Newly purchased Colerain swamped barrel, 42", .40 cal, "A" wt. definitely curves a little to the right, as you sight down the barrel. looking down the bore, it appears to follow the same slight bend, but it may be my imagination. How can I determine the straightness of the bore?
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determining the straightness of a bore
- Thread starter rmann
- Start date
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Try laying a 4' long straight edge along side of the barrel.
Firstly talk to the supplier
Secondly remember most barrels will have a bend but not perceivable. Wherever the last bit points is where the bullet goes.
Also remember that the outside may not be concentric to the outside. Most barrel makers essentially label the runout by putting there marks on what is supposed to be the bottom of the barrel such that the bore points up to the exterior.
If you wish to measure outside runout then measure from flat to tabletop on each flat at the same point lengthwise. But this will not tell you where the bore points.
To measure run out at breech or muzzle fit a tight and straight mandrel to the bore and measure flat to mandrel. Again this does not tel you if the bore is straight.
To get some idea if the bore is straight.
Can you remove the breech plug?
If so look through the bore. Depending on your eyes the shadow may allow you to see a bend. Especially as you turn the barrel as the shadow wobbles and orbits around.
I have not tried it but I am told that the old barrel makers used to make a bow such that the string is strung at tension through the bore.
By then looking down the bore at the string against the bore wall bore run out was visible.
Secondly remember most barrels will have a bend but not perceivable. Wherever the last bit points is where the bullet goes.
Also remember that the outside may not be concentric to the outside. Most barrel makers essentially label the runout by putting there marks on what is supposed to be the bottom of the barrel such that the bore points up to the exterior.
If you wish to measure outside runout then measure from flat to tabletop on each flat at the same point lengthwise. But this will not tell you where the bore points.
To measure run out at breech or muzzle fit a tight and straight mandrel to the bore and measure flat to mandrel. Again this does not tel you if the bore is straight.
To get some idea if the bore is straight.
Can you remove the breech plug?
If so look through the bore. Depending on your eyes the shadow may allow you to see a bend. Especially as you turn the barrel as the shadow wobbles and orbits around.
I have not tried it but I am told that the old barrel makers used to make a bow such that the string is strung at tension through the bore.
By then looking down the bore at the string against the bore wall bore run out was visible.
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