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Old December 23, 2009, 12:16 PM   #1
Join Date: December 12, 2009
Location: Southwestern USA
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Blown door on a 45-70 H&R Trapdoor Carbine

Need someone experienced on repairing trap door rifles.

I have an H&R Cavalry Carbine. Door blew with a Remington .405 grain JSP factory load. It was a clean barrell, no oil in bore, ambiant temperature of about 78 degrees. Bullet cleared the barrel and struck and pierced the target on the mark. The breech popped open and the case glanced off of my left eye brow (I am a left handed shooter most of the time) cutting me, though not deeply. Very minor wound. No stitches. The hammer was now sitting at half-cock. The case looked normal when I picked it up off of the ground. Primer was seated OK, and the case was not ballooned or split.

Took it to a gun smith who had never repaired on a trapdoor. He looked it over and said he could do the work. He re-worked the cam, made his own shaft for it, used a dremel tool to hog out the wood under the lever (this was strange, because the cam lever never touched the wood before) on the stock. He said he test fired it. I believed him.

I took it to Europe. Was on a range in Europe. I had not test fired the weapon either. On the first shot since the gunsmith, I dropped a Remington facatory load into the breach. I pulled the trigger. The bullet cleared the barrel and struck the target as before. Breech flew open. A bystander said he saw a small bit of flame at the breech. Casing flew out of the breech, missing me this time. Hammer was again sitting on the half-cock. The Schutzenhaus Meister told me to get that thing back into the case and not to pull it out again.

Brought it back to the USA and gave it a good cleaning. On inspection, the cam appears to be slipping on the shaft, and the clocking of the shaft versus the cam lever and cam, seems to be off. In addition thereto, it appears the gunsmith made himself a hinge pin for the breech. The hinge pin seems too small in diameter as the breech block rattles and shakes from side to side on this pin when the breech is open.

What I need, is someone who has repaired many trapdoor rifles, who knows his **** on these weapons. Parts appear to be very limited in availability for the little H&R. Some parts will probably have to be made.

DOES ANYONE KNOW OF A GOOD TRAPDOOR SMITH OUT THERE? I really like this rifle and want to put it back in shooting order.
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Old December 23, 2009, 03:09 PM   #2
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I have a Officers model made in 1973 I understand the early ones had the problem you are talking about but it is a easy fix.
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Old December 23, 2009, 03:24 PM   #3
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Call John at Taylor Machine. I think he knows everything about old firearms, it's his specialty. 253-445-4073
Never try to educate someone who resists knowledge at all costs.
But what do I know?
Summit Arms Services
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Old December 24, 2009, 10:04 PM   #4
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Location: Lincoln, NE
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Post this on the gunsmithing forum at There's a lot of guys who know their way around single shots there.
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Old December 24, 2009, 11:44 PM   #5
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i dont know all the details but from what i have read> there is a two piece part on the h&rs that was a one piece on the originals. some thing about the locking cam and it can fail. perhaps somebody with more knowledge can chime in and help with the exact info.....bobn
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Old April 21, 2013, 08:54 AM   #6
Gator Weiss
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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.
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Old April 21, 2013, 09:20 AM   #7
Gator Weiss
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Clocking the CAM and THUMB LEVER

To clock the cam, the thumb lever should be in a position so that it barely clears the under-side of the hammer, when the thumb lever would be sitting in the breech-closed position. To achieve this, loosen your set screw and then tighten the set-screw only to the degree it is just putting very minor resistance to the shaft. In this way you can rotate your parts to a proper position and they will remain in the position until you secure them. To move the thumb lever upward on the shaft, insert a wedge or old screw driver blade behind the top edge of the cam, up against the breech block by the spring cavity and hold it there while you rotate the lever upward to the proper position. Then tighten the set-screw to the correct degree. Then close the breech and determine if the cam has fully extended into it's recess or cradle in the rear of the breach. If the thumb lever is in the wrong position, it may rest against the lock-plate edge and not allow 100 percent engagement of the cam. It will look somewhat right. It will feel somewhat right. But that breech WILL come open on firing. You have to ensure the cam is resting in it's cradle all the way for this breech design to work. Move your hammer and check the clearance over the top of the thumb-lever. Adjust everything until you get it perfect. Tighten it down.

To test fire, you need to lash your rifle to an old tire with the butt resting either within or on the bead of the tire. Tie off the trigger and load and fire.

Dont close your breech on loose cam. The shaft will slip and you wont be able to get the breech open. This is a real problem. Dont get yourself into this position. Watch what you are doing.

If you dont know what you are doing, and cant tackle this operation, you need to take the rifle to a gunsmith so you dont injure yourself or someone else.
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