However large you want, though the nature of foam makes them rather useless after a certain distance. Mine is probably about two feet of reach total, eight inches being the gun itself.
A slight correction: No bayonets were awarded this mission. Two (maybe one) more must be completed before we get them. Anyhow, the mission proceeded as easily as planned. The zombies, being limited in number, chose to camp out at the drop-off point. The humans split up into three teams and sent in three directions. My team, being the smallest and most proficient at moving rapidly and safely, arrived well before everyone else. We numbered about nine, against the ~twelve zombies. One moved in behind us, so I told two humans to engage. Two more humans split off to come in from the zombies' side, leaving four-ish (honestly, I can't recall) facing the zombies, with myself on the left. We were on a relatively narrow walkway, with a hedge (barely leapable by me, probably not leapable by anyone else there) on the left, a tree three meters ahead of me, and about ten meters of open path to my right until a building. About ten meters behind me was a broad, shallow stairway leading to the lawn below and to the left.
We formed up there while we waited for the other human groups to arrive, facing off against the zombies. A group of ~15 came over the hill far to the left-front, and proceeded to do exactly nothing. Seeing this, the zombies decided to rush us. Now, normally, this wouldn't have been an issue. Unfortunately, a run of bad luck was nearly catastrophic. The two people on the right flank both suffered gun failures. One, using a battery-powered 22-round semi-automatic, apparently ran out of batteries. The other was using both an air-powered 10-round auto and the standard six-shot revolver. For whatever reason, the air-powered failed to fire and the six-shot jammed. Since those two were responsible for covering each other, this didn't end well. The dual-wielder took off for the stairs behind me, while the other decided to try and use his socks. He took one out, but was ultimately tagged by a diving zombie (and knocked over, somehow).
In the initial rush, I took out one with a long-range shot from my left-handed single-shot, which I dropped. A second zombie approached from behind the tree, dodged a shot, and was dropped by combined fire from myself and the person on my right. Hearing running behind me, I turned and chased down the zombie who had followed the dual-wielder down the stairs. I tagged him, then returned to find that the four who'd split off earlier had returned and mopped up the rest. About two minutes later, the second human group arrived. We then waited for about five minutes until the third group (which was carrying the "fuel cell" we needed) arrived, got our points, then left. On the return journey, we encountered no humans or zombies, except for one that was actually hiding in the goal building, dispatched by me as he rushed out.
End result: one third (potentially more) of the way to acquiring bayonets; one human down through very unfortunate luck.
As a fun sidenote, when we walked to the human rendezvous site, there was a pretty impressive welcome, based on our reputation from last year.