Air Gun Home :: View topic - Barrel re-crowning methods

Admin · Site Admin

The idea behind barrel re-crowning is to improve upon most air guns quick/cheap mass-produced production techniques which often results in a poor crown. A poor crown generally results in a gun that shoots off-center as the pellet gets hung-up on the barrel tip as it exits, pulling it to one side or another.

Barrel Re-crowning

By Larry Durham

Materials

1- 5mm-7mm roundheaded brass screw depending on caliber ... use screw head dia slightly larger than caliber.

1- Gram very fine lapping compound (I use JB Bore Paste, but Toothpaste can work too).

1- Magnifying glass, 4-10X

1- Electric Drill

5 -Airgun pellets

Directions

1. Insert an airgun pellet into the muzzle and push it in with a pencil to a depth of 4mm.

2. Chuck the brass screw in the drillmotor or press chuck, setting the rpm a the slowest speed if possible.

3. "Charge" (gob some on) the screwhead with lapping compound.

4. Very lightly engage the screwhead against the crown area of the muzzle and start the motor.

5. Using a rocking, rotating motion, lap the crown until a slight ball-shaped depression is lapped into the crown. Rotate the barrel 90 degrees every few seconds during the lapping process, all the while "rockin" the screw head or barrel to maintain the round shape of the screwhead and distribute the lapping action across the entire screwhead surface.

6. Check your progress every 50-60 seconds by wiping the crown clean and examining the edges of the rifling lands where the meet the lapped crown surface. When there is a perfectly even, sharp margin on every land and groove as it meets the crowned surface you are done. If it becomes obvious the original crown is so deep and ragged the lapping is not effective the barrel must be carefully filed or machined back to eliminate all or most of the original crown before lapping (only expert metalworkers should perform this phase).

7. Push the pellet out of the bore from the breech end and clean the barrel (from the breech of course).

8. Testfire ... it is not uncommon for the Zero to shift, this is nearly always a sign the original crown was bad, and accuracy will improve.

Notes (added by Administrator):

If you don't have access to gunsmithing materials like bore paste- automotive valve lapping compound works great.

Magnifying glass not needed if your eyes are decent.

Putting a pellet in the barrel isn't required- a cleaning pellet works A-Ok or even some paper towel pushed in (gently) to plug up the bore. To get it out again you need to use a compressed air source (i.e. compressor) to blow it out, an air gun cleaning rod to push in from rear end of barrel, or you need to completely reassemble the gun and shoot it out.

Using a commonly available 6-7mm steel ball used for slingshots as a "smoothing" tool after boring the crown with the brass screw head works well (turn it by hand with the lapping compound).

______________

Here is another source for barrel re-crowning which is essentially the same- but I personally prefer the above method- it's easy to follow and works very well.

http://www.spiralsol.com/airgunmod/1001.htm