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The crown of a barrel is the "edge" where the bore
meets the end of the barrel. Uniformity of the crown is important to the
accuracy of the airgun. An uneven, or damaged crown will allow the
high-pressure gasses pushing the pellet down the barrel to escape
unevenly. At the moment the pellet leaves the bore, this will
push the rear of the pellet in the direction of the escaping gasses.
Furthermore the portion of the bore still in contact with the pellet will
cause drag which will add to the affect of the gasses. Any deviation in the
shape of the crown will cause this to happen with varying degrees of severity.
1 Metal Ball Bearing
The ball must be larger than the bore. A screw
with a ball style head can be used if you are using a power drill
or drill press. A suggestion from Rogue Possum is to use 3/8 inch
sling shot ammo as the polishing tool. You can even chuck this in
a drill or drill press to accomplish the task quicker.
Metal Polishing Compound
Two different grits will allow you to rough out
the large imperfections and then put a fine finish on afterwards
(example #120 grit rough, and #280 grit fine).
1 Pellet
This is used to block the bore of the barrel and keep
grinding compound from going farther down the barrel than necessary.
A Wooden or Plastic Rod
This rod will be used to remove the pellet from the end of the bore.
The rod must be able to fit inside the barrel and be longer than the length of
the barrel.
Magnifying Glass (optional)
This makes it easier to inspect the initial condition
of the crown and check on the progress of your work.
Cleaning Supplies
You will need some paper towels, cotton swabs, and standard
bore cleaning supplies
Procedure
Conclusion Once the crowning process is complete you may have to sight your
gun in again. It is common for the Point of Impact to shift after the crown has been
re-ground. Depending on the initial quality of the crown you will see varying degrees
of improvement. This is only one method of recrowning a barrel. You can use power tools to speed the process. There are dedicated tools that are made specially for recrowning barrels. You can also have a gunsmith perform the operation for you. When done correctly, recrowning a barrel can be one of the greatest improvements in accuracy. Fill out our Feedback form by Clicking Here Please take a moment to provide us with some feedback.
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It is important to inspect the crown so that you are familiar with it's
irregularities. Once you have identified the irregularities
you can plan on how you are going to remove them. It will be easier to inspect
the crown if you use a magnifying glass. If the crown is out of center it may help
to mark the end of the barrel to show the point where the crown is closest to
the bore. If the crown is damaged, you may also want to mark those spots. A fine
point permanent marker works well for this.
Push the pellet into the muzzle of the barrel with the skirt
of the pellet towards the crown. This will
keep the polishing compound from getting too far down the bore. Be careful
not to push the pellet in too far. The closer to the crown, without
interfering, the better.
Begin the rough grinding by making sure that you know where the grinding needs
to take place. Once you are orientated coat the ball with rough grinding
compound. Start grinding away the existing crown. During the grinding
process be sure to use the entire surface of the ball. If you do not constantly
rotate the ball it can be ground to the shape of the crown. This will
affect the final outcome of the process. Check your progress often.
It is better to go slow than have to undo damage. Whenever the gritty feeling
stops you will need to add more grinding compound to the ball. Once you have
the new crown shaped and uniform you can move on to the finishing stage.
Clean the grinding compound off of the front of the barrel.
Using the paper towels and cotton swabs remove as much grinding compound as
possible so the bore will not be damaged during
the normal cleaning. Remove the pellet from the barrel using the wood or plastic
rod, forcing it out from the chamber end of the barrel. Clean the barrel
thoroughly to remove any residue that may be left behind from
the grinding process. Once the barrel is clean, install your freshly crowned
barrel back on the airgun.