Significant drop in FPS with suppressor?

[Jkuhn22]

Today at the range I worked on my set up for this elk season. I am shooting a Browning Hells Canyon in 300WSM with a banish 46 suppressor in the 7.8 inch configuration. My load is 166 Hammer Hunters with 66 grains of reloader 19. My groups were great (well below 1 MOA). My avg FPS was 2814…..I was expecting close to 3200 fps. We shot the same rounds through a Remington 700 non-suppressed and hit the 3200 fps mark.

I shot a few rounds of HSM Trophy Gold at 185 grains as was at 2858 and the box was rated at 2991.

Would my suppressor cause that much drop in FPS?

I am doing direct thread….. is there a special way of installing it (does it need to be oriented a certain way? )

I needed to head back to the range to shoot without the suppressor to get another FPS reading…but this drop in FPS did not occur to me until I got home.

Thanks for any help.

 

[bradgrace]

I always thought a suppressor added a few FPS. Was the barrel length the same between the two rifles?

 

[RuggedYogi]

You can’t use a comparison from another rifle. You would need to chrono with/without the suppressor from the same rifle.

I can’t imagine a scenario in which a suppressor causes the velocity to decrease.

 

[ChrisAU]

Always adds a few fps for me. What barrel lengths on the two?

 

[thinhorn_AK]

Mine picked up 20-30fps with the silencer.

 

[SomeJackassOnAForum]

I have 2 rifles that are the same chambering, same barrel length, and have muzzle velocities that differ by 100 fps.

It's not the can.

 

[Tahoe1305]

Can always added a bit for me. Guessing your chambers/barrels are making difference.

Underperforming box fps is completely normal. Can or no can.

 

[doc holiday13]

you will not get velocity loss with a suppressor. You will get a POI change(generally 1" lower)

 

[Pharmseller]

When my brother added a can to his Tikka 7mm-08 I had to rework the seating depth on the load to regain precision. Same powder charge. He gained 60 fps I believe.




P

 

[Boarmaster]

You can’t use a comparison from another rifle. You would need to chrono with/without the suppressor from the same rifle.

I can’t imagine a scenario in which a suppressor causes the velocity to decrease.

This

 

[Jkuhn22]

Yes the point of impact was 1 inch lower compared to no can.

Barrel length was 23 inches on both guns.

I am not concerned about the slower speed than the box, but I assumed my custom hammer loads with a lighter bullet would out run the heavier round. I will shoot across the crono with out the can next week.

Thanks for the help. If I get a big jump in speed after removing the can, I will be back looking for help!

 

[WKR]

Fast Twist rate will decrease muzzle velocity as well

 

[Formidilosus]

Fast Twist rate will decrease muzzle velocity as well

No it doesn’t.

 

[WKR]

No it doesn’t.

 

[Loo.wii]

You can’t use a comparison from another rifle. You would need to chrono with/without the suppressor from the same rifle.

I can’t imagine a scenario in which a suppressor causes the velocity to decrease.

This guy missed the elementary school lesson on the scientific method

 

[Pharmseller]

I’d trust this guy.

Does Barrel Twist Rate Affect Muzzle Velocity? (Litz Test) « Daily Bulletin

The Applied Ballistics team tested six (6) same-length/same-contour Bartlein barrels to observe how twist rate might affect muzzle velocity. This unique, multi-barrel test is featured in the book <a href=http://www.amazon.

bulletin.accurateshooter.com

“We proceeded with the testing in all 6 barrels from 1:8” to 1:12”. After all the smoke cleared, we found that muzzle velocity correlates to twist rate at the rate of approximately 1.33 fps per inch of twist. In other words, your velocity is reduced by about 5 fps if you go from a 1:12” twist to a 1:8” twist. [Editor: That’s a surprising number — much less than most folks would predict.] In this case the math prediction was pretty close, and we have to remember that there’s always uncertainty in the live fire results. Uncertainty is always considered in terms of what conclusions the results can actually support with confidence.”

1.33 fps per inch of twist. All data points within SD, much less ES.

I’m with Form on this one.



P

 

[Firth]

@WKR
Without seeing exactly how their tests were conducted, it would be impossible for me to state with any degree of conviction as to why they saw what they saw. Small differences in bore diameter or chamber dimensions can certainly affect velocity.

Years ago, I was curious about this myself and a ran some calculations looking at conservation of energy with respect to differing barrel twists. It's been too long for me to remember specifics, but the gist of it was if the total energy associated with the projectile is kept constant (kinetic + rotational) increasing the rotational speed will result in a small decrease in velocity, but the change is small enough that it would be hard to measure as compared to other uncertainties. The kinetic energy of a bullet is just a lot bigger than the energy required to spin it faster, so spinning the bullet faster has an almost negligible effect on velocity. My numbers generally matched up with what Pharmseller posted.

 

[ScreamingPotato]

I am doing direct thread….. is there a special way of installing it (does it need to be oriented a certain way?

I don't have an answer for you, following along as I also have a Speed in 300WSM so I'm curious. I'm surprised you found a direct thread can for that goofy M13 thread pitch though.

 

[Formidilosus]

View attachment 589864

I have a feeling I am not guessing.

 

[zrodwyo]

If barrel lengths between the two rifles are similar a 400 fps difference between the two rifles using the same ammo is surprising. I have my calibers I like and have done many barrels in those. I generally see no more than 100fps variation from barrel to barrel.

I would be pulling bullets and making sure my charge weights aren’t all screwed up.