Barrels unscrewing from the action.

[memilanuk]

Barrel was hand tight. Shot 3 rounds, removed & used to bludgeon a cinderblock to pieces.
Then hand tightened back onto the action &shot another 3 rounds with virtualy no POI shift.

That's great... if the barrel is hand tight to begin with (as in that example).

If it starts out torqued, and becomes hand tight over time... I'd put my money on there being a POI shift.

If it goes from 'hand tight' to 'about ready to unscrew on its own'... again, I'd wager on a POI shift, with a fair bit of 'random walk' to it.

 

[billlarson]

So when I did mine I chucked up my barrel in the vice, put my action wrench in and then attached my handle. Normally I have to apply a decent amount of force to pop it lose but in this case without even thinking, I just started spinning the action off and after about half a rotation it occurred to me that something was a astray....that was my experience. Hope it helps.

Oh, once I torqued it back it shot great again. But as always, YMMV.

How much torque do you put on a barrel...???

 

[F Class John]

How much torque do you put on a barrel...???

80ft/lbs every time now. I know it can vary by action manufacturer a little as well. I’m shooting Defiance.

 

[jr600yd]

WOW!!....I’m lost. Never was that good in math

 

[mturner]

If a case head has an internal dimension of .4", and the pressure is 70,000 PSI, not copper units. The thrust on a lubed case would be around 8800 pounds of thrust. Because the case head will grip the chamber walls, this is reduced somewhat. I have always torqued to 100 ft/lbs. In theory, a thread needs to be stretched in order to perform the way it is designed to perform. A rod bolt in a engine will break if it is not torqued to the proper stretch. On a barrel, if the thrust on the case head ever exceeds the clamping force against the action face, accuracy will suffer. Imperial wax is still on the cases after we wipe it off. Cleaning the cases with an alcohol rag would greatly reduce case head thrust. Everything becomes way more critical as the case head diameter increases. Tighten the barrel even more on a 378 Weatherby case.

Michael

 

[Coyotefurharvester]

So if 35 ft lbs torque =2000# clamping force how does that relate to thrust force, especially the difference between a cartridge with lube residue(like one shot or wax) and a lube free case? Does the clamping force need to exceed the thrust force value?

 

[ebb]

One of the posters mentioned harmonics. I know nothing of this but would not the the harmonics be much different if the before had 80 or 100 lbs torque and the after has almost 0 lbs of torque?

 

[mac86951]

Hmm, Carrol smith might have much to say in this subject. Different application; but physics are the same. Torque applied then stretch threads / shank to produce clamping force. In this application, thermal cycling will loosen clamping force if; 1. Not enough clamping force which loosened by thermal cycling; or 2. Lots of thermal cycling which may loosen any clamping force.

I don't have solutions, I'm curious and I would reinstall with and keep notes to share with the rest of us. I've seen barrel torque as a 'gray' value of 20-120ft-lb

Look at an AR; 30-80ft-lb which really means torque to 30 and increase to align gas port...

-Mac

 

[MikeMcCasland]

One of the posters mentioned harmonics. I know nothing of this but would not the the harmonics be much different if the before had 80 or 100 lbs torque and the after has almost 0 lbs of torque?

This could be a complete coincidence because it still shot pretty crappy the following day, but in the process of troubleshooting mine I pulled my mirage shield and things improved drastically. These groups were shot nearly back to back, only thing changing is the shield. Included the chronograph just so nobody says the load was screwy.

I pulled the mirage shield at the very last string of the day. I thought I had it figured out, and that entire evening I was thinking "damn, that gun was on the ragged edge of a tune window for a mirage shield to make that much difference".

The gun didn't shoot well the next day, but it was MUCH better than what it had been doing (i.e the first image)...the barrel was still loose though, and I didn't discover it until days later.

Edit: Tight barrel or not, this does change my laissez faire attitude about attaching a mirage shield to a barrel. I need to research more repeatable ways to attach them, and I'll probably test shield-on/shield-off in load dev for future barrels.

Harmonics are weird.

Stock/Loose Barrel (Mirage Shield Attached):



Removing Mirage Shield (Troubleshooting)



Chronograph:

 

[Dusty Stevens]

This could be a complete coincidence, but in the process of troubleshooting mine I pulled my mirage shield and things improved drastically. These groups were shot nearly back to back, only thing changing is the shield. Included the chronograph just so nobody says the load was screwy.

I pulled the mirage shield at the very last string of the day. I thought I had it figured out, and that entire evening I was thinking "damn, that gun was on the ragged edge of a tune window for a mirage shield to make that much difference".

The gun didn't shoot well the next day, but it was MUCH better than what it had been doing (i.e the first image)...the barrel was still loose though, and I didn't discover it until days later.

Edit: Tight barrel or not, this does change my laissez faire attitude about attaching a mirage shield to a barrel. I need to research more repeatable ways to attach them, and I'll probably test shield-on/shield-off in load dev for future barrels.

Harmonics are weird.

Stock/Loose Barrel (Mirage Shield Attached):
View attachment 1203414


Removing Mirage Shield (Troubleshooting)
View attachment 1203415


Chronograph:
View attachment 1203417

Youd be surprised what some of these heavy shields do. I always encourage their use by fellow competitors especially those heavy carbon fiber ones

 

[Dusty Stevens]

One of the posters mentioned harmonics. I know nothing of this but would not the the harmonics be much different if the before had 80 or 100 lbs torque and the after has almost 0 lbs of torque?

One of the posters mentioned harmonics. I know nothing of this but would not the the harmonics be much different if the before had 80 or 100 lbs torque and the after has almost 0 lbs of torque?

Only if one torque was loose enough for the joint to vibrate. Dont think youd see a difference in harmonics from 80 to 100 but you might from 15 to 40

 

[Rsadams]

Torque can make a huge difference... Torque it back up and shoot it... Even action screws torqued up properly can make a huge difference... It would be nice if you knew how much torque you were setting up at...

 

[Oleg S]

This could be a complete coincidence, but in the process of troubleshooting mine I pulled my mirage shield and things improved drastically. These groups were shot nearly back to back, only thing changing is the shield. Included the chronograph just so nobody says the load was screwy.

I pulled the mirage shield at the very last string of the day. I thought I had it figured out, and that entire evening I was thinking "damn, that gun was on the ragged edge of a tune window for a mirage shield to make that much difference".

The gun didn't shoot well the next day, but it was MUCH better than what it had been doing (i.e the first image)...the barrel was still loose though, and I didn't discover it until days later.

Edit: Tight barrel or not, this does change my laissez faire attitude about attaching a mirage shield to a barrel. I need to research more repeatable ways to attach them, and I'll probably test shield-on/shield-off in load dev for future barrels.

Harmonics are weird.

Stock/Loose Barrel (Mirage Shield Attached):
View attachment 1203414


Removing Mirage Shield (Troubleshooting)
View attachment 1203415


Chronograph:
View attachment 1203417

I’m just curious what shield was it?

 

[MikeMcCasland]

I’m just curious what shield was it?

It's one Bryan Blake sells on his website.

I want to be clear for those that might misinterpret this; Bryan sells amazingly good stuff. The problem isn't the shield. This barrel was screwed on at like 5ft lbs as all this is going on. It's just that the shield seemed to have a fairly profound impact on vertical when the barrel wasn't torqued down all the way.

Here's a picture of it on a scale. Weight includes the shield and the 3 pieces of velcro (not pictured) on the underside.

Excuse the crack; it got a tagged by a pelican case.



FWIW - I cleaned the hell out of the barrel, borescoped it to confirm everything is still looking good. I'm hoping to get a chance to take it out to 300 yards this Sunday. Winds will be 10-15mph where I'm shooting, but I should be able to get a feel for if it's shooting better now that it's on there tight.

The gun had been 'hammering' it's entire life leading up to this point, so I'm hoping I get a few nice little clusters despite the wind. If not, I'll pull it and screw in a new barrel.

 

[billlarson]

If a case head has an internal dimension of .4", and the pressure is 70,000 PSI, not copper units. The thrust on a lubed case would be around 8800 pounds of thrust. Because the case head will grip the chamber walls, this is reduced somewhat. I have always torqued to 100 ft/lbs. In theory, a thread needs to be stretched in order to perform the way it is designed to perform. A rod bolt in a engine will break if it is not torqued to the proper stretch. On a barrel, if the thrust on the case head ever exceeds the clamping force against the action face, accuracy will suffer. Imperial wax is still on the cases after we wipe it off. Cleaning the cases with an alcohol rag would greatly reduce case head thrust. Everything becomes way more critical as the case head diameter increases. Tighten the barrel even more on a 378 Weatherby case.

Michael

Mike, I use your torque specs. Plus some.esp.on big calibers.mausers also ...
Omho.
Bill

 

[Oleg S]

It's one Bryan Blake sells on his website.

I want to be clear for those that might misinterpret this; Bryan sells amazingly good stuff. The problem isn't the shield. This barrel was screwed on at like 5ft lbs as all this is going on. It's just that the shield seemed to have a fairly profound impact on vertical when the barrel wasn't torqued down all the way.

Here's a picture of it on a scale. Weight includes the shield and the 3 pieces of velcro (not pictured) on the underside.

Excuse the crack; it got a tagged by a pelican case.

View attachment 1203464

FWIW - I cleaned the hell out of the barrel, borescoped it to confirm everything is still looking good. I'm hoping to get a chance to take it out to 300 yards this Sunday. Winds will be 10-15mph where I'm shooting, but I should be able to get a feel for if it's shooting better now that it's on there tight.

The gun had been 'hammering' it's entire life leading up to this point, so I'm hoping I get a few nice little clusters despite the wind. If not, I'll pull it and screw in a new barrel.

Thank you for clarification.

 

[skeeljc]

When I torque a barrel nut on an AR I always tighten it then back it off a couple of times to seat it properly. Do you do that with a bolt action barrel?

 

[Brians356]

My first (twisted) thought was "knock-off hub nuts on race cars." Many are threaded so that wheel rotation tends to tighten the nut. Why aren't barrels threaded and rifling twisted such that torque from the latter tightens the former during bullet launch? Or if they are, why doesn't the torque so imparted prevent a barrel loosening (assuming it was reasonably tight in assembly)? Too little torque compared to other vibrational forces or thermal effects?

Inquiring (twisted) mind wants to know.
-

 

[47WillysGuy]

Use a barrel with left hand bore twist. Shouldn’t loosen with that feature.

 

[Rwfish]

Let’s hope after 4 Years the OP hasn’t had to revisit the issue….