Lapped lugs??

[Bluestem]

I was wondering if someone could explain to me what is meant by lapping the lugs on a bolt-action rifle, and why this will improve accuracy.  Thanks - I've learned a lot from reading this forum.

[Tc300mag1]

Ill take a stab at it.. you lap the lugs in to get a Full grip on the reciver when in lock up other wise you mostly get maybe 60-75 % lock up ..

Maybe more now adays but thats how it used to be and how my 300 mag i bought in mid 90's was.. So by getting full lock up you know that the bolt isnt tweaked and not in a straight line  which will alter how the cartridge goes into  and sits in chamber if this makes any sense.. Thats how it was explaned to me

[Zachary]

To say the same thing a different way, think about it this way...

Machines cut and make most, if not all, of the parts to a rifle.  This obviously includes the bolt, the barrel, the chamber, the action, etc.  

The problem is that the machines that make these parts do not make them to very tight tolerances.  Think of it as kindava a sloppy job puttering all the parts together (not that they are sloppy, but for this explanation, just think of it that way.)

If the parts that are put into a gun do not fit precisely, then that means that when the cartridge is put into the chamber, it will not be perfectly fit in there.  Also, when you turn the bolt, since the lugs are not perfect, when you shoot the gun, there will be more pressure on one side of the lugs than the other.

Enters lapping or "blue printing."  Lapping occurs when a gunsmith gets to work where the machine left off.  As was stated, at the factory, you may only have about 60% or 75% contact between the lugs and the chamber.  However, a gunsmith will take the time to make it right, and you will have a much higher contact rate.  This in turn means that accuracy will generally be better.

Blue printing is more than lapping because blue printing invloves work on the chamber and the way it fits to the barrel.

Hope this helps.

Zachary

[gunnut69]

Lapping is simply put the introduction of an abrasive grits between the locking abutments in the receiver and the locking lugs on the bolt.  The bolt is then worked against a solid stop to remove metal from the the high spots on the lugs and abutments.  This allows for a fuller contact between the two.  Combined with blueprinting which aligns the barrel, chamber, bolt face and locking surfaces.  In the lapping process the ways in the receiver that the bolt moves in are also polished and cam angles may be polished, the latter only if needed..  All of this is to avoid any flexing of the action under the stress of firing.  Poperly done the result is a rifle that functions as smoothly as oiled glass and will deliver the best posible accuracy..