When your accurate rifle suddenly starts misbehaving and spraying the target with patterns instead of groups, don’t panic. Any good rifle that’s gone to the darkside can be rescued.
Here is a checklist on how.
The Bore is Lousy with Copper
The number one reason for accuracy deterioration that I encounter is a fouled bore. The key is to clean it correctly. Just running a few patches with a solvent designed to remove powder fouling does not remove the copper fouling. Metal fouling will continue to accumulate until the rifle begins to shoot poorly.
To correct the problem, you must remove all the copper fouling from the bore, which can take a lot of time and effort.
I can’t say how many patches or how many swipes of the brush will be required to clean any specific rifle, nobody can. If you read something or saw a video of a “system” where “X” number of passes with a patch will clean your bore, you have witnessed the work of a charlatan.
No two rifles are the same and there is no possible way to predict the number of patches needed to clean a fouled bore. It might be four or it might be 400. In this situation, it’s more likely to be the latter.
I have had rifles that I worked on for days and thought I would never get the copper out. There is no way to know how long it will take, but there is a way to know when you are finished. So, keep cleaning until you achieve your goal.
You must use a good copper removing solvent. The key word is good. Not all copper solvents work. I am not going to name names, but I have tried several that claim they remove copper, but failed to do that.
They are nasty liquids, so glove up, use eye protection and lots of ventilation. Follow the instructions with the solvent. They are not meant to be left to soak overnight, but are designed to be used during an active cleaning process.
Use snug fitting patches so they will get down into the corners of the rifling, but not so tight that the solvent is squeezed out of them as they go down the bore.
I often use the next smaller size jag and double up on the patches so the cotton will be thicker and will shape to the lands and grooves better.
The goal is to get to the point where you can let the solvent sit in the bore for at least five minutes and have no blue stains on the next patch through, indicating that there is no remaining metal fouling.
Once it’s clean, remove all traces of the solvent and oil the chamber and bore for storage. Wipe out the oil before firing.
Shake the scope to see if it rattles. If it does, clearly something inside is broken. This is more common than you might think.
Time to send that optic back to the factory for repairs.
Make Sure Scope Adjustments Work
Additionally, you can test your scope by using a laser boresighter with a grid target to make sure the adjustments you are making to your scope's reticle are tracking correctly.
The laser will provide a constant reference point and let you know if those crosshairs are moving up and left when you tell them to.
Most gun shops have a good boresighter and will do this for you.
If your optic doesn't pass the boresighter test, something is possibly broken or loose inside, causing your accuracy problems.
You can install another scope to confirm. It’s only temporarily to help diagnose the problem, so consider borrowing one from another rifle.
If the rifle starts shooting well again, send the original scope to the factory for repairs and return the loaner to where it belongs.
The Barrel Crown is Damaged
The crown is the end of the rifling at the muzzle. A bad crown is probably the second most common reason guns go bad, right behind a fouled bore.
It is the last part of the rifling to contact the bullet before it leaves the barrel. If the end is marred in some way, it can cause the bullet to take an erratic flight. The crown essentially sets the end of the rifling into the barrel so it's less likely to be damaged.
Use a magnifying glass to visually inspect the crown for damage or wear. Run a cotton swab around the crown. Damaged areas will often pull a few fibers off the swab.
If there is any doubt, re-crown the rifle.
Any gunsmith can repair the crown for a small fee. It’s also easy to do yourself with a brass lapping tool and #600 grit lapping compound, available from Brownells.
The Stock Has as Issue
If it isn't the bore, the optic, or the crown, the problem could be in the the stock.
This mostly goes for bolt action rifles. It’s not uncommon for the screws to be loose or the stock to be cracked.
Make sure the action screws are tight. If they are loose, that is likely the problem. If not, pull the stock off the gun and check for cracks or splits.
I struggled for a long time with my custom .280 Ackley Improved rifle. At first the rifle would group sub MOA reliably. Good ammo would always put five shots into .75-MOA. Sometime later the gun started shooting groups twice that size.
I tried everything, including checking the stock visually multiple times. I could never find any problems. Perhaps the third or fourth time I inspected the stock, I noticed an odd shadow. I bent the stock over my knee to stress it a little and a small crack opened up.
I replaced the stock with a new Bell and Carlson stock with an aluminum bedding block. The gun now shoots .75-MOA with Nosler factory ammo and .6-MOA with my tuned handloads.
Check the Bedding
You can check the bedding by holding your fingers on the line where the action and the stock meet. Then alternately loosen and tighten each of the action screws. If you can feel any movement of the action in the stock, the bedding is incorrect and putting stress on the action. With your fingers on the junction you can feel movement that often you cannot see.
If the bedding is the problem, it can usually be repaired by glass bedding the action. Any gunsmith can do that, or if you are a brave soul, it’s a great DIY project.
Check Barrel Float
Also check to see that the barrel is floated, or that it isn't contacting the forend of the stock anywhere. A dollar bill is still the best way to check this.
Wrap the dollar around the barrel and pull the ends up. If it can pass between the barrel and the stock for the full length without binding, the barrel is floated with enough clearance.
Be aware that some stock designs have contact with the barrel near the front. For example, many Remington Model 700 rifles use a pressure pad at the tip of the stock.
If a stock with tip pressure has warped it can really mess with the gun’s accuracy. If you suspect that has happened, remove the pad with a file or sandpaper and float the barrel.
Warping or Swelling
With wood stocks, warping or swelling can be the source of problem. Any wood stock that has been subjected to moisture can cause problems. Remember, humidity is moisture.
The easiest way to eliminate the stock as the problem is to install another stock temporarily on the gun. Don’t hesitate to rob a stock off another gun long enough to test if the issue is the stock or bedding. Glass bedded stocks do not swap rifle to rifle well, but any factory stock, chassis or stock with a bedding block should work fine to eliminate another check mark off the list.
If the stock is the source of the problem, start looking for a new one.
The Barrel is Shot Out
If the rifle is still not shooting well, use a bore scope to make sure the barrel is not shot out, meaning the rifling at the chamber end of the bore has been worn away.
If your accuracy problems came on suddenly, this is likely not the issue. Throat erosion comes on gradually as a rule. But, rules are meant to be broken and nothing is set in stone when it comes to misbehaving rifles.
Many gun shops and gunsmiths have a bore scope. They used to be incredibly expensive, but no longer. Lyman sells one that is very reasonably priced. It's a handy tool to see if the bore is cleaned properly as well, so it's not a bad idea to buy one for your gun tool kit.
Look for serious erosion in the throat, which where the rifling starts, just ahead of the chamber.
If the barrel is shot out and the throat eroded enough to ruin the accuracy, the barrel will need to be replaced.
You can return the gun to the factory. Or better yet, have a gunsmith fit a good aftermarket barrel to your action. It’s a bit expensive, but the results can be outstanding. If he does it right, accuracy will be better than ever.
Still Not Working?
If none of this works, then the issue is clearly demonic possession.
Take the rifle to a priest and have him perform an exorcism.