Ruger OMSBH Question
A friend of mine recently inherited an Old Model Super Blackhawk, and he asked me to take a look at it for him because it was "jammed."
The gun has a 5-digit S/N and is in excellent condition, but it does have a problem: The base pin all too easily flops out of line when it is withdrawn.
If it simultaneously rotates part way around -- which it does every time -- then the relief cut on the flange of the base pin goes with it, and the flange wedges itself against the bottom of the barrel.
The base pin is left hanging at a downward angle and can only be removed by force (e.g., a light tap with a mallet) after first removing the ejector rod assembly.
Of course, the cylinder cannot be rotated nor the hammer cocked with the gun in this condition, so it is indeed effectively "jammed."
This problem appears to be caused by an undersize base pin, excessive tolerances in forward aperture in the frame, ot both.
Will a Belt Mountain base pin 'cure' it? I've never used one or seen the problem described here occur, so I don't really know if it is likely to or not.
I've only heard that Base Mountain base pins are well made and, I believe, "oversize" relative to the factory part, hence my question.
TIA
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Cylinder should rotate freely
The cylinder should rotate freely over the base pin and not exert enough torque on the base pin to force it to turm. Take out the pin and cylinder, put the pin in the cylinder and see how freely it will turn. May need some cleaning, or the pin or cylinder has been damaged
RE: Cylinder should rotate freely
The cylinder rotates freely when everything is in its place.
It doesn't when:
• the base pin is withdrawn,
• the base pins gets slightly out of hand and rotates a bit,
• the flange of the base pin "jams" up against the barrel as described.
I think you'd be surprised how easily this happens with this gun. I know I was.
When it is is withdrawn, the base pin flops around like a wet noodle in the forward aperture of the frame. The tolerances are very poor.
In addition, detailed inspection reveals abnormal wear of the screw fixing the ejector rod shroud to the barrel. The screw slot is pretty worn compared to the rest of the gun, indicating the previous owner probably had the same problem arise.
So, the question remains whether Belt Mountain Base Pins are "oversize" and whether one might help solve this problem.
Thank you for your interest. 
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Belt Mountain pins are
by Paul 
, Saturday, January 05, 2013, 15:35 (4322 days ago) @ FOG
ground to .2495" You could mic your pin and compare it. I'd suggest taking a look at their standard locking or their number 5 pin.
OEM pin is
I only have a 6" dial daliper, but it's a pretty good one.
It says 0.248 so perhaps a BM pin would help.
Thank you for your reply.
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It's necessary to remove . . .
. . . the ejector assembly to get the base pin completely out of the gun. The fact that the screw is messed up does indicate he's had it out one or more times.
I'd carefully remove the ejector assembly and then pull the base pin all the way out so you can then remove the cylinder and see how the pin fits in the frame without the cylinder and how it fits the cylinder alone. Make every effort to keep the cut in the base pin collar properly oriented to the barrel, as this keeps the base pin properly positioned with respect to the pin latch. This is tricky sometimes.
With the cylinder out, you can see if the pin appears to be appreciably undersized with respect to the holes in the frame. It is not uncommon for it to appear undersized and yet still function well. The pin should spin freely within the cylinder as mentioned above. The hassle comes when attempting to remove or install the cylinder. Just be careful and make sure all the holes are clean, the pin is properly aligned, and the pin latch is depressed. It frequently helps to spin the cylinder a little while inserting the pin, and one should take care to not force it if it hangs up.
Be exceedingly careful when re-installing the ejector assembly as that's a very small screw in a very small tapped hole. DO NOT overtighten.
A Belt Mountain pin may be a final resort, but it will NOT make things easier to remove and re-install as it will merely fit tighter although I don't believe they have the collar to complicate matters.
It's necessary to remove . . .
by Dennis Eugene 
, Prince of Wales Island Alaska, Saturday, January 05, 2013, 17:12 (4322 days ago) @ Kentucky
very good advice by kentucky
re: KY's advice
It sounds like a BM Base Pin -- one minus the flange or collar -- would probably be the best bet.
I appreciate the advice and will include it with my other recommendations (basic tools, cleaning gear, etc.) to my friend who recently inherited the gun.
On a related note, I'll also be recommending a new base pin latch assembly. I took it completely apart, cleaned it, etc., but the original parts are pretty tuckered out from all the 'stress.'
Thanks again.
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RE: Cylinder should rotate freely
by bj , Saturday, January 05, 2013, 19:43 (4322 days ago) @ FOG
The cylinder rotates freely when everything is in its place.
It doesn't when:
• the base pin is withdrawn,
• the base pins gets slightly out of hand and rotates a bit,
• the flange of the base pin "jams" up against the barrel as described.
This indicates that there is a problem somewhere other than the base pin being loose in the frame. The cylinder should not try to rotate the base pin no matter how loose the base pin is. And rotation of the base pin should not tie up the cylinder. I've seen Rugers with loose enough springs/plungers that the base pin could back out slightly from recoil, but the gun will still operate and not lock up.
With the gun at half cock the cylinder should rotate freely. You can try this and rotate the cylinder as you rotate the base pin or move the base pin back and forth and find out when and why the cylinder is binding. If the hole in the front of the frame is REALLY big and allows the base pin to move sideways significantly then the cylinder could start to bind up on the barrel extension or top or bottom of the cylinder window, something like that. I haven't seen this happen from wear but maybe someone really messed with the frame. If your base pin pulls out about halfway from recoil then you will see a gun get harder to cock but I haven't seen one that locks up. If it is that bad then a base pin that is half a froghair bigger than the standard base pin won't fix it, and the 0.001" that the BeltMountain base pin is bigger is a very tiny amount. And if the base pin is rotating because it is dragging inside the cylinder, a bigger base pin will make it worse.
RE: Cylinder should rotate freely
by Paul , Saturday, January 05, 2013, 20:55 (4322 days ago) @ bj
And if the base pin is rotating because it is dragging inside the cylinder, a bigger base pin will make it worse.
But not if the basepin is bent, perhaps? It would be interesting to see if the basepin is still true, or if it's got a kink somewhere along it. I'd be tempted to swap in a different basepin to see if the problem goes away or not, it could be from another Ruger, wouldn't even have to be oversize.
RE: Cylinder should rotate freely
by bj , Saturday, January 05, 2013, 21:10 (4322 days ago) @ Paul
But not if the basepin is bent, perhaps?
Well it seems that something is wrong somewhere, maybe the base pin is bent, maybe the hole in the cylinder has carbon buildup, maybe the cylinder was dropped and the front bushing was deformed, maybe there is a problem with the barrel/cylinder gap.
It will take some experimenting to figure out the solution. First the OP can experiment with the parts that he has just by moving things around. If he had another base pin to try then that might be helpful too.
RE: Cylinder should rotate freely
Just to be clear, the cylinder isn't rotating the base pin.
The problem only occurs during "takedown." ("When the base pin is withdrawn.")
Otherwise, the gun works fine.
I will stick with KY's advice and pass it along.
Thanks again to all who responded.
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