Not 100% settled on it but I'm starting to think a 300bo with the right ammo/bullet or a kids' medium sized game gun for under like 150yds. I have a receiver set and other parts, including a 5.56 bcg. While the 6.5grendel was what I wanted but now think the 300bo is a good alternative for slightly cheaper without sarficing the main purpose of less than 150yd kids' hunting gun.

Are 300bo barrels ever longer than 16"?
Is the carbine gas length good enough?
Who makes a good barrel that I can expect one moa-ish within 100yds for less than @200 for just us barrel?

Thre is no reason to go longer than 16" with the 300 blk. Sounds like carbine or pistol gas will work for what you need. I have also been thinking about building a 2nd 300blk on the cheap for the kids to shoot. AR-Stoner makes a inexpensive barrel that gets good reviews.

http://www.midwayusa.com/product/2228320...e-moly-melonite

http://www.midwayusa.com/product/211944/...stainless-steel

Or, Brownells has their uppers on sale right now. $229 seems like a a pretty good deal.

http://www.brownells.com/rifle-parts/rec...-prod97307.aspx

But dont you know the 300blk is only tacticool and serves no purpose lol. You wont gain any more velocity out of a longer barrel since all the powder will be burned in 16" or less.

Adequate to at least 150yds, economical as it takes minimal parts to convert from 5.56 and also dirt cheap to load - that is what most people overlook. I have thought about a 6.5 Grendel build, can't really justify the cost. Maybe if I had other 6.5 cartridges already in the fleet but I don't. I have enough 300blk stuff stocked to last well into the next apocalypse.

Do u plan to shoot subs withba suppressor? An adj gas block is a must and will help fine tune the recoil a bit.

Yes, me too. I'm just realizing that overall (ammo consideration too) that the Grendel was going to start climbing much faster in cost. Also, if the main purpose was supposed to be a shorter range hunting gun for the kiddos, then the Grendel was quickly not becoming worth it. The extra cost would mostly be for my own personal. lol factor.

And no plans currently to suppress. Once again, the main official premise is a kiddo hunting gun that's better than a 223/556 option.

Not true. You will still gain velocity with more barrel length, but gains will be minimal since the 300 BLK is so efficient.

With that said, 16" is as long as I would go on a 300 BLK barrel.

I would look at Ballistic Advantage barrels. They make a line of barrels called the "Modern Series" that are melonited with M4 feed ramps and 1/7" twist. They fit your budget and are good shooters. Great barrels for the money. I have an 8" BA modern series on one of my guns, and it shoots great.

Link to barrel: http://ballisticadvantage.com/16-inch-300-blackout-pistol-length-barrel-modern-series.html

Adjustable gas block is completely unnecessary on a 300 BLK barrel with a properly sized gas port and proper gas system length.. One of the big advantages of 300 BLK is that it can cycle subs and supers both suppressed and unsuppressed with no need to adjust the gas system at all.

I built an upper with a 16" CMMG barrel that is very accurate. The barrel was under $100.00