38-55 Trapdoor

The main reason I abandoned the trapdoor and got the Pedersoli rolling block was the barrel.   I’m not convinced that the rolling block action is any better than the trapdoor, and in some ways it is worse, but there was no getting around the worn and slightly pitted barrel.  The long term solution was a new barrel.

I pondered four options.  The first was to get an original barrel with crisp rifling.  I found that hard to find, and believed it to be too expensive, though it wasn’t bad compared to my final solution.  The second was to get a new barrel made to the original external shape.  This would allow me to move away from the original three groove, twenty two inch twist if I wanted.  This option is easier to find, but again money held me back.  The third option was to reline the barrel to 45-70.  This could either be the original three groove configuration or something different.  The last option, and the one I chose, was to reline to a different caliber.

The reasoning for the change in caliber was twofold.  The first was strength.  The relining process bores a hole all the way down the barrel and fills it with a thin barrel.  How strong this system is depends greatly on how well the inner liner transmits load to the outer remains of the original barrel.  When I looked at the wall thickness of the liner for the 45-70, I decided I just liked the 38-55 wall thickness better.  Both liners had the same outside diameter.  The second reason was accuracy.  The 38-55 has a fine reputation at medium ranges, and since I normally shoot at 200 yards, it seemed to be the cat’s meow.  A third, more subtle, benefit is reduced recoil.  I’m not much affected by recoil, but it could be a driving factor for some lighter framed shooters.

The  Process:

I’ve never done a reline of a barrel before, but I’ve spun a lathe a bit.  I knew that the #1 problem in most repair jobs is how to accurately and rigidly hold the work piece.  With the outside of the barrel tapered along the full length I knew that no chuck or collet I owned would do the trick.  I opted to pick up 2 “soft” collets.  These are steel, though they also can come in brass or plastic, that is machinable.  I set my lathe to cut the same taper as the barrel in the bore of the collets.   One grips the barrel a few inches from the breech, with the breech sticking out.  This is where 90% of the work is done.  The other grips a few inches from the muzzle for cleaning up the crown.  I will issue a warning that the collet near the breech left a few light scratches that seemed to have been put in just as I was seating the collet.  In my case I was unconcerned because I had bought a crusty rust pile barrel to do this to.  It was going to get a full refinish.  Also, the front collet struggles to get over the front sight.  The removable blade sight needs to be pulled, and a notch cut in the collet.

Before machining can begin, a bit of tool fabrication is required.  The main task is to make a long drill bit.  I purchased a bit with a bore riding pilot from Pacific Tool and Gauge.  It is a well made unit ground to the OD of the liner.  The trouble is that the shank is short.  I took a length of precision ground rod and bored a hole in the end that is a slight press fit for the shank, then pushed it in with Loctite.  Some people claim to weld the extensions on, but I can’t see how there isn’t heat warping involved.  The drill loads seemed very light anyway.

 

The shot above is the drill being held with the pilot in the chuck for alignment, being pushed onto the end of the steel rod that has been bored in the lathe collet.  The rest of the rod is about 3 feet long and rests inside the lathe spindle.

There are a few accuracy concerns in this job.  The first is that the drilled out bore needs to align with the original barrel for a neat, concentric crown.  The piloted drill pretty much assures this.  The second is that the chamber need to be concentric to the new bore, aligned to the new bore, and of the right dimensions.  Some of this is assured by using a piloted reamer.  The front of the reamer is thus forced to be true to the bore.  The rear of the reamer remains true to the bore solely by dint of all the cutting steps being taken in the same setup.  No removal and realigning of the barrel is required.  It is also a good idea to check alignment of the lathe tailstock in preparation for this job.  If the tailstock is offset, the reamer will be pushed to the side and will cause an excess taper with too large an ID at the breech.  You may also see an uneven amount of cutting on each of the reamer flutes in this situation. 

This shows a tap handle driving the reamer and a dial indicator to show the depth of cut, for when the final headspace is being cut.  Some companies make a floating reamer driver that can be aligned perfectly to the bore.  This is probably a good idea if you were super serious about accuracy.

The last accuracy concern is headspace, the control of the depth of cut.  In a rimmed cartridge, this becomes simply controlling the seating face for the cartridge rim.  You can choose to set per SAMMI specs, which will allow all cartridges to load.  Most target shooters set for minimum clearance on whatever brass they choose to shoot.   I used Starline and found they tended to have thin rims.  This allows me someday to do a cleanup cut on the chamber and use brass with a thicker rim.  It also means some other brass might not allow the action to close right now.

If the old action had good headspace, a simple depth measurement from the end of a seated cartridge to a fixed feature like the thread shoulder is all you need.  If you want a different headspace, some corrections can be made from there. 

The drilling went easily, with the trapdoor barrel being fairly soft and making “crumbly” chips.  The liner was glued in with green “shaft lock” type Loctite.  A little facing was done on the breech, then the chamber was cut.  This was done unpowered using the lathe for alignment.  The final cuts took a few iterations of fitting the breech block to check headspace.  When the barrel is removed and flipped the crown could be cleaned up.  I’m a little displeased with the crown.  When the cutter skims over the lands and grooves, it leaves little uneven burrs that I couldn’t quite control with any of the normal cutter tricks.  I’m also unable to prove the crown is truly concentric with the bore, since the setup had to be dismantled and flipped.  People seem to rave about an 11 degree crown.  It seems to me a true zero degree crown could be machined more reliably, and that might overcome a poorly made 11 degree crown.  Either way, I have ordered an 11 degree piloted hand crowning tool and will give that a try.

One final challenge.  The original extractor is too thin to reach the smaller cartridge rim.  I fabricated a new one and cut the notch for it in the relined breech.

 

This standard T-slot cutter fit the bill nicely.  I have never had nice "clinky" ejection, even with a 45-70.  I have seen it done and it is pure magic when the indians are raiding.  For target work, I am fine with the more restrained control of spent brass that my trapdoor ejector gives me.

 

Here's a shot of the 38-55 nestled in the big-bore-breech.  Cute!


Cost totals  (Some are guesses):

Old barrel, receiver, door. $75-100
Liner  $5.39/inch   Track of the Wolf.com
Drill  $75
Shank  $20
Reamer $95
T slot Cutter  $15
Crown tool  $85
Brass  $62
Dies  $50
Headspace gauges - cheap, but a total waste.  In bottleneck cases they measure something difficult to measure and important for safety.  In rimmed cartridges, they are glorified washers, and you should learn basic measurement techniques instead.

How does it shoot?  Well, I can’t let all my secrets out in one blog.   Stay tuned.