I know this may draw some hate, but I’ve been kicking around the idea of having my 30-06 bolt gun barrel cut and threaded at 18 inches. There are a few reasons I think this would work well for me. 1) I got my stamp back for my Nomad and I obviously would like to run suppressed when I hunt...and it would be nice to offset some of the length of the suppressor. 2) Where we’re at in Georgia, you’re going to be hard pressed to take a shot on a deer over 200 yards, and most shots are well within 100 yards. 3) With advancements in bullet technology, it seems like a lot of designs will still reliably expand at lower velocities. I know Kevin Brittingham has said that with their new production Fix rifles, they are no longer offering the 22 inch barrels and are swapping to 16 inch barrels for both 6.5 Creedmoor and .308 rifles, as both cartridges will do what 99% of people need them to do out of that length barrel. Is there anything I’m missing before I take the plunge?

The ONLY way I would remotely consider this is with a suppressor attached.  Period.  End of story....

I've hunted 25 years with a 20" 308 Win.  This effectively takes the 308 Win and turns it into a 300 Savage.  Velocity losses are right at about 130-50 fps for my  little rifle.  I do like how handy it carries, but it does come at a price:  Muzzle flash is substantial (not a real issue hunting, since 99.8% of the time its one shot, and start filling in the tag).  And the noise is elevated.  I have fired a Ruger 77 Carbine equipped with a 16" barrel and I did NOT like it; It was abrasively loud, seemed concussive, and was just harsh.  It's not a recoil thing:  I regularly shot a .350 Rem Mag in a lightweight rifle with 225 grain Partitions.  The short 16" was just loud and nasty....

When cutting the 30-06 down, you have greater case capacity than the 308.  Depending on bunt rate for the powder used, a lot of combustion will be taking place outside the barrel, or so it will seem!  A suppressor will really tame this, so 18" can make sense.  With the can attached, its likely a good idea.  Take the can off, and it would likely, in my best guesstimate opinion, be less than wonderful...  If you are convinced you will be hunting with the can, have at it.  Gonna hunt without the can?  Its a hard pass...

As for loads....  With the reduced velocity you can expect some loss in the sort of rapid expansion you see now.  My carbine pushes 165's to about 2600-2650.  A regular old school cup and core bullet like the Hornady Interlock, Remington Corelokt, or Win PowerPoint will reliably take deer.  However, in my case, deer very nearly always ran.  Even with an absolutely perfect heart shot, deer always ran somewhere between about 60 and 100 yards before dropping.  Even when I reduced bullet weight to increase velocity some (using Hornady Interlock BTSP 150), I got the same long runs.  Never lost a deer, but in some cover, a 100 yard run can make for a deer that's hard to find...

The Nosler 165 Ballistic Tip is freaking wonderful AT THESE SPEEDS.  They are soft and open fast.  With muzzle velocities running about 2600-2650, and 75 to 125 yard impacts, these BT's are reliably putting the hammer on deer.  Expect 2-3" of penetration, followed by a decent 6-8" "melon" of tissue that's just gone (liquified), and then a rapidly tapering wound channel that ends up with a dime sized exit.  I'm getting complete broadside penetration, and have never recovered a bullet.  In most cases my deer are quite literally dropping on the spot.  Boom.  Flop.   I would NOT use these BT's in a fast cartridge!!!!  However, they are near ideal for this specific application.

I would not, under any circumstances, use a "hard" bullet like the Barnes TTSX or a similar monolithic all-copper bullet.  Forget it.  These are fantastic bullets but really seem to need high speeds to open well, and they are not forgiving of low impact speeds.  Use a TTSX at a little longer than expected range, and failure to expand is very very real...

One thing to consider:  Various 'LR' bullets are designed for lower impact speeds.  Example, Nosler's Accubond LR.  High BC's preserve velocity, and a softer bullet makes for easy opening at the reduced impact speeds that happen at 600, 800, 1000 yards....   Reduced impact speeds are what you will get with an 18" barrel.  Even though you are shooting at 80 yards, a LR bullet might make sense...

If you are reloading, I'd opt for a powder on the faster end of the spectrum.  Something on the order of Win 748, AA 2520, or IMR 4895, IMR 4064 probably would work well.  Start getting into slow powders and while the reload manual might suggest higher speeds, the short barrel likely wouldn't take advantage of the slower burn rate.  I'd leave off powders slower than 4064...

Not 18", ... but I've long thought about getting CZ's Model 4154 20" '06 carbine in the Kevlar stock, if I could find one.

For the lower 48, that's plenty of short-range, 'brush-bustin' power for any large game with 200gn or 220gn loads. Mauser-claw extraction, impervious-to-weather stock, and a great set of iron sights.

https://www.gunsinternational.com/guns-for-sale-online/rifles/cz-rifles/cz-usa-cz-550-carbine-30-06-sprg-20-6-5-rds-04154.cfm?gun_id=101139299

That said, my 16.1" Mini-G in '06 is just as handy, or maybe more, for any of the same roles as an 18" or 20" '06 bolt-gun.

It will no doubt be being run 100% of the time suppressed. However, you did bring up a few concerns that I had been thinking about. Like you brought up, I’ll definitely have a decent amount of unburnt powder leaving my barrel so a muzzle brake is going to be a requirement for me. To elaborate, while my Nomad doesn’t have any barrel length restrictions, the brake will help preserve my blast baffle. This being the case, an 18” 30-06 with muzzle brake installed definitely would open up my sinuses.

To your other points, I “lucked” up that my particular rifle seems to like pills in the 150 grain range, so I should already be squeezing about as much velocity as I can out of the system without using super light projectiles. Of course, this is all before I put the counter weight known as a silencer on the end of the barrel. I do like your idea about the use of a LR bullet. Back when I was playing around with what would be a good hunting round at bow ranges for a 7.5” 5.56 pistol, I looked at using the 55 grain V-MAX as it performed more like a traditional hunting bullet at the lower velocities my pistol would be pushing. Seems like the same method would be used in this case.