Head Space and Barrel Torque

[M-61]

Quote from Savagedasher:
"When you tighten a nut their is no pushing it is all pulling the barrel away from the action the action and barrel both must be held while secure and not be allowed to move. Action wrench and barrel block is must Now you tightent the nut. All the clearance in the treads is being pulled forward The tighter the nut is the more head space you will get Larry"

Yes Larry you are correct. The head space will INCREASE as you continue to tighten the jam nut. How much? Well that surely depends on the threads in the action, on the barrel, the material itself, and the lubricant. I have never measured it but it is certainly a measurable amount albeit small. The threads on both are not cut like Rolex micro stella screws nor do they need to be, so there will be movement. The tightness of the jam nut is to secure the barrel in position in relation to the action. I know that I have the head space set at the VERY minimum and tightening the jam nut will leave me with the amount of head space I want which is just greater than the Very minimum. Around 40-50 lbs ft. And yes, as you said the action and barrel MUST be secure or you will chase the head space for hours.
All of what I said is from personal experience with zero scientific testing.

 

[Alex Wheeler]

Since headspace is measured from the bolt face to shoulder and the shoulder is in front of the part of the barrel that stretches how can headspace change?

 

[savagedasher]

Since headspace is measured from the bolt face to shoulder and the shoulder is in front of the part of the barrel that stretches how can headspace change?

Alex if you set the headspace at 20 foot pounds correct then tighten the barrel up to 60 foot pounds is a headspace going to be the same Larry

 

[Alex Wheeler]

Since headspace is measured from the bolt face to shoulder and the shoulder is in front of the part of the barrel that stretches how can headspace change?

Alex if you set the headspace at 20 foot pounds correct then tighten the barrel up to 60 foot pounds is a headspace going to be the same Larry

On a barrel with a shoulder, yes. You may reduce bolt nose clearance, but the shoulder of the chamber is forward of the part of the tennon that can stretch.

 

[M-61]

Since headspace is measured from the bolt face to shoulder and the shoulder is in front of the part of the barrel that stretches how can headspace change?

I may have not understood your question correctly so....The head space is from the closed face of the bolt to the shoulder which is in the chamber. The bolt is not moving anywhere however (Savage) when the jam nut is tightened it pulls the barrel forward (slightly) as it takes up the slop in threads etc. This moves that shoulder away from the bolt face in doing so. Thus rather than 'screwing' IN the barrel to the action the jam nut pulls it away.
I think I wrote this correctly.

 

[Alex Wheeler]

Since headspace is measured from the bolt face to shoulder and the shoulder is in front of the part of the barrel that stretches how can headspace change?

I may have not understood your question correctly so....The head space is from the closed face of the bolt to the shoulder which is in the chamber. The bolt is not moving anywhere however (Savage) when the jam nut is tightened it pulls the barrel forward (slightly) as it takes up the slop in threads etc. This moves that shoulder away from the bolt face in doing so. Thus rather than 'screwing' IN the barrel to the action the jam nut pulls it away.
I think I wrote this correctly.

It was a rhetorical question, but it was directed toward a barrel with a shoulder. Your correct in regards to a Savage.

 

[M-61]

Got it, yes with a shoulder you are correct, I jumped in when the Savage statement was made and stayed with it.
The rhetorical question I'll ask is how is this head space ever changed in a design like Blaser or Heym have? To me you have machine it and it's either correct or not....don't see how you change it since the bolt lugs lock IN the barrel not the action. In fact, to me, the action is nothing more than a guide for the bolt (and of course as a point to secure the action to the stock). I like the design but don't know what you do with the head space.(if anything).

 

[fguffey]

It is a mechanical thing. The lock nut pushes on the front receiver ring, allowing the barrel to rotate at the same time the nut is secured is a bad habit.

I do not remember who said it but it went something like "There is no free lunch", now?

it is all pulling

It is a mechanical thing, the nut is pushing on the front of the receiver.

I have worked with individuals that had no mechanical aptitude, they thought if tight was good really tight was better. They could not understand overtight bolts pulled the threads, the pulled threads raised the part that was being secured. If that part was designed to hold water and or combustion there was always time to do the job over. Then there are Helical Inserts.

http://rivetsonline.com/thread-repair-kits.html

F. Guffey

 

[gunsandgunsmithing]

For purposes here, it won't make a difference. I use 60-70ft.lbs. The method many use of a light feel when closing the stripped bolt is extremely accurate if done carefully. I often use the analogy, if you will, of a 1.000" peg not fitting into a 1.000" hole...It won't fit without resistance as they are the SAME. Same doesn't fit. There must be clearance or interference. In the case of a brass cartridge and the light feel technique, we have interference fit.
I'd like to know how people are measuring all this "difference" they say happens. Oh... and at what temperature?

 

[Eddie Harren]

+1 Mike.

 

[fguffey]

I'd like to know how people are measuring all this "difference" they say happens. Oh... and at what temperature?

for me I there is no procedure for setting the distance from the shoulder to the bolt face that calls for increasing the torque.

I do not have a head space gage that allows for a crush fit.

F. Guffey