Youve received bad info my friend.
You can call the ATF EVERY day and it WILL NOT slow down transfers. When you call the ATF NFA Branch @ 1-304-616-4500 you will be greeted by a polite call taker (one of three) where you will tell them (politley) that you would like to check the status of your F4. They will ask the serial number of the item and your name. They can then tell you if its gone pending or approved. This is their job, they ARE NOT examiners.
Outline:
When you mail the F4 to GA, they take the check out and foward the packet to WV. Once in WV it sits until the check is cashed. Once the check is cashed its fowarded to the examiners where it waits again until its sorted by the 1st intial of the transferrer(dealer). Once sorted it will goto the assigned examiner (one of 12) depending on what initals they cover (this means its gone pending). THEN is goes into their pile using the roman calendar for what day your check was cashed. Then it waits again untill they get to your stack and your paperwork. Once the examiner actually has your F4 in hand it only takes 2-3min to approve it.
So depending on the examiner your dealer gets it could take anywhere from 30-100days or longer if you forgot to sign it or some other stupid mistake.
My last 3 transfers took 38days mailbox to mailbox because my dealer by luck gets one of the fastest examiners.
I generally call in 30 days increments from when I mailed the check. This way by the time i called I can find out who my examiner is (just ask the call takers if yours has gone pending, they can tell you who has it) and estimate a completion time depending on that persons history. Calling every 30days also lets you catch mistakes early. Sometimes they will set a bad F4 aside and forget about it or send it back when they have enough. So calling every 30 can speed up the process for fixing a mistake. Ive seen guys wait 100 days to find out it was lost in ATF limbo because of a stupid mistake on the paperwork.
Thats all I can think of. Im tired of people saying not to call as it will slow down everyone paperwork. Unless you ask to speak to your examiner(why?) then everything is fine.
*Wanted to add that the examiners go through over a million forms every year. Remember they also go through the Form1's, 3's, everything. The F4's are just a part of the workload.