Rifle Tuning

1995
By Dave Reed

Before we delve into specifics I would first like to give you an idea of what we are trying to accomplish. There are a lot of things that must work together for a rifle to shoot straight. Basically, in order to get a bullet to fly straight we must first get it out of the barrel straight. That is what this section deals with. For all examples we will assume we are talking about a bolt action rifle. Specifically, a Remington, Model 700, bolt gun.

The rifle has 5 basic parts. They are:

  1. Barrel
  2. Action
  3. Bolt
  4. Stock and
  5. Trigger Group

Barrel

The bullet must come out of the barrel straight. An important concept is the "centerline" of the barrel. This is an imaginary line running right down the center of the barrel bore. We want the centerline of our bullet to match the centerline of the bore. The chamber is reamed into the breech of the barrel. The chamber also has a centerline and it must be the same as the centerline of the bore. Stock rifle barrels are usually pretty good. But for our purposes lets assume price is no object. We want to start with a high quality barrel. Schneider, Krieger, Douglas and others all make match quality barrels.

When a bullet passes down a barrel the barrel goes through a whipping action. The longer and/or thinner the barrel the more it will whip. Benchrest shooters have long held for a shorter and very thick barrel. Lately the trend is toward a little longer barrel with fluting. I can't pretend to be an expert on all aspects of barrel making. Call the people who make accurate rifles (list enclosed) and see what they think. Let's assume though that we want a very thick barrel in the 20 -22 inch range. Fluting a barrel means cutting grooves in the outside of the barrel. They must be equidistant around the barrel and must be cut very precisely. Fluting a barrel changes the internal dimension and can put stress in the metal. If I were to buy a fluted barrel it would be one made by an expert who will take the time to do it right, and stress relieve the barrel properly. Fluting does three things, increases stiffness, reduces weight, and improves cooling (because there is more surface area exposed to the air). Zareh Ohanian - two time winner of the Canadian Sniper Competition, taught me a pretty slick trick that would be a lot cheaper than fluting. Most of you are should be familiar with a process called "bead blasting". It is used extensively in repair shops to clean metal parts. It is not as destructive as sand blasting. Bead blasting is usually done in an enclosed cabinet. The cabinet's hopper is filled with glass beads and high-pressure air and beads are forced through a nozzle -- just like sand blasting. Zareh reports that initial testing showed that a bead blasted barrel cooled faster than a fluted barrel.

I do have some experience with bead blasting, though not on rifle barrels. Glass beads actually remove very little metal. To verify this, bead blast a piece of stainless steel. Before you do it, measure the surface profile of the metal using a profilometer. Imagine dragging a needle across the surface of a record. The record is rough enough that you can feel the needle's vibration as it runs across the grooves. Profilometers measure the roughness in a similar manner, and record the surface finish on a chart. An old measure of roughness, "rms", is an average of the recorded difference between high spots and low spots. (A scratch is a "ditch" in the metal, with high edges and a low bottom.)

Bead blasting knocks tiny dings and scratches in the metal. Just as big grooves (flutes) on a barrel increase surface are, 10 billion tiny microscopic grooves do the same thing. I believe that the roughness increases the surface area of the barrel slightly more than the big grooves!

WARNING: Knowledgeable engine builders never bead blast internal engine components. This is why: those beads are so small that you will never get all of them out. Many are actually embedded in the micro scratches of the metal's surface. They will work loose, get into the engine, score cylinder walls and worse, bearing surfaces. This can cause early engine wear, or at high rpms (like a racing engine), catastrophic engine failure. What do you think will happen to the inside of your barrel when beads are trapped between a bullet and the bore? If you choose to do this to your stainless rifle barrel, do a VERY good job of sealing the barrel at both ends before you do it. After blasting, carefully scrub clean the barrel before you remove the seals. Keep your rifles stored in a different building than the cabinet.

Now while we are on the subject of slick tricks, I'll tell you one I have been thinking of but have never tried. You will need to locate a shop that does "electropolishing". Electropolishing does the opposite of bead blasting, it removes high spots. The metal is submerged in a weak acid mixture. An anode is placed next to the surface of the area to be polished. The ground is attached to the metal itself, and the positive is attached to the anode. Electrolysis causes the tiny ridges to dissolve into the solution. Now here is the idea, for an anode could you not use a tightly strung thick wire/rod running down the centerline of the bore? It would be shielded from the barrel using plugs similar to the buttons used to align cleaning rods. They already make electric bore cleaning systems, could not one of these be adapted to perform electropolishing? This process should make the bore EXTREMELY slick if done properly. Electropolishing removes only traces of metal, and would not change the bore diameter any at all.

The transition area between the chamber and the rifling is called the throat. The bullet will move out of the case neck and move down the throat until it hits the rifling. We will want to make this dimension long enough for our bullet to fit without touching the rifling. If we jam the bullet into the rifling it may stay there if the round is ejected. Also, there is a potential for dangerously high pressures if the bullet is in contact with the lands. The lands are the raised surface of the rifling. If our throat is too long, our bullet will have to float farther before it comes back under control by the lands. Keep in mind that if the bullet floats it will probably start down the barrel a little off-center. We want our bullets to be as close to the lands as is safe. This is usually .003 - .005 of an inch. You may have heard someone say they can't make their rounds long enough to get close to the lands and still fit in the magazine. In that situation, the throat is too long. I have heard many say that the cartridges like the .220 Swift and 7mm Remington Magnum are hard on the throats. This is because there is a large amount of powder burning (heat) at the throat area. In the 7mm RM the problem is more often found in Auto-Loaders (like the BAR) where the owners have engaged in rapid-fire practice. The 220 Swift is just a bad ass cartridge! I think the heat and velocities are enough to burn out the barrel and throat even if the owner is careful and cleans the barrel properly. Beware used .220 Swifts! I have never owned one and I'm only repeating the advice I've heard often from others. They are rumored to have a very short barrel life. (If there are any experienced Swift -O-Philes out there who would care to elaborate on or contradict this assertion I'd love to hear from you.) But I digress.

Zareh also adds that new barrel steels have largely solved the .220 Swift problems, letting the barrel cool between shots, and proper cleaning. Now before we go on lets consider something else. The barrel is threaded into the action. In the factory the machines that thread barrels and cut the threads in actions are different. Each machine cuts the same size threads a little different. Each barrel threaded on the same machine will be a little different because the tooling is being dulled. If we want our action and barrel to fit perfectly we need to have the threads on the barrel cut to match the threads on the action. Machinists call this "chasing" the threads. If I were to spend $1,000 dollars or so on a barrel, I'm not sure I would want someone else cutting threads on it! The preferred method would be to have the barrel guy do the entire fitting. This is not something most people can do in their garage. Good barrels can be had already chambered for $250 - $500 dollars. Add to this the cost of fluting, bead blasting, cryogenic treatment and fitting, and you are getting close to $1000 worth of barrel.

The Action

A good action has a number of important qualities. The action must be rigid. Because, its face fits against the barrel, the face of the action needs to be perfectly square, if the barrel is to fit perfectly against it. The spacer between the barrel and action needs to be milled perfectly flat also. On the 700, this is the only change I know of that really needs to be made. Be careful when using actions other than the Remington. The Savage is pretty good, but the Winchester is rumored to be overly flexible.

Rifle Chamber
A = Face of action, B = Throat, C = Bolt face (Note: Spacer between action/barrel omitted).
Bolt

Now that we have a perfect barrel fitted perfectly to a square action we need a square bolt. On the 700 the bolt has two locking lugs. These lugs lock-up at the 12:00 and 6:00 positions. If the locking lugs do not contact the grooves evenly, when a round is fired the case will move up or down in the back. This of course is a very slight movement, but it is enough to start our bullet out on a crooked path. "Lapping" the lugs, means polishing the one or both lugs so that each will lock up with the same "0" clearance in their grooves. The base of our cartridge rests against the face of the bolt. If the face of the bolt is not perpendicular to the centerline of the chamber, the case can move in whatever direction the face is canted. We must then have the face of our bolt ground perfectly square. The tolerances we are dealing with are on the order .001 - .005 of an inch. This is best left up to people who have the precision equipment to cut and measure things this close.

Stock

When the gun fires we do not want it moving around in the stock. If the barrel touches the stock anywhere past the first 1 -1/2" from the action we will have a problem. The stock must be relieved until the barrel floats freely over it. Bedding is the term used to describe filling all voids in the stock next to the action. This provides a strong smooth surface for the action to bind tightly to. Accuracy International has designed a sniper rifle for the British Army that needs no bedding. The action is attached to a steel skeleton that the stock clamps to with bolts. This rifle is also being built under license at the Gunsite Training Center in Arizona. Word has it that all of the current production run is already spoken for.

Bedding an action using Acra-Glass and aluminum powder is pretty easy to do yourself. You may want to try it first on an older/extra stock first. This is how I do it. Take some fine powder like carpenter's chalk and very lightly oil the all of the outside of the action -- anywhere contact with the stock is likely. Now dust the action with the chalk. You want a very light coat of dust all over the parts that may come in contact with the stock. Now fit the stock carefully and tighten down. Carefully remove and observe where the action touched. Anywhere the chalk is light or non-existent is a void that needs to be filled. Now instead of just smearing in the acra-glass as is, it is a good idea to hog out the stock everywhere you have enough material to work with so you can put a lot of filler in. You will not have to worry about the filler being so thin that it doesn't stay put. A Dremel tool is good for this job. You need to pencil the outline of the action on the stock so you know where to cut. I have always bedded out to the first 1-1/2 " of barrel.

Follow the instructions on mixing the glass and aluminum powder. Don't get cheap and do it without the aluminum. Acra-Glass comes in a kit that includes this blue stuff that you apply to the action to keep it from sticking to the glass. Do a very good job on this part! After you lay in the filler press the rifle back together and tighten. Be careful not to get filler where it can get into the trigger group! Let the stuff set and after it's almost hard, remove the action. Trim off the excess and let it dry completely. Now you clean the action and you have a bedded rifle. Follow all kit instructions completely and you should not have any problems.

McMillan Fiberglass Stocks, Inc. is the world's premier synthetic stock manufacturer. Consider that McMillan has supplied over 1,000 stocks to the military and federal agencies for use in sniper systems. All spec-ops unit's use the McMillan stock, as does the USMC.I had the pleasure of meeting the McMillan family at the SHOT Show '96 and was most impressed by the quality and variety of their product line. If you have ever wondered what the difference is between a McMillan and "all the rest", you really need to take a look at both. The difference is obvious, even to a novice.

Trigger Group

I don't think I'm going to go to deeply into this for a couple of reason. First of all I have always had someone else do my trigger work. There is a reason that most sane people recommend pulls of AT LEAST 3 pounds. Any less and the chance of an accidental discharge becomes a very likely possibility. "Set" trigger systems are triggers that require two stages to pull. The first stage sets the trigger. Then the trigger can be set to a very low pull. Target shooters have been known to set theirs in ounces, not pounds. Of course, you would not set the trigger until you are certain that you are ready to fire. Many factory rifles now come with pulls set around 7 pounds. It is almost impossible to shoot accurately with the pull set that high. The pressure you must exert on the trigger to fire the rifle is so great that it moves the muzzle too much. (See section on basic marksmanship). I do recommend that you have your trigger set by an expert. I do not mean the guy down the street whose main work includes recoil pads, cold bluing, and cleaning. Find someone who does a lot of this so your trigger and safety will be safe for you to handle.

References

Gunsite Training Center
PO Box 451
Paulden AZ 86334
ph.(520) 636-4104.

Schneider Rifle Barrels, Inc.
Dept GA
12202 N. 62nd Place
Scottsdale, AZ 85254

McMillan Fiberglass Stocks, Inc.
21438 N. 7th Ave, Suite E
Phoenix, AZ 85027



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