More info - reviving the topic
It has been a while since we discussed Trap Door Rifle repairs. I have had occasion to continue to study this subject and learn some things. I am seeing other posts out on the net; and with all the political nut-talk on attacking owners of semi-automatic weapons in the press as of late, I do think single-shot rifles are going to spike in popularity. Especially antiques and repros and BP cartridge models.
The H&R Trapdoor is somewhat controversial in that you find followers that either love the H&R or hate it. Many opt for the Italian models. As for wanting the old Springfield originals, I totally understand the interest there. Old originals are a caution because you cant see cracks and changes in the metal so you need to be careful what you do with those. Old guns can burst if you are not careful and intelligent with your catrdige-loadings and care in the inspection and maintenance of the old guns.
Blown doors on the H&R seem to be common because of the unique method H&R employed in locking the door. H&R used a two-piece thumb/cam lock, on which the cam is on a round shaft, held in it's precisely clocked position by a single set-screw that tightens with an hex-wrench to the smooth surface of the cam. It drifts under pressure and loosens and the door pops open.
Here is what I have learned and I am looking for any corrective info from experienced riflemen and smiths:
1. The door pivots on a hinge-pin. If it pops open with enough force, the hinge pen warps or bends and it adds to the problem of the door popping open. REPLACE BENT HINGE PINS. If it is straight and true, it enhances the security of locking the breach.
2. The door is designed to swing closed to a position slightly past the "0" degree mark - ever so slightly - so that the emphasis of the recoil is not fully on the cam, the shaft, or the hinge pin. It is designed to line the breech up to place recoil mostly on the back of the receiver. As there are pivots points involved in the breech mechanism, some force is obviously transferred to the pivot points and the cam and shaft, but most of the force is on the back of the receiver if the door is correctly aligned.
3. At the pivot point under the hinge pin, there are recesses machined in which the edge of the breech block swings into place up under the ears in which the hinge pin passes through, providing some security under pressure.
4. The cam on the H&R is on a round shaft and not a square shaft. The set screw is all that holds it into place. Originals had a one-piece shaft and cam. Italians seem to have a square shaft and a square hole in the cam so it cant rotate on the shaft. Italian cams and original cams and shafts dont readily fit the H&R. It takes some very creative and intense machining to use those on the H&R. Some gunners will replace the breech block in order to get a better cam lock arrangement and this too requires grinding, filing, fitting and perhaps some very creative light machining. You really need a machinist-type smith at your disposal to do this.
5. If you fix the H&R by drilling a dimple in the cam or by filing a flat spot in the cam for the set-screw to bite, there is a problem that can arise. The cam slips and distorts the set-screw and this affects the set-screw threads to the degree you cant get it to back up, or in some cases to go forward and you wont get it OUT of the cam if this happens. Leave the shaft alone. Dont drill and dont file.
6. The best fix for the H&R seems to be to place a minute bit of anti-seize compound on the set screw threads - very minute - and using a new set screw, clock the cam and tighten the set screw on a normal shaft. The anti-seize will allow you to get it out if you need to, but it will also provide some resistance to the set-screw loosening on it's own. Using lock-tite makes it difficult to get the set screw out if you need to. Replace any worn or bent hing pins. ALWAYS use a fairly strong coil spring behind the cam, not a weak one. Use a clean, round shaft and not a torn up shaft. When you fire your rifle, you need to ensure the set screw is fairly firm as a part of normal maintenance. The hex-key over time wears out the socket in the set-screw; therefore you need to keep extra set-screws in your kit and replace it with a fresh one BEFORE the socket wears too much from regularly tightening it. You need to keep FRESH hex-wrenches in your kit because they too wear from regular use - particularly the small sizes. Buy extra screws and wrenches and throw away any that become the least bit worn. You need to keep your loads conservative because we are firing a trap door and not a bolt gun or falling block. You never, ever close the "door" without raising the thumb lever, so you dont put wear and tear on the surface of the cam.
7. The cam need only stay in place. The set screw is not the entire locking mechanism. Having the cam clocked precisely in place will transfer the bulk forces that make it to this part of the action to the surface of the shaft.
Of course the ultimate FIX is to have a competant smith machine breach block from a pedersoli or a decent original to fit the H&R thus completely eliminating the cam problems. However; performing maintenance on the H&R in it's pristine form will see you through. It is not a bad system but you cant neglect it. The H&R is a wonderful gun with decent steal and excellent wood and excellent machining. Definitley it is worth your while to own if you are a BP cartridge fan.
This is what I have learned in working with my H&R Trapdoor Carbine.
Last edited by Gator Weiss; April 21, 2013 at 09:08 AM.