An accurate rifle will have a blueprinted (trued) action,
properly fit barrel with a concentric crown,
trigger job, good bedding,
and quality ammunition made to match the chamber.
The following suggestions are developed from many years of experience as a full time professional gunsmith. Maybe more important is our experience in shooting and hunting. The idea is to give you an overview of what it takes to build an accurate hunting rifle. If you are looking for bench rest magic that requires lots more time and money than the suggestions below. I have never seen an animal that was impressed by sub- quarter minute of angle groups, have you?
Action tuning (blueprinting) is the process of making all the parts that make up the action square and true to the bore. First the locking lugs of the bolt must be lapped to insure even solid contact with the locking surfaces in the receiver. When finished the lugs should have equal contact area and contact should exceed 80%. This is accomplished using professional lapping compounds which produce smooth even surfaces.
Once the lugs are lapped, it's time to face the receiver.
At right are examples of why facing the receiver is necessary. The
light areas visible should make a symmetrical circle around the recoil
lug. Because this action was not properly squared the barrel did not seat
square to the barrel. The dark area are the places where the bluing salts
were able penetrate gaps between the barrel and the receiver. Just
in case your curious, this lug is perfectly square. We see this on nearly
every brand of action, although it does vary in degree.
To resolve this problem, a precision mandrel is inserted into the action to hold it true to the axis of the bore. The mandrel and action are then placed on the lathe and a small amount of material is cut off the front of the receiver where it will contact the shoulder of the barrel. Only enough material is removed to square up the front of the receiver, so no strength is lost.
Then we insert the bolt in the action and measure from the receiver face down to the bolt face. We hold a standard for the bolt face of plus or minus .0005 inches across the face. If this standard is held along with the facing of the receiver and the lapping of the lugs, sub minute of angle groups will result. In cases where the bolt face does not meet this specification we use a precision mandrel and a steady rest to hold the bolt in a lathe to face the bolt face square.
Barrel Lapping is available for new barrels upon request. Lapping the bore can offer more uniformity, velocity, and accuracy. This process removes the small burrs and marks left in the bore from the machine process. It also polishes the bore, which reduces fouling. A side benefit is that, there is little or no break in for a lapped bore. Which saves lots of time, money, and tedious cleaning. We now offer "Montana Rifle" barrels which are hand lapped. All the top match barrels are lapped, Hart and Lilja are two examples.
Barrel fit is the next consideration. The barrel must be set up on the
lathe so that it is centered perfectly on the bore. Centering the
barrel on the bore insures that it will be mounted squarely in the
action. The shoulder will be exactly 90 degrees to the bore and the
threads will be concentric to the bore, all essential to accuracy. Equally as
important is the crown. It also must be concentric to give best
accuracy. Over the years we have tried many styles of crowns at
many different angles to the bore. Some work better than others
but the bottom line is always the same, if it is concentric it will be
accurate. More about barrel jobs.
Cryo Treatment can improve accuracy. Our clients report reduction in group size of from 30 to 50%.
Trigger jobs can do more for accuracy than you might think. These days the factories are shipping guns with trigger pulls of five to eight pounds. To add insult to injury they include lots of sear engagement (shooters call that 'Creep'). Winchester and Remington triggers can be stoned and adjusted to good hunting weights. There are aftermarket triggers available for most actions these days. Pull weights with these triggers vary according to the manufacturer and or model chosen. Group size can be greatly reduced by a good trigger, just ask a bench rest shooter.
Bedding varies a little from one action to the next. The best method
is to free float the barrel and bed the action. This can be
accomplished a few different ways. H-S Precision offers a line of
stocks that have a milled aluminum bedding block which takes care
of bedding, some tuning can make the H-S system even more
accurate. The other options are pillar bedding and glass bedding.
Pillars are made from metal usually aluminum, the purpose is to add
a support to the stock so that it cannot be crushed by the action
screws. The pillars also add stability to the bedding job. Glass
bedding is the most common method used. Fiberglass and epoxy are
used to bed the action of the rifle. This adds stability and protection
from humidity. Proper bedding requires an understanding of the
pressure points of the action and the methods that will provide the
best support and results. A good bedding job will improve
accuracy.
Quality ammunition is a product of good reloading skills and tools. There are many makers of reloading dies. Quality varies widely from one manufacturer to the next. All will work to produce usable ammunition. Accurate ammo requires better quality dies. Just like the rifle, the dies must be concentric in order to be accurate.
Think of it this way, if you were to draw a 12 inch
long line on a piece of paper with a ruler held
firmly down you will get a single clean line from
end to end. What happens if you stop every inch
and pick the ruler up, replace it on the paper, and
continue the line? Likely no matter how careful you are the line will
not be perfectly straight. When we reload ammo we are picking up
the ruler with every component used and with every process
executed.
Each component must be as concentric and accurately made as possible. This is why you often hear reloaders talk of using brass from 'one lot,' it provides uniformity. Primer pockets must be the same depth from case to case. The primer must be seated to the same depth on each case. The cases must not be bent, some dies will actually bend the neck of the case. Powder charges must be carefully weighed so that each charge is the same as the last. Good quality bullets must be used, if they are cheap there is usually a reason. Care must be taken when seating bullets not to bend the case in the die. Conventional bullet seaters will often bend the neck because the bullet is not held concentric during the seating process. Inline bullet seaters will solve this problem. The idea is to hold the case and the bullet concentrically while seating the bullet. The last consideration is seating depth, here again uniformity is the name of the game.
Seating depth is established best by using one of the commercial devices available on the market for this purpose. Once the seating depth is established start by seating your bullet .050 inches off the lands. Do some shooting to find your most accurate powder and charge. Once you have located a good load varying the seating depth will help tighten the groups. Start by seating the bullet deeper by an additional .010 inches at a time. Fire test groups, when you find the best group sometimes adjusting the seating depth by .005 inches one way or the other will tighten the group even further. Best accuracy usually occurs between .050 and .080 inches. On rare occasion seating the bullet closer to the lands will be more accurate.
I often hear shooters talk about seating out the bullet to touch the lands of the barrel. Bench rest shooter get away with this practice because they are normally loading at relatively low pressures. Conditions for bench rest shooting also allow the shooter to spot problems that a hunter could easily miss in the field.
Seating to the lands is OK for forming brass but is dangerous in hunting situations, as bullets can stick in the throat when extracting live rounds. Also pressure spikes can occur if the bullet is touching the lands. Testing had proven over and over that a bullet seated touching the throat can raise peak pressure by as much as 8000 PSI, that is substantial! Better consistency and therefore accuracy will come from bullets seated away from the rifling lands. Never seat any closer to the lands than you have to to achieve accuracy.
This is by no means a complete description of
loading techniques, tools, or processes. I suggest
you look to other sources such loading manuals
from the various manufacturers of components.
They offer a wealth of knowledge that many shooters overlook. If
you are serious about accuracy you should be reading Precision
Shooting Magazine, or Accurate
Rifle 
tell them we sent you.
Email Z-Hat for an accurate Barrel job
for your hunting
rifle: Rifle.Builder@z-hat.com
or go to our Custom Rifle Barrel Quote form.
|
Born on:
August 25, 1998
|