The pdfs you fill out online on the US Customs website are tiny. Not enough room to fill out your entire address. And they print out about the size of an index card.
Is this the 'correct' size?

4457 forms are slightly larger than an index card. Bear in mind, they need to be signed and verified by US Customs. They have the forms at their offices and they are good as long as you have the rifle or other declared items.

Its been a few years since I have had to get a new 4457 but the last time I did in 2009 I filled out the ones online to take to the customs office. They printed out larger than the ones they have at the customs office.

I printed mine out on a full page of paper. Nothing says what size the form has to be. All it's for on this side, is to keep you from paying tax on your own guns.
Take the form to the idiots at CBP and have them wet stamped. Carry extra copies. Put one in carry on, checked, gun case, + 5 more for the wanna-be cops that say they have to have a copy.

Remember, most of the "authorities" you'll be dealing with are dumber than a post.

Just make them think they're cool and all will be fine.

Trophyman

I made color copies of mine and had them laminated.

Just last week I completed and printed out mine letter size and had no issue with the customs folks.

I also color copied and laminated. You CAN NOT tell which is original and what is a copy. I made a handfull and they should last me forever!

I filled out the online forms and took them down to the Atlanta CBP office yesterday. Lady behind the counter wouldnt even look at them or even respond when I asked what is the purpose of having the forms on-line if I can't complete them ahead of time. Made me fill out the forms all over again. I have little tolerance for bureaucrats, but was able to hold my tongue.

I completed a 4457 online and printed it both sizes, went to a Customs office on Friday, March 30th. The officer chose the larger size (8 1/2 X 11) and checked the serial number matched the rifle.

Easy process, but a pain to travel to a Customs office.

I fill out the online form, take it to the CBP local enforcement office. They accept it, check the serial numbers, sign it and place their seal on it (all in the index card size). I then color copy it and have the original laminated. I put the laminated one in the gun box with the firearm and keep the copy in my carry on (just in case). Never a problem locally or at the airport.

If you're a perfectionist and really wanted to type it out from the internet and use smaller type. You could print it out with everything that fits as you like it from the net. Then open up a blank document in word or other text editor, and then line it up print it over the other form you already printed out. Basically using the preprinted 4457 instead of a blank piece of paper for the text you need to change the font size for.

Or if you save it as a PDF, you can also open the PDF in software that lets you edit the PDF, then change the font size to whatever you need.