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Directions for BB replacemnt in H&R TDs....

Posted by Larry Gibson on Wednesday, 11 February 2009, at 8:42 p.m., in response to Re: Trapdoor receiver strength w/COW, posted by Dick NieKamp on Wednesday, 11 February 2009, at 4:41 p.m.

I have done this to 4 H&R trapdoors with complete satisfaction and no further problems with the breech block popping open. It is not hard to do but you must pay attention to what you are doing. If any one has any questions don't hesitate to contact me.

Larry Gibson

H&R breech block replacement with an original TD breech block

A fine file and a large new mill bastard file were used along with a Dremel tool with a small fine grinding wheel ½” wide and a new grinding stone flat across the point ¼” or so in diameter. Lapping compound of 220 grit or so and some cutting oil may be needed for fitting the breech block hinge. Some crocus cloth was also used to fit the latch into the new locking recess. The outside diameter of the breach block hinges had to be reduced so the hinge pin could be inserted. The ejector hole in the bottom was slightly elongated so it would fit over the edges of the ejector. A very small amount was taken off the bottom of the breach block (only one required this) in the front of the arch so it would close. The thumb latch assembly was removed and the rear face of the breach block was then judiciously (very carefully) filed and tried until it closed and mated with the rear of the receiver. The thumb latched was then assembled and filed to fit the slightly shortened breach block. The crocus cloth over the fine file was used to slightly remove enough of the latch so the hammer just cleared it when locked and the hammer was in the fired position. The process took a couple three hours to do as I took my time at it.

Fitting the original breech-block to the H&R trapdoor;

The hinge of the original breech block was a little larger in diameter than the H&Rs. The hinge-pin would not quite line up. I mixed some 220 grit lapping compound with cutting oil to thin it out. A small amount was put into the hinge recess in the receiver. Then with my left hand I put a punch through the left hinge-pin hole and exerted pressure pushing the hinge into its recess. At the same time with my right hand I moved the breech-block up and down lapping the hinge into place. Periodically I cleaned the hinge and checked the hinge-pin to see if it would go into place. It took three or four applications of lapping compound and about an hour to complete this. I did most of the lapping while watching TV. This went a lot easier on the next two breech blocks I fitted to other rifles. With some very judicious filing with the fine file on the exterior rounded portions of the original breech blocks hinges I removed enough of the hinge to just be short of lining the hinge pin up with the receiver holes. Doing this then took a lot less lapping. Be very careful and go slow checking the fit frequently as you can't replace the metal you file off.

With the breech block hinges fitted the next step was to put a piece of flat stock steel across the flats at the rear of the receiver and measured the distance from the underside of the flat stock to the bottom of the receiver. I then ground the bottom of the breech block fore and aft of the arch that distance minus about .01as measured from the flange of the breech block to the bottom. The grinding was done with the ½” wide grinding stone in the Dremel tool. The breech block was held upside down in a vice. I was then able to move the grinding wheel following the curvature of the breech block and keep the grind parallel as the original. Take your time and be careful to maintain the curvature of the bottom of the breech block. A little polishing with the crocus cloth and some cold blue touch up will make the change hardly noticeable.

On the original breech blocks the recess for the ejector in the bottom of the receiver may not quite line up. The ejector may be a little too far forward or back. I simply measured the distance from the face of the H&R breechblock to the front and back of the recess. Careful use of a Dremel tool with the small ¼” grinder in the forward or back edge of the original breech block recess elongated the hole to match the the measurements of the H&R breech block. Once again it didn't take much for a perfect fit and a little touch up with cold blue made it almost look original.

The above steps must be accomplished before proceeding with the next step. It is necessary for the breech block to be hinged and able to go down into the receiver to properly index and fit it to the rear mating surface in the receiver.

With the breech block cap, thumb latch and cam-lock assembly of the original breech block removed I slightly ground off the hardened surface off the back of the breech-block where it fits into the receiver. Judicious use of the ½” wide grinding wheel in the Dremel tool is sufficient for this. It doesn’t take much to remove the surface hardening. A new 1” wide mill bastard file was used to file the back of the breech block down until it was a very close fit. I don’t know exactly how much I filed off but it wasn’t that much. I was careful to maintain the correct angle and used the “file a little – test the fit – see where to file a little more, etc.” method. What you want is the back of the breech block to fit evenly and parallel to the sloped rear surface of the receiver I stopped filing as soon as the flanges of the breech block rested on the flats at the rear of the receiver. This is where the breech block needs to be closed to. It’s harder to describe than to do.

The breech block cap, thumb-latch and cam-latch assembly were re-installed on the breech-block. A scribe mark was made on the breech-block cap marking how much had to be removed from the end. The assembly was removed and that amount was ground and filed away. The breech-block was assembled and installed in the receiver. The cam-latch fit into the receiver recess perfectly but required a small amount to be ground (to hard to file) off with the ½” grinding wheel in the Dremel. The crocus cloth over the fine file was used to slightly remove enough of the latch so the hammer just cleared the thumb latch when locked and the hammer was in the fired position. Once again go slow here taking off only a little at a time until the breech block closes and opens easily and the hammer, in the down fired position, just clears the thumb latch. Touch up with cold blue worked here as well.

I had some concern as to whether I should have the bolt re-hardened since I had ground and filed away some of the hardened surface. To date, after literally thousands of rounds through my own OM and LBH Carbine, there have been no sign of wear on those surfaces. Total time for installation was 4-5 hours at first but I did the lsat one just short of 3 hours.

As the original H&R bolt was so poorly fitted and finished, which I believe is why nothing would keep the action from popping open upon firing, the replacement with an original Springfield breech-block was worth while. It made a dangerous rifle entirely safe, sound and serviceable.


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