I have been doing a lot of reading concerning my new SBR build with suppressor.  I really want the rifle to be compact.  I have decided, after much thinking about it, to go with the 7.5" barrel with the silencer rated for that length.  Now I need to figure out what length to put on Form 1.  I laid the 7.5" AR pistol on top of an existing similar lower with a Magpul stock and adjusted the stock to full length.  I removed both flash hiders.I measured the length from the longest part of the Magpul to the front of the pistol barrel.  It was 25 1/4".  I checked the 7.5" barrel using a long dowel and it was 7 3/8".
A lot of suff on the internet indicates a 7.5" AR should be 26 1/2" long.  Am I overthinking this?  I am thinking I should put the 25 1/4" on Form 1.

Close is good enough...as long as it's a plausible/possible length; the ATF doesn't care.

This.

I'd just put 26" for OAL and 7.5" for barrel length and call it a day.

OAL can be measured with the flash hider installed, maybe that's the disconnect you're experiencing.

If you measure it, and record a length, that's the length it is.

Thanks for the inputs.  My concern was the 26" definition of SBR along with the under 16" barrel.  One thing for certain, the rifle I am building surely is a SBR.  Time will tell if I find the short barrel is OK or do I try out a 10.5" to see if there is much difference.  The whole process is fun and enjoyable learning about all this new stuff. Again, thanks to all in the Forum that take the time to read and to read and reply to questions.

Sounds like you might have a bit of a misunderstanding of the federal "SBR" definition.

A rifle is a Short-barreled Rifle when it has a barrel less than 16 inches long, -OR-, it has an overall length less than 26 inches long.

The key word there is "or", meaning the only one of the two conditions need be met for it to be an SBR, not both.

As an aside, that's why the Tavor bullpup rifles come with a 16.5" barrel instead of a 16" barrel.  The 16.5" barrel gets the OAL to just a bit over 26".  If they had a 16" barrel, their OAL would be under 26" and they'd have to sell them as SBRs.

Thank you for that info. Didn't know that about the Tavor