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#1325331 - 04/29/09 01:27 AM Rifle accuracy
Terry Offline
trapper

Registered: 12/26/06
Posts: 2554
Loc: White Sulphur Springs, MT
Since I have been a gunsmith and custom rifle builder for most of my life, I thought that I would share a little of what I have learned about accuracy with you. Some of it you probably already know. In fact, some of you may know more about it than I do. I simply offer this for what it is worth to those that may not know these things in the hope that they will be of benefit to someone. This is a short work; not an exhaustive study. That would take a book. This is just an article.

There are two primary things to consider; the rifle and the ammo. The skill of the shooter also comes into play, but I have no control over that, so it will not be covered here.
First, the rifle.
For a rifle to shoot with any degree of accuracy, there are several things that must be taken into consideration, so we will start at the butt and work our way toward the muzzle.
The first thing we see is the comb or the cheek piece. This area should be configured so that when you put the rifle to your shoulder, you are looking through the sight/s instead of looking for them. It is almost impossible to get and hold a good sight picture if your head is not resting on the stock. If you are having a rifle built just for you, the gunsmith will take some measurements and build your stock accordingly. If you are dealing with a factory stock, you can shave some wood off or glue on a piece of leather to build it up. Too long or too short? Add a recoil pad or cut some off.
Next thing we come to is the bolt. That is the thing that has a firing pin inside it. It does not have to be a bolt action to have a bolt. Lever guns, semi-autos and pumps have bolts too.
Ideally, the bolt will lock up tight, in line with the bore, and will have a short lock time. Lock time is the time that it takes for the firing pin to go from an unfired to a fired position. The stronger the mainspring and the shorter the distance the firing pin has to travel, the better. Some of the hammer guns have to have the hammer travel an inch before even contacting the firing pin. This results in a long lock time. Some of the WW1 bolt action military rifles had lock times almost as long because the firing pin traveled so far. More modern guns, like the Ruger 77, the Remington 700 and the Sako have very short lock times. This means that the rifle comes closer to firing when your intend for it to fire. This gets really important when you are wobbling around and trying to shoot offhand.
While we are looking at the bolt, we also need to look at the locking lugs. On the ones with the fast lock time, the modern bolt actions, these will be visable as opposing lumps of steel on each side of the bolt face. They are called locking lugs because they lock the bolt in a closed position when the rifle is fired. After firing, you lift the bolt handle to unlock the lugs from the lug recesses and draw the bolt back to eject the spent cartridge.
You would think that these two lugs would lock up equally, but on a factory gun that is seldom the case. It is far more common to find a rifle where only one lug is taking all the strain when the rifle is fired. This allows the bolt to flex and throw the round out of perfect alignment with the bore. The solution is to pull the barrel and lap the lugs with valve grinding compound until you have good contact on both lugs. If much metal is removed, the headspace may become excessive, causing the barrel to have to be set back to correct the headspace problem. Some of you are now wondering what headspace is, so I will tell you. Headspace is the space between the bolt face and the cartridge case head when the bolt is closed. I always tried to keep it within .002" when fitting a barrel, but most factory guns will be around .006". It does make a difference in accuracy.
Next thing is the bolt face. It should be at a right angle to the bore, but again, on some factory guns you will find the bolt face at eighty-five degrees instead of ninety. Again, this allows the round to flex and not only affects accuray but the life of the brass cartridge case.
Assuming that the bolt is all square with the bore, we now look at the trigger. Bad triggers probably cause more misses than any single thing where accuracy is concerned. The Savage 110 had the most miserable trigger ever known to man until they got smart and went to the Accutrigger. The most miserable trigger award now goes to Ruger. They build a fine rifle, but their triggers stink. Fortunately, a good gunsmith can do something with a Ruger trigger, which is more than could ever be done for the old model Savage. Remington and Sako have good adjustable triggers, and there is no reason to walk around the woods with an eight pound trigger on your rifle when you can have one with a two and a half or three pound trigger at little cost or effort.
That pretty much covers the action of the rifle except for the bedding. Bedding means how the metal fits into the wood. It has as much to do with accuracy as the trigger.
If you take the average bolt action rifle apart, you will find that there is a metal lump hanging down from the front of the action. This lump, called a recoil lug, fits into the stock material (Wood, fiberglass, plastic, etc.). The fit should allow no movement of the metal in the wood when the rifle is fired. If there is movement, the bullets will strike differnt places on the target, if they hit the target at all. It is almost impossible to carve a stock or mold a piece of plastic so that the stock will perfectly fit the metal. When the fit is not perfect, the metal will move from shot to shot. The solution to this problem is to glass bed or epoxy bed the stock so that it fits perfectly to the metal. This assures that the metal is in the same relationship to the stock on every shot, and you have eliminated one of the biggest causes of inaccurate rifles.
There isn't much you can do about the chamber without getting help from a gunsmith, so now we go to the bore of the barrel.
First thing we want to do is make certain that it is clean. A fouled bore can really mess up your accuracy. I usually start with a good copper solvent. I wrap a patch or a piece of paper towel around a worn out bore brush and dip it in copper solvent. Working from the breech, I swab the bore a few times, then let it set a few minutes. Following that, I swab it out, running patches through it until I don't get any more green guk on the patch. I follow this with a liberal swabbing with Marvel Mystery oil, and let it set a while. I have found that most copper fouling will be in the front half of the barrel, and most of the powder fouling will be in the back half of the barrel. Either one will ruin accuracy. The Marvel Mystery oil gets under the powder fouling and loosens it up so that a good bronze brush can scrub it out. If any fouling remains, I go to a tight patch covered with J-B Bore compound and get the cleaning rod running in high gear.
If you have fired hundreds of rounds in this barrel, that is about all you need to do or can do to help the bore. If it is a new bore, now that you have it squeaky clean, run a tight patch through it. If it goes from one end to the other smoothly under the same pressure, you have a fine bore or your patch is too loose. If you try to maintain the same forward pressure on the rod and find that there are places that it runs smoothly and other places where it is harder to push, then you have a bore with tight and loose spots. This is almost normal with a factory barrel. It means that as the bullet travels down the bore, it is being squeezed down to fit the tight spots, which of course means that it no longer fits the loose spots. This too hurts accuracy. The solution to this problem is to lap the bore until it has no tight spots and the bullet can ride the rifling as it is supposed to. This can be done by fire lapping, or by using a lead lap.

Next thing to consider is the barrel contour. I have found that most bull barrels and heavy or medium weight barrels shoot best if they are free floated. That means that the barrel does not touch the stock. On a free floated barrel, you should be able to slide a piece of notebook paper between the barrel and the stock from the forearm to the action without having the paper bind at any point.
On lightweight barrels, I have found it usually helps accuracy to put a little glass bedding under the barrel right at the fore end. If you have a light weight barrel and want to try this, loosen your front guard screw just enough to slide a business card under the forearm, then tighten the screw and shoot a group to see if fore end pressure will solve your problem.
Other things that can affect accuracy when it comes to barrels are barrel band swivels and barrel bands with upper hand guards like most military rifles have. Not much you can do about that if you have a lever action 30-30.
Final thing on the rifle that can ruin accuracy is the crown. That is the front of the barrel where the bullet comes out. This area has got to be ninety degrees to the bore and free of burrs.
I have had some guns come in that had half the crown worn off from riding the muzzle on the sandy floorboard of a pickup truck. The owner can never figure out why his gun quit shooting where it is supposed to. I cut off a half inch of barrel and recrown it and they think I am a gun fixin' wizard when they shoot it. I have seen some of them so bad that the sand had vibrated the rifling out of the first half inch of the bore.
That is about it for the rifle. Keep all your measurements to a minimum, keep everything in a straight line, keep the bore clean, and you are half way to having an accurate rifle.
The other half of the accuracy problem can be solved by having the right ammunition.
That, to me, means loading my own. I know that some guy somewhere has a factory gun that shoots factory bullets and they all go in the same hole. That happens sometimes, but it is not the norm.
Every barrel vibrates as the bullet travels down the bore. This vibration does not follow the bullet down the bore, nor does it travel ahead of the bullet as it goes down the bore. Odd as it seems, the vibrations will travel up and down the barrel several times as the bullet goes down the bore. The secret to accuracy, therefore, is to develope a load that has the bullet leaving the muzzle when the vibrations are at the breech end of the barrel. When all other things are right with the shooter and the rifle, and the group is all over the target, you can bet that the bullet is leaving the barrel when the vibrations are at the muzzle.
These vibration patterns can change with the diameter of the barrel. They can change with the length of the barrel. Thay can change with a change in powder or bullet or velocity or even the brand of primer. That is why no factory cartridge can fill the bill for every rifle. For the best accuracy, you need to custom load for that one particular gun.
Youwould be amazed at what a difference three tenths of a grain of powder can make in the size of a group, sometimes cutting it in half or making it twice as large. Considering that there are seven thousand grains in a pound, you can see that a very small difference can make a major difference in how your rifle performs.
If you find this hard to believe, take any cartridge, pick an appropriate bullet, powder, and primer, and start working up loads. Say your loading manual says start with fifty grains of powder and top end is fifty-two grains. Just to be safe, you have always loaded fifty-one grains. Trying to stay in your comfort range, we will now load four rounds at 50.5 grains, another four at 50.8 grains, another four at 51.1 grains, four at 51.4 and four at 51.7 grains. We go to the range, taking our cleaning rod along, and we shoot one fouling shot, followed by three for the record. We then clean the bore and repeat the process with each of the five samples. I will guarantee you that within those five samples you will find one that outshoots all the others. That is the one you want to work with.
When you have found that magic load, then you start to tweak it a little. You weigh your bullets and you find that they can vary by three tenths of a grain, so you sort them into groups by weight. Then you weigh your brass and find the same thing to be true with it, so you sort it by manufacturer and by weight. For hunting purposes, these last two may not make a lot of difference, but they will make some, and it will be for the better. When you think that you have the best load for your rifle, play with the seating depth of the bullet. Most rifles will shoot best when the bullet is within .010 of the lands. Sometimes you can seat the bullet that far out and sometimes you cannot, depending on how it fits in the magazine and how it feeds. Finally, you try different primers to see if they help you or hurt you.
When you have done all this to your rifle and your ammo, you have as accurate a gun as you are likely to have without buying another one.
Being retired, I don't use this infomation much any more. I hope some of you find it helpful.
Terry


Edited by Terry (05/04/09 12:16 AM)
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#1329768 - 05/03/09 12:05 AM Re: Rifle accuracy [Re: Terry]
45/70 Offline
trapper

Registered: 12/23/06
Posts: 3847
Loc: Georgia
I may have missed it, but the barrel needs to be fitted 90 degrees to the reciever.
45/70,

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#1330789 - 05/04/09 12:20 AM Re: Rifle accuracy [Re: 45/70]
Terry Offline
trapper

Registered: 12/26/06
Posts: 2554
Loc: White Sulphur Springs, MT
You are correct Sir. Like the locking lugs, you would expect the receiver face to be true, but that is seldom the case.
Probably just one of many things I missed mentioning.
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