Indexing a prefit barrel

[darkangel_r2]

I did some measurements yesterday and I need some info before I try anything.

The first question Is for people who index your barrels. Do you think I can use thickness between the bore and the outside of the muzzle to determine muzzle runout? Is that a fair indicator of where the bore is pointing? My thought is the thinnest measurement would indicate the bore is curved in that direction.

The second question is for anyone who makes barrels for savage rifles. What is the exact function of the inside bevel that I highlighted in the picture below? Is it necessary? if it is how small can you make it and still have proper function?

Thanks guys.

 

[matthias]

Barrel Indexing and Barrel Nut

I was reading this thread and a response by Trevor (screen name Hengehold), and it got me to wondering about a potential downside of a barrel nut design. http://forum.accurateshooter.com/threads/indexing-a-rifle-barrel.3902203/ Bottom line, with a barrel nut, the barrel is screwed in until...

forum.accurateshooter.com

 

[B Nettesheim]

The hole in the barrel is not necessarily concentric to the outside, to answer your first question, no. With your prefit, once you set headspace it will “point” wherever it points

 

[6MMsteve]

The hole in the barrel is not necessarily concentric to the outside, to answer your first question, no. With your prefit, once you set headspace it will “point” wherever it points

correct

 

[6MMsteve]

you can get a shouldered savage barrel, with the correct numbers and it can be timed, if you shot the same action and the GS had the numbers he can clock and time a shouldered barrel, I tink

 

[darkangel_r2]

The hole in the barrel is not necessarily concentric to the outside, to answer your first question, no.

So the thinnest wall at the muzzle has no correlation to bore curvature? Is that what you are saying?

 

[PigButtons]

So the thinnest wall at the muzzle has no correlation to bore curvature? Is that what you are saying?

Yes, that is what he was saying.

 

[darkangel_r2]

Yes, that is what he was saying.

Is there a good way to measure that without a lathe?

 

[DirtySteve]

Is there a good way to measure that without a lathe?

Not that I know of...

 

[whatsupdoc]

Typically a "prefit" has a shoulder and is prefit for a particular action so there is no indexing, what you have there in the image is a barrel nut setup and it would index on where the go gauge stops it.

The inside bevel is kind of a feed ramp to guide the case into the chamber smoothly, how
small it can be would require trial and error depending on the rifles configuration.

What are you trying to achieve? That is the real question.

 

[darkangel_r2]

What are you trying to achieve? That is the real question.

Indexing a barrel nut prefit.

 

[Dusty Stevens]

Only way to index it is to set it up in the lathe and adjust the chamber to clock it to your action. At that point you can get rid of that curiously large case base swelling bevel.
but to tell you the truth, if its a halfway decent barrel done by a halfway reputable company its going to be a waste of time. You wont be a minute off on a real cheap barrel. By the time you have this done you can get a shouldered barrel installed perfectly clocked

 

[darkangel_r2]

Only way to index it is to set it up in the lathe and adjust the chamber to clock it to your action. At that point you can get rid of that curiously large case base swelling bevel.
but to tell you the truth, if its a halfway decent barrel done by a halfway reputable company its going to be a waste of time. You wont be a minute off on a real cheap barrel. By the time you have this done you can get a shouldered barrel installed perfectly clocked

Let me explain my measurements and my thought process. From the bottom of my brass to the case web is .150". My boltface is .110" deep. Savage actions are 20 turns per inch so a full rotation is .050". So max travel to a vertical 6 or 12 o clock indexing would be around .025".

If that breech bevel was eliminated I would have .040" of slop available for me to position the barrel before the case web would start to be unsupported. I only need .025" for vertical indexing. If that bevel can be minimized or eliminated I think I can do the following.

Thread the barrel all the way down until it contacts the bolt face. Then thread it out until its in its first vertically indexed position. If that position has sufficient gap between the Bolt and barrel and is shorter than go gauge I can progressively sand a shell holder to get brass resized in my die to fit the chamber after trimming the extra neck off.

If its longer than no go gauge I would just do a jam fireform light load fed from the magazine to reduce case head wall thinning on this first shot then just size my brass long for use in that gun.

If that position falls between go and no go its business as usual.

It depends on that back bevel cut. If I can eliminate it or significantly reduce it I can do this procedure without the case web of my brass losing support and ruining brasslife or blowing primers every shot.

I'm pretty sure savagedasher used to do this.

Just need to find a way to measure bore curvature without a lathe.

Suppose if I need to I can just write a clock face on the muzzle and shoot some excessively shortened brass light jam loads with the barrel indexed in these different positions and just mark which position shot high and which shot low. That sounds like a lot of work.

But I bet I can get close just by checking chamber and muzzle wall thickness with a ball mic and comparing their max and min thickness positions.

 

[Dusty Stevens]

Let me explain my measurements and my thought process. From the bottom of my brass to the case web is .150". My boltface is .110" deep. Savage actions are 20 turns per inch so a full rotation is .050". So max travel to a vertical 6 or 12 o clock indexing would be around .025".

If that breech bevel was eliminated I would have .040" of slop available for me to position the barrel before the case web would start to be unsupported. I only need .025" for vertical indexing. If that bevel can be minimized or eliminated I think I can do the following.

Thread the barrel all the way down until it contacts the bolt face. Then thread it out until its in its first vertically indexed position. If that position has sufficient gap between the Bolt and barrel and is shorter than go gauge I can progressively sand a shell holder to get brass resized in my die to fit the chamber after trimming the extra neck off.

If its longer than no go gauge I would just do a jam fireform light load fed from the magazine to reduce case head wall thinning on this first shot then just size my brass long for use in that gun.

If that position falls between go and no go its business as usual.

It depends on that back bevel cut. If I can eliminate it or significantly reduce it I can do this procedure without the case web of my brass losing support and ruining brasslife or blowing primers every shot.

I'm pretty sure savagedasher used to do this.

Just need to find a way to measure bore curvature without a lathe.

Suppose if I need to I can just write a clock face on the muzzle and shoot some excessively shortened brass light jam loads with the barrel indexed in these different positions and just mark which position shot high and which shot low. That sounds like a lot of work.

But I bet I can get close just by checking chamber and muzzle wall thickness with a ball mic and comparing their max and min thickness positions.

Think about coming thru a door straight and right thru the middle, now think of coming thru that same door at a 45deg angle but as you clear the plane of that door you are exactly in the middle. This is why you cant measure it- its the approach. Remember they profiled the outside with centers in that hole youre measuring.

 

[darkangel_r2]

Think about coming thru a door straight and right thru the middle, now think of coming thru that same door at a 45deg angle but as you clear the plane of that door you are exactly in the middle. This is why you cant measure it- its the approach. Remember they profiled the outside with centers in that hole youre measuring.

I got ya thats my misunderstanding. What kind of rod do you use in the bore to indicate runout?

 

[Dusty Stevens]

I got ya thats my misunderstanding. What kind of rod do you use in the bore to indicate runout?

Deltronic pin

 

[sdean]

Deltronic pin

If you indicate both ends how do you clock a barrel. Each end would be running true? I do my 2 points at the chamber.

 

[Dusty Stevens]

If you indicate both ends how do you clock a barrel. Each end would be running true? I do my 2 points at the chamber.

You have it right. Use the deltronic to see where it goes. Never said i indicate both ends but i do move both ends. Cant get my words out right