New to the forum, but not necessarily reloading. Question is, I have been fire forming some .338 lapua brass (Lapua headstamp), and after the first neck size and trim, some of the cases seem awfully tight when chambering, and I'm no where near touching the lands, is that normal? Do I need to get some bump dies and bump the shoulder, or will it hurt to fire them tight? They extracted fine, just a little tight, but not like an over pressure tight.

Were they all fired in your rifle previously?

That's the risk you take neck sizing. In theory, once the brass is "fire formed" to your chamber, the brass is perfect and all you need is a neck size to hold the bullet in place. In reality, you will have cases that will chamber tight or not chamber at all when neck only sizing. If you neck only size, you will want to chamber check each piece of brass to make sure they chamber properly. If they don't, you will need to size the case body and shoulder some. You can FL size them, or do a partial shoulder bump of about .002"-.004" and this will solve your tight chamber issues. Just chamber check the brass after sizing to make sure they go in without resistance.

Can a I just back a FL die off to bump the shoulder back a couple thousandths? Or do I need a bump die specifically?

^^^ Yes, that should work. But you have to measure the head space of the shoulder to know how much you are bumping it. In doing this, you are sizing the brass short. You can also have chamber issues related to the case web area being to wide at some point. After sizing, you need to chamber check the brass in your rifle to make sure it is working and not a tight fit.

Is it worth neck sizing as compared to FL? My load I've developed was shooting under Moa@200 yards, groups at 600 are around 4-5"....

welcome, you can get all the info you need here, some you may not want.