Originally Posted by
Valorius
Obviously any comparison between 5.7mm and 5.56mm would be restricted to 200m or less, and IMO, really we as civvies don't even need to concern ourselves with anything beyond 25m anyway. Outside 200m, i agree that 5.56mm has a big advantage.
But.....a 5.7mm completely blows away a 5.56mm's ability to compete in 2 key categories. Recoil and ammo mass/size.
If your sidearm is also a FN Five Seven, it also blows away 5.56mm in ammo compatibility/standardization.
A single .30 cal ammo can filled with 5.7mm holds 1200rds.
For the same approx weight you can carry 101rds of M14 ammo in 5x20rd mags, 211rds of M16 ammo in 7x30rd mags, or 361rds of 5.7x28mm ammo in 12x30rd FsN magazines.
5.7mm recoil is about 30% less than 5.56mm in a carbine, and also about 30% less than 9mm from a pistol.
Clearly, in these categories, the 5.7mm blows 5.56mm away.
I would put the top 5.7mm rounds (which IMO is the Elite S4M) about on par with the lethality of 5.56mm M193, and the FN 28gr OTM loadings about on par with 5.45mm ball.
Because it is a low volume item, 5.7mm is not cost competitive with 5.56mm at this time.
That would be a huge advantage for 5.56mm, if cost is a key factor in your decision.
The FsN and FNP90 are both very robust and simple designs, both were designed specifically for combat use, and both have been used extensively by elite units since their introduction. The P90 is used by the USSS to protect the White House, and the FsN is used by the Queen of England's elite body guards. While both platforms are very expensive, they are both combat tested and proven.
The 5.7mm carbine that i want to get and that really intrigues me is the MPA 5700sst. It is based on a Mac-10, but uses the FN Five Seven's pistol magazines. Despite having a 16" bbl it is also very compact and comes with a quad rail and side cocker design. Folding stocks are available for it. If you armed yourself with that and a Five Seven pistol you'd have one kind of ammo with one universal magazine type that fits both your weapons. An absolutely ideal situation.