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

Posted by Larry Gibson on Thursday, 12 February 2009, at 1:40 p.m., in response to Re: Directions for BB replacemnt in H&R TDs...., posted by Ernie Brandt on Wednesday, 11 February 2009, at 9:10 p.m.


Not sure I'd charge as I gave up my FFL a few years back and thus no longer "gunsmith". Thus shipping would also be a problem. If you build custom rifles on the TD then you should have little problems with the conversion, just follow the directions, and think about what you are doing that is making the original BB fit the H&R and go slow.

The recasing of the BBs would sure make them look nice but I've not found it necessary. The part where the casing and some metal is removed receives little wear and has no strain applied during firing. Email me and I can send some pictures of the completed BB on my OM.

Some years back on another forum I was engaged in discussions of the ways to "fix" H&R BBs that popped open. I tried these but soon the "fix" failed and the actions popped open again. One poster who apparently had knowledge of H&R operations posted this;

"The problem is that H&R built a run of these rifles with the wrong cam geometry. The original design cam was designed with a thrust line below the pivot point of the cam. What this did was use the rearward thrust of the cartridge to force the block DOWNWARD tighter into the trap. Properly set up this works quite well, The army was in fact prepared to chamber the Trapdoor in the .30-40 Krag cartridge if congress had delayed adoption of the Krag-Jorgensen another year. (The Army had been ready to adopt the Krag in 1890, but congress refused to appropriate the funds until more domestic designs were considered.) The Krag generates 40,000 psi chamber pressure, yet the only modification needed was a collar on the cam shaft to help UNLOCK the action. In any case, H&R some how reversed the geometry on some cams, thus the cartridge thrust the block upward, opening the cam. This overloaded the set screw H&R used to attach the cam to the shaft. Though many complain about this arrangement, remember that if the cam is properly designed, that screw should see no load."

I do not know the facts of H&R production but I do know that the majority of H&R TDs do not pop open. Thus there may very well be validity to what the poster said. If your H&Rs do not pop open then I wouldn't worry about it and would keep shooting them. I would loctite the set screw that holds the cam to the cam shaft though. I had lots of "pop opens" with both of my H&Rs before I solved the problem. This was with reduced loads and with full power smokeless and BP rifle loads. I never had either pop open hard enough to eject the case. Most only popped open leaving the case partially extracted. On those the thumb latch extension that fits under the hammer blocked the BB from flying open. It takes quite a bit of force for the extension to pivot the hammer back out of the way before the BB can open. On the loads (usually the full power rifle loads) where the BB did come all the way open and the cases partially extracted you could see where the cam and thumb latch were pivoted down too far. While disconcerting to say the least I never even got any powder blown back in my face when the worst of pop openings occurred.

Others may have faired worse though but I shot both the OM and LBH through a lot of pop opens (at arms length) observing what was happening in my attempts (all failed) to fix the original H&R BBs. My recommendation is if the H&R BB pops open even once don't waste time on "fixes". Just replace the entire BB with an original SA BB.

Larry Gibson


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