Update: so far for me its been consistent and works with the nail gun and the triple shot nailgun.

It also works if you switch your currently equipped weapon or even if you switch to the lighter

I was playing on current patch and in the Slaughter Room when you step on the platform that slowly goes down you can speed it up if you reload the shotgun from the inventory? i dont know if its actually faster since i have snail hands but maybe someone can make use of it? I also dont know if it only works with the shotgun or if you can use the nailgun too

heres a link to a clip of it