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While discussing the bobcat. Are the barrels the same size between the 50 and the 36?
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They're the same size, but that doesn't mean they're interchangeable. There are differences in how the barrel fits into the tang. I don't know if the differences are strictly between these two calibers, or if it's due to changes in manufacturing specs regardless of caliber. With CVA (and also with Traditions, because their guns are made by the same manufacturer in Spain), their parts had a tendency to change over the years for unknown reasons. A particular part might have a change in measurements or shape (style) after being made a certain way for so many years. Sometimes these changes make no difference regarding fit, other times it means you can't swap them (unless you want to modify them to fit).
Regarding the Bobcat barrels, I also have a .50 Bobcat with a synthetic stock. These pictures are of the tangs, you'll see several differences. The blued one is from the .36 (the .50 is sort of a project gun and the bluing has been removed).
The most obvious difference is the hole for the breech button to fit into. The hole of the .36 tang is larger and has a rounded bottom. What this means in the case of my rifles is that the breech button of the .36 barrel won't fit into the smaller opening of the .50 tang. Another difference you can see in the side view is a small cutout on the underside of the tang. Also, the height of the hole is different. It's hard to tell in the pictures, but when I measure the distance from the top surface of the tang to the upper edge of the hole, one measures .240" and the other is .295".
Yet another difference is the ridges on the sides. The ones on the .36 are lower than those on the .50. However, this makes no difference when installing them in the stocks. Both tangs are a perfect fit in either stock. Just another small manufacturing change that amounts to nothing, I suppose.
And both barrels fit just fine in either stock. So it appears the issue isn't fitting the barrel to the stock, but matching up the barrel with the correct tang. In my case, I can switch barrels/stocks without a problem, but I can't use the .36 barrel with the .50 tang. The hole is too small. So I have to swap the tang along with the barrel (unless I want to do some filing to make it fit).
Does this mean you can't buy a .36 barrel online and put it in your .50 stock (or vice versa)? Not really, as long as you keep a couple of points in mind.
One option is modifying parts to fit. If you have a barrel and tang that don't fit, you can simply file the hole larger if necessary. You can also file the breech button to fit. So it can be made to work if you don't mind putting a little effort into it.
You can also get spare parts from other people. When CVA got out of the sidelock business and went strictly with inlines, their entire inventory of unsold guns and spare parts was bought by Deer Creek Products in Waldron, Indiana (not to be confused with another company by the same name in Florida). They're a small operation and they don't have a website. You have to call them and ask if they have what you need. (765) 525-6181 I've dealt with them plenty of times, they're the place to go when you need spare parts (while they last). In fact, I bought all three of my .36 Bobcats from them.
There's also ebay. You can find parts there with a search, but there's one seller in particular you should contact if you can't find what you need. He goes by the name muzzleloader707 and he sells parts for CVA, Traditions, and Thompson/Center. I've bought several parts from him. His prices are a bit on the high side, but he can often find the part you need even if he doesn't have it in stock.
Another thing to keep in mind is that my Bobcats don't necessarily represent all Bobcats made over the years. Like I said, I don't know if the difference is the caliber or just manufacturing changes (the latter would be my guess, since the barrels are otherwise interchangeable, and there's no point in making the tang hole a different size just because the caliber is different; but who knows?). If it's due to manufacturing changes, there might be other .36 Bobcats that were made (unlike mine) with the smaller button and hole, and other .50 Bobcats that were made with the larger button and hole. So my example of the tangs not being interchangeable is only a possibility, not a rule (as far as I know).
But if they don't fit, you should be able to make them work with a little effort.
Sorry for the thread derail. Back to smallbore squirrel guns.