Turning a barrel blank

[cdhknives]

Offering this up for comment and constructive criticism...no old guys around that I know to mentor me and I have read all I can, time to give it a try! Please be gentle! LOL

I may be biting off more than I can chew but here goes. I bought a Green Mountain blank on special, only 21", Stainless Steel, 6mm, 1:9 twist, to build a handy (hoping to get a 20" working barrel but 18" would be ok) 243Win rifle on an old Rem 700 action I have been working with. I have a couple of takeoff barrels thanks to another member here and have swapped them a couple of times, so I have a good working vise and action wrench.

First step, turning to shape. I want a slightly heavy barrel, basically minimum taper forward of the chamber...somewhat because I like the look and somewhat because I don't want to mess with turning a taper. I have a 3/4" spindle bore so I want to turn the forward 3/4 of the abrrel to about that diameter, then flip to turn the chamber end. I will blend the transitions in later. I have to work between centers due to the small spindle bore. That leaves me either losing a lot of barrel to chop off the section under the dog or resetting it to turn the other end. Good or bad? Pic of setup below.


Second question, the blank was off center when I started. I took an hour thinking my pins were bad but in the end I think the blank was really a good 8-10 thou off at one end. Is that common? Pic of center pins below.


My order of operations, let me know if I am missing anything:

1) Rough turn 3/4 of barrel length including muzzle end between centers
2) Flip and rough turn chamber end and taper (steps and grind to shape later in step 4?) transition. Cut and thread receiver tenon.
3) Switch to 4-jaw, use spider on left end of spindle and 4 jaw to align, then cut face for Rem 700, rough chamber (I have Forster reamer and gauges)
4) Go back to centers, use belt grinder to finish sand to final surface (protect lathe from grit!)
5) Return to 4 jaw, final finish chamber by hand
6) Crown
7) Final install on receiver, final verify headspace, reassemble and test fire...

 

[mickri]

I am curious why you don't chamber between centers? Chambering some barrels is on my project list. I also plan to buy my barrels from Green Mountain and will need to contour the barrels. So this thread is of interest to me.

 

[Tozguy]

I think the blank was really a good 8-10 thou off at one end. Is that common?

It is not uncommon.

rough turn chamber end and taper (steps and grind to shape later in step 4?)

Could you not use the compound set at the desired angle to cut this taper in sections?
There would be much less blending to do with the belt sander.

 

[Tozguy]

I have a 3/4" spindle bore so I want to turn the forward 3/4 of the abrrel to about that diameter,

If I understand correctly you plan to turn 3/4 of the length of a 21'' barrel between centres down to 3/4'' diameter so it will fit through the spindle bore.
Do you have a means of controlling deflection of the barrel during the cut?

 

[cdhknives]

If I understand correctly you plan to turn 3/4 of the length of a 21'' barrel between centres down to 3/4'' diameter so it will fit through the spindle bore.
Do you have a means of controlling deflection of the barrel during the cut?

The best I can do is either a steady rest I have never used (another reason to not taper the barrel) or trust to light cuts, sharp tools, and lots of patience. It is relatively short for a rifle barrel and I am maintaining a moderately heavy diameter.

 

[cdhknives]

I am curious why you don't chamber between centers? Chambering some barrels is on my project list. I also plan to buy my barrels from Green Mountain and will need to contour the barrels. So this thread is of interest to me.

The right center is located where the chamering reamer would have to be. I have read that some use a steady rest, others chamber through the spindle. Looking at my equipment I think through the spindle is better but this is a first for me.

 

[Tozguy]

It is relatively short for a rifle barrel and I am maintaining a moderately heavy diameter.

However by machining standards that is a very long skinny piece that best requires a follow rest.
A steady rest could be used but you would have to cut the barrel down in two sections. The steady would be moved over after the first section so the sections overlap.

I humbly submit that cutting the barrel to fit in the spindle bore is an unnecessary constraint. Learn to use a steady rest and follow rest if you have them. Regarding chamber work, the reamer itself becomes the centre. The steady rest is set loose so it does not interfere with the reamer and its only function is to hold the barrel in position while the reamer is withdrawn from the cut for cleaning and lubing.

 

[cdhknives]

I said steady rest above, I meant follow rest. I have both, use rollers for the steady, never tried the follow rest.

 

[Tozguy]

Then you are looking at some fun learning experiences.

 

[mickri]

I recently used my follower rest for the first time. The biggest thing that I learned was that the follower rest needs to be either just ahead of or just behind the tool bit. If not the two will work against each other causing the work to flex. This is what you want for your setup.



This is what you don't want



If the tool bit is just ahead of the follower rest then you have to cut an inch or so, stop the lathe and then place the follower rest against the work. If the tool bit is just behind the follower rest then you can make the cut without having to stop to put the follower rest in position.

There is lots of info online about chambering between centers. Here is one example. Chamber reaming between centres (practicalmachinist.com)