Best gas tube length for 16" 300AAC Blackout barrel

Hi guys,
I am new to the forum. I am planning a new build. I would like to know what you think is the best gas tube length for 300 AAC Blackout with a 16" barrel. I have found barrels with pistol length and carbine length.

Go with Pistol length if you plan on shooting anything subsonic

It’s finally here! FAQ’s, located under Pinned Posts

Some fairly straightforward questions get asked regularly, and while we don’t mind helping, you may be directed here to avoid redundancy.


1: What’s the perfect barrel length?

-Generally 8-11" is considered a good balance between compactness and velocity for supersonic loads. For subsonic loads, 8" is plenty of barrel to reach the speed of sound. That being said, the Blackout like any bottle necked cartridge continues to gain speed with longer barrels. 16" barrels will typically give 150-300fps increases over short barrels. Typically when 16" barrels are chosen, it’s simply to avoid pistol or SBR status.

2: Do I need a pistol length gas system, or carbine, and why?

-The best way to get a gun that cycles reliably is generally going to be a pistol length gas system, ESPECIALLY for barrels under 16", and/or guns that will be used with subsonic loads. If you’re fairly sure that you won’t want to use subsonic loads, a 16" Carbine gas barrel will be fine.

3: Is it true you need an a adjustable gas block?

-As a general rule, no. Some shooters enjoy being able to fine tune their gas to match a particular load, but a 300 Blackout built to correct specs will work just fine with a standard gas block.

4: Would a pigtail gas tube help my 300 run better?

-NO. Save your money. Pigtail gas tubes weren’t made for 300 Blackout.

5: Does anybody make piston uppers? Would that be better than a regular gas system?

-Piston uppers for 300 Blackout exist, but aren’t generally recommended.

6: What’s the best rifling twist rate?

-The vast majority of blackouts are 1 in 7" or 1 in 8" twist. Of the two, 1 in 7" is better suited to stabilize heavy subsonic bullets (210-245gr). Either will work fine for supersonic loads.


8: How much does it cost to buy everything I need to handload? How much do the components cost?

-A basic reloading kit will run $150-400. Component cost for reloaded ammo averages 20-50¢, depending on type.

9: How many times can you use brass?

-Many. It varies.

10: What are some good powders?

-Supersonic: H-110, 4227, 300-MP, Lil’ Gun, and many others
-Subsonic: 1680, H-110, 4227, and many others
Nosler, Sierra, Barnes, and Hodgdon all have free data online that will allow you to compare.

11: Can I convert any 5.56/223 brass, or only certain kinds?

-Lake city and Federal work well, along with numerous others. The most important factor is the sidewall of the case that becomes the new neck of the 300 Blackout case. If that area is over .013" you will likely have trouble. Under .013" is ideal.

12: Should I crimp my handloads?

-Most of us do. It’s an easy insurance against bullet setback. That being said, many hand loaders don’t crimp, instead using neck tension to keep the projectile from moving. Regardless of what dies you’re using, the Lee Factory Crimp die is a popular add-on for crimping after seating.

13: My fired cases have a flat spot on the mouth. Is that a problem?

-Perfectly normal. The case mouth contacts the case deflector during ejection. The flat spot disappears when the case is resized.

14: Should I be using a magnum primer? Will that help/hurt?

-Not necessary, but as always, the safest bet is to use what your published data calls for.

15: What load recipe will work best in my particular gun?

-There’s no way to be sure until you work up a load in your individual weapon. Welcome to reloading.

16: Where can I get load data?

-Nosler, Sierra, Accurate, Barnes, and Hodgdon all have free load data online.

17: What are some good hunting bullets?

-The most popular is the Barnes 110gr Tac-tx “black tip.” The Nosler 125gr Ballistic Tip & 110gr Varmageddon, the Hornady 125gr SST and 110gr V-max, and the Lehigh Defense 110gr Controlled Chaos are also highly regarded. Generally projectiles from 110-130gr are best suited to hunting with 300 Blackout. Heavier 150+ grain bullets often don’t expand reliably at the blackouts speeds.


18: What buffer should I put in my build?

-Carbine works, but H2 is recommended.

19: I heard 300 blackout can make my 5.56 explode and kill me. What’s up with that?

-Don’t put 300 Blackout in your 5.56. It can be made to fit, and explode when fired.

20: Can I stick an AFG on my pistol? Is that legal?

-Angled foregrips such as Magpul are legal on a pistol. Traditional stick or pistol-grip style foregrips are not.

21: I have a gun/barrel/ammo/brass/dies/recipe that says “300 Whisper.” Is that ok to use?

-S&W rifles marked “300 Whisper” and Hornady factory ammo marked “300 Whisper” are interchangeable with 300 Blackout. All others may not be.

This is from 300AAC discussion FB page. Obviously nothing is ever set in stone but it seems to be general consensus for most things.