How much does the Point Of Impact shift with your switch barrel rifle when reinstalling a barrel?

[MagnumManiac]

You do not want one so loose that the bolt will close on the no-go. Head space off the go gauge, that is what it is for.

^^^^^^^^^
This!!!!


Cheers.

 

[MagnumManiac]

I am headspacing off my GO gauge and am screwing my barrel until engaged the GO gauge enough to eliminate any wobble between the threads of the action and the receiver. I suspect this is slightly compressing against the gauge ( perhaps half a thousandth). With the NO GO gauge, the bolt handle only moves down about 1/8 inch, so my headspace is on the extreme short tolerance.

I was wondering if there's any disadvantages of having the headspace this tight.

The only thing you may encounter with using a go-gauge is that the brass may not always fit when the nut isn't tightened exactly the same each time.

My early switch barrels were on Mauser '98 actions and I used witness marks and about 25 lbs/ft torque to tension the barrel. Early on, I discovered that the torque wasn't required as long as there was a precise fit. Mauser action barrels abutt twice, on the back of the 'C' behind the lugs, looking in as if the barrel was removed, and on the front of the receiver.
A trued Mauser dimension is always taken from the contact point behind the lugs, this is the trued section, so you can have either 1 true contact point, or 2 by turning a barrel shoulder that precisely matches the 2 measurements. The barrel can then only stop in the same spot each time.

This is the best way because the barrel stops precisely, the threads also have to be square and spot on too.

Cheers.

 

[kai]

I tested a new series of procedures to improve the consistency of the POI with my .223 barrel and Nucleus action using the ARC BarLoc.

Previously I just mounted the barrel to the action while the rifle was on a bipod. I was experiencing POI shifts of 2 to 4 inches with the same barrel. Perhaps because the threads between the barrel and the action fit rather loosely.

The new procedures reduced the POI shift to range between .1 inch and 1.1 inch in 4 mountings of the barrel at 100 yards.

Here's what I did:

1. Held the rifle vertical to eliminate lateral pressure on the barrel and receiver threads.
2. Hand screwed the barrel into the receiver until it snugged up against the GO gauge.
3. Tightened the barrel nut until the gap in the BarLoc clamp opened to .105 inch wide.
4. Tightened the BarLoc screw to 60 inch pounds of torque.

The maker of the BarLoc clamp recommended 60 - 90 inch pounds of torque. I'll try increasing the torque to see if it reduces the shift in POI. My FAT torque gauge only has indications up to 65 inch pounds.

It's impossible to get the barrel nut to go exactly to the same place on the barrel every time. I was wondering if it would be good (or bad) to permanently affix the barrel nut to the barrel with Locktite or JB Weld so that it acts like a shouldered barrel. That would eliminate the variable of having the barrel nut in a slightly different position on the barrel.
However, fixing the barrel nut to the barrel would require me to hand tighten the barrel to preload and open up the BarLoc while trying to judge (feel) the engagement of the barrel to the GO gauge.

This is my first switch barrel gun, so pardon my ignorance.

What do you gents think about the idea of fixing the barrel nut to the barrel?

Any other ideas or suggestions for reducing the POI shift are greatly appreciated.

 

[WiscGunner]

First things first...I don't own a barloc.

Obviously repeatability is synonymous with consistency. My understanding of the barloc system is the torque applied the the screw seperates the barrel from the receiver thus applying the same type of force on the threads as would be if it was torqued against a shoulder like a regular barrel.

If it were me, I would do your proceedure as but tighten the barlock much higher than the minimum. Then I would place fine witness marks on the barrel, nut and barloc.

Then I would disassemble and clean the barrel and nut thouroughly. Then lictite them together with their respective witness marks aligned. This will create a shoulder and eliminate the need for the go-gage. You can certainly test this later.

Now test your results with the exact same torque and witness mark alignment.

 

[ShtrRdy]

Hey Kai - thanks for the update. Glad to hear that the vertical installation helps. Thread-locking the barrel nut seems like a possibility. Using a witness mark after you turn the barrel on to spread the Barloc seems like a good thing to do.

When you were testing this, did you fire multiple shots to see if the barrel needed to settle in to the re-install?

I was thinking about one other thing to consider trying. Since the Barloc loads the barrel/action threads by using a spreader, I was wondering if it would be better to measure the gap on the spreader instead of the torque on the screw to arrive at a consistent thread loading?

 

[kai]

ShtRdy... Thanks for mentioning using a vertical position of the rifle when tightening the barrel/BarLoc. It definitely reduced the POI shift.

I did fire 3 shot groups and there was no settling in of the barrel with the BarLoc.

I took actual group measurements tonight and here are the results for my 100 yard groups with the barrel re-installed for each group:

The first 3 shot group measured .15 inch. (No settling in here!)
The second group shifted about 3/4 inch to the 10 o'clock direction and grouped at .7 inch.
The third group shifted to the 6 o'clock position and measured .8 inch.
The fourth group shifted back to the original position and measured .3 inch.

It may be a coincidence, but the first and last groups had the same POI and they also had the smallest group sizes.
I wonder if this could have been the sweet spot for the barrel nut and the BarLoc.... and if so, how to best achieve this sweet spot each time I install the barrel.

One issue I've noticed.... when torquing the barrel nut to preload and open up the BarLoc, it's very difficult to keep the BarLoc from rotating. This makes it difficult to have the BarLoc perfectly level each time the nut is torqued.
I'm thinking that a possible solution might be to temporarily replace the BarLoc allen screw with a much longer bolt that could be used as a wrench handle to keep the BarLoc perfectly level when tightening the barrel nut.

It may be better to just Locktite the barrel nut to the barrel.... I don't know.
I've been reading other forums for Savage type switch barrels and others have used Locktite and JB Weld.... but without the BarLoc.

Again, any comments from experience switch barrel users is greatly appreciated.