Favorite pistol calibers:
.22 LR - It's inexpensive, available, accurate enough and the best way to teach a new shooter how to shoot a handgun.
.38 Special - it's accurate and great utility given the wide availability of loads from 400 FPS cowboy loads and 500-600 FPS target loads to 1150 FPS +P self defense loads. Brass and bullets are also readily available and usually inexpensive.
9mm Luger - It's readily available and about as inexpensive as factory ammo gets. Brass and bullets are cheap and the wide range of bullets from 115 to 147 grains gives it a great deal of flexibility. Modern 9mm Luger hollow point ammo perform well and give up very little or nothing to ta .45 ACP or .357 Magnum. I discovered years ago that I could put three 9mm holes in the A zone in the same period of time it took me to make two A zone hits with a 1911. When I did the math I found the would track volumes for those three 9mm holes was identical to the two wound track holes of a .45 ACP, but with one extra wound track and one more opportunity for a cardio vascular or CNS hit. Plus you have more rounds on the magazine. The 9mm is also available in a number of handguns I enjoy and that fit my hand well, like the 1911, Hi Power, CZ-75 and S&W 39.
.357 Magnum - nothing does self defense any better bullet for bullet than the .357 Magnum. The larger magnums do as well, but not better and they do it with excessive recoil and slower follow up shots. It's also a credible handgun round for medium sized game. The .357 Magnum is also available in enjoyable K & L frame handguns as well as the older Security, Speed, Service Six Ruger revolvers.
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Favorite rifle or carbine calibers:
.22 LR - it's inexpensive and usually 1 MOA accurate in mid range match loadings like SK Std Plus or CCI SV. It's perfect for teaching new shooters to shoot, or shoot position shooting, and it's a fun round to practice residing wind and elevation at ranges out to 25 yards or so.
9 mm Luger - it's a great companion/carbine round. Out of a carbine or braced pistol with a 10" barrel it will deliver .357 Magnum performance and with a quality barrel will deliver 2 MOA accuracy out to 200 yards.
.357 Magnum - like the 9mm it's a great companion round in a carbine or rifle. In a 20-24" rifle it will give excellent performance on medium sized game out to 150 yards and in a quality barrel will deliver 2 MOA accuracy out to 200 yards.
.308 Win - I'm old school and still like the .308 for long range shooting. I put tens of thousands of rounds down range in service rifle completion in the 1980s and 1990s and I know the ballistics of the 168 gr SMK well. It's my go to round for 800 yards or less. The 165 gr Game King mirrors the ballistics out to 500 yards and is my go to long range hunting round. With a 175 gr SMK or a 175 gr RDF it's a capable 1000 yard round. It's also chambered in semi auto rifles I enjoy like the M1A, the FAL, and the BM-59.
.30-30 - I grew up despising this round, but came to love it when I lived in the black hills and needed a good rifle and round for 100-150 yards heavily wooded mountains. It's 1.5 MOA accurate in all of my pre-64 Model 94 rifles and carbines and it's 2 MOA accurate in my post 1963 rifle pattern Model 94s. It offers solid performance on medium sized game out to 225 yards. It's readily available almost everywhere in the US and cheap for a center fire rifle cartridge. Brass and bullets are also readily available.
.22 Hornet - it's a very accurate cartridge and the noise is significantly less than the .223 making it a neighbor friendly choice for unsuppressed varmint and target shooting.