Can switching muzzle brakes change muzzle velocity??

[Timber338]

So I recently had a new muzzle brake installed on my 338 RUM, and my muzzle velocity dropped about 47 FPS.

With the last brake I had this rifle/load dialed in. I'm using a Magnetospeed and have fully characterized this load several times across temperatures and it has always been very predictable. This morning I chrono'd at an exact temp that previous data was collected. Same brass (resized and annealed), same box/lot of bullets, same jug of gunpowder... The only thing that changed was the new brake. And I did verify that no length was removed from the barrel.

I used to have a 4-port brake and the new brake has 5-ports of a different design/manufacturer. the same load still shoots sub 1/4 moa with the new brake.

Anybody seen this before or is something else going on? What am I missing here??

 

[J E Custom]

So I recently had a new muzzle brake installed on my 338 RUM, and my muzzle velocity dropped about 47 FPS.

With the last brake I had this rifle/load dialed in. I'm using a Magnetospeed and have fully characterized this load several times across temperatures and it has always been very predictable. This morning I chrono'd at an exact temp that previous data was collected. Same brass (resized and annealed), same box/lot of bullets, same jug of gunpowder... The only thing that changed was the new brake. And I did verify that no length was removed from the barrel.

I used to have a 4-port brake and the new brake has 5-ports of a different design/manufacturer. the same load still shoots sub 1/4 moa with the new brake.

Anybody seen this before or is something else going on? What am I missing here??

Muzzle brakes should not effect velocity unless you are experiencing bullet strikes and if that occurs
it will effect accuracy also.

The best way to rule out the brake is to shoot the rifle over a chronograph and then unscrew the brake and shoot without it to see if the velocity changes.

J E CUSTOM

 

[geo4061]

I do not know about velocity. However, they will and do effect accuracy. I bought one off the shelf and screwed it on my threaded 223. Bad mistake.

 

[Timber338]

Muzzle brakes should not effect velocity unless you are experiencing bullet strikes and if that occurs
it will effect accuracy also.

The best way to rule out the brake is to shoot the rifle over a chronograph and then unscrew the brake and shoot without it to see if the velocity changes.

J E CUSTOM

Thanks JE, I just don't have enough experience with various brakes on rifles. The velocity drop must be coming from somewhere else, I just can't figure what the cause might be. Bullet strike is definitely not happening here, I am getting the same excellent accuracy that I was getting with the previous brake. This is a full custom built by Jim Borden and it shoots better than I can.

 

[geo4061]

Why did you change brakes?

 

[Timber338]

Why did you change brakes?

The truth is I can never leave well enough alone. I had a 4-port muscle brake on it and it worked great.

But I ended up installing a Terminator T2 brake on my 300 win mag and I was very impressed with not only the recoil reduction but also the quality of the machining. The machining is of very high quality and compared to the muscle brake, the wall thickness around the ports is thinner which makes for a much lighter brake.

So I decided to give the Terminator T3 a try on my 338 RUM. I personally think the T3 reduces recoil noticeably more but that is subjective without any real testing to back that up. But it did lighten my rifle up and make it noticeably less nose heavy as well.

I was really worried it would change the accuracy or make me retune my load, but this 338 has been a dream to shoot. It never was finicky with hand loads and shoots everything to just about the same POI, so I took the gamble. I'm the end it shoots just as good as it used to, with the exception of this muzzle velocity difference. That's still got me scratching my head...

 

[North Idaho Hunter]

is it possible you got your primers mixed up on this batch of loads? I accidentally did this once with large rifle instead of magnum.

 

[bigngreen]

It could be the brake a scrubbing of more pressure sooner than the previous brake removing pressure on the base of the bullet, when you install a suppressor you gain 30+ fps on the ones I've seen which amounts to the bullet not escaping the pressure as soon. I've never done a study on brakes vs velocity cause I pretty much set it and forget it.

 

[Timber338]

is it possible you got your primers mixed up on this batch of loads? I accidentally did this once with large rifle instead of magnum.

Actually this was very possible so I went and checked. I've got GM215M and GM210M, same color box, siting right next to each other on the shelf. But I definitely was using the box of 215's. I really wanted this to be the case since it would be such a simple answer to this problem!

 

[Timber338]

It could be the brake a scrubbing of more pressure sooner than the previous brake removing pressure on the base of the bullet, when you install a suppressor you gain 30+ fps on the ones I've seen which amounts to the bullet not escaping the pressure as soon. I've never done a study on brakes vs velocity cause I pretty much set it and forget it.

Something along these lines is definitely where my mind is heading, especially with how consistent this rifle has been over time, until this new brake.

I am pretty maticulous with my reloading procedures that I have a good amount of confidence it's not a stupid oversight on my part. Although the wrong primer idea from North Idaho was definitely a possibility with my 3 & 4 year old running around distracting me. Haha.

Just thinking out loud, here are the variables I have double checked:
Seating depth is the same verified again my my calipers/comparator block.
Powder charge was documented as the same and I use an RCBS charge-master.
Primers have now been verified.
Same lot of bullets/powder/primers
Annealed the case necks with the same procedure I've been using
FL resized with .002 interference (.364 bushing)
Redding wax inside case necks to seat bullet.
Temperature the same as the last time I chrono'd at 46 degF
Barrel had 5 shots through it since the last cleaning, I shot a fouling round last week and then a 4 shot group this morning, let the barrel cool, then chrono'd

am I mIssing anything that could be root cause? 47 FPS is not just a blip... It's gotta be caused by something, and it's driving me nuts not knowing.

Battery on the Magnetospeed seems OK, but maybe sormthing with that??

 

[Timber338]

Ok, here's something... I looked back in my log book and before the brake swap, I was using a .363 bushing with my FL resize operation, for .003" of interference.

This last batch of reoads I used the .364 bushing for .002" of interference.

Is this .001" of less neck tension enough to drop pressure enough for a 47 FPS drop in muzzle velocity????

 

[bigngreen]

Ok, here's something... I looked back in my log book and before the brake swap, I was using a .363 bushing with my FL resize operation, for .003" of interference.

This last batch of reoads I used the .364 bushing for .002" of interference.

Is this .001" of less neck tension enough to drop pressure enough for a 47 FPS drop in muzzle velocity????

I don't discount anything when it comes to neck tension, depending on the powder and where your at you can see some real changes how things start out.

 

[WildRose]

So I recently had a new muzzle brake installed on my 338 RUM, and my muzzle velocity dropped about 47 FPS.

With the last brake I had this rifle/load dialed in. I'm using a Magnetospeed and have fully characterized this load several times across temperatures and it has always been very predictable. This morning I chrono'd at an exact temp that previous data was collected. Same brass (resized and annealed), same box/lot of bullets, same jug of gunpowder... The only thing that changed was the new brake. And I did verify that no length was removed from the barrel.

I used to have a 4-port brake and the new brake has 5-ports of a different design/manufacturer. the same load still shoots sub 1/4 moa with the new brake.

Anybody seen this before or is something else going on? What am I missing here??

It sounds like there was a constriction between the crown and first baffle or perhaps it was also not opened enough through the bore area and that this one is relieving that back pressure.

If it bothers you to lose that velocity you might want to try coming up in half grain increments until you get it back barring pressure signs or a loss of accuracy.

 

[WildRose]

Ok, here's something... I looked back in my log book and before the brake swap, I was using a .363 bushing with my FL resize operation, for .003" of interference.

This last batch of reoads I used the .364 bushing for .002" of interference.

Is this .001" of less neck tension enough to drop pressure enough for a 47 FPS drop in muzzle velocity????

Neck tension can certainly have an effect on accuracy. A little too tight and you build up excess pressure.

Try going back to the same setup you had previously and see if that makes you a significant difference.