Alternatively, if your field allows for this method, you could run like I did.
The primary field we played on had a short average engagement distance to begin with (50-100ft), so I simply ran my VSR-10 at 380fps so I didn't HAVE a minimum engagement distance.
At 50ft, if someone has the drop on you, you don't have time to transition to a secondary and take aim.
However, even at 380fps my VSR was still very effective out to 240'
Worked out to be all good for me, I found it was easiest to snap the rifle up, take quick aim and pop one sure-thing shot at someone who got the drop on me, rather than fall back, and wait for a good shot with a pistol that's only accurate out to about 60ft anyway.
Also, I'll fill you in on three secrets;
1) Most people's AEG's are really inaccurate on full auto, or they cheap out and use ammo that's too light, causing the gun to shoot perfect circles on full auto rather than a spray or straight line. They legit shoot CIRCLES and can't hit the target in the middle (I and many other can attest, people shooting full auto right at you and it feels like you have a BB deflector lol)
2) Many people, specifically the new guys, tend to panic when confronted with someone they know is a good shot. Then tend to shoot in circles due to panic, and not just the gun. Show no fear when they start shooting at you. You'll get the hang of knowing when you need to reposition and when you have time to take a shot.
I've done that to a guy with an M249 from no more than 60 feet, He had the drop on me, was laying fire into a pallet I was behind, just a continuous stream of fire. I could hear it was highly inaccurate so I just popped up quick and took a shot, hit him center mass. But stupid me, I waited to see where it would hit and got a stray BB graze off the top of my hat lol
Which brings us to #3: Never wait to see where that BB hits unless you're absolutely sure you're safe