Dial indicator, bedding check

Dogleg

Dogleg

CGN Ultra frequent flyer
Rating - 100%
113   0   0
Location
Where dem buffalo roam.
Could someone fill me in on the finer points of checking bedding jobs with a dial indicator? I'm not dealing with a specific case, just want to learn as much about the technique as I can, in a general sort of way.

The limited understanding and beliefs that I have can be summarized like this:

Mag mount a goose-neck base to the free floated barrel with the indicator pointer touching near the forend tip. Alternately loosen and tighten the front and rear action screws, watching for movement of the needle. I beleive the movement should be between zero and 2 thousandths, with zero being a undesireable bind fit and .002 being about as loose as you could go. At this point it gets a little fuzzy for me. I believe that this limited movement should show the barrel rising about a thou when the front screw is loosened, if it drops that could indicate that the screw tension is bending the action, perhaps because the lug is bottoming in it's recess.

Thats all I have at the present, could some of you ace gun mechanics either straighten me right out, or add to this scimpy base? It cold out, and I need something "gun nutty" to brood about.:D
 
I don't think that the fit between the action and the stock can be too tight and I have a couple of rifles that I have to tap the action screws once loosened to get the action free of the stock. What I like about pillar bedding is that the action screws cannot normally be over tightened, and it is easy to get equal torque on both the front and rear action screws.

A run out indicator will show that the barrel defects as the action screws are tightened, if that barrel is not free floating, and I suppose that a zero reading would occur when the barrel is truly free floating. But attempting to find a numerical sweet spot to determine when there is just enough upward pressure on the barrel to dampen the vibration, strikes me as tedious exercise. If the barrel is fully free floating and doesn't group well, adding shims of a known thickness just behind the fore-end tip would seem to be the fastest way to solve the problem. I don't think a given numerical defection will resolve the problem with all rifles although it might with an individual rifle with a barrel of a specific contour. The heavier the barrel contour, the greater the pressure it will require to achieve any given defection. You'll still have to go and shoot the rifle to determine the effect of adding or removing shims to the barrel channel. Using a dial indicator might be interesting, but it could become frustrating if the improvement occurs outside of the parameters you expect, or if there is no improvement at all.
 
Boomer,
I was thinking more of free floated barrels, but a incremental and repeatable way of adjusting forend pressure is to hang a weight from the front swivel while bedding a forend pad. If you hang 10 pounds of weight it will be 10 pounds of upward pressure when it is removed, and the stiffness of the forend, lack thereof,or amount of thickness of shims is taken right out of the equation.
 
Splatter said:
If a 0.000 fit is undesirable... How come benchrest guys do glue-in bedding? That seems like as close to 0.000 fit as it gets.
Click to expand...

Splatter,
The little I know or think I know about this method was taught to me by a benchrester, and local barrel maker. The difference is that a glue-in doesn`t move at all during firing so it doesn`t have any option but to be in the same position, plus is stress free by default. A bedding job that is held in by the action screws with zero movement to tension variations is in a sticky,squeeky, bind fit and may not return to a constant position since it can`t be counted on to bottom out on each shot. There`s probably about 1000 theories about bedding, and this is only one.
 
carbonrod said:
A glue in for benchresters is new to me. How do they rebarrel their rifles so often if the action is glued in? Smash it out, and glue it back in each time?
Click to expand...

Sometimes they do not remove the action from the stock to change barrels... and when a glue in requires removing a hot iron on top of the action for a while will soften the grip of the epoxy.
 
A zero reading on the dial is absolutely desirable if that reading is the result of a perfect bed. Such a reading is easier to achieve with some actions than with others. In the end, the use of a dial guage to check bedding is a decent diagnostic tool but not a garantee. In other words, a zero reading may or may not indicate a perfect, stress free, bedding job. Just as a .010 reading may not mean the rifle will be inaccurate. With some bedding techniques on some actions, a certain amount of deflection might even be desirable.
Anyone who has spent much time working with accuracy oriented rifles- especially BR rifles- can appreciate that exceptions continue to plague those who would like the pursuit of ultimate accuracy to be simple and straghtforward; with hard and fast rules that always made sense. We're not there yet. Regards, Bill.
 
Dogleg, I place the magnet base that holds the dial indicator as far forward on the barrel as I can and still be able to set the dial indicator tip on the stock beside the barrel. I would think this would show you the stress induced when you loosen or tighten the action screws better, especially with a heavy barrel, than if the dial was near or on the action itself.

Were do you guys put the device.. Bill or Dennis?
 
You must log in or register to reply here.
Back
Top Bottom