Suppressor and BC

[Megalodong]

Dumb question about cans and BC, but wanted to ask before I head out and do something stupid.

Will a can, properly installed and sized, have any affect on the BC of a bullet? I'm hoping to get time on the AB mobile lab here soon at a match and want to get a CDM for a gun I'll be shooting 95% suppressed, but it's not the gun I'm shooting in the match so my can will be on that match gun. Hoping to avoid switching things around match day if there's no need.

 

[Ledzep]

Yes. Muzzle devices are one of the main reasons that the Hornady 4 DoF app has "Axial Form Factor" correction built in as a end-user option.

Different brakes and suppressors in conjunction with different barrels, rifling types, twist rates, powders, etc... can all affect the drag of a projectile.

It is usually a very small thing, though. In almost every circumstance where we've had the big Doppler head there to verify downrange velocity to correct for axial form factor changes, the true effect of the barrel+muzzle device is >5%. The vast majority of that is >3%.

 

[TheJeanyus]

Yes. Muzzle devices are one of the main reasons that the Hornady 4 DoF app has "Axial Form Factor" correction built in as a end-user option.

Different brakes and suppressors in conjunction with different barrels, rifling types, twist rates, powders, etc... can all affect the drag of a projectile.

It is usually a very small thing, though. In almost every circumstance where we've had the big Doppler head there to verify downrange velocity to correct for axial form factor changes, the true effect of the barrel+muzzle device is >5%. The vast majority of that is >3%.

Any chance we can get a podcast episode (or part of an episode) diving a little deeper into that? I'd be curious to learn more about how/why the muzzle device would affect drag.

 

[C130]

I was surprised at how much speed I gained when I added a suppressor, about 50fps average.

 

[Fig]

I don't get that at all. How would a muzzle device, that never makes any contact with a bullet to deform it's shape or effect it's mass, change it's ballistic coefficient?

 

[C130]

Someone much more knowledgeable than me can explain it I'm sure but I'm assuming it (suppressor)has to affect the airflow/drag exiting the barrel. That's in very simple terms, the exact how it does it is above my level.

I've flown airplanes for a long time and taken several aerodynamics classes but that was a long time ago. I know there are lots of little things that can affect drag and some are pretty crazy.

 

[Ledzep]

I don't get that at all. How would a muzzle device, that never makes any contact with a bullet to deform it's shape or effect it's mass, change it's ballistic coefficient?

The shape doesn't change, but drag is dependent on the orientation of the object to the oncoming airflow. If the bullet is pointed perfectly straight forward to the oncoming airflow it will have certain Cd. If the bullet has .01 degrees AoA (angle of attack) to the oncoming airflow it will have some small percentage higher Cd. If the bullet has 0.10 degrees AoA it will have some considerably higher Cd.

When the bullet exits the muzzle it always has some level of yaw and yaw rate. The conditions of the muzzle exit gas flow (brake, suppressor, etc.) can affect that yaw and yaw rate, causing higher AoA, causing higher (typically) drag throughout the trajectory.

 

[Long Range 338]

Purely anecdotal but it has not been my experience that the BC is changed by adding a suppressor. Typically velocities will change a few fps but we’re talking 15-20 fps. It makes sense that as you are capturing the gasses you would see a slight boost…. Seeing that velocity is one factor in time of flight, it could affect the BC in a very minuscule amount. I would not anticipate it to be in the realm of 3-5% however.

Perhaps @Ledzep will expound a bit with real empirical evidence vs my simple anecdotal experience. I’m not trying to be sarcastic, I am being sincere in the request in case this sounds like sarcasm.

 

[Ledzep]

As a related topic, if you make bullets with eccentric mass on purpose (non-concentric jackets, drilled holes, etc...) you see similar effects. I have loosely correlated this to poor dispersion loads, too. The center of rotation isn't about the center of mass or center of form and it causes increased drag.

 

[Ledzep]

Purely anecdotal but it has not been my experience that the BC is changed by adding a suppressor. Typically velocities will change a few fps but we’re talking 15-20 fps. It makes sense that as you are capturing the gasses you would see a slight boost…. Seeing that velocity is one factor in time of flight, it could affect the BC in a very minuscule amount. I would not anticipate it to be in the realm of 3-5% however.

Perhaps @Ledzep will expound a bit with real empirical evidence vs my simple anecdotal experience. I’m not trying to be sarcastic, I am being sincere in the request in case this sounds like sarcasm.

I'll dig through the radar folder and see if I can find something they'll let me post publicly.

 

[Long Range 338]

The shape doesn't change, but drag is dependent on the orientation of the object to the oncoming airflow. If the bullet is pointed perfectly straight forward to the oncoming airflow it will have certain Cd. If the bullet has .01 degrees AoA (angle of attack) to the oncoming airflow it will have some small percentage higher Cd. If the bullet has 0.10 degrees AoA it will have some considerably higher Cd.

When the bullet exits the muzzle it always has some level of yaw and yaw rate. The conditions of the muzzle exit gas flow (brake, suppressor, etc.) can affect that yaw and yaw rate, causing higher AoA, causing higher (typically) drag throughout the trajectory.

Annnd you beat me to the punch. @Ledzep thank you for the information!

 

[Megalodong]

Cool, sounds like I got my answer straight from the horses mouth! I'll be monkeying around with my suppressor.

I think I used the wrong term in my OP, hoping to get a PDM for these 138 ATIPs since there isn't a CDM yet.

 

[Long Range 338]

@Ledzep do you have any data showing the effect on BC broken down by bare muzzle vs suppressors vs muzzle brakes? That would be very interesting data indeed. I’m sure the drama caused would be popcorn worthy!

 

[Ledzep]

@Ledzep do you have any data showing the effect on BC broken down by bare muzzle vs suppressors vs muzzle brakes? That would be very interesting data indeed. I’m sure the drama caused would be popcorn worthy!

Yes we have a few examples of that. I'm asking around to make sure if I can share and if I can it will be sanitized so as not to cause any cataclysm. Some designs are definitely worse at increasing drag, but there are other metrics involved (flash, recoil, sound, etc...) so it's not an end-all-be-all metric. Again the difference is typically <3-5% on extreme swings. Twist rate typically causes bigger variation. Rifling type and barrel-to-barrel variation on this exists, too. If you could stack all of them one way and another rifle all the other way you could probably see an 8-10% difference. Luckily most of the time there's some level of cancellation around "average".

 

[spife7980]

 

[MrMcCrackin]

very cool

 

[Ledzep]

Oh well if the slide show is out there...