Difference in Ammo Accuracy

Have you ever heard the United States Marine Corps Rifleman’s Creed? It begins; “This is my rifle. There are many like it but this one is mine.” Perhaps you have? If you haven’t, look it up. Marines train as riflemen first and they learn the creed in turn to accept their rifle as a brother in arms so that they will know their rifle so well inside and out that it will become a part of them. While they defend our freedoms with those rifles most of us reading this article simply possess our own rifles for hunting, target shooting, and pleasure. But that doesn’t mean we can’t master our own sporting rifles just like we master our lives as is also written in the creed.

Every rifle is unique in it’s own way. Don’t think so? Just grab the ammo that shoots great in one rifle and feed it through another rifle. Chances are that it won’t shoot quite so great. Each rifle is finicky on what it likes and to get the ultimate performance out of your rifle there’s a lot of things that come into play. This article focuses on ammunition, your rifle’s characteristics and the reasons certain rounds perform better than others do.

First let’s start off with developing test loads. Unless you are extremely lucky and your rifle will shoot tiny groups with factory ammunition, handloading will be the only way to realize your rifle’s true potential. Begin with a trusted reloading manual and follow the data listings within the manual when working up different test loads for your rifle. Know the twist rate for your rifle and what you are trying to accomplish with the round such as big game hunting, or just varmint hunting. Take those things you already know and do your research on where to start with things like bullet selection and powder. Once you’ve picked out a few different bullets and matched them with different powders, primers, cases, etc. you’re ready to test those rounds to see if your rifle likes how they fly.

I like to build anywhere from four to five different loads per bullet selection working my way up in powder charge increments a half of a grain at a time until I hit the ceiling of a safe load. I’ll build three to five rounds of each to test fire for groupings then I move on to a new bullet and or powder and repeat. This gives me anywhere from 70 on up to 100 rounds to fire depending on how many combinations of bullet and powder I choose to try. If none of those are to my liking, I can always change a component and try something different.

We’ll only briefly touch on the reloading aspect, as this article will focus more on the reasons why those test loads succeed and fail. Now let’s get into those reasons a little.

Barrel
The barrel of your rifle holds many of the secrets of success, as does the load that you are sending down it. Barrel length is an important factor in efficiency as it relates to chamber pressure and the expansion of gas. The combustion of powder should all be in the cartridge case. Pressure accelerates the bullet down the barrel because it has no place else to go. Barrel lengths are best at a length that lets the gas expansion be most efficient. As the bullet travels down the barrel, the space behind it is being filled with an ever-increasing gas pressure and at some point the pressure will drop. In excessively long barrels that pressure drops to the point that it can’t continue acceleration against the friction created in rifled barrels. So this is where a powder charge can play a role in affecting velocities with different grain bullets. Bullet weight, cubic capacity of the cartridge case, burn rate of the powder, length of bullet travel, and bore volume in cubic inches of the barrel all play a role in figuring what is called the expansion ratio. Generally speaking however, longer barrels translate into increased velocities under certain circumstance in even though it may be small.

Now let’s describe how the rifling of your barrel affects the bullet. Gripping your bullet to stabilize it, the helix grooves travel the length of the barrel in slow or fast twist rates. If the rifling groves make one complete turn in 10” inches of barrel length it is called a ten inch twist and written as 1:10 for example. The barrel may be any length but it would still have a 1:10 twist. Finding the twist rate for your barrel will help you in selecting appropriate bullet weights for your firearm. A general rule is that the faster the twist rate for a caliber, the longer the bullet you will be able to stabilize. Usually longer bullets translate into heavier bullets as well. The twist rate can often dictate what bullet your rifle likes best because of its ability to stabilize the bullet as it leaves the muzzle. A bullet not correctly stabilized leaves the muzzle with a slight yaw and unbalance. This may be as small as a degree or two but that can have a substantial influence and the yaw becomes more and more severe with the use of mismatched equipment.

Children’s toys such as a top will spin on its axis of just a single point but when force is applied to the outer edge of the top while it is spinning it causes deflection. The same holds true for the bullet as it travels down the rifling of your barrel. Any excessive force applied to the sides of the bullet before it leaves the muzzle causes it to become poorly stabilized in the air and leads to poor groupings and can even cause the bullet to begin to tumble. At the very least it can cause a spindrift as well, which causes poor groupings.

Bullet seating depth and cartridge length also plays a role in stabilization. You want the bullet to begin its journey down the barrel in the correct way. Sometimes a simple correction in seating depth can stabilize the bullet as it enters the lands making for a less bumpy ride.

Barrel harmonics is another variable worthy of consideration when trouble shooting. Every barrel develops harmonic vibrations when a cartridge is fired. The vibration can be described as a shockwave along the barrel caused by the bullet’s rapid acceleration and spin by the rifling. It is impossible to eliminate barrel movement and most gun builders agree that it is best to let the barrel flex. This is why you see free-floating barrels attached to their stocks. The velocity of the bullet passing through the barrel affects the way the barrel flexes so it is important to find a load that delivers a consistent velocity from shot to shot as is possible. These velocity ranges are called the “sweet spot.” So once you’ve found a bullet weight that shoots well, note the velocity as well. You may want to fine tune your final round selection based off of those characteristics.

I like to use a chronograph when shooting test loads. The chamber and barrel of your rifle doesn’t change but the different test loads you’ll be firing do. Using a chronograph shows you if your velocity readings are changing and corresponding correctly with the changing loads that you are shooting. If you see a velocity reading that doesn’t correspond with your load development it may also show in your groupings and can likely be a problem caused back at the reloading bench when creating that individual round or could indicate an expansion ratio problem as described earlier. When this occurs pay special attention to the other rounds you’ve loaded of the same powder charge and bullet type to see if they demonstrate the same characteristics. Chronographs can also tell you if your rifle likes higher velocities of the rounds you’ve built in general or lower velocities.

Be Observant With Load Development
Entire books have been written on the subject of ballistics and handloading accuracy and it would be silly of me to think I could cover it all in one simple magazine article. However, hopefully I can point out some of the things that can be tried to obtain the best accuracy for your rifle when it comes to your handloading. By explaining some of the reasons why your rifle may or may not like certain ammo it may help in eliminating redundancy in your loading or at the very least, help you find ways to make the bullet you want to work perform even when your rifle has shown it won’t shoot the best. If the bullet you desire to use hasn’t shot great initially, go back to the bench and try some different components.

Remember velocity and try a faster or slower burning powder with that bullet than you tried previously. A change in primers can also alter the pressure of the cartridge. Seating depth may be worth a double check and possibly even a slight difference in the bullet type may be worthwhile. If you tried an 85-grain, 6mm bullet with a hollow-point tip for instance and it wouldn’t group well, switch it out for an 85-grain ballistic tip with a boat tail. Just the difference in the bullet may be all it takes. There are so many options of things to play with and switch that it is almost endless.

After you’ve narrowed it down to a few possibilities that look very promising to mass produce for your rifle, go back to the bench and make up several more rounds of each final candidate and test fire them again just to make sure that your initial results match up. This may give you a clearer look at just which combination of bullet and powder is perfect.

Shooting Conditions
Give your rifle every chance to succeed by limiting the variables that you can control when you test fire the rounds you want to try. Shoot when winds are calm so that wind drift has no influence on your results. Shoot from a prone position with shooting bags or a reliable rest or from a solid comfortable shooting bench. Make sure the firearm is comfortable in your hands and that you are relaxed so that your sight picture comes to you easily for each shot. Don’t force it if you are not comfortable or are straining. You’ll affect the potential of the round. Keep your point of aim the same for each test round and remember to control your breathing. Eliminate human error as much as you can so you factually determine how your gun will fire the rounds you’ve created.

Lastly keep a tablet and a pen handy to record the loads you are shooting and the velocities of the shot strings when using a chronograph. If you do pull a shot in human error, record it. Write down the conditions, the distance, the bullet type, powder used and powder weight, primer type, cartridge type, and velocities of each shot so that you can go back later and look at results.

My Testing
To show an example of testing I’ve included some results from a rifle of mine. The rifle is a Tikka Hunter series chambered in .223. I use it primarily for coyote hunting and so it was only natural that I was testing a variety of varmint bullets to get that perfect match. I wanted a round that would have a great terminal velocity combined with supreme accuracy. Speed is not usually a concern for me. I like to let the rifle tell me what it likes instead of trying to force something down it’s throat that isn’t perfect. The coyote usually doesn’t notice if the round was traveling an extra 100 fps faster.
I tried several different bullets including a Hornady 50 grain V-Max, Sierra’s 50 grain Blitzking, 52 grain Match and their 55 grain boat tail along with a Nosler 50 grain Spitzer boat tail. Each was initially tested with different powder charges of Accurate’s 2015 and 2230 powders respectively. Winchester cases were used with CCI small rifle primers. Cases were trimmed to 1.760” and the overall cartridge lengths were 2.235”.

Of those test loads I narrowed down the list to the 50 grain Hornady V-Max against the 50 grain Blitzking Sierra bullets and retested. Each bullet lost some accuracy out of my rifle when pushed by larger powder charges and I found that the lower end powder charges grouped best. The Hornady V-Max loads seemed to perform slightly better in most instances and the best overall load grouping was with 23.5 grains of Accurate powder 2015 pushing a V-Max 50 grainer about 3100 fps and grouping at 0.416”. I seemed to have trouble grouping other loads at under an inch but after shooting several groups, the 23.5 grains of 2015 V-Max bullets showed a consistently smaller pattern. The second best grouping was also 23.5 grains of 2015 powder from a Sierra bullet measuring 0.757. So you can see how the rifle liked pushing a 50 grain bullet down the rifling followed by that particular charge as other powder charge incremental changes produced worse results. The third and fourth best groupings were attained using 24 grains of 2230 powder. Both the Sierra and the Hornady bullet achieved grouping sizes between .0886 and 0.893 with that charge.

Overall I have been happy with the accuracy of the V-Max load I mass-produced for hunting and the terminal velocity of the bullet on coyotes and bobcats. Pelt damage has been to my liking for the most part and most animals stay anchored not necessarily because of the bullet’s great energy as much as my ability to put the bullet where I want it because I’m very familiar with the rifle and the load. Shot placement is more important to me than having a higher terminal velocity of a larger bullet. Most of my shots are on stationary coyotes as I call them in and it has worked well.

To get the most out of your rifle follow some of these steps and try numerous loads. It’s both fun and informational and it provides you with a confidence that can’t be equaled when taking that all important shot at the next game animal in your crosshairs. Give your rifle the best shot you can!