Cutting and crowning

D

Doc Hoy

New member
I bought a Trapdoor Springfield cadet rifle with a 29 inch barrel. The rifle has the stock cut down to look like a cavalry model. But it sure looks funny with that 29 inch barrel. Because of the shortened stock and a bunch of missing stock hardware the collector value of the rifle is almost nil. I bought this rifle specifically because of that fact and hence I got it for a good price. (About $425.00).

I have not shot it yet but I think that it will be a relatively consistent shooter. The bore looks good.

I think that eventually I will want to cut the barrel to 22 and then recrown it.

Cutting the barrel.......

I have a lathe and know how to use it. It is up to the task as far as precision is concerned. But I have read and viewed a couple sources that imply that it is better to cut the barrel with a saw. Is this because most sources assume that a lathe is not available? I'd like to cut it with the lathe unless there is something I am missing.

Crowning the barrel.......

I can easily crown the barrel by changing tools and resetting the tool post. But I am concerned that the bore may not be concentric with the outer diameter of the barrel. Is it better to just do the crown with a hand reamer?

Mounting the sight.......

My plan is to solder a sight in place before cutting the barrel. I intend to use the existing sights to line up the sight on the shortened barrel. Is that a good plan?

Tnx in advance folks.
 
Doc,

Can't address the last questions but being a lathe-friendly guy: I'd cut off the bbl as square as possible with a saw and then true it on the lathe. Face it off, and then see about crowning it in the lathe. It's probably concentric to bore anyhow. You'll know once you spin it. Your lathe will accept the bbl thru the headstock and chuck, I assume?

Willie

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Yep

Willie,

Yes, I have had the barrel in the lathe just to check the fit.

I will have to shim the barrel at the back of the lathe spindle. I figure to make the shims from brass stock.


Thanks for the response.

This present sight is not dovetailed to the barrel and I am fairly certain I will apply the new sight the same way.

I am seeking a foolproof way of locating the new sight in proper alignment.

Any advice is much appreciated.
 
I think your proposal to silver solder it in place using the original sight as an alignment jig before you shorten the bbl has merit.

What do you need to shim? 3 jaw chuck I assume?


Willie

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Yep

Willie,

Yes the chuck should be padded with something and I am thinking I will make some brass pads.

Also, the diameter of the barrel at the spot where it passes out of the back throat of the spindle is slightly smaller than the diameter of the throat. So I will need something to shim the barrel there.

I have some rubber sheet stock but I have never tried that and I am afraid the barrel will not be held secure enough in the chuck.
 
Really, if your chuck jaws are not buggered with any burrs, you can wipe them down with a clean rag, msking sure there are NO chips on the jaw faces, and clamp the bbl in them tightly without marking the barrel. Marks come from two things: high spots (burrs and debris) or movement. Clamp the crap out of it and you should be fine. You DO NOT want to use (rubber, leather, cloth, etc) as you will not be able to clamp it rigidly, or it clamp it true. You're better off "steel to steel".

You "can" use thin brass shim stock (0.020 or so) but you might reconsider this.

At the point where the action sticks out of the headstock, the bbl should be rigid enough to not need more than a rag stuffed into the back of the spindle to keep things ok. Moderate turning speed unless you want to dynamically balance the entire thing. You can set up a lot of vibration as the action puts asymmetrical mass on the rotating assembly. Just take your time.


What lathe?


Willie

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I would clean and degrease the crap out of the jaws, clamp it tight as you can, and have at it.

If you need/want to pad the jaws, consider using a cut up business card with one pad placed on each jaw.


Willie


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To shorten our barrels, we used a hacksaw instead of a parting tool mounted on a lathe. We had lead jaw pads on our vise to prevent the polished barrel from being scratched and then went at it with a hacksaw.

The barrel was then wrapped in masking tape to prevent it from being scratched when placed back into a four jaw chuck. Shim made from a soda can protected the barrel where the jaws clamped down on it. Then a spud the diameter of the bore was inserted into the bore and a dial indicator placed against the spud to ensure that the barrel was concentrically mounted in the four jaw chuck. Remember, all that tape and the aluminum shims can cause the barrel to be mounted some what offset. Hence the use of a four jaw over a three jaw chuck. With the four jaw you can adjust the jaws until the workpiece is perfectly concentric.

Next we ground a crowning bit which was placed against the muzzle to crown it. The bit was placed 90 degrees to the muzzle and was concave shaped. It was fed straight in when we moved the saddle forward (toward the headstock). That gave us the decorative crown. For the actual crown, we used the Brownell hand turned crowning tool that had a pilot that dropped into the bore to keep the tool straight. Gentle pressure and the crown has to be chatter free to be acceptable.
 
I was taught to use a 4 jaw chuck and adjust to the bore of the rifle. I usually make a set of bushings that fit the bore and hold a ground rod that sticks out the bore, then dial indicate and adjust off of the rod.
 
^^^

Both of those are pretty much how I would do it with a 4 jaw in a shop set up to do this. My advice is based on a low volume home job using a 3 jaw chuck. Remember also that this is not a new-blue sporting rifle. Finish is already 125+years old. Three jaw, lock headstock, tape bbl, towel over ways, and hacksaw to start. Unlock headstock and face to square. Very likely could crown to "19th century contour" with a file against the spinning work.

Now if he has a 4 jaw... Mandrel and dial indicator = perfection. You guys are dead on right.


Willie

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Guys.....

...Y'all are great....

This is where I had hoped the question would go.

As it happens, I do have a four jaw chuck and a dial indicator.
 
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