just wondering what the thought was concerning these calibers. .22 Cheetah Mark II and the .220 Jaybird. Are these considered over bore? What is barrel life and accuracy? They seem to have plenty of zip but I have never heard of anyone shooting them. Thank you for your help.
I have had the Cheetah Mkl and Mkll. Also a couple of 22-250AI's. To me, the most sensible one is one I have not tried yet, the vanilla 22/243 although the 224TTH (22/6mmAI)is calling my name as well. I liked them ALL so far, and the faster the better for me so far but once past the 22-250 one really needs to go with a faster twist bbl and use the heavier bullets to see any real gains. Not a nickels worth of difference in how fast any will push a 40-50gr bullet, and surely no real world benefits. That said, it IS really fun to blast small rodents with 36gr Barnes Varmint grenades started out at 42-4300fps
The term "overbore" is not a technical term used in official ballistics, however much is discussed on this term and what it means.
Basically overbore is a term that describes the efficiency of a particular cartridge. 25%-30% is about the limit of powder efficiency as the limit of bore capacity. The remaining energy is lost to heat, friction, expanding the brass, etc.
25% is generally considered the lower end limit for average efficiency. Anything above that is an "efficient" cartridge design.
Overbore then, can be considered any cartridge/powder capacity that produces less than 25% efficiency.
No official measurement of overbore exists, but some simple math can help in defining overbore. We are looking for a way to define the amount of powder used for any given caliber and the resulting velocity so that we find the point where increase in powder begins diminishing returns in velocity. The point where you start burning lots more powder just to get a small increase in velocity.
The entire exercise is a relationship of bore diameter and case capacity in grains of water ( a standard used to measure case capacity. This does NOT mean that is the maximum load of powder as powder has air spaces between the kernels, always consult published load data).
An easy, consistent formula to use is Bore diameter x bore diameter x 1000 = maximum case capacity (in grains).
So, for your question of the 22 Cheetah, let's look at what our formula finds:
.224 x.224 x 1000 = 50.1 grains
So, any 22 caliber round that uses more than 50.1 grains of powder is technically "overbore".
Hodgdon reloading data for the 22 Cheetah MkII shows the following loads for 50 grain HDY SP bullets at maximum loads:
47 grains H380 for 4057 fps
51 grains H4350 for 4069 fps
Clearly the 47 grain load is within the 50.1 grain overbore limit and this efficiency level is shown when compared to the 51 grain load of H4350 (overbore) which only increases velocity by 12 fps. Obviously, using 4 more grains of powder to eek out an extra 12 fps increase in velocity is not efficient and wastes powder. It's also interesting to note that 51 grains of powder is only slightly over the 50.1 grain limit, yet it already clearly shows diminishing returns in velocity.
Please note too that different powders will return different efficiency numbers and load tables can also show efficiency for a single powder type if the min and max loads cross the overbore capacity limits.
In your case it would seem the 22 Cheetah MkII is right at the verge of being overbore, but most published loads for it keep it just inside the overbore limit. Technically speaking then, it is not an overbore round.
Interesting treatise, frome where did you get the basis for the formula? Not doubting it, neccesarliy, just curious. You speak as though you might be in the ballistics field in some capacity, Mind sharing something about yourself? THANKS
22Cheetah and 22-250AI are best suited to push the heavys at good speed. 90VLD @ 3200, 80Amax @ 3350, 75Amax @ 3500. At this level I prefer to step up to the 6mms and take advantage of the 105s; a little better at extreme yardages.
..... 224TTH (22/6mmAI)is calling my name as well....
The 224 TTH is a straight 22/6mm, not the Ackley version.
Great fun! hell on varmints...and barrels. I might still have a die set around here if you're lookin'.
The term "overbore" is not a technical term used in official ballistics, however much is discussed on this term and what it means.
Basically overbore is a term that describes the efficiency of a particular cartridge. 25%-30% is about the limit of powder efficiency as the limit of bore capacity. The remaining energy is lost to heat, friction, expanding the brass, etc.
25% is generally considered the lower end limit for average efficiency. Anything above that is an "efficient" cartridge design.
Overbore then, can be considered any cartridge/powder capacity that produces less than 25% efficiency.
No official measurement of overbore exists, but some simple math can help in defining overbore. We are looking for a way to define the amount of powder used for any given caliber and the resulting velocity so that we find the point where increase in powder begins diminishing returns in velocity. The point where you start burning lots more powder just to get a small increase in velocity.
The entire exercise is a relationship of bore diameter and case capacity in grains of water ( a standard used to measure case capacity. This does NOT mean that is the maximum load of powder as powder has air spaces between the kernels, always consult published load data).
An easy, consistent formula to use is Bore diameter x bore diameter x 1000 = maximum case capacity (in grains).
So, for your question of the 22 Cheetah, let's look at what our formula finds:
.224 x.224 x 1000 = 50.1 grains
So, any 22 caliber round that uses more than 50.1 grains of powder is technically "overbore".
Hodgdon reloading data for the 22 Cheetah MkII shows the following loads for 50 grain HDY SP bullets at maximum loads:
47 grains H380 for 4057 fps
51 grains H4350 for 4069 fps
Clearly the 47 grain load is within the 50.1 grain overbore limit and this efficiency level is shown when compared to the 51 grain load of H4350 (overbore) which only increases velocity by 12 fps. Obviously, using 4 more grains of powder to eek out an extra 12 fps increase in velocity is not efficient and wastes powder. It's also interesting to note that 51 grains of powder is only slightly over the 50.1 grain limit, yet it already clearly shows diminishing returns in velocity.
Please note too that different powders will return different efficiency numbers and load tables can also show efficiency for a single powder type if the min and max loads cross the overbore capacity limits.
In your case it would seem the 22 Cheetah MkII is right at the verge of being overbore, but most published loads for it keep it just inside the overbore limit. Technically speaking then, it is not an overbore round.
A cacophony of B.S. for a first post
No, I don't work in the ballistics field. Just been a long time shooter. I have a passion for ballistics, and all things around cartridges, reloading, shooting, etc. I also tend to listen to people who do work in the field and those with vastly more experience. I don't recall exactly who came up with the formula, but it is something I learned a long time ago and although it's not an exact science it holds true in the overwhelming majority of load data. It's every bit as good an explanation for overbore as any that exist.
Hey rockchuck, BS??? You have something to refute it? What's your credentials in the professional ballistics field, bubba?
I have two 22 CHeetahs, both Mark II, one custom Shilen DGA and one heavy barreled Rem 700 sleeved BR stocked. Great cartridge and shoot 52 grain Bergers into a ragged hole. If I want to shoot a heavier bullet, I move to one of my hot 6mm's, 6x284, 240 Gibbs, 240 Weatherby or 6mm Mach IV. Get yourslf a CHeetah, you will not be disappointed. Every so often one pops up for sale on the gun auction sites.
My two have been 22-250's that were merely re-chambered. My next one I hope to do a real build with a new barrel etc. Might go vanilla 22/243 as well, though.
had several. Some of the best shots i ever made were with them. If you like to spend lots !!!!!!!!!!!!! of time makeing brass theyre great. I have been running a 22-243 for maybe 10 years the only differance a lot less case prep! i did run one 22/6mm between the 22 CHeetah and the 22-243. 6mm brass and taper sucks @ very best. I due have some dies and brass i think (any trades)
Yeah, If you happen to have such, I need dies for 6mmAI and maybe 22-243. Let me know what you have and what you need or want.
I went with a straight-up 22-250 1:8 McGowen on a Savage Striker at 16". Think i'm driving the 80 A-Max at 2800ish. At work now and don't have my data with me.
I went with a straight-up 22-250 1:8 McGowen on a Savage Striker at 16". Think i'm driving the 80 A-Max at 2800ish. At work now and don't have my data with me.
You should get more than that. I've seen 3000 with the 80s in a 223AI and a 20" tube; course, I prefer 75s at 3100.
I cant comment on the cheeta but love my 22-250AI and since this thread is discussing dies I am looking for a 22-250AI In line seater die with micro top. Safari man sold me his and it has dissapeared.