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

[kai]

I am new to switch barrel rifles and am working on my first. It's an ARC Nucleus action with their BarLoc device to tension the barrel in place.

I have a 28 Nosler Proof Carbon barrel for hunting.
For practicing, I also bought a Criterion 223 Match prefit (Savage type) barrel and am using the ARC Barrel nut and their BarLoc device.

Today for the first time I tried loosening the BarLoc device and unscrewed the barrel 2 revolutions with the rifle supported by a bipod, then screwed it back into place using a GO chamber gauge, and tightened the BarLoc device to check for any Point Of Impact shift.

To my surprise, the Point Of Impact shifted about 4 inches to the right and 3/4 inch low.

I'd appreciate any comments to help me learn how to achieve consistency in the point of impact and would like to hear your thoughts and experience on the following:

1. How much shift in Point Of Impact is typical on a switch barrel gun when re-installing the same barrel and when installing a different barrel?
2. Is POI shift less with a shouldered barrel than with a barrel that uses a barrel nut?
3. Does anyone have experience with the ARC BarLoc, and if so, can you comment on the POI shift with vs without using the BarLoc?
4. When tightening the BarLoc (or the barrel) should the rifle be vertical (instead of supported horizontally with a bipod) to even out the lateral stresses on the barrel threads?
5. Do you have any other suggestions to help maximize the POI consistency?

 

[MagnumManiac]

I have had a 1-2" difference when changing barrels, this is why I limit barrels to 2 for hunting rifles, and 3 for comp rifles.
The lighter hunting barrels tend to deviate more. I also do not use 'tools' I simply screw them on by spinning the barrel, when it snaps into place, it's done. I use shouldered barrels only.

Cheers.

 

[kai]

MagnumManiac... When you loosen and retighten the same barrel does the POI still shift 1-2 inches? If not, how much, if any, does it shift?

Do you have a special action that allows the barrel to "snap into place" or do you just screw it on hand tight?

Thanks!

 

[ShtrRdy]

I haven't characterized this extensively but it seems when I loosen and then tighten the same barrel I can see up to 3/4" change in POI. This is with a shouldered barrel method.

Changing to a different barrel can be much different.

I stand the rifle on it's butt when tightening the barrel by hand. Then torque the crossbolt.

 

[kai]

ShtRdy...... What kind of cross bolt do you have? Is it the BarLoc?

I'll try standing rifle on the butt to keep it vertical and see if that helps.

Your 3/4 inch shift is a lot less than the 4 inch shift I've seen on my heavy 223 match prefit barrel using a barrel nut.

 

[ShtrRdy]

It's an AI AT rifle.

One thing I noticed after changing or removing a barrel is it takes one to three shots to settle the barrel into where it wants to seat.

 

[Plinker147]

Some shift a couple of inches, some I have had no shift. All of mine are rem 700 with staked lugs. The shifts should be predictable after you have switched them a time or two you should have the same shift each time.

I have not seen a meaningful shift from taking on and off the same barrel. Keep in mind I'm not removing the scope on some, on some I have to because the scope is too large and gets in the way.

 

[ShtrRdy]

Some shift a couple of inches, some I have had no shift. All of mine are rem 700 with staked lugs. The shifts should be predictable after you have switched them a time or two you should have the same shift each time.

I have not seen a meaningful shift from taking on and off the same barrel. Keep in mind I'm not removing the scope on some, on some I have to because the scope is too large and gets in the way.

How much torque do you apply when installing a barrel?

 

[jamiebolseth]

I don't have a ton of experience with this, but decided to get into a switch barrel setup 8 months ago. I'm using shouldered barrels on a Deviant action (no locking nut or locking device) that I secure in a barrel vice and torque to 50 ft/lbs. I don't have perfect data on the amount of shift with the same barrel because when I've switched I always went to a different barrel and had to re-sight in. But I would say I'm seeing 1-2 MOA shift from a particular barrel to the same barrel being remounted. Another note about my setup is that I need to unmount the scope from the pic rail to get the barrel vice on, so some of my POI shift could actually be zero shift from removing and remounting the scope.

The one thing I will say with my setup is that I have had to re-sight in EVERY time I've done a switch. It's not repeatable enough that I would be comfortable just using data from a previous zero without shooting it to verify zero.

 

[Dean2]

Put two real fine witness marks on your barrel and action. Put both where you can see them without removing the scope or taking the stock off and get them as close to touching as possible. For each barrel you mount, add the same witness marks to line up with the action ones, once you have it head spaced and torqued. The witness marks are far more accurate than torque or feel for getting the barrel in the EXACT same orientation each time. This won't eliminate POI shift from one barrel to another but it should make going back to the other barrels POI far more predictable. This will give you as repeatable/predictable a POI shift as I have been able to come up with.

 

[MagnumManiac]

MagnumManiac... When you loosen and retighten the same barrel does the POI still shift 1-2 inches? If not, how much, if any, does it shift?

Do you have a special action that allows the barrel to "snap into place" or do you just screw it on hand tight?

Thanks!

No, if I screw a barrel on as I described, which is by 'spinning' it with the rifle between the legs, the barrel is turning until it stops. I do not then grab the barrel and try to twist it further. My barrel/action shoulders are precisely machined, so once abutted, they are precise each and every time. If you over-torque them, you change the abutment and headspace/clearance.
Switching barrels of different cartridges/length in the same cartridge, for me is where the 1"-2" POI shift occurs, and it is always the same each time. I simply know how much to adjust the scope between barrels and back again.
I also use a nickel based anti-seize paste on the threads. I used to use Moly Assembly Lube, which is great stuff, but is messy.

Cheers.

 

[kai]

MagnumManiac...... Thanks for your detailed explanation.

I'm encouraged to hear that you're able to get repeatable POI using the same barrel because I'm working on developing a scope turret system that makes it easy to reset the various zeros used for multiple barrels, while maintaining all of the functionality of the turret including the zero stop.

With my Criterion 223 match Savage style prefit barrel, there's no shoulder to abutt against the receiver... or in my case, the BarLoc. So what I'm going to try, is holding the rifle vertically between my legs and screwing in the barrel until it contacts the GO gauge. ARC, the maker of the BarLoc, said to then pre torque the barrel nut to open the gap at the top of the Barloc the same amount (i.e. .105 inch) each time. Then tighten the screw on the BarLoc to secure the barrel.

I dont know if using the GO gauge or using the NO GO gauge is best in my application.

Does anyone have thoughts on which headspacing gauge would be better to use?
I only use hand loads and can bump my case shoulders to fit as needed.

 

[Dean2]

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.

 

[kai]

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.