There are many things that can affect a rifle’s accuracy; some of them you can fix yourself, but others require specialist attention, says Bruce Potts
Next to calibre or cartridge choice, the subject of rifle accuracy (or lack of it) is the one that most frequently frustrates rifle shooters. It is a problem usually associated with older rifles, as new rifles these days are well made and accurate “out of the box”. However, even the best rifles can go sour.
The rifle is a finely tuned instrument — all the parts need to work in harmony if it is to perform at its best. The cause of inaccuracy could be as simple as a maintenance or cleaning problem, which can be diagnosed through a visual inspection; however, there may be times that a more in-depth investigation by a gunsmith is required.
Here are four things to check.
1. BARREL, MUZZLE CROWN
This is one area of the barrel that takes a lot of abuse from the outside and the inside. Whether you fit a sound moderator, muzzle brake or not, any damage, corrosion or imperfection here will cause problems down range. The muzzle is the last part of the rifle to influence the bullet’s flightpath and any damage, wear or obstruction here is detrimental.
This is one area that I would get a gunsmith to sort out for you. There are tools that use calibre-specific spigots to locate in the barrel muzzle and re-cut the crown, but you can do more harm than good. It is best to get a barrel professionally re-cut in a lathe. While you are at it, get the gunsmith to radius the crown or use a stepped crown to give some protection to the rifling in future.
THROAT: this is the area of the barrel at the chamber end where there is free bore before the rifling begins. Due to the initial movement and obturation (swelling of the bullet to fit the barrel grooves) and immense pressure generated behind the bullet, a lot of problems can occur. Any wear in this crucial part of the barrel will send a bullet down the barrel “out of true” — that is, non-concentric to the bore axis. This cannot be corrected farther down the barrel so inaccuracy will occur, usually noticed as a slow deterioration. Key points to look for are shallow rifling depth in the first 2in to 3in of the barrel compared with the rifling farther up the barrel.
With excessive wear, the bullet can wobble as the pressure behind it builds and it will never move true up the barrel thereafter. If the wear is small and you reload your own cartridges, you can seat the bullets farther out of the case to engage the bullet closer to the lands. But there comes a point when the extra length of the cartridge will not feed through a magazine. If this does not work, there will be no alternative but to re-barrel the rifle.
RIFLING CORROSION / EROSION: this can be found either in certain parts of the barrel or in patchy areas and is due to neglect in maintenance. If the rifle has been used and not cleaned, the repeated deposits of burned powder and then copper from the barrel can trap moisture and combustion chemicals that will eat away at the metal and deteriorate the rifling. One of the main causes of this is the non-removal of a sound moderator after use and then storing the rifle muzzle up. This allows the toxic chemicals and moisture from firing to seep back down into the barrel and start the corrosion process, usually the first 5in or so. The only remedy is to cut the barrel and redrawn but not all barrels respond to a shorter length, so consult your gunsmith.
BEDDING VIBRATIONS: these are the cause of more inaccuracies and barrel problems than many realise. The barrel vibrates as the bullet passes along its length, so it is best to keep that vibration as smooth and uniform as possible. If the barrel is impeded from having a free vibration anywhere along its length it can cause inconsistent harmonics and thus affect accuracy — that is, alter the movement or position of the muzzle as the bullet exits.
Most barrels these days are free-floated — they have support at the receiver end but 90 per cent of the barrel does not touch the fore-end. Check by sliding a piece of paper between barrel and fore-end — it should move freely. If it is touching, that area can be relieved to cure the problem. Some barrels, however, have pressure points to the fore-end, usually at the fore-end tip, to give a small amount of upward pressure, which is normal. Other, older guns are fully bedded along the entire barrel length. When a sound moderator or bipod is fitted, it can alter the weight and recoil characteristics of the barrel, so check that the barrel is still free for the fore-end.
2. ACTION, BOLTLUGS
Many rifles have differing ways to lock up the bolt in the action body or back of the barrel. Regardless which type, it is essential that the lugs mate/locate perfectly to the action to ensure a positive union and thus strength. Many rifles are mass-produced so you will find that bolt lugs only contact with 50 per cent of their area or worse, unevenly. This puts a strain to one side, affecting the firing cycle and ultimately accuracy. This can be cured by lapping the lugs into the action using valve-grinding paste, but it is best to take the rifle to a gunsmith, for whom it is a simple job.
BOLT HANDLE BINDING: quite often the bolt handle will bind on the stock, be it wood or synthetic, and this causes a problem with vibrations on firing. It is simple to sort out by relieving/removing excess material from the binding area so that the bolt moves freely.
CONCENTRICITY OR WARPAGE: some rifles are just made badly. If the action is non-concentric to the barrel — threaded on the skew — or the bore is non-concentric to the cartridge held by the bolt in the action then accuracy will suffer. This is an issue that should only be tackled by a gunsmith. It can also be caused by the bedding block that the action sits on being warped or badly made. This can be removed from the stock and placed on a piece of steel or flat glass; if it rocks from side to side with pressure applied, it is warped, so replace it or have a gunsmith skim it flat.
3. STOCK, BEDDING
This is probably the single most important point to look at if accuracy fails. The way the action sits into the stock is crucial for best accuracy. It has to be rock-steady on firing so there is no movement, which translates into consistent accuracy.
This can be best obtained by a synthetic bedding compound that fills the gap between action and stock to mimic accurately the underside of the action so it sits perfectly true. Materials such as Acraglas, Marine Tex and Devcon can be used, in conjunction with stainless steel or aluminium pillars that offer the perfect solution. These pillars are where the stock screws fit through and support the action so when the screws are tightened they tighten to a set torque and do not compress the stock material.
Do not forget where the recoil lug from the action sits into the stock — it must be square to the lug’s surface with even pressure and benefits from a synthetic bedding compound.
Don’t forget that accuracy can be lost by ill- or loose-fitting accessories such as scopes, sound moderators and bipods. Scope mounts are a problem area where accuracy is concerned. Get the best you can afford for your rifle and do not mix two different types of metal for base and scope rings because they can wear differently under recoil and sloppiness will occur. Scopes do go wrong and swapping one for another instantly detects if accuracy problems lie here. I would certainly use a proper torque screw to fit a scope to recommended tightness, and I always use Loctite for the scope bases so that they do not work loose.
As mentioned earlier, bipods cause different pressures to the stock under firing and this can cause all sorts of inaccuracies if the barrel touches the stock. Similarly, a badly fitted or loose or heavy moderator will affect accuracy. It is best to test with and without one fitted to see if this is the cause of bad groups.
Conclusion – small adjustments can make a big difference to rifle shooting
Some of these techniques are quite simple to carry out, while others are best left to a qualified gunsmith. Very small adjustments or improvements can make a big difference with rifle shooting. Indeed, sometimes the most frustrating cases of inconsistent accuracy can be pinpointed to minor causes that can be rectified relatively easily.