“Possibly believable”? [insert emoticon of extreme incredulity and amusement] Awww…
Here’s a picture of a flagpole truck.
Here’s another version.
http://www.flagpoles.com/fcbta.html
More light. The “truck” is the pulley that holds the ropes. The “ball” is the decorative ball on top of the “truck”. Pix of both.
http://usflag.com/accessories/hardware/hardware3.htm
The biggest one this website has for sale is 12" in diameter.
Okay, first of all, the “truck” is either cast bronze or cast iron, depending on manufacturer. Flagpole balls are metal, too, with an anodized coating, whether gold, copper, whatever.
I think your friend means the BALL is designed to break into 13 pieces. First of all, the ball is metal–how are you supposed to get it open to get the bullets in there? You’d have to cut it open with a welding torch. Or is it supposed to have perforations or something? Don’t see any mention of it on any of these websites. It would have to be manufactured that way at the foundry. (Oooh, are they secret perforations, known only to the Illuminati?) 
And just who, exactly, is doing this? The federal government? Your local sheriff? Who are the public-spirited citizens climbing flagpoles all over America and putting bullets in them? Or is it just “they”? Oooh, I love it when it’s “they”…
At the base of most flagpoles is a big cement pad. Is there perhaps a secret trap door in the pad, concealing the box with the weapons? Or are the 3 guns and the sabre buried in the dirt a little farther away, the better to rust quietly over the years?
And only 3 bullets? Doesn’t sound like much to fight off the Commie Hordes. Oh, wait, each Yank bullet is worth 20 Commie bullets, right?
So lemme see if I have this right–you’re gonna save America from the Commies with 3 guns, each of which has only 1 bullet. And when your 3 bullets are gone, you’re gonna eliminate the rest of 'em with your sabre. And you can use the matches to blow up their ammunition dump…
BTW, Snopes doesn’t even mention it. I supposed it’s beneath their notice.
The Duck’s vote: “load of crap”. 