Home Forums Hunting & Shooting Hunting Rifles Do muzzle breaks damage scopes?

had to laugh, thinking back...the first time I tried to sight in my 378 wby (no muzzle brake)the only spare scope I had was a 30 plus year old weaver 4x , I bore sited it then went to the range and set up a target at 25 yards the first two shots were virtually touching , I looked thru the scope to fire a third shot and it looked a bit blurry , I really did not pay a good deal of attention to that little detail until I found the front and internal lenses on the bench after the third shot

I had an AR-10 with a 16" barrel and brake. It was pretty fearsome on blast. Usually when I shot it the benches on either side of me would clear out. One day I had a spotting scope set up on a small tripod beside me on the bench, and my brother told me it was jumping slightly into the air with each shot. I've since put an 18" on it with a Vortex flash hider, and it seems to be more civil.

What happens is that when you shoot your braked rifle at the range, when you go to change targets during the ceasefire the people sitting either side of you will beat your scope with blunt heavy objects. (I'm not a fan of brakes, if you can tell.)

I guess my .338 Win. Mag with a brake didn't get the e-mail about breakage. With about 1200 rounds through the rifle the scope is going along just fine.

Previously had a .223 Rem. in a Browning rifle with BOSS system with way more rounds through it and it was still shooting bug holes when I traded it on something else.

I say hogwash on the idea. A .378 Weatherby by itself is enough to break a lot of scopes.

Jim

So you don't believe a sudden change in acceleration during heavy recoil caused by a muzzle brake would be any rougher on the scope than the unchanged heavy recoil of the unbraked rifle?

Imagine two nearly identical roller coasters. They both accelerate to the same speed and pull the same G-forces. However the track on one is very smooth, and the track on the other is rough and very jerky (i.e. sudden rapid changes in acceleration).

Which one do you think is going to put the most wear and tear on you?

Of course a .378 Wby is hard on scopes. Why is it hard to imagine, as some have found, that a braked .378 Wby is even harder on scopes?

Other changes could also increase the force that a scope is subjected to, such as decreasing the weight of the rifle, or increasing the load and weight of the bullet. Using a Lead Sled also increases the forces placed on the scope.

It is very reasonable to suspect that a muzzle brake could have some negative effect on a scope.

I am glad you have a good, reliable scope on your 338. I see that your 338 is braked. Perhaps the effect on scopes occurs somewhere between the 338 and the 378 recoil levels. What is your scope so that we can have the benefit of your long-term test with that scope. Thanks.

So jerk would be the derivative of acceleration.

I have a couple questions about the physical explanation for muzzle brakes increasing jerk.

First, the total weight of the gas is almost certainly much less than the weight of the bullet, powder weigh vs bullet weight. Much much less considering the gas is actually originally a contributor to the rearward force.

Second, not all of the gas will leave thru the brake.

Even if we accept that the velocity of the gas is the same as the final velocity of the bullet, which is generous considering it gets there later, the force it can generate should be directly proportional to a far smaller mass.

The reverse acceleration caused by the the break will occur after the bullet has passed so it will be a smaller force against the rearward momentum of the gun, and stilla smaller force than the original force which caused the rearward movement.

I am open to the possibility that I am missing something, but with a small force in a subtraction against a momentum caused by a larger force, even in the derivatives I can't see how we arrive at a higher value.

Please explain.

Someone needs to measure the acceleration - I don't think it's all that hard to do with the right gear.

I can see the points being made - initial recoil acceleration occurs from the instant of firing until the brake starts working, and then forces start countering the initial acceleration. I'm guessing that the "counter" acceleration force from the effect of the brake is less but happens over a longer time, comparitively. Still, measurements would show this. Although even with accurate measurements, it would be hard to quantify what it actually means.

[I think vibration is also a contributer in killing scopes, and I think that is a key factor with air rifles. Vibration will destroy lots of things, not just in shooting.]

Peator,

So jerk would be the derivative of acceleration.
Yes, that is the precise definition of jerk. The first time derivative of acceleration, the second time derivative of velocity, or the third time derivative of position.

I have a couple questions about the physical explanation for muzzle brakes increasing jerk.

First, the total weight of the gas is almost certainly much less than the weight of the bullet, powder weigh vs bullet weight. Much much less considering the gas is actually originally a contributor to the rearward force.
You are correct, although I am not sure what you mean with the last sentence. Assuming all the powder burns, the weight of the gas is exactly the weight of the powder. (There is no matter to energy conversion as in a nuclear reaction.) Let us assume the powder is 1/3 the weight of the bullet, say a 150 grain bullet in a load using 50 grains of powder. More on the forces below.

Second, not all of the gas will leave thru the brake.
This is true as well.

Even if we accept that the velocity of the gas is the same as the final velocity of the bullet, which is generous considering it gets there later, the force it can generate should be directly proportional to a far smaller mass.
Actually, here you are incorrect. At the instant the bullet leaves the muzzle we now have a cylinder (the barrel) open at one end and filled with high-pressure gas. The gas still back in the cartridge case is not moving, the gas at the muzzle is moving at the velocity of the bullet, and the gas in between is moving at some velocity between those two values. The expansion or “blowdown” of this cylinder of gas is not terribly easy to analyze, especially in this “less complex” discussion. Most things I have read concerning calculating the total recoil impulse (change in momentum) suggest, for a center fire rifle at about 3000 ft/sec:
(mass of bullet X muzzle velocity) + (mass of the powder X 4500 ft/sec)
Again, this is just a rough approximation for the total recoil impulse, but it does account for the gas.

The reverse acceleration caused by the the break will occur after the bullet has passed so it will be a smaller force against the rearward momentum of the gun, and stilla smaller force than the original force which caused the rearward movement.
Please see below.

I am open to the possibility that I am missing something, but with a small force in a subtraction against a momentum caused by a larger force, even in the derivatives I can't see how we arrive at a higher value.

Please explain.

Consider a rifle in free recoil, i.e. not being held by a person. As the propellant begins to burn, pressure is created in the case. The pressure in the radial directions cancel each other and do not contribute to the acceleration on the rifle. The (pressure X the interior area of the cartridge head) produces a force that begins to accelerate the rifle rearward. The bullet is being accelerated forward by the (same pressure X the area of the bore), but we need not consider this as a force on the rifle. The movement of the bullet is being resisted by the frictional drag of the barrel on the bullet, and this same force that is pulling “back” on the bullet is pulling “forward” on the rifle. Obviously, this force is small compare to the forces trying to accelerate the rifle rearward and the bullet forward. Let us ignore this small force. If we do, then all we have to consider, again in free recoil, is the (pressure X the interior area of the cartridge head.)

In a rifle without a brake, this pressure (as shown by pressure gauges in the breech that many labs use when developing loads) rises in a smooth curve to a peak and then smoothly goes down to zero as all the gas leaves the rifle. (Here we are ignoring any shock waves in the powder gas that may be moving back and forth from bullet to breech. They are secondary to our discussion, but they cannot be ignored when you are designing the gun. Neither can inconsistency in how the powder ignites, particularly in large artillery pieces. We are also ignoring any frictional drag of the gas on the interior surface of the barrel. Again, we don’t have to concern ourselves with these “second order” things in our discussion.)

Without a brake, the jerk is not zero, but note that if the pressure curve rises and falls in a smooth continuous manner the jerk is not too bad, at least relatively speaking.

Now imagine a rifle with a brake. After the bullet has left, as the gas in the barrel is still expanding and “blowing down”, we introduce another force on the rifle. If we accept that the brake is effective, then it must be introducing a forward force on the rifle. Remember, until we added the brake all we had to concern ourselves with was the force created by the pressure on the interior area of the cartridge head. Now, at the same time, at the muzzle, the gas is being redirected. Some of this is simply the gas blowing out radially through the holes in the brake, “pushing against itself”, for lack of a better term. But there is undoubtedly some additional rapid redirection of the momentum of the gas, indeed even a redirection of the gas rearward in the most effective brakes. The force to redirect this gas is supplied by the rifle, and “equal and opposite reaction” means there is now an additional force on the rifle.

Again, the force of the pressure during blowdown is still operating on the breech, and the NET force on the rifle is likely still backward. I sincerely doubt the brake can develop enough force to change the acceleration from rearward to forward, and I am even more sure forces could not be developed to actually stop the rifle and reverse the direction of the velocity. BUT if the brake is effective in changing the recoil, the forward force on the rifle must be significant. This means the acceleration curve is greatly affected, experiencing a relatively sudden and rapid change. This is high jerk, and as we have learned, jerk is hard on machines.

The example nifty-two-fifty used concerning a smooth vs. not smooth roller coaster is one I have seen before, and it is a very good analogy. Both roller coasters give you the same accelerations, but one does so with much less jerk than the other. In the case of our rifle, the brake is actually changing the acceleration a good bit, and the jerk values are high.

I hope this helps.

Gun Doc

All I know is that Melvin Forbes, who has now been making Ultra Light Rifles for 30 years, says his customers who insist on brakes on his rifles have a higher percentage of scope problems than those who don't--so much that Melvin will try to talk them into a smaller cartridge, rather than the brake.

Thanks for the excellent explanation Gundoc.

Excellent comments. One does need to also address the mental and physical aspects of the shooter. Advertising does much to contradict the laws of physics in the human mind. The perception of recoil or anticipation of recoil is a contributing factor of how well a muzzle brake works for a given individual. Light rifles recoil more than heavy ones in the same caliber. Light rifles could definitely be more likely to contribute to scope damage when a brake is installed. The scope manufacturer would likely blame the brake and the brake devotee might blame the scope. If you like a brake use it but be aware of the unintended consequences to yourself and those around you. Scope damage is only one thing that can happen there is also hearing damage as well flying debris and sand when shooting prone etc. I have a brake on a 416 RM but use the thread cap for hunting. I don't believe small calibers benefit much from a brake but that's just me.

I haver brakes on my 223s, and they definitely benefit.

They are called compensators on handguns.

Many years ago I heard of someone making their own compensator for a 38Super and at one stage did have it venting up too much, to the point when the muzzle actually dipped upon firing. Very weird.

I should add - compensators are intended to reduce muzzle "flip" whereas brakes are intended to do this and reduce recoil. Some guys I know with muzzle brakes use them so they can see the shot travelling through the scope and not recoil reduction - I mean, these are on 223s and 308s.

I just recalled, I had a compensator on my M14, but they called it a stabiliser. Worked extremely well.

You are welcome. However, I did make a small mistake. The NET force pushing on the rifle is not (Pressure X area of the interior of the case head). Instead, it is (Pressure X bore area), again, neglecting the friction between the bullet and bore. I don't want to type all the "why", but trust me on this. The explanation of jerk, where it comes from, and how it can contribute to the failure of parts still applies.

Gun Doc

GunDoc,

Your explanation is very much appreciated.

I believe there is another factor contributing to the jerk when a braked rifle is fired.

For a split second during firing as the rifle is recoiling backwards and the high-pressure gases are exiting the brake vents, there is a sudden creation of drag opposing the rearward motion of the rifle as the wall of high-pressure gases created perpendicular to the rearward motion push back against the ambient air.

This drag is extinguished a split second later as the pressure of the vented gas drops to ambient. But for that split second the effect is not unlike having a golf umbrella or drag chute attached to the rifle barrel.

Many designs of thrust "reversers" on jet aircraft don't actually reverse the direction of the thrust at all. They direct the thrust vertically to create a "wall" of drag that slows the plane as if that wall of re-directed air was a solid surface. As the aircraft slows the drag decreases as it becomes easier for the ambient air to get around the moving wall of air.

A similar, but very quick effect is happening with our braked rifle during firing, and, I believe, adding to the jerk forces or changes in acceleration that our rifle and scope are subjected to.

I never would have believed that until it happened to me. I mounted a brand new Leupold 4x on a 10/22 and the reticle broke before the first box of 22 lr's were gone.

Sorry to laugh at your hardship, but I have a visual in my head that just made me laugh.

[quote=nifty-two-fifty .....

I am glad you have a good, reliable scope on your 338. I see that your 338 is braked. Perhaps the effect on scopes occurs somewhere between the 338 and the 378 recoil levels. What is your scope so that we can have the benefit of your long-term test with that scope. Thanks."

Sorry for the delay in responding. The scope in question is a Leupold VariX III, 3.5X-10X. As best I can recall the scope was purchased in the mid-80s and has been on a number of rifles of various calibers. It has been mounted on the .338 since 1992. The scope has never been serviced.

I have a number of Leupold scopes and my only complaint with them is that I find they seldom take a correction in setting without a number of shots being fired to "settle them down."

Jim

Thanks, Jim.

The Leupold VariX III, 3.5X-10X is one of my favorite scopes. I have one on my M-700 250 Savage. (Un-braked ,LOL).

I like that Leupold stands behind their scopes, but I have only ever had to send one back to them, and that was decades ago due to some bad anodizing on the scope body. They just sent me a new scope.

That was smart on their part, because I have bought a couple dozen more Leupold scopes over the years. Have a good day.

You must be one of the ones that sent a purple scope back...