Magazines, magazine springs, recoil spring, under powered ammunition, bad extractor, out of spec ammunition, chamber too tight, bur in chamber, incorrectly cut feed ramp...
What kind of gun are we talking about?
I have heard that the most common cause of FTF malfunctions is "limp wristing" but I don't believe that this is the case, simply because I don't have this issue with any of my others...
So what's the most likely reason? Recoil spring?
...And what exact kind of failure?
Dirty magazines will do the trick, as will bent or out-of-spec magazine feed lips.
Gun in question is a Star Megastar .45 shooting standard Federal 230gr FMJ
Magazine is a 12 round double stack... unfortunately the gun & parts (and specs for that matter) are rather rare so I only have the one factory mag & nothing to compare it to
It fails to feed (sort of gets the round halfway into the chamber but not all the way closed)
It will jam here and there on a couple random rounds, but its definitely most prevalent on the last round
Two things to try:
First, disassemble (if possible) and clean the magazine and its innards. Also clean the pistol's feed ramp and its barrel hood.
Second, if the first step doesn't solve the problem, carefully observe the movement of the round from the magazine toward the chamber.
The round being fed should probably slide up the feed ramp, and than be directed into the barrel by the chamber's mouth or, if there is one, the barrel's hood.
• Does the round hang up on the feed ramp? If it does, polish the feed ramp. (Just polish, and very carefully at that—don't remove any metal.) If this doesn't fix the hang-up, it's probably a magazine-feed-lips problem: The magazine is sending the round out at too shallow an angle.
• Does the round slide up the feed ramp, only to impale itself on the top edge of the chamber's mouth or the barrel hood? This is most likely a magazine-feed-lips problem too: The feed lips are probably sending the round out at too steep an angle.
An experienced pistolsmith might be able to reform the magazine's feed lips, if that is indeed where the problem lies.
As VAMarine stated, since the glitch occurs most often when the last round feeds, the problem could also be, or be compounded by, a weak spring.
You might be able to find original-replacement magazines from Numrich Arms/Gun Parts Corp., or new replacements from Triple-K.
(If you buy a Triple-K magazine, try swapping its spring into your old magazine. Triple-K magazines and followers are not always of the best quality.)
Also keep an eye on GunBroker.com. Right now there are two different, brand-new Star Megastar magazines for sale there. The bad news is that these particular magazines are for the 10mm version.
Great info from everyone.
I'd add that if you've only tried one or two types of ammo, then testing a couple more brands might find you one that works better.
If the nose of the cartridge is hitting the middle of the feed ramp and stopping there, then you might try a dab of lube (single wipe of an oily patch) on the feed ramp to see if that helps smooth out the travel of the bullet up the ramp. It's not nearly as good as the actual smoothing/polishing that Steve suggested, but it's quicker and cheaper to try.
Finally, I'd recommend removing and visually inspecting every round of ammo that fails to feed. Sometimes they can give hints as to the nature of the problem. Examples include deformed areas of the case (nick/burr on the edge of the case rim might indicate a too-sharp-edge on the interior of the extractor hook); a small circular nick on the outer-rear edge of the case rim (might be a sharp edge on the firing pin hole in the breechface that is "catching"/slowing the round as it slides up the breechface); a chip (material missing) out of the bullet nose (catching on the bottom edge of the feed ramp, or the top edge of the barrel hood), etc. If it can be done safely, taking a good digital photo of the jammed round can also be helpful when trying to diagnose, or explain the problem to other folks (like a gunsmith).