Chamber Measurement Changes?

[AICS308]

I removed the barrel on my .308 then reinstalled a few weeks later. No changes were made just off and on. Before removing the barrel my fired brass was consistently measured at 1.629 base to shoulder. Now the fired brass measurement is consistently 1.627. The barrel torque was set at 65 ft/lbs when reinstalled. I do not know what the previous torque was.

Should I be concerned about the change or is this considered within range?

Thanks

 

[TTE]

Do you have a go, no go gauge(s) ?

 

[Coyotefurharvester]

Did you have a witness mark before barrel removal?

 

[AICS308]

I do not have the gauges but will be getting a set. The measurements were done with the Hornady kit so it is a relative number but consistent. This was the first time removing a barrel so I know now it was a mistake to not use a witness mark. But a lesson was learned.

 

[Webster]

I removed the barrel on my .308 then reinstalled a few weeks later. No changes were made just off and on. Before removing the barrel my fired brass was consistently measured at 1.629 base to shoulder. Now the fired brass measurement is consistently 1.627. The barrel torque was set at 65 ft/lbs when reinstalled. I do not know what the previous torque was.

Should I be concerned about the change or is this considered within range?

Thanks

My guess is the barrel is OK. The problem is using case length measurements to determine if the barrel was threaded on the same as before. Just shoot the rifle and quit worrying about 2 thou. If you know the thread pitch you can easily determine how much the barrel would have to turn to equal .002". When you screw the barrel on you have metal to metal contact to stop rotation. I don't see how you could position the barrel beyond metal to metal contact. Once you have metal to metal contact you could get any torque value you want, it doesn't mean the barrel is getting coser to the bolt face. 65 ft/lbs should be a proper torque to seat properly. A witness mark would be nice but once the barrel shoulder contacts the action I don't see how it can screw on more.

Don't know what the thread pitch is but a madeup example goes like this:
thread = 32 per inch
1 turn = 0.03125 (1/32)
.1 turn = 0.003125
.002" diff on case length would be around a tenth of a rotation of the barrel. Torqueing after metal to metal contact you cannot turn the barrel down 1/10 of a rotation.

I hope I did all this correctly?

 

[DaveTooley]

Once the shoulders make firm contact you, me or anybody cannot change the HS with hand tools

 

[AICS308]

Thanks for the information guys. I use the same tools for that measurement so I will check those to see if something changed.

Thanks again!

 

[William Vogel]

If the torque is not equal to what was used originally, the Tenon will have different stretch. It sounds to me like the barrel was tighter before and now it’s 0.002 shorter @ 65 ft lb torque. I don’t recommend tightening it tighter than 65 though.

 

[marazzi59]

Was this a factory installed barrel, and was it a pain in the ass to break free?

 

[AICS308]

It is a custom rifle I bought used. It actually came off without too much trouble once I got a longer heavier breaker bar. It was a situation where I needed the right tools.

 

[Thud]

Why did you torque the barrel 65 foot lbs.

 

[jelenko]

It is a custom rifle I bought used. It actually came off without too much trouble once I got a longer heavier breaker bar. It was a situation where I needed the right tools.

Sounds like it was a bit more than 65 ft-lbs.

 

[Thud]

30-40 foot lbs is normal torque. Get the right tools before doing stuff

 

[jackieschmidt]

I think 65 is just about right. I tighten my Benchrest Barrels more like 75.

If it will chamber a factory round ok, .002 shorter isn’t going to hurt anything.

 

[Alex Wheeler]

The shoulder is in front of the action face. Any tenon stretch is behind the action face and wont change headspace. The only way your doing that is to compress something, like a recoil lug. If its not flat or the action face not square and you torqued it more I could see shrinking up a bit. If everythings good, your not going to change it with a little more torque.

 

[AICS308]

Why did you torque the barrel 65 foot lbs.

I saw a wide range of torque values while researching here. The consensus seemed to be 65 to 75. Also looked at recommendations from highly regarded folks here and decided 65 would work.

 

[AICS308]

I think 65 is just about right. I tighten my Benchrest Barrels more like 75.

If it will chamber a factory round ok, .002 shorter isn’t going to hurt anything.

Tried a factory round with no issues. Good suggestion, thanks.

 

[AICS308]

The shoulder is in front of the action face. Any tenon stretch is behind the action face and wont change headspace. The only way you’re doing that is to compress something, like a recoil lug. If it’s not flat or the action face not square and you torqued it more I could see shrinking up a bit. If everythings good, you’re not going to change it with a little more torque.

Very good info, Thanks

 

[JLT]

.002" is within observable error with calipers. How does it shoot? If it shoots like it used to, I wouldn't lose any sleep over it.

 

[Webster]

If the torque is not equal to what was used originally, the Tenon will have different stretch. It sounds to me like the barrel was tighter before and now it’s 0.002 shorter @ 65 ft lb torque. I don’t recommend tightening it tighter than 65 though.

The tenon extends away from the shoulder. You cannot increase stretch of the tenon if you cannot rotate the barrel. The shoulder to action contact surfaces are large flat fixed locations, they cannot change. If you quit measuring things you won't have any problems. The rifle should be OK. Just shoot it.