading because a rifle that leads tends to lead in more than one place at a time and the leaded spots tend to counter one another to a certain degree, but leading still affects accuracy from the very beginning. Fouling will also affect accuracy from the very first speck for the same reasons, but we generally do not notice the accuracy either one steals from us until it causes accuracy problems large enough to be outside our comfort range.
Now that we have the bullet headed up the barrel smoothly, let’s see what it takes to get it out the end and on its way to the target. In reality, the muzzle of the barrel is no more than the end of a hole and has about the same effect on the bullet. There have been a number of muzzle designs worked up over the years and there is really no best one. I have been asked many times which muzzle design is the best and the answer is about like the one I give when they ask which receiver is best. It really just doesn’t matter.
There have been two tests done that I know of along that line. The first was done over a hundred years ago and the second more recently was done for a bench rest magazine. Both tests experimented with various muzzle designs and found no difference between them as far as accuracy was concerned. Both tests went on to try a barrel that was just hacked on the end. The one from a hundred years ago used a muzzle cut with a coarse rasp at a five degree angle across the face of the muzzle with burrs left in the bore; the later one used a milling machine at a three degree angle across the end of the barrel.
Amazingly enough, the best groups were fired in both cases with the muzzle cut at an angle and left rough. So much for fretting about muzzle design, I guess. In both cases the groups moved on the target in direct relationship to the angle of the cut on the barrel, etc., but they shot fine.
So if you should happen to drop your rifle on the way to the firing line and a big rock creates a burr on the muzzle, just don’t worry about it. It will not affect the accuracy of the rifle greatly because it throws the bullet out of balance exactly the same each time. On the other hand, if your bore has cleaning rod damage at the muzzle, it may affect accuracy because it will have the same general effect as a loose spot in the bore.
Now then, one last thing before we turn the bullet loose. The last effect that the bullet gets from the act of firing is the muzzle blast that pushes against it after it exits the muzzle. The effect of the muzzle blast dies off quickly as the pressure dissipates, but it does actually serve to accelerate the bullet minutely after it leaves the barrel. But most importantly, if the base of the bullet is crooked, the jet blast of the gases react with the angle of the base of the bullet to push the bullet off its intended flight path just a little.
The most common ways in which the base of the bullet can become crooked are: 1) They get cast that way with a faulty mold or a sprue plate that is not fitting right on the face of the mold. 2) They end up that way because of damage during the loading process, or the bullet gets loaded crooked in the case and then obturates out to fit the chamber and bore with the base set crooked. 3) The lube grooves are not full on one side of the bullet and the base of the bullet shoves forward during the obturation process.
So now we are done. I apologize for the length of this article. I started out to make it as short as possible, and yet still touch on everything that I feel is important, and some that aren’t; but it kind of got away from me. There are times when I have told a story when perhaps I did not need to, and other times when I cut a subject short when I could have perhaps expanded upon it some more. I’m sure that when I finish this article it will be too long, but to conclude I want to tell one more little story as a perfect example of why I wanted to write it.
A good friend of mine that has been shooting black powder silhouette for over ten years got a new rifle chambered in 45-90 a couple of years back and started shooting it. He doesn’t get to shoot as often as he likes due to work, etc. So there isn’t always a lot of testing that gets done; just load and shoot. Anyway, after a couple of years of shooting the rifle, he decided that he thought he was shooting better than his rifle was. So he began an extended test period in which he became convinced he was indeed shooting better than the rifle. He went on to test various powder brands and granulations, compression rates, bullets, etc. He set up the chronograph and spent hours tweaking his load until he had his extreme spread down to well under five feet per second and his standard deviation to nearly nothing, but he was still shooting minute of disgusting. He was lucky to keep all his shots on the pig.
To make a long story shorter, all that minutia was not the problem. If it had been the problem, the groups would have improved at some point, but they did not. While discussing it with him, Mon Yee realized that he most likely had a fouling problem as his first shot out of a clean barrel would be a little high, then his second and third shots would be fairly close together and then the group started opening up badly after that. Since Mon has been a part of my experiments for years, he has a good understanding of what I have discussed in this article, and felt certain right off that he knew what the problem was. It is what I call a “fouling management” issue. With black powder rifles there is always fouling, it is just how we manage it that matters.
Mon suggested that he try cleaning between shots with a cleaning technique we have developed for testing purposes, and the groups immediately shrunk to his ability to aim and fire the rifle, meaning a minute of angle more or less. He did not want to clean between shots during competition so we suggested using a grease cookie in his loads between the bullet and his wad. A grease cookie is just a layer of lubricant about 1/16 of an inch thick placed between the base of the bullet and the wad underneath. The grease cookie simply leaves a thicker layer of lubricant on the surface of the bore than the bullet is able to do, thereby helping to make sure the powder residue is laid down on top of a layer of lube instead of burning through to bare steel and sticking. In this case, it was enough to make the rifle perform as it should. With the proper use of a blow tube, he is now able to get fine results with the same loads he shot badly with.
The moral of the story is this…If what you are doing doesn’t fix the problem; then it probably isn’t the problem. Keep in mind that all the minutia is what you do after the basics are taken care of, and not a replacement for the basics. The better you understand what happens inside of the barrel from obturation to exit, the better foundation you will have to build upon when searching for accuracy-related problems.~