Originally Posted by JCHannum
Actually a switch barrel is exactly what I have in mind for the 22 magnum and the 17 HMR but I sure like the idea of the Hornet too, just not sure if what I have in mind would work for that higher pressure round.
Here's the plan and what I have done so far, after the 45/90 Highwall project I started thinking about what to do next and I came up with the idea of a scaled down Highwall in a small caliber. While working up the mods to get it downsized I thought a lot about how to make a switch barrel design that would not involve screwing in the barrel with all the problems that would lead to. I was aware of how the Ruger 10/22 barrel is attached by using a lug extending from the front of the receiver and a draw wedge to hold the barrel in place and thought this to be the perfect solution, not exactly a tool-less take down design but quite simple and quick to do requiring only a screwdriver and a small Allen wrench with no indexing problems like a screw-in barrel. When I machined out the mini-highwall receiver I left a 1" lug extending just under the barrel with a channel for the barrel to rest in, as does the 10/22 barrel, and the receiver is bored to accept the barrel stub without threads in a very snug fitting receiver bore. The lever spring will still work like in the original since it won't need as much arc travel because of using the later design coil main spring for the hammer. This barrel attach design works just fine for the rim-fires on the alloy receiver of the Ruger so I think it should work just fine on this rifle using 4140 steel, at least for the rim-fire rounds.
It turns out that scaling down the original design was not nearly as simple as just reducing everything a certain percentage because some things,such as the trigger, lever/trigger guard, etc would be too small if everything was scaled down proportionally. I have it all worked out now with all the internals finished and I have the receiver about 70% completed but it may still be a while before I can finish this project, this time of year the farm comes first!
Last edited by radkins; 05-29-2012 at 06:39 PM.
I think what you have outlined would work for a .22 hornet. Lining up the firing pin could be accomplished by turning a offset barrel shank. You would also need two firing pins. One with a flat face for the rimfire and one with a rounded face for the centerfire. I believe a hornet will do anything that the 22 mag or 17 will do and a little more, but if you want a switch barrel then 17- 22 mag would be easier to make. Looking forward to seeing whatever you do.
When I considered the Hornet I was thinking of other center-fire calibers to switch out with or maybe just as a single caliber conventional screw in barrel, I only briefly considered trying a switch setup between the Hornet and the rim-fires but dropped the idea because of the firing pin issue. What you suggested has me re-thinking the Hornet as a possible option but this brings me to the other question of how secure would that barrel be for higher pressure rounds using the Ruger type barrel attach method? It's not that I would be looking at large bore or magnum rounds (with the exceptions of the rim-fires) but maybe the Hornet, 218 Bee or possibly a .223? Just looking at possible ideas here.
Having seen the job you did with the 45/90, we will all be looking forward to seeing your progress with this project. The switch barrel set up sounds reasonable for lower pressure cartridges. Switching between rimfire and centerfire in a falling block usually entails use of two breech blocks, which should not be too difficult to accomplish given your skills.
There is a bit of a difference between a Hornet and a 218 Bee, but not enough to warrant two barrels. I would suggest using the 218 Bee and taking a look at either the 25-20 or 32-20 as alternate barrels. The three share the same basic case and would use the same extractor.
I suspect the 223 would be pushing the limits of your set up, and would recommend sticking with lower pressure black powder or pistol cartridges.
That's good info on the 218 Bee, 25-20 and 32-20 sharing the same case, I had not thought of that. The 223 was just a thought as the maximum but it presents so many problems I probably would not consider it anyway, the rim-less design causes an extractor problem in addition to the pressure issue.
I have looked up and calculated strength of grade #8 socket head screws and back thrust of calibers mentioned.
Grade # 8 10/24 has a yield strength of 3300 pounds tension
10/32 has a yield strength of 3800 pounds tension
This is with the 10/24 torqued at no more than 64 inch pounds or the 10/32 torqued at no more than 76 inch pounds.
Using 50,000 psi for all cartridges and Stuart Otteson's method of calculating back thrust I come up with the following.
.22 Hornet 2650 pounds back thrust
.218 bee 3532 pounds back thrust
.223 Rem 4025 pounds back thrust
Using 2 - 10/32s would give you a max of 7600 to counter the Hornets 2650 pounds thrust 2.86 times more than needed. Most rifles strive for 1.5 times more than needed.
The 22 mag and 17 have a maximum pressure of 25600 which calculates to a 1008 pounds back thrust.
The Ruger 10-22 uses a course thread 10/24 because of the aluminum.
3300 times 2 equals 6600 divided by 1008 gives you a safety margin in the Ruger of 6.5 times needed, but remember the aluminum will fail before the screws.. This helps explain why they have held up well over the years. 22s are fired much more than centerfires and badly mistreated.
Wow! That's the very thing I have been researching today, until now without much luck, but you just answered all my questions before I even asked! That's a lot of very important info there and certainly will be copied into my references, thanks a bunch Bob I genuinely appreciate that!
After reading your reply I looked on the net. These figures are a little bit lower than my old ones so I would go with them. If you could fit a 1/4 screw it would greatly increase strength.
Back thrust for 40,000 psi.
22 Hornet = 2123
218 bee, 25/20, 32/20 = 2826
Problem using these figures is people can load hotter.
The lug and wedge will be 4140 and the lug is machined as part of the receiver so it should be substantially stronger than the Ruger 10/22 frame that I took the idea from. The bolts are to be grade 8 Allen head cap screws, 1/4" fine thread. I was certain this design would be more than adequate for the rim-fires, overkill really, but I was not so sure about anything heavier than that. What I would really like for a center fire version would be a 22 Hornet and the new Hornady 17 Hornet in a switch barrel setup. Lot's of possibilities but for now I am too deep into the rim fire project to change my plans this time but who knows, if this works out really good I might need something else to work on this fall when the weather starts getting cold again!