cold weather air gun hunting?

Might be a silly question but I am going to ask anyways lol do any of you find that the speed of your pellets or to be more presise the lethalaty of your pellets are somehow lessened in cold weather -21 today and I hit some pigeons solid and watched them fly off? ...very well could have been my error and I will own that up front but I saw the pellet strike the upper crop/neck on 2 pigeons at 41 and 46 yards and then watched them fly. I have shot about 40 pigeons with this gun and pellet combo at that range and much further and have not seen this before ...could it be the cold or just bad luck?
thanks folks for your thoughts 
Jonathan 
 
hmm must be just me lol...I actual set out steel targets at my known ranges to see if it was dropping or something but it all looked ok ..guess it was just a few bad ass birds
I just hate the thought of wounding any game ...it was a little windy so i opted for more forgiving body shots instead of head shots at 33 fps it has worked well before and I assumed would today but maybe I will stick to head shots for a little bit 
Jonathan
 
In my experience pigeons and doves are tough critters. If their crop is full a shot in that area is like hitting a sand bag, the seeds absorb the shock of the pellet. I have hit collared doves solidly and then had to track them visually as they flew from one tree to another eventually falling to the ground dead. They'd fly off on a descending angle, land on a lower and lower perch till they hit the ground. This can make them very difficult to recover as you can imagine! 
John
 
I think i might have figured it out ...I bought some H&N Baracuda power pellets to try out and there copper coated I shot two mags of them two days ago and thats when my issues started to happen I tried shooting an hour ago with my JSB's indoors and first shot dead nuts second .5 to the right ...third dead nuts ...then .5 to the left?
....i checked the scope and everything was tight so I thought i would clean the gun .....tada just put 40 pellets in one hole? ...maybe the pellets were not centered and were just plucking feathers off?!?! ...as for the crop shots John i agree with my TrailXL 1100 .22 at 22fpe I dont use that shot often for that reason but with my FX Independence at 33 fpe I actually really like that shot and use the energy transfer to my advantage ...rather then pencil through it unloads a hell of a shock wave on the bird and you can actually hear the pressure on impact ...i will try it again and see if that is what it is!
Thanks for the replies folks
Jonathan
 
Though you seem to have found your problem, keep the lubes you use in mind when it comes to bitter cold temps. I do alot of late season hunting and had a similar issue as you. It ended up being the lube I had used on the trigger parts and hammer didn't like the cold. The hammer was actually slowed down creating low velocity and drastic POI change. I switched to polishing everything as much as possible and only using a light spray of silicone spray. Problem solved, but had me baffled for awhile!!
 
Copper-plated pellets had weird effect on my Indy .22.
I was doing chrony testing of various pellets when I first acquired the gun, and if when I shot a JSB after copper-plated H&N, I saw up to 50 (!) fps drop in muzzle velocity. Took 20+ shots of lead to bring the velocity back to normal (880fps with 18gr JSBs)

Shooting cleaning pellets has the similar effect.

In general, I've heard seasoned people say that switching from pellet to pellet (esp from different manufacturers) can open up groups until barrel get's 're-seasoned' to the new pellet. Kinda makes sense if you think about it. 
 
I agree with the copper coating comment. After all, lead is a fairly good lubricant all by itself. 

Recent, we had a cold snap along with winter storm Goliath. The unheated barn was full of pigeons hunkered down by the cold. The only thing I noticed was the muzzle report sounded a bit different, even with my ear muffs off. Denser air I assumed.