Here is my list of the top 5 dumbest calibers. I chose these based on their lack of availability, cost, and substitutes. Here we go:

1. .45 GAP - Chalk this up to Glock trying to re-invent the wheel.
2. .357 Sig - Only the US Government would be dumb enough to buy into such a caliber.
3. 4.6x30 - HK figured this would be the best way to prevent the MP7 from being adopted... and it worked.
4. 5.7x28 - For the cost of this cartridge, I'd rather shoot .45 ACP.
5. 5.45x39 - Most decently priced 5.45 ammo is corrosive and few weapons are designed to chamber it.

How about an honorable mention? I'm going to throw the 10mm on the list. Of course another US government agency would adopt this cartridge for a short time. It's lack of supply, price, and weapon options put it in the same category as the 5.7x28. The 10mm and some of the cartridges above were created as a way to bring more stopping power (traditionally found in wheel guns) to semi-autos. While the ideas were good, they never caught on and these are what I like to call "novelty calibers." If you are not going to buy something in a common caliber:

• 9mm
• .40 S&W
• .45 ACP
• .38/.357
• .223/5.56
• 7.62x39/.308

Then you're better off buying something in a "semi-novelty" caliber that is a little more common or leaps and bounds above calibers in it's arena. What comes to mind? These:

• .44 Magnum
• .50 AE
• .45-70
• .17 HMR

.17 HMR and .44 Magnum are fairly easy to find but are a little pricey. However, with the .44 Magnum you get massive energy and the .17 HMR provides a very flat trajectory. The 50AE and .45-70 are harder to find, but you'll have a blast (pun intended) shooting either one.