Hornady .300 Blackout 208gr. Amax Subsonic ammo not consistently subsonic?

[Aim1]

So, I've shot Remington, Sig Sauer, and Lellier & Bellot subsonic ammo and it has all been subsonic. I bought some Hornady .300 Blackout 208gr. Amax subsonic ammo on sale and shot some and I'd say that the majority of it is not subsonic.

I wasn't sure if it was just me so I loaded my Ruger American Ranch Rifle with my Sig Sauer suppressor on it with 1/2 Hornady and 1/2 Sig Sauer subsonic ammo and shot it with my friend. The Sig Sauer was definitely quiet while the Hornady appeared to not be subsonic.

Anyone else having this problem?

 

[jmorris]

If I pick a powder that is temp sensitive or run right on the edge of super, sometimes I'll get some that cross the line.

Like #7 & 8 in this video.

 

[Aim1]

If I pick a powder that is temp sensitive or run right on the edge of super, sometimes I'll get some that cross the line.

Like #7 & 8 in this video.

Thanks.


Not sure what powder Hornady uses but it was about 70'.....not sure what velocity.

 

[AK Hunter]

If you are right at the edge of Supersonic it makes a difference your elevation above sea level & the humidity.

 

[jbmillard]

If you are right at the edge of Supersonic it makes a difference your elevation above sea level & the humidity.

I don't think the elevation above sea level has any effect other than to change the average temperature. The speed of sound is proportional to the square root of the absolute temperature. The change in the speed of sound from humidity changes is very small -- much less than the accuracy of the average chronograph.

 

[mcb]

What barrel length are you using? I found a lot of factory subsonic ammo would actually be supersonic from my 16 inch carbine. From my 9-inch AR pistol I have not had the same problem.

 

[Aim1]

What barrel length are you using? I found a lot of factory subsonic ammo would actually be supersonic from my 16 inch carbine. From my 9-inch AR pistol I have not had the same problem.

Sig MCX with a 9.5" Sig suppressor and Ruger American Ranch Rifle with a 16" barrel and same suppressor.

 

[wiscoaster]

I don't think the elevation above sea level has any effect other than to change the average temperature. The speed of sound is proportional to the square root of the absolute temperature. ...

Yes, and we're pushing winter in much of the country, so if the OP is shooting subsonic ammo that's borderline, and the speed of sound in winter is slower, then his ammo is more likely to exit the muzzle at a supersonic speed.

 

[mcb]

Sig MCX with a 9.5" Sig suppressor and Ruger American Ranch Rifle with a 16" barrel and same suppressor.

Are they super-sonic in both guns or just the 16-inch gun? I would be suprised with the 9.5 inch but not in the 16 inch gun from my experience.

Yes, and we're pushing winter in much of the country, so if the OP is shooting subsonic ammo that's borderline, and the speed of sound in winter is slower, then his ammo is more likely to exit the muzzle at a supersonic speed.

Yes buts as it's getting colder you're going to loose muzzle velocity due to temperature dependence of your propellant.

Speed of sound at 95 deg F is 1154 fps and at 20 deg F it drops down to 1073. Probably loose that much velocity with many common 300 BO subsonic propellants over that temperature range, certain the very common H110/W296 would probably loose more velocity over that range.

Reloading is the ultimate answer here. You can tailor the bullet and velocity to exactly what works best in your particular firearm.

 

[Aim1]

Are they super-sonic in both guns or just the 16-inch gun? I would be suprised with the 9.5 inch but not in the 16 inch gun from my experience.



Yes buts as it's getting colder you're going to loose muzzle velocity due to temperature dependence of your propellant.

Speed of sound at 95 deg F is 1154 fps and at 20 deg F it drops down to 1073. Probably loose that much velocity with many common 300 BO subsonic propellants over that temperature range, certain the very common H110/W296 would probably loose more velocity over that range.

Reloading is the ultimate answer here. You can tailor the bullet and velocity to exactly what works best in your particular firearm.

Super-sonic in both guns.


This was about a month ago and the temps were in the 70's. So, shouldn't change, correct?

 

[wiscoaster]

Yes buts as it's getting colder you're going to loose muzzle velocity due to temperature dependence of your propellant.

Ah ... ya ... forgot that (but had no idea which was greater, anyway). Thanks....

 

[mcb]

Ah ... ya ... forgot that (but had no idea which was greater, anyway). Thanks....

All powder are at least a little temperature sensitive but some are more so than others (H110/W296 is one of the more sensitive). I would not be surprised if you could find one that was sub-sonic at warm temps and was super at low but I think that would take some work to find.

 

[Aim1]

All powder are at least a little temperature sensitive but some are more so than others (H110/W296 is one of the more sensitive). I would not be surprised if you could find one that was sub-sonic at warm temps and was super at low but I think that would take some work to find.

So the colder it gets the more chance of it going super-sonic, correct?

 

[mcb]

So the colder it gets the more chance of it going super-sonic, correct?

The colder the air gets the slow the speed of sound through that air is, per my earlier post. There are a few other minor factors but temperature is the predominate property driving the speed of sound in air.

But also the colder it gets the slower your ammunition is also likely to get so frequently if you're sub-sonic in warm weather you will still likely be subsonic in cold temperatures.

Seem like you are just going to have to avoid Hornady .300 Blackout 208gr. Amax in your guns. There is not much you can do to change it.

 

[Englishmn]

Pull the bullet weigh the powder drop a half grain see what happens.

 

[jonnyc]

Wait a sec.....hold the techno-babble.....I want to know where you found subsonic 300 BLK ON SALE!!!!!

 

[Aim1]

Wait a sec.....hold the techno-babble.....I want to know where you found subsonic 300 BLK ON SALE!!!!!

Ha, I've had this ammo since before the craziness.