Remington 700 project - the LUG!

April 9^th  Laping the Lug!

Nothing says” I love you” like a well laped lug.  Ok…that’s gross, and probably not a realistic statement, but I thought I would throw it in anyway. 

Actually a laped lug does have its advantages.  Chief being improved accuracy.  To understand why we have to do this nonsense we have to go back to the factory and the production process. 

It is a lot quicker and more efficient to manufacture like items on the same machine at the same time.  So as a result a milled part is going to be made on a dedicated machine, and hundreds of them will be produced at one time.  A part that is married to it will be made on a separate machine, and hundreds of those will be made at one time.  If everything goes according to plan the two parts will fit together and function as intended.  For the most part this works, but no two parts are ever exactly the same and as a result you need someone at “QC” to make sure everything makes it to within minimum standards. 

So this brings us to the Lug….the part of the bolt that slides behind the locking rings and holds the bolt fast during the firing process. 

Think of it this way…you have a closet in your house with a dead bolt installed.  You grab an angry bear…(ok….this may be a weird analogy, but just go with it for a second) and you throw the bear into the closet and slam the door shut.  Now just holding the door closed with your body probably won’t work real well, eventually the bear will weaken you and push you out of the way.  So you throw the dead bolt to lock the door  and with your body still against the door, you hold the bear inside.  Yeah, your body is doing something here,…but the real work at holding the door closed is the dead bolt.  This is kinda what the locking lug on the bolt is doing.

When you push a cartridge into the chamber of the rifle with the bolt the bolt slips past a broken ring in the receiver then you push the handle of the bolt down.  What is happening is the locking lugs on the bolt are being pushed through the open holes in the ring and rearward pressure is keeping the whole kit and caboodle in place.  Now when the cartridge is ignited the bolt won’t come flying back at you during the explosion.  (Well…we hope this is the case!) 

This brings us back to the factory.  Remember how I said that parts are made separately then fitted together?  Well the locking lugs on the bolt and the internal ring on the receiver are made on two different machines at two different times.  Hence the amount of contact between the lug and the receiver will vary from rifle to rifle.  When you have gaps in contact you end up with excess vibration, and to make maters worse the vibration is not predictable.  Therefore, with an unpredictable explosion propelling a bullet at 1800 feet per second you have only a rudimentary idea of where it will go. 

So what to do???? 

Lap your lug!

What I mean is put 600 grit laping compound on the contact point of the lugs, close the bolt and open it about 100 times until the metal is ground down between the two surfaces giving you at least 95% of contact.

On this Remington I tested the contact surface area at the beginning and found there was a whopping 20% amount of contact.  Now that the lugs have been laped we have almost 100% of contact. 

Now, before I reattach the barrel to the receiver I will take some sand paper and smooth out the action surface…ummm…the metal to metal contact that the bolt makes as it is pushed up the receiver.  The channel that it travels up is called the race way, and I’ll use a little tool I fashioned to make sure the race way is smooth and shinny. 

Now when you work the bolt on this beast it will feel more like a fine piece of machinery then some cheap toy manufactured by political prisoners in China. 

The shooter will also have the confidence to know that the vibrations of the lug have been eliminated, and if they can’t shoot a good group it is their fault not the firearm!

Picture time!: 

here is the bolt on the 700,..notice the small projections on the bolt at the right had side of the photo?  Those are the locking lugs.

The lugs are now lapped!  

This is the bolt in the receiver.  Notice the shiny inside?  That is the "raceway" and it has been polished.

This is my patent pending, super secret, finely engineered shop made raceway polisher.  I stick with sand paper on it.