.300 AAC Blackout - 'Enabling' Thread (Mags, ammo, optics, barrels, etc.)

[Welder]

So what I found out was this upper was available separately or on AAC's MPW rifle that they made years ago when they were making rifles. Found some links to articles on that rifle:

https://www.personaldefenseworld.com...ockdown-power/

https://www.gunsamerica.com/digest/s...k-full-review/

The MPW was made in 9, 12.5, and 16" barrel lengths.

Here's an old ad for the upper by itself with a picture (obviously out of stock at this point):

https://www.cheaperthandirt.com/adva...128006848.html

The specifics I can find are the following:

-KAC URX III 8.0 forend, P/N 30210
-9" 1-7 twist nitrided 4150 barrel
-5/8"-24 muzzle with 51-tooth 3-prong flash suppressor
-Nickel-Boron UCT EXO BCG
-Bolt is Carpenter 158 phosphated / shot-peened w/ green o-ring
-Standard charging handle, forward assist, upper has T-marks and is lettered "300 AAC BLACKOUT (7.62x35mm) ADVANCED ARMAMENT CORP."
-The rail has the standard KAC markings and name, and is also marked AAC with the AAC logo on the forward right side of the upper quad section

Your opinions welcome. I'm ambivalent about the .300....might be fun, and here's a way to shoot it...but is it worth more selling? There aren't any current or completed listings for AAC MPW's with the 9" barrel; there are some for the 12.5 and 16's but unsure what the value on those is relative to the 9.

[LittleLebowski]

So what I found out was this upper was available separately or on AAC's MPW rifle that they made years ago when they were making rifles. Found some links to articles on that rifle:

https://www.personaldefenseworld.com...ockdown-power/

https://www.gunsamerica.com/digest/s...k-full-review/

The MPW was made in 9, 12.5, and 16" barrel lengths.

Here's an old ad for the upper by itself with a picture (obviously out of stock at this point):

https://www.cheaperthandirt.com/adva...128006848.html

The specifics I can find are the following:

-KAC URX III 8.0 forend, P/N 30210
-9" 1-7 twist nitrided 4150 barrel
-5/8"-24 muzzle with 51-tooth 3-prong flash suppressor
-Nickel-Boron UCT EXO BCG
-Bolt is Carpenter 158 phosphated / shot-peened w/ green o-ring
-Standard charging handle, forward assist, upper has T-marks and is lettered "300 AAC BLACKOUT (7.62x35mm) ADVANCED ARMAMENT CORP."
-The rail has the standard KAC markings and name, and is also marked AAC with the AAC logo on the forward right side of the upper quad section

Your opinions welcome. I'm ambivalent about the .300....might be fun, and here's a way to shoot it...but is it worth more selling? There aren't any current or completed listings for AAC MPW's with the 9" barrel; there are some for the 12.5 and 16's but unsure what the value on those is relative to the 9.

Check Gunbroker, see what others are selling for. If I were you, I’d buy a PSA upper now and sell this AAC around election time, during the next panic.

[Corse]

So what I found out was this upper was available separately or on AAC's MPW rifle that they made years ago when they were making rifles. Found some links to articles on that rifle:

https://www.personaldefenseworld.com...ockdown-power/

https://www.gunsamerica.com/digest/s...k-full-review/

The MPW was made in 9, 12.5, and 16" barrel lengths.

Here's an old ad for the upper by itself with a picture (obviously out of stock at this point):

https://www.cheaperthandirt.com/adva...128006848.html

The specifics I can find are the following:

-KAC URX III 8.0 forend, P/N 30210
-9" 1-7 twist nitrided 4150 barrel
-5/8"-24 muzzle with 51-tooth 3-prong flash suppressor
-Nickel-Boron UCT EXO BCG
-Bolt is Carpenter 158 phosphated / shot-peened w/ green o-ring
-Standard charging handle, forward assist, upper has T-marks and is lettered "300 AAC BLACKOUT (7.62x35mm) ADVANCED ARMAMENT CORP."
-The rail has the standard KAC markings and name, and is also marked AAC with the AAC logo on the forward right side of the upper quad section

Your opinions welcome. I'm ambivalent about the .300....might be fun, and here's a way to shoot it...but is it worth more selling? There aren't any current or completed listings for AAC MPW's with the 9" barrel; there are some for the 12.5 and 16's but unsure what the value on those is relative to the 9.

I have the same upper, it has been one of the best performing 300 blk s I have used. Good accuracy and no issues with function (sub or super). They had blow out pricing on these years ago, which is when I bought it.

[El Cid]

That's a nonsensical criteria, that may be right by coincidence in certain circumstances, like the two times a day a broken clock is right on. It's not that there aren't good barrels that satisfy it, it's that it implies things are connected in a way that they aren't. At all.

If you have a 16-inch barrel, is a 16-inch twist rate OK for .300 BLK?

Pistol-cartridge barrels are generally rifled with twist rates several times longer than a typical pistol barrel and it doesn't impair their accuracy. Would a J frame snubby be improved in any way if the twist changed from whatever it is (1:18, maybe) to 1:2?

It's hardly nonsense. He asked specifically about 300BLK in 8 to 8.5" bbls. My comments about twist rate were to his specific question. With an 8" bbl in 300BLK a twist rate that of 1/7 is good to go. A 1/9 or slower would not stabilize the bullet.

I have no idea why you are talking about 16" bbls or J-frames...

[OlongJohnson]

The twist rate that is appropriate for a given cartridge and loading is almost completely independent of barrel length (significant differences in barrel length leading to increased velocity when playing with marginal stability can make a difference, but that's not relevant to .300 BLK short barrels), so to state the required twist in terms that implies there's something important or even related about the bullet making a complete rotation while it's in the bore is misleading. 1:7 or 1:8 is an appropriate twist for .300 BLK (assuming subs will eventually be used, at some point on somebody's part) whether the barrel is 5.5 inches or 16 or 20 inches.

The way you stated it could be interpreted as:
If you have a 9-inch barrel, then 1:9 twist is good.
If you go with an 8-inch barrel, you need to tighten up to 1:8.
If you go down to a 7-inch barrel, you better make sure it's a 1:7 twist.

Which is not how it works.

[Welder]

Check Gunbroker, see what others are selling for......sell this AAC around election time, during the next panic.

Yeah, I should've been more clear -- I checked GB and there aren't any AAC 9" uppers or complete 9" MPW rifles for sale, either currently or in the completed listings. Only the 12.5 and 16"ers.

But I think you're right about the next panic; I'm gonna cash out on an NOS Colt Socom II rifle for sure then, maybe a second Socom II upper, and maybe this AAC also. I think I'll stand to double or triple my $$ that way.

[El Cid]

The twist rate that is appropriate for a given cartridge and loading is almost completely independent of barrel length (significant differences in barrel length leading to increased velocity when playing with marginal stability can make a difference, but that's not relevant to .300 BLK short barrels), so to state the required twist in terms that implies there's something important or even related about the bullet making a complete rotation while it's in the bore is misleading. 1:7 or 1:8 is an appropriate twist for .300 BLK (assuming subs will eventually be used, at some point on somebody's part) whether the barrel is 5.5 inches or 16 or 20 inches.

The way you stated it could be interpreted as:
If you have a 9-inch barrel, then 1:9 twist is good.
If you go with an 8-inch barrel, you need to tighten up to 1:8.
If you go down to a 7-inch barrel, you better make sure it's a 1:7 twist.

Which is not how it works.

It’s certainly possible I misunderstood and I can’t find my original source. I was at least led to believe that the bullet needs a minimum of one revolution before leaving the bbl. Is that not the case? Why did Sig use a 1:5 twist on their 5.5” bbl? And most 8” bbls for 300BLK have a 1:7 twist.

[OlongJohnson]

Unfortunately, Sig doesn't consult with me on its design and manufacturing decisions, so I can at best speculate in a slightly educated manner. If I had to guess (and I do, if I am to answer your question at all), I'd say something like the shorter barrel is going to give up even more velocity, so they spin the bullet a little faster to keep the heavies that people will inevitably want to shoot out of it stable.

There's a page in this PDF from AAC that suggests very minimal increase in pressure with 1:5 vs. 1:7 twist, so that can be set aside as a concern.

https://ndiastorage.blob.core.usgovc...590Silvers.pdf

The rotational velocity of the bullet is:

rpm = ft/sec * 60 sec/min * 12 in/ft * 1/#in

with # representing the inches of the twist, i.e., for 1:7 twist, # = 7.

I wouldn't necessarily rely on Courtney as a simple authority for testimony, but he has a discussion in this paper of several stability factors that have been used successfully:

https://arxiv.org/ftp/arxiv/papers/1410/1410.5340.pdf

On p. 2, he presents the Miller formula. It's clear by simple examination that an L^3 (length of bullet cubed) factor appears in the denominator, so it quickly becomes a dominant factor. Which explains why shooting long, skinny, heavies at subsonic speed requires a really fast short twist.

The key elements are how fast is it rotating relative to its velocity, mass, geometric factors and atmospheric conditions.

Note that the length of the barrel is entirely absent from the formula.

The twist rates that are popular in .300 BLK barrels are driven totally by the 220gr and heavier match bullets being fired at subsonic velocity. Long, skinny bullets at very low speed require extreme twist rate to get the rotational velocity up to stabilize them. If everybody stuck to 125gr and lighter supersonic, it's likely that 1:10, maybe even 1:12 would work just fine. I believe there is an extensive history of .308 shooters running 1:12, maybe even longer twist with 155gr bullets at long range (much greater velocity causing the bullet's rotational velocity to be correspondingly higher for a given length of twist).

I initially mentioned pistol barrels of 2-5 inches length with 16-20 inch twist rates simply to provide an example of barrels that readily stabilize their projectiles without the projectile coming close to completing a rotation while still in the barrel. Off the top of my head, I think there are even a lot of Marlin 1894s with ~38-inch twist. They're OK for 240gr .44 Magnums, even when the barrels are only 18-20 inches long.

There are other factors that come into play with other scenarios. In .224 caliber, lightly-constructed varmint bullets fired at very high speeds from a fast-twist barrel created to stabilize heavies can actually disintegrate in the air, just from the centrifugal force as they are driven well past 200,000 rpm. The prairie dogs will laugh and flip you the bird until you go get a different rifle. There's an issue with extreme long range that an overstabilized bullet may hang onto its original nose-up orientation rather than tipping and aligning its long axis with the flight path, leading to reduced effective BC and other issues with external ballistics. These are examples of why we don't just run super-short twist in every gun.

Long-winded dipping of toe into pool to explain my point...

[Welder]

....I believe there is an extensive history of .308 shooters running 1:12, maybe even longer twist with 155gr bullets at long range (much greater velocity causing the bullet's rotational velocity to be correspondingly higher for a given length of twist)....

Before bed every night, I read back issues of "Precision Shooting" magazine. Last night there was an article from July '98 about Palma rifles, and the author was saying his was running 1 turn in 13.5", shooting Berger 155 VLD's. Another recent evening an article in the same year range was mentioning 1 in 14" for his Palma rifle.

ETA we're talking .308 cal here.

[echo5charlie]

So what I found out was this upper was available separately or on AAC's MPW rifle that they made years ago when they were making rifles. Found some links to articles on that rifle:

https://www.personaldefenseworld.com...ockdown-power/

https://www.gunsamerica.com/digest/s...k-full-review/

The MPW was made in 9, 12.5, and 16" barrel lengths.

Here's an old ad for the upper by itself with a picture (obviously out of stock at this point):

https://www.cheaperthandirt.com/adva...128006848.html

The specifics I can find are the following:

-KAC URX III 8.0 forend, P/N 30210
-9" 1-7 twist nitrided 4150 barrel
-5/8"-24 muzzle with 51-tooth 3-prong flash suppressor
-Nickel-Boron UCT EXO BCG
-Bolt is Carpenter 158 phosphated / shot-peened w/ green o-ring
-Standard charging handle, forward assist, upper has T-marks and is lettered "300 AAC BLACKOUT (7.62x35mm) ADVANCED ARMAMENT CORP."
-The rail has the standard KAC markings and name, and is also marked AAC with the AAC logo on the forward right side of the upper quad section

Your opinions welcome. I'm ambivalent about the .300....might be fun, and here's a way to shoot it...but is it worth more selling? There aren't any current or completed listings for AAC MPW's with the 9" barrel; there are some for the 12.5 and 16's but unsure what the value on those is relative to the 9.

I have one of the 16" MPWs. It's a hell of a rifle! I have shot it to 750 yards on several occasions - not for serious as that is far beyond the ballistic realistic of the .300 - at 1 gallon paint cans in a stripping pit. Never got a direct hit, but made more than a few tumble down the bank, the hold over using the .300 BLK Trijicon 3x30 ACOG was simply silly and combined with unreadable wind it was a fool's errand but still fun. With subs at that distance it was impossible to even spot impacts into the silt bank.

I want to say that we were blowing these out (the 16", had over 100 of them) for around $1100 back in 2014/2015. Anyway, I regret not buying into a 9" MPW upper (or complete SBR) back then.

Anyway, to answer your question, there is no way I would ever sell my MPW. Ever.