Kind of a noob here, I've built a few ar15s and have acquired quite a bit of tools.  Would like to build something for home defense and range plinking.  Have been looking at the 300 blk but concerned about feeding issues.  Is their a certain length I should be looking at where the 300 blk isn't as touchy as the shorter 7.5"?  Was looking at faxon firearm barrel or Wilson combat. Any help and or advice is appreciated!  Haven't even started a build list so that might be helpful as well!

The barrel length is irrelevant to feeding, and not sure what you mean by touchy. Most people experienced in 300 BLK can usually tell you just by parts combo if you'll have cycling issues. Those are readily fixed though.

What feeding issues are you speaking of? Only issues that 300 BLK may run into is trying to feed subs from a standard 5.56 magazine. The ribs push the noses inward. That is easily fixed with 300 BLK specific mags, such as the Lancer or PMAG offerings.

From some of the other threads I read it sounded like people were having cycling or feed issues with barrel lengths less than 8 inches.  Thank you for the magazine tip, I'll note that in my build list.

You can run into cycling issues if you don't know what you're doing, particularly with light sub loads or running unsuppressed. Even then if you reload it is easy to overcome, or a simple swap to a carbine buffer or lighter spring does the trick.

Other than that the only "special" consideration is if you run both subs and supers you may, may need to consider an adjustable gas setup, either via an adjustable gas block (AGB) or adjustable bolt carrier group (ABCG). I personally recommend the adjustable carriers, and the Bootleg is my preferred carrier.

Ive never played with 300bo. If a person were to buy a 300 barrel would it be safe to say it would be gassed to run with supers?

I'm planning on running no suppressor until it comes, which I was told could be 6 to 10 months.

Depends on length and manufacturer but generally most shorter barrels will need a carbine buffer, lighter spring, or both when running unsuppressed subs.

Supers are never an issue, suppressed or not, short barrel or not.

A properly set up 300blk should be able to subs/supers, suppressed/unsuppressed with an H buffer. If you want to focus on subs vs supers or suppressed vs unsuppressed, or a combination thereof, there are different steps you can take to achieve those goals. Adjustable gas blocks, adjustable BCG, gas port size, heavier buffers, etc.

Don't take any chances with reliability,  or  the wimpy blackout. 6.5 grendel is what God wants you to build.Power, reliability,  range, BC, feels so right

I haven't looked into the Grendel.  I already have one useless build I'm not sure is going to lasts (224 valkryie).  Don't want another.  I'll have to look into the Grendel.  Thanks for the suggestion!

Sub's?

9" barrel is the sweet spot for supers and subs, suppressed and not.
I dont know what size port they used, but I have 2 AAC 9" barrels and they work with everything I have fed them.

That's what I'll go for then, any other recommendations to make the build more reliable.  Putting the list together now.  Evey tip in the right direction helps!

If you want to shoot heavy subs, you need a fast twist.  1:8 and 1:7 twist for 300Blk are the most common available, and short of a custom twist or a Q barrel, 1:7 is about the fastest of the readily available twists you'll find. If you have any inkling to shoot 210 to 220 grainers, then 1:7.  That's all well and good for the heavy subs, but what happens when you shoot 110 grain supers through that fast twist?  It's not uncommon for accuracy to go to crap (my 1:7 twist 7.5" 300 won't shoot anything under 150 grain supersonic worth a hoot) because over spinning a bullet causes accuracy issues.  Lower twist to get good supersonic light bullet accuracy, then it won't stabilize heavy subs.  It's all a trade off.

I'll probably catch flak for this, but IMHO, 300 is best at heavy subs, suppressed in short barrels...it's more or less what is was designed for (since it was spun over from AAC's 300 Whisper).  The fact that 308 bullets in lighter weights are available and you can load them in 300 at supersonic speeds is just a byproduct of component availability and parameters.  Scaled up to carbine or rifle lengths is where supersonic 300 really "works."

Since you mention home defense, that puts this gun in a completely different category than toy, plinker, fun gun, etc.  It means you want to trust your life to it.

My list of criteria for that (and again, I might draw some fire), but this is MY list:

#1 criteria for any defense gun is it must function reliably.  The best caliber, the best tacticool toys attached to it, etc don't make a hill of beans if the damn thing won't run reliably.  When I hit the bang button, it has to go bang, every time.

#2 The gun must function reliably.

#3 The gun must function reliably.

#4 Tack driving accuracy is not required.  Unless you're an NBA player with a mansion the size of your local mall, most home defense encounters are going to be at very close range.  There are very few, if any modern firearms that won't hit an intruder across your living room.

#5 If it's adjustable, it has an unknown and unpredictable life span or reliability.  Adjustable gas blocks and BCG's are cool and all, but adding them is adding potential failure points.      

#6 Whatever you settle on for you home defense arm, practice, practice, practice. The best firearm, the best caliber, the best everything is no good if you can't hit the target.

Attached File


Something, something....bolt face, mags and extractors?

OP is building something for home defense.  If you are talking short barrel, that is .300blk territory.

OP is also building something for plinking....unless you reload....that is NOT .300blk territory unless you are simply loaded.

Have been looking at the 9" BA barrel or 8" Wilson combat barrel.  I guess more or less looking for a PDW.  I would like to be able to plink but if I have to choose then it would be for a defense weapon.  I'm going to have a can on it eventually its just going to be that waiting game for it.

There's also a little more than just energy in play in ballistics, especially subsonics.  Some people will tell you 300Blk is shite for defense because of low energy and will tell you to just use a pistol instead...much easier to handle in close quarters, but..................

Another parameter that is important is SD (Sectional Density), this is the ratio of the bullet's length to diameter and is a big factor in penetration.  Watch videos of pistol's vs soft body armor, then watch a video of subsonic 300 vs that same armor.  300 will go through it like hot butter where pistol calibers won't.  

What's the chances of an intruder wearing body armor?  I dunno, I suspect it's probably pretty low, but the availability of it these days, and much lower costs than it used to be, you never know.  If that's a criteria you want to account for, then 300 wins over any pistol caliber.

Either way, anyone and everyone will argue with you as to which is the best for X, Y or Z, but physics doesn't lie, and "A" gun is always better than "no" gun.  A suppressed 300Blk pistol length AR for home defense is a perfectly fine solution.  

This thread interests me.

Going to be doing a 8.3 inch Hanson 300 BO build when the barrel arrives. Still trying to decide between a 7 inch BCM MCMR or a Forward Contriols 6.7 inch handguard.

Should be a fun project .to complete.

Also, it just may spur my desire to get into handloading afterall

300 BLK was my first cartridge I loaded for, in March 2013. Loaded about 18k rounds of 300 since then. Jumped into it and 9mm at the same time.

With ammo prices as they currently are, I reload every caliber I shoot, except of course 22LR...but there are kits to do that if you want.

Used to be 5.56 and 9mm were cheaper to buy than you could reload it.  Not anymore.

IF you do get into reloading and shoot 300Blk, you can save even more by converting 223/5.56 to 300 (since 300 is based on that case) because once fired 223/5.56 brass is way cheaper than 300 brass.

6.5 Grendel is for rednecks with too much free time.

OP 300 is a great choice. Get the 7.5 in Q barrel. It’s a 1:5 twist. Stabilizes subsonic rounds to be more stable at further distances. It’s delightful with a silencer. Its cartoonishly quiet. Supers run flawless, and subs are more “sensitive.”
When you set up the gas and buffer system, optimize it to make sure they cycle reliably AND last round allows for bolt hold open.
Optimize it around supers, then adjust to run  subs erring on the side for supers. For defensive situations, this gun should be loaded in supers, anyway, right?

Enjoy it, its the superior caliber to 5.56. RIP 5.56, long live 300BLK