The 300 blackout sucks, or does it....

[perentie]

I was going to ask how the 6mmARC is better than the old 6BR but should probably be another thread.

[straightshooter]

Many posts attempt to explain shooting phenomena with regurgitated prattle or advertising sloganeering but this one caught my attention for it's originality on the one hand and the degree of uninformed assertiveness on the other.
"My theory of the shortcomings of the factory 300 blackout are as follows:
a) The tight 1:7" twist barrel was over-stabilising the light 125gr supersonics, meaning any "wobble" was exaggerated once the pill moved beyond 50m."
Briefly.
A bullet in flight will be deemed stable or unstable by it's gyroscopic stability (GS) which is given as a calculated dimensionless number and if the value is 1 or greater then the bullet is stable and if it is less than 1 (say 0.9 for example) then it is unstable.
What is meant by GS? Essentially if it is stable then pitch and yaw tend to diminish with time and if it is unstable then pitch and yaw will increase with time.
Pitch and yaw are the two components of what is perceived as 'wobble' seen in a bullet in flight.
Generally, and particularly where long range accuracy is concerned, a GS of between 1.5 and 2 is desirable as it permits pitch and yaw to diminish fairly quickly but with a gyroscopic rotation slow enough to allow the bullet longitudinal axis to follow the line of the bullet's trajectory. If the GS is high, as in the original poster's example, then the bullet will tend to be stable but the longitudinal axis of the bullet while in flight will remain as it was as it left the barrel. This will result in what appears to be an apparent poorer ballistic flight performance than one would expect from it's nominal ballistic coefficient, particularly at longer ranges.

[in2anity]

Thanks for the in-depth explanation SS it makes sense, I'll be sure to work on my nomenclature in the future.To be fair, as assertive as you may have interpreted it, I did say it was "My theory", not some scientific principle.

What you say matches what I've observed time and again on the line - recipes that "should" shoot well at moderate distances (based on closer range group sizes) in fact, do not. And over a big sample, you can start to see when a gun/barrel is paired well with a pill/handload, because it, well, brings home the medals

Also observing the vapor trail through fancy glass also gives you clues into how the round is flying - I've recently learnt it pays to have the spotting scope positioned directly beyond the shooter to best observe that.

[SCJ429]

You are correct that the 1:7 twist barrel is not suited to your lighter projectiles because it raises the RPM of the bullet to a level that costs you some accuracy. If you raise the RPM of a bullet enough, you can make the jacket come apart and not hit your target at all. A good example of the wobble you are describing is an out of balance wheel on your car which is fine at speeds under 60 MPH but when you go over this speed you feel the vibration through the steering wheel. If your bullet jacket has a little runout, you will find an RPM where it begins to become unstable.

Have a look at short rest Benchrest, where they use light projectiles and shoot them through barrels with only 1:14 or there abouts twist. They only want to keep the RPM low, just enough to stabilise the bullet.

[wanneroo]

The one 300 Blackout rifle I have is 1/8 and the same vendor also has 1/10 barrels. The other 300 Blackout rifle I don't know what it is.

[in2anity]

Thanks SCJ, that makes sense. Looking back, I probably could've gone even slower, perhaps a 1:12". That's perfect given the input parameters. Nevertheless I guess the 1:10" would also shoot say a 155.5gr palma pill decently. That'd be a fun experiment to try. In2.

[Fionn]

How loud is the 300blk in a 16" barrel unsuppressed? Compared to say a 223 or 308?

[straightshooter]

You are correct that the 1:7 twist barrel is not suited to your lighter projectiles because it raises the RPM of the bullet to a level that costs you some accuracy.

Understanding why that is the case is somewhat elusive if one has little grasp of the gyroscopic behaviour of a spin stabilised projectile.

If you raise the RPM of a bullet enough, you can make the jacket come apart and not hit your target at all.

Jacket/core separations are a lot more common than one may think and are a function of how well the core is bonded to the jacket. Velocity, core slump and barrel friction and then air friction all play a role not just twist. Generally jacket/core separations only become apparent when they are catastrophic.

A good example of the wobble you are describing is an out of balance wheel on your car which is fine at speeds under 60 MPH but when you go over this speed you feel the vibration through the steering wheel. If your bullet jacket has a little runout, you will find an RPM where it begins to become unstable.

This example is a complete misconception, as the unbalance forces are constrained by and transmitted to the axle. In the case of a bullet it is constrained by the barrel to rotate around it’s center of form but on release from the barrel it immediately rotates around it’s center of mass. This sudden translation is what initially sets up the pitch and yaw in the bullet which then damps in flight if the bullet is (sufficiently) stable.

[JimTom]

How loud is the 300blk in a 16" barrel unsuppressed? Compared to say a 223 or 308?

About the same as a 223 mate.

[wanneroo]

How loud is the 300blk in a 16" barrel unsuppressed? Compared to say a 223 or 308?

Probably if you decibel metered it, it's probably close to both. However I find it not as loud or obnoxious as 223 or 308. I find 223 has more of a loud bang and 308 more of a loud boom. Also for new shooters, the plinker load where I use just over 16 grains of Lil Gun with a 150g bullet is a nice mild load that is very accurate but not intimidating.

Eventually my plan is to move more in the direction of using suppressors more often to help protect my hearing long term. Even with hearing protection you can still have long term hearing damage.

[in2anity]

I don’t know the science behind it - but the perceived recoil is less with a comparatively faster powder. I’ve been using AR2206H in my 303 service rifle for this reason. The blackout basically runs on Lilgun/AR2205, which is verging on pistol territory. It hardly recoils - definitely less than an equivalent 223. One can easily see the fall of the shot, even at close range, say 100m. There’s another couple of reasons I’m a fan.

[Fionn]

How loud is the 300blk in a 16" barrel unsuppressed? Compared to say a 223 or 308?

About the same as a 223 mate.

Same as a 223 in a 16" barrel or in general.

[Fionn]

How loud is the 300blk in a 16" barrel unsuppressed? Compared to say a 223 or 308?

Probably if you decibel metered it, it's probably close to both. However I find it not as loud or obnoxious as 223 or 308. I find 223 has more of a loud bang and 308 more of a loud boom. Also for new shooters, the plinker load where I use just over 16 grains of Lil Gun with a 150g bullet is a nice mild load that is very accurate but not intimidating.

Eventually my plan is to move more in the direction of using suppressors more often to help protect my hearing long term. Even with hearing protection you can still have long term hearing damage.

I have read that it's about the same as a 223 but seems to not sound as loud.

I like a short barrel but don't want an obnoxious muzzle blast that often goes along with them.

I am thinking of getting one with 16" barrel as I want a medium range cartridge that's good in the dense bush and when hunting I don't normally wear hearing protection.

[wanneroo]

I have read that it's about the same as a 223 but seems to not sound as loud.

I like a short barrel but don't want an obnoxious muzzle blast that often goes along with them.

I am thinking of getting one with 16" barrel as I want a medium range cartridge that's good in the dense bush and when hunting I don't normally wear hearing protection.

I think the decibel level for all of it is around 160 db.

I'm so used to 300 Blackout that when people bring 223 ARs to my range or if I am at work and they are shooting M-4 AR-15s at the range, I'm like damn that is annoying. I find the crack/bang of 223/5.56 annoying to my ears, even with hearing protection.

One thing you could try is electronic ear protection. These allow you to hear normal conversation but as soon as the microphone detects any sound over 85 db, it cuts the mic instantly.

[JimTom]

How loud is the 300blk in a 16" barrel unsuppressed? Compared to say a 223 or 308?

About the same as a 223 mate.

Same as a 223 in a 16" barrel or in general.

Mate my 300AAC is a 16” barrel however my comment suggesting it is similar to a .223 is a generalisation mate. I can’t really notice the difference noise wise when firing them. In saying that I have never fired them side by side with the intention of determining which one was louder. Might need a decibel meter or someone with keener hearing than I have mate.

[in2anity]

The obvious parallel to draw is the report from an kalashnikov vs ar15. Two different beasts. Certainly can hear the difference on the line beetween a 7.62x39 bolt gun and 223 bolt gun, (like for like, i.e. No4 conversions) - 223 being a much sharper crack. Powder speed also plays a part.

In terms of raw DB though - probably similar.

[Blr243]

Pretty sure I saw blackout brass and ammo on special in Qld shop last night

[Wyliecoyote]

I still have a 300 BO but rarely use it these days. It came about by collecting dumped brass from the range, having and action and barrel lying about and a reamer acquired during a horse trade some years back.
More recently I converted a Howa mini to 30 Apache by simply running the AAC reamer in to 223 length. From there a single pass in the Hornady AAC dies, wound up of course, expands the neck and forms the brass. A single one pass process like a normal decapping session of fired brass.
From there loading is comparable to a 7.62x39 using 30 grains of CFE BLK for 2650 fps with either a 125 TNT or SST. The barrel i used is an old 30 BR match barrel at 1 in 17 twist from my days in Hunterclass. Accuracy is in the sub half MOA with the TNTs and around 3/4 MOA with the SST. Lighter pills see no gain in velocity, actually a loss as pressure cannot be attained as the case cannot hold enough powder and maintain magazine length and the short bearing length does not allow enough resistance to build pressure.
This is not a new thing as the Apache has been around for a long time now. The HAMM'R more recently is between the two but the ease of one pass with an elliptical expander using 223 surplus brass makes for a very cheap and better performing cartridge that cycles in any 223 based action.
I have two very accurate 7.62x39s that never get used because of the brass being less easily attainable and expensive being Lapua. Both have 308 bores in either 14 or 17 twist and both have now been sidelined because the Apache is as efficient in cost and performance.
I have since advised any who are disappointed with their 300 AAC's performance to do the conversion. Though doing it with a 7 twist barrel will most likely exacerbate any accuracy issues. These rifles and cartridge were specifically designed for suppression using 200 plus grain bullets.

As a point, i see mention of SF of 1.5 as a reference to bullet stabilization. That number is relative only to high BC VLDs at extreme ranges to maintain maximum balistic performance at supersonic velocity. This thinking has tagged in along with the exponents of the 6.5 Creedmoor in the way Safe Schools came with SSM.
At ranges under 300 yards any bullet measuring a SF of 1.0 is stable and will remain stable beyond that range albeit not maintaining optimim BC. A 30 cal 125 grain match bullet will and does remain stable in a 1 in 19 twist barrel, also 115 grain and under bullets will and have shot extremely well in competition both here and in the US for a few decades now using twists as low as 21 in velocities of 2500 fps and above. Unless you are looking to shoot beyond 600 yards, both BC and SF numbers are less important than accuracy at the target.
There is no such thing as over stabilization. There is however such a thing as ogive slump, comet tails and bullet disintegration where these indicators begin to appear in the area of around 260,000 RPM and above, irrespective of caliber, velocity or SF. There has been a great disservice passed on to novices by promoting via the internet the thinking that a minimum of a 1.5 SF is a requirement for every shooting application. It is not a requirement and many including myself have shot and won many 600 and 1000 yard matches using bullets and barrels running far less SF numbers than 1.5.

[in2anity]

They had Winnie ammo, at 90c.

[straightshooter]

The obvious parallel to draw is the report from an kalashnikov vs ar15. Two different beasts. Certainly can hear the difference on the line beetween a 7.62x39 bolt gun and 223 bolt gun, (like for like, i.e. No4 conversions) - 223 being a much sharper crack. Powder speed also plays a part.

In terms of raw DB though - probably similar.

Apparent muzzle blast SPL is directly proportional to muzzle discharge pressure.
So cosider the report of a shotgun using not much powder, a fast burning powder that has mostly been consumed before the shot has moved any appreciable distance in the barrel and a long barrel. Now compare that with just about any high intensity high velocity centerfire rifle. Not only is there more powder but it is also selected for the longest time/pressure curve in a standard length barrel to maximize velocity.

[GCol]

I have been going through a few forums as I am keen on getting a bolt action in 300 Blackout. It seems to me that there quite a few people who expect a lot out of what is a compact and efficient cartridge. One thing that has not been pointed out anywhere that I have seen is the similarity between the 30/30 and the 32/20 and the modern 308 Win and the 300 Blackout. if is interesting to look at the physical dimensions these cartridges in the photo. To me as someone looking to replace a Martini Cadet 32/20 with a Blackout rifle it is a good choice but one that I will know is never going to be a 308.

P1030727.2.JPG (6.84 KiB) Viewed 4433 times

[wanneroo]

I've got a lot going on with 300 Blackout, have lots of different bullets and been working on a load for Nosler Varmageddons. I'm up close to 2400 FPS on speed.

I'm working on getting a Youtube channel going. The weather is very cold and wintry so it limits what I can do outside but have already filmed some videos and will be doing a lot more if it goes well.

[JimTom]

Although I have developed some subsonic loads for mine i shoot it at around 2000fps with 125gn pills for hunting. Not expecting 308 performance out of it but for a close range pig rifle it goes well.

[wanneroo]

Although I have developed some subsonic loads for mine i shoot it at around 2000fps with 125gn pills for hunting. Not expecting 308 performance out of it but for a close range pig rifle it goes well.

What sort of 125g bullets are you using? I can't remember, you probably mentioned at some point.

I just got a container of Speer TNT 125g and also loaded Hornady 125g SSTs last year.

[JimTom]

Yeah mate the 125gn SST. They are bloody accurate and seem to do a good job on the oinkers.

[JimTom]

How did you find the Speer TNT mate? Have you taken any hogs with them?

[wanneroo]

How did you find the Speer TNT mate? Have you taken any hogs with them?

No feral hogs up here, I think the terrain up here is too tough for them, Pennsylvania is one series of endless mountains and hills, there are very few flat areas. The feral hog problem seems isolated to the deep south where they have more mild weather and flatter terrain. We have lots of bears though, coyotes, bobcats and plenty of deer and turkeys.

I just bought the Speer TNTs about a month or so ago so haven't had time to play with them yet. Haven't decided what powder to use for them yet. I have Lil Gun, IMR 4227, H110 and CFE BLK on the shelf.

[JimTom]

Mate my go to powder for 300BLK is AR2205 which I believe is the equivalent to H110.
I do have a tin of Win296 which also goes ok however the ADI AR2205 works a treat.

[linkoln]

As most of you probably know 300 black out was designed to hunt down Osama bin laden so it was never meant to make tight groups it was a powerful close quartets round that fit into current 5.56 magazines. I'm sure some good hand loads would get accuracy but don't expect much from it.

[JimTom]

Mine is quite accurate. I was fairly impressed to be honest, and out of a cheap rifle also.