GT40, I also would have loved to see a photo of the 22/243 with the 175 grain bullet, and learn the configuration of the rifle, and the velocities it produced.
A 175 grain .224 bullet is an interesting concept, on the basis of trying to get a bullet with an incredibly high BC. However, once you start analysing the components required, you realise it is impractical in the extreme.
The length of a 175 grain .224 bullet with a 10 caliber ogive or greater would have to be way over 1.750 inches, and possibly up near 1.900 if using a conventional lead core/copper jacket bullet design. My basis for this is:
.224
70 grain Berger VLD - .948 inches length
90 grain JLK VLD - 1.230 inches "
100 grain Wildcat ULD - 1.300 inches "
107 grain Wildcat ULD - 1.350 inches "
From those figures there is a .402 inch increase in length from a 70 grain VLD to a 107 grain ULD, and another similar increase in bullet weight to 144 grains would give a length of 1.752 inches. So a 175 grain bullet would be much longer than that, especially if you use the 142 and 156 grain ULD's 257 cal bullets as a further guide.
In 257 caliber
142 grain Wildcat ULD - 1.360 inches
156 grain Wildcat ULD - 1.550 "
On that basis, a 175 grain .257 cal ULD with similar profile would be 1.730 inches in length.
It is interesting to note that the length of a .224 107 grain Wildcat ULD (1.350 in) and a .257 142 grain Wildcat ULD (1.360 in) are almost identical.
To get sufficient length to create a 175 grain .224 bullet, you would probably have to draw down a 7mm jacket that is used to make a 160 grain bullet.
I am currently using a .224 Clark (22/257 Roberts imp/30 deg) which has a case capacity of about 63.8 grains, and with a Krieger 26 inch 6.5 twist barrel, and using 56.0/H870, it achieves 3,200 fps with the Little 100 grain soldered core HPBT.(1.260) I have discovered that a 7 twist would have been sufficient to stabilise the Wildcat 100 grain .224 bullet.
I am also currently using a .257W with a Krieger 26 inch 7.0 twist barrel and using 70.0/H50BMG it achieves 2,900 fps with the Wildcat 156 grain ULD. A 1 in 6 or 5.5 twist would probably be needed to stabilise a 175 grain 257 cal ULD.
On the basis of my experience with the above, I am guessing that a 1 in 4 twist (maybe less) .224 barrel would be needed to stabilise a 175 grain bullet.
It would have to be a stout bullet, as just 2400 fps would produce 432,000 rpm in a 4 twist barrel, and 576,000 rpm in a 3 twist barrel. However, a 22/243 (case capacity about 51- 52 grains) would probably struggle to achieve 2400 fps with a 175 grain bullet.
Another practical problem when using the 175 grain bullet, would be finding a powder with a burning rate that would be give an acceptable loading density.
I estimate that in my .224 Clark which holds about 60.0/H870 to the base of the neck, I would be using about 40.0/H870 to achieve max pressure with the 175 grain bullet. This would represent a loading density of about 67.0 - 75% depending on how the barrel was throated.
A 22/243 would probably only be using about 33 grains of H870 with a 175 grain bullet at max pressure.
Although I have been wildcatting with various cartridges for about 40 years, the concept of a 22/243 with the 175 grain bullet is even way to radical and impractical for me, and I am content to sit back and watch someone else do all the development work. Brian.
