Machinist advice for making a Handi stub barrel and the exact procedure to do so.

[corbinace]

I have done very little on a lathe and want a bit of hand holding if you are game. Feel free to critique anything you do not see as correct.

I am turning a Handi 12ga Shotgun into a small garden gun in 32 S&W Long.

I have decided that the way I want to proceed is to turn the Stainless Green Mountain 19" raw 7.62" barrel https://www.gmriflebarrel.com/GMRBIt...f-8bc26e0bc27e down enough to insert from the breach of the shot barrel.

The shot barrel will be left about 12" long to the front of the handguard and cut off diagonally top being shorter.

The rifled barrel will fit firmly in the shot barrel. It may be epoxied, set screwed, or maybe just held by the interference of heated outer and cooled inner.

I would like for you to look over my shoulder and see if the machine work is going to be done in the most efficient manner, so here goes:

Barrel turning sequence to fit a rifled barrel into a 12 ga., 2-3/4” chambered Handi barrel.

Install the 19”x1.250" raw rifled barrel into the lathe.

Muzzle onto the centering tailstock and breach end in the four-jaw chuck about one inch.

Install the follow rest to support the long thin barrel. Or do I use a steady rest in the middle and turn the barrel one half at a time?

12ga chamber dimensions; http://www.dave-cushman.net/shot/shotshellloads.html

Cut the 1.250” barrel down to 0.866 for the rim of the shot shell bore.

Leave 0.250 for this rim diameter and move to the next step cut.

Cut the next step of the barrel to 0.812” for 2.740”. This should make the forward portion to the chamber step become an interference fit just before the end of the chamber.

The next step is to turn the rest of the barrel down to 0.7285 or what ever will allow the shotgun barrel to slide over the rifle barrel.
I will be able to remove the tailstock to check fit before removing the barrel from the chuck. This way I get to test fit without removing from chuck and changing things.

Once I am satisfied with the rifle to shot barrel fit, I can use a parting tool to cut the barrel off from the chuck inside the ¼” of 0.866 first turn, being sure to leave more than 0.074 for the rim thickness.

Now I can turn the barrel around, stick it into the chuck and face off the breach face to the exact length for flush fitting into the shotshell chamber and nearly zero headspace against the receiver.

Now turn the barrel around in the chuck again, to face off and crown the muzzle.

[Der Gebirgsjager]

Hi corbinace-- you might find an interesting thread or two by doing a search of our archives about stubs, written by Texas by God with photos.

DG

[corbinace]

Hi corbinace-- you might find an interesting thread or two by doing a search of our archives about stubs, written by Texas by God with photos.

DG

I have seen TBG's thread. That is my plan once I get the rifle barrel turned down. I have never gotten to do much lathing and am hopping for some hand holding in the actual removal of the excess metal. Maybe it is not all that tough, but not having done it, I am a bit apprehensive.

I guess worst case is that I mess it up and have to spend another C note on a second try barrel.

Thanks for the direction.

For others, here is the thread mentioned; https://castboolits.gunloads.com/sho...ht=stub+barrel

[country gent]

Several things to know starting out.
1) have the tool on center if the piece sharp and lightly honed.
2) experiment with speeds and feeds. There are charts that give a starting point or 4 x 100 / diameter for cold rolled steel
3) Use a 4 jaw chuck indicate bore in on a pin and cut the centers with a small boring bar both ends. leave extra length to remove these once installed.
4) use copper brass or aluminum shims between jaws and parts.
5) Dont worry about being efficient, take your time and make sure its right. Work slow and easy enjoy the process.
6) Instead of scrapping a barrel, buy a length of steel of the same as barrel. Machine it first working thru each step.

Not knowing the lathe your using, swing,length between centers, tooling available, its hard to give specific help

[country gent]

Several things to know starting out.
1) have the tool on center if the piece sharp and lightly honed.
2) experiment with speeds and feeds. There are charts that give a starting point or 4 x 100 / diameter for cold rolled steel
3) Use a 4 jaw chuck indicate bore in on a pin and cut the centers with a small boring bar both ends. leave extra length to remove these once installed.
4) use copper brass or aluminum shims between jaws and parts.
5) Dont worry about being efficient, take your time and make sure its right. Work slow and easy enjoy the process.
6) Instead of scrapping a barrel, buy a length of steel of the same as barrel. Machine it first working thru each step.

Not knowing the lathe your using, swing,length between centers, tooling available, its hard to give specific help

[kenton]

If you want to do a shrink fit you will need to accurately measure (not the ID jaws on your calipers) your shotgun and make it to the numbers calculated by the expansion ratio of steel. The worst case scenario is not getting the barrel fully inserted before the temperatures normalize. If that happens there is basically no non destructive method to separate them.

tube expansion calculations
https://www.engineeringtoolbox.com/t...ge-d_1612.html

Saami Shotgun chamber specs
https://saami.org/wp-content/uploads...2019-04-23.pdf

[Somebody]

Why are you cutting the shot barrel diagonally? Is that just an aesthetic choice?

You can simplify the barrel contouring by boring the shot chamber to a plain cylinder all the way past the forcing cone. Then your insert barrel only needs a single step.

[corbinace]

Thank you contry gent and kenton. Those are the kind of tips I was hoping to learn. There is just so much we do not know that we do not know.

Your posts give me a lot to research and learn.

Thank you both.

[corbinace]

Why are you cutting the shot barrel diagonally? Is that just an aesthetic choice?

You can simplify the barrel contouring by boring the shot chamber to a plain cylinder all the way past the forcing cone. Then your insert barrel only needs a single step.

Yes, purely aesthetics for the diagonal cut. The shot barrel is blue and I intend to leave the SS rifled barrel silver, so I thought it would look better than a blunt cut.

I had considered reaming the shot barrel straight through, but I had thought that I may not have the skills or tools to do that job. The shot barrel will be almost 12 inches long to the front of the handguard and nine inches of boring/reaming seemed a bridge too far.

Thank you for weighing in with your suggestion, I do appreciate it.

[Texas by God]

I can’t help with machining advice, but I will tell you that they are habit forming…and quite fun. Great choice of cartridge, too.
Show us your progress as you go, please.


Sent from my iPhone using Tapatalk

[corbinace]

I can’t help with machining advice, but I will tell you that they are habit forming…and quite fun. Great choice of cartridge, too.
Show us your progress as you go, please.


Sent from my iPhone using Tapatalk

I will try to serve up a step by step, but you have set the bar pretty high with your photography posting skills.

[Reg]

Thru the years I have turned quite a few barrels and the one big trick I have found that has helped more than anything is when turning the OD is a razor sharp high speed tool turning at a low rpm and turning from the headstock to the tail stock. Keep the barrel cool, keep adjusting the tail stock. Sharp high speed steel will cut with less tool pressure than carbide. I am not sure why but cutting from the headstock to the tail stock just seems to work better and it’s easier to control size and taper.

[corbinace]

Thru the years I have turned quite a few barrels and the one big trick I have found that has helped more than anything is when turning the OD is a razor sharp high speed tool turning at a low rpm and turning from the headstock to the tail stock. Keep the barrel cool, keep adjusting the tail stock. Sharp high speed steel will cut with less tool pressure than carbide. I am not sure why but cutting from the headstock to the tail stock just seems to work better and it’s easier to control size and taper.

Thank you for that tip Reg. Due to my lack of experience at sharpening tools, I would have immediately opted for a new carbide insert, had you not spoken up.

I will remember the Head to tail order as well. Lucky for me, I am not planning to taper the barrel to the muzzle, so that takes a bit of the challenge off the plate for this first attempt.

I have a Word document with all of the steps in the OP. As I get these pointers, I am updating the document. I intend to have it right there with me on the machine so I can follow along and not miss a step/tip.

Thank you for taking the time to post.

[Tatume]

That 12" shotgun barrel may cause trouble with the ATF if the attachment to the longer rifled barrel doesn't meet their definition of permanently affixed.

[corbinace]

That 12" shotgun barrel may cause trouble with the ATF if the attachment to the longer rifled barrel doesn't meet their definition of permanently affixed.

That is a valid concern, as most of the stubs that I see are only using the chamber portion of the barrel. I wanted to use more to retain the snap on forearm and the stud it snaps onto. The snap on forearm also snaps up tight against the existing barrel. That is the reason for retaining so much of it.

I had not thought of the actual ATF definition of "permanently affixed". I guess I need to look at their definition and make sure I install whatever provision they need to see. Safeguarding yourself from possible incrimination due to ignorance is paramount. As for me, I had not thought of it as removable, but rather, permanent and never going to be disassembled.

Thank you for your input.

[Jedman]

Hi corbinace, I have built dozens of barrels with a method similar to what you are thinking of doing.
First off unless you want the barrel to be stainless, Green Mountain sells a 17” blank in 7.62 cal. for quite a bit less and should work as well. When I turn blanks I use a steady rest somewhere near the center to keep chatter down and don’t mess with a follow rest. I will tell you I have used many GM blanks and they are quite good but no blank I have ever started with is ever turned true from the bore to the OD of the blank.
So what I would do to start is face off both ends of the blank, and if you have a large center drill just hold it in your hand while the blank if running as true as you can chuck it up and just use the 60 degree center drill to slightly chamfer the bore at both ends. Then set the blank between centers and take a couple very light cuts only a few thousands deep until you have the whole diameter cleaned up where you want to run your steady rest. Then once you have it set up between centers, the center in your tailstock must be a live center - take some light cuts cutting towards your steady rest. You will probably need to play with spindle speed and feeds to get the tool to cut good but once you have a smooth cut between the live center and the steady rest stop and measure both ends of the new cut surface.
You will most likely have some taper from one end of the cut to the other. So figure how much you need to move your tailstock to correct the taper and the steady rest must be backed off the blank then make your adjustments. Then you need to recut the surface where your steady rest runs then reset it and make a few more light cuts and measure again for taper and repeat until you have the lathe cutting straight.
Then flip the blank end for end and set the steady rest to run on the area you just turned true.
Again make some cuts towards the middle of the blank and stopping to measure well before you are close to your finished diameter. Once the blank gets warm / hot enough where it’s uncomfortable to grip it with your hand and hold it stop and let the blank cool for 15 mins.
I generally swap the blank end for end several times and each time making sure you are cutting strait and resetting the steady rest as as the blank gets smaller the wear surface on your steady rest wears and needs reset and lubricated.
I generally leave around .005 between the finish turned liner and the bore of the shotgun and chamber.
I have used several different 2 part epoxy’s , acraglas, loctite, to bond the liner to the shotgun barrel the only thing I will say about whatever you use DONT use any fast setting adhesive! You will find that it takes some time to coat the OD of your liner, coat the ID of the shotgun barrel and once you try to push the liner into the barrel you will have quite the mess of excess epoxy or loctite squeezing out and there will be trapped air at the front of the chamber that will resist seating the liner. I use a length of 1/4 x 20 all thread rod with flat washers and nuts to draw the liner in tight and keep it there until the adhesive is set up. That’s the reason you don’t want any quick set adhesive as it will start setting up and most likely you wount have the liner installed all the way and it will freeze up making for a real bad experience.
It is also not a bad idea to drill a 1/8” hole through the shotgun barrel on the bottom side about 3 3/16” from the breech if it’s a 3” chambered barrel in front of the lug so trapped air and excess adhesive has a place to exscape when assembling the barrel. If you got the picture of what a mess this usually makes it makes sense to cover all areas of your shotgun barrel with masking tape before you start and where disposable gloves and have everything you can think of that you will need right where you are going to work as it’s stressful when you are working against the clock with adhesive and you don’t want to be rushed as to get screwed up, I have learned the hard way !

I have made barrels where the inner barrel is recessed from the outer barrel like what it sounds like you plan to do. Nothing wrong with that except if you are using the all thread rod to pull the liner barrel into the longer shotgun barrel be sure you have the process figured out first and be prepared.

This was super long winded and you probably already had most of this fiquered out so I will stop writing about this as it was a lot of things learned from the first barrel to the dozens I have built.
Added : After rereading you are using a 2 3/4” chambered barrel if you drill the hole I mentioned it would be about 2 15/16” ahead of the breech that puts it in the forcing cone area.
When I first read the 12” barrel ahead of the hand guard I thought you were talking a longer outer barrel and the muzzle of your inner barrel would be recessed so I had that wrong.
I also recommend using a hi speed or cobalt steel tool bit sharpened with a small ( tiny) radius at the tip of the tool and honed with a stone as sharp as you can get it. GOOD LUCK !
Jedman

[corbinace]

Hi corbinace, I have built dozens of barrels with a method similar to what you are thinking of doing.
GOOD LUCK !
Jedman

Quote redacted for space.

Wow Jedman, that is a mouthful!

I saw the 17" barrels, but was concerned that I would not have enough excess to comfortably make the 16" rule after trimming the ends. The 24" ones were out of stock.

I did not know the tail stock could be misaligned until you posted and I went researching. Great tip.

Another great tip is the bleed hole for air and epoxy at the step of the chamber, and clamp-bolt for holding against the hydraulic effect.

You say: "if you have a large center drill just hold it in your hand while the blank if running as true as you can chuck it up and just use the 60 degree center drill to slightly chamfer the bore at both ends"
I am not picturing that and country gent mentioned something very similar, I will do some research and see if I can get my head wrapped around your instructions.

Thank you for taking the time to write such a concise narritive.

[Jedman]

Basically you are just just saving time in stead of trying to indicate each end of the blank in perfectly to cut 60 degree centers in the bore. By just holding the center drill in your hand it’s kinda like a floating reamer holder. You really don’t have to have angled centers in the blank because you are turning the blank strait without taper so you’re just slightly chamfering the ends.
Also to save time, if you have a 3 jaw chuck installed on your spindle just chuck a 1/2” bolt or whatever and set your compound rest to 30 degrees and cut the bolt to a point. So now you have a 60 degree center that’s true to the spindle, no need to remove the chuck and use a dead center and face plate all you need is a lathe dog on the barrel with the end against the side of one of the chuck jaws to drive the blank.
On my lathe I don’t have coolant so I use a small acid brush and slop on a thin coating of automotive ATF fluid for cutting fluid. I take light cuts and it seems to work well for me.
If you turn the blank between centers the way I mentioned the end you chamber should be good as is but the muzzle I usually cut back 3/32 or so and crown it so any damage to the lands is removed.
You should be able to use that 17” blank and finish the barrel no shorter than 16 3/4” if that looks OK to you. It’s plenty to get all there is power wise from a 32 S&W long.
One other tip, if you are going to D&T the top of the barrel for a scope base do it before you glue in the liner, you can drill clean thru the barrel and it makes the chance of breaking a tap much less. When you have everything clean before gluing in the liner put the scope base screws in the tapped holes and make sure the liner slides in and doesn’t hit the ends of the screws and after the barrels are glued together remove the screws before the adhesive starts curing.
Jedman

[marvelshooter]

Basically you are just just saving time in stead of trying to indicate each end of the blank in perfectly to cut 60 degree centers in the bore. By just holding the center drill in your hand it’s kinda like a floating reamer holder. You really don’t have to have angled centers in the blank because you are turning the blank strait without taper so you’re just slightly chamfering the ends.

Jedman

For what you are doing I would recommend a 3 or more flute 60 degree countersink instead of a center drill which is only two flutes. The counter sink will jump around less and produce a smoother cut when hand held. Just my two cents from the cheap seats.

[Jedman]

For what you are doing I would recommend a 3 or more flute 60 degree countersink instead of a center drill which is only two flutes. The counter sink will jump around less and produce a smoother cut when hand held. Just my two cents from the cheap seats.

Yes absolutely! That’s what I use most of the time is a case inside/ outside deburring tool, LEE maybe ?

Jedman