effects of using a trued action without proper fit std dia barrel shank

[Dusty Stevens]

I hear some folks say with proper grip on the chamber there is no thrust to speak of. Makes sense, but then i think back at that one run of farley actions that were shearing the lugs off and wonder whats different? I know chamber finish, cleaning and proper case prep makes all the difference but who sets the standard? I know mine never has issues but what can you do wrong to cause it?

 

[gunsandgunsmithing]

I hear some folks say with proper grip on the chamber there is no thrust to speak of. Makes sense, but then i think back at that one run of farley actions that were shearing the lugs off and wonder whats different? I know chamber finish, cleaning and proper case prep makes all the difference but who sets the standard? I know mine never has issues but what can you do wrong to cause it?

Oil in the chamber or on the brass. I don't doubt some of the claims about the case gripping tight enough to hold some cases. I just don't think a short case like a ppc at 65,000+ psi is anything I'd bet on holding. Kinda like figuring how much forward thrust the barrel actually feels propelling a bullet down the bore. The thrust will drop as the bullet begins to move, and pressures build for a couple of inches rather than happening all at once...but there ain't a lot of difference in all at once and 1.5 milliseconds either. Maybe some smart person on here will roughly calculate both for us...the thrust reduction by the bullet moving and the amount of pressure it takes to push a ppc case in two. I'd guess the barrel threads have more thrust load than the bolt lugs but I don't for one minute believe the lugs have no thrust load imparted. We've all seen over pressure loads create ejector swipe and tight bolt lift.

 

[AckleymanII]

1.072-1.079 max thread dia on action-Trued action

1.060-1.062 max thread dia on barrel tenon-non trued action

 

[tomswede]

Oil in the chamber or on the brass. I don't doubt some of the claims about the case gripping tight enough to hold some cases. I just don't think a short case like a ppc at 65,000+ psi is anything I'd bet on holding. Kinda like figuring how much forward thrust the barrel actually feels propelling a bullet down the bore. The thrust will drop as the bullet begins to move, and pressures build for a couple of inches rather than happening all at once...but there ain't a lot of difference in all at once and 1.5 milliseconds either. Maybe some smart person on here will roughly calculate both for us...the thrust reduction by the bullet moving and the amount of pressure it takes to push a ppc case in two. I'd guess the barrel threads have more thrust load than the bolt lugs but I don't for one minute believe the lugs have no thrust load imparted. We've all seen over pressure loads create ejector swipe and tight bolt lift.

The only way bolt thrust is reduced is through case stretch (what causes case head separations). A case that fits the chamber perfectly will not reduce bolt thrust regardless of friction in the chamber. Harold Vaughn (spelling?) did actually test this in his book rifle accuracy facts. For the barrel threads the load situation depends on the preload, it is basically a bolted joint set up a little bit different. Those calculations quickly become complicated but sufficient preload is important to reduce joint movement.

 

[gunsandgunsmithing]

The only way bolt thrust is reduced is through case stretch (what causes case head separations). A case that fits the chamber perfectly will not reduce bolt thrust regardless of friction in the chamber. Harold Vaughn (spelling?) did actually test this in his book rifle accuracy facts. For the barrel threads the load situation depends on the preload, it is basically a bolted joint set up a little bit different. Those calculations quickly become complicated but sufficient preload is important to reduce joint movement.

Oh, I agree with you. If you go back a couple of posts, the old tests were brought up where cases were fired with no receiver at all on the barrel. Of course brass will hold some amount, given that it does indeed grip and hold the chamber walls, before stretching and/or failing...but I don't want to be the one standing behind it. No way it holds roughly 7,000-8,000lbs of thrust. That was my point as well.

I've got Vaughn's book and have read it over several times. It's spendy and rare to even find but hopefully this will help others...It's one of the best publications ever made on what makes a gun tick...and it's free to download here.
https://archive.org/details/RifleAccuracyFactsFullV1.0FirstFullScan

Some of what he wrote has been proven wrong over time but it is still very much THE best book of its kind I've ever read or see. That's why so many people reference it when making a point.

FWIW, I think Keith is trying to get people to think about thread strength and how much it is compromised by being so loose in the receiver. You can calculate how much of the thread is doing anything and it's not much..and is thin near the crest.

 

[tomswede]

Oh, I agree with you. If you go back a couple of posts, the old tests were brought up where cases were fired with no receiver at all on the barrel. Of course brass will hold some amount, given that it does indeed grip and hold the chamber walls, before stretching and/or failing...but I don't want to be the one standing behind it. No way it holds roughly 7,000-8,000lbs of thrust. That was my point as well.

I've got Vaughn's book and have read it over several times. It's spendy and rare to even find but hopefully this will help others...It's one of the best publications ever made on what makes a gun tick...and it's free to download here.
https://archive.org/details/RifleAccuracyFactsFullV1.0FirstFullScan

Some of what he wrote has been proven wrong over time but it is still very much THE best book of its kind I've ever read or see. That's why so many people reference it when making a point.

FWIW, I think Keith is trying to get people to think about thread strength and how much it is compromised by being so loose in the receiver. You can calculate how much of the thread is doing anything and it's not much..and is thin near the crest.

Curious what Harold V got wrong. The max help the bolt can get from case stretch is of course the tensile strength of brassxcase head cross sectional area.
I got the book just in time before they were all gone, read most of it up at Perry one year.
The good thing about thread strength is that for most applications the treads will fail from the preload not the operating load ( given an appropriate preload).

 

[gunsandgunsmithing]

Curious what Harold V got wrong. The max help the bolt can get from case stretch is of course the tensile strength of brassxcase head cross sectional area.
I got the book just in time before they were all gone, read most of it up at Perry one year.
The good thing about thread strength is that for most applications the treads will fail from the preload not the operating load ( given an appropriate preload).

Not going to go back and review his writings on this specific topic because that's not what I was referring to specifically. I was referring specifically to the chapter on vibration. Technology has allowed us to prove much of his writing as being correct but not all, on that subject in particular.

I'm in no way looking for a debate over something that we mostly, if not completely agree on.