Muzzle brake

Hey Boyd,

There is so much noise flying around on this thread that I'm staying out of the broad discussion in the interest of time. Besides, Al is well equipped to hold his own. But I have to respond to a statement you made that pointed bullets drift less than a round ball because they slow down less and consequently have less time exposure (shorter time of flight) to the cross wind.

This notion is pure BS.


Wind drift of a spin or fin stabilized projectile has absolutely NO correlation to time of flight. Wind drift is ENTIRELY dependent on time lag. For a ballistic object, that is one devoid of thrust, time lag is purely a function of drag. Wind drift is a function of drag because of time lag. There is no wind on the "side" of an elongated stabilized projectile to push it over.

You need to get this.

Best regards,

Greg
 
Boyd Allen said:
Just for purposes of discussion, please define time lag.
Click to expand...
The difference in the amount of time WITH drag as compared to the same shot WITHOUT drag.
Measured time of flight minus (Muzzle to target distance divided by muzzle velocity) = Lag Time.
 
The only way that there could be no lag time, for an unpowered projectile, would be if it were fired in a perfect vacuum, in which case there could be no wind. For a given MV, distance, and atmospheric density, lag time should be a constant, leaving crosswind as the variable that controls bullet drift. In the common use of the word, we say that a thing has been blown when it is moved by action of the wind.
 
Boyd,

Vibe's description of lag time or time lag is correct. It is the difference in time between actual time of flight and time of flight if the object didn't slow down. And everything in your post is correct except you need to include cd or drag function along with the other variables you list as determining lag time. Also "we" don't say "blown" because that is not what happens. "We" say drift because that is what it happens. Of course, those are big exceptions.

Greg
 
Last edited by a moderator:
When I say blown, I am making a general description that means the bullet was moved by the wind. Be it a thrown rock, or spin stabilized projectile, when the wind comes from the left, either will deviate from from their probable still air trajectory to the right, with the exception that the spinning one will show some rise or fall, depending on the direction of the wind and spin. When I say blown, it is not to challenge anyone's theory of the mechanism, but merely use of the word in the common way that is found in the dictionary. Actually, I don't care about the finer points of the discussion that invariably takes place. I just need to know where the wind will take a bullet when it changes, and I surely don't have time to do any calculations to find out. I must rely on my memory of what has happened under similar conditions.

As to my previous leading question...less than .3 of a degree..... The point is that most illustrations that use vectors to describe resultant direction of flight when a cross wind is acting on a bullet are schematic, not drawn to scale, and can therefore be deceptive unless you take the time to plug in the numbers and do a little math. Some time ago it occurred to me that the "explanation" that I was reading was probably the result of someone interpreting a schematic drawing as if it was to scale. My other point is that correlation is not causation. Just because two thing happen at the same time does not mean that one caused the other.
 
Last edited:
Boyd,

By "general description" we say the sun comes up in the east. If the discussion were planetary systems, to say that the sun rises in the east would be incorrect and if trusted, would do nothing to increase understanding but would in fact confuse and confound persons hoping to understand planetary behavior.

For you, a generally well informed, articulate, genial and trusted Super Moderator to spread nonsense and justify it by writing that you "don't have time calculate and must rely on memory for what has happened under similar conditions" doesn't help advance the knowledge that folks coming to this board hope to find.

A "thrown rock" and a "spin stabilized projectile" exhibit profoundly different behavior beyond the fact that both will eventually hit the ground.

If you "don't care about the finer points of the discussion" why contribute a general description" that is flat (earth) wrong?

Greg
 
When shooting, do you take time to calculate, during a match? Do you actually convert flag ribbon angles into MPH?

This started out as a post about muzzle breaks, and became a meaningless back and forth about the mechanics of wind drift. Given that all of the more technical participants seem to disagree so completely, I doubt that there is much that can be much that can be concluded, with any degree of certainty from what has been written here. One would simply not know who to believe. One thing for sure, there is obviously more than one way to interpret the same information.

How many of us have developed formulas to predict trajectory and drift that have been verified as to their accuracy? I certainly have not. We can all say that this is the way it works, and you are wrong. What is learned from that? At some point one needs to show all of the information that led to the conclusion. I don't think that this has happened here (nor would I expect it to be) given that, I think that not taking the discussion too seriously is not at all out of order. The thought that one can explain in a post what authors who have specialized in the subject needed a book to do may be just a tad unrealistic, don't you think?
 
Boyd Allen said:
The thought that one can explain in a post what authors who have specialized in the subject needed a book to do may be just a tad unrealistic, don't you think?
Click to expand...
Now THIS is one of the most profound statements that's been made in this thread. And true as well.
 
No physics

http://www.jprifles.com/1.4.2_re.php

http://www.jprifles.com/v/v_d.php?v=recoil

http://www.harrellsprec.com/muzzle_breaks.html

http://www.ar15.com/forums/topic.html?b=3&f=118&t=427948

I've played with several designs. Muzzle jump or flip is improved more than recoil reduced. Why?

Bullet Weight Mass contributes to recoil more than powder charge.

Force=Mass * Velocity Where V = f(powder charge grains).

http://www.nasa.gov/audience/foreducators/topnav/materials/listbytype/Force_Equals_Mass_Times.html

Change in Mass of 10 grains has a greater effect on Force than a 10 grain change in powder charge. It takes more energy to accelerate a greater mass to the same velocity than a lighter mass.


Last comment. The bullet (mass) and Propellant (Burning Gas) have to travel
95-98% of the barrel length before a muzzle break takes effect.

This much recoil energy is encountered. The muzzle break reduces the force of the gases acting on (escaping) the crown and creates a vacuume or reduced turbulence behind the escaping bullet.
 
Boyd,

The answers to your questions are no and no. In fact I don't own any flags, have never set a flag and when range or other shooter flags have been available to me I make modest use of them. Seems ironic I know. In spite of my failure to fully utilize all available inputs I have at time found enough positive reinforcement in competitive long range shooting games (1K BR, 600Yd BR and Palma) to keep me interested. Maybe understanding wind drift helps while making shooting judgments on the fly. Maybe not. As you stated correctly, correlation doesn't necessarily indicate causality. But sometimes it does

I answered your questions. Will you now answer mine?

If you "don't care about the finer points of the discussion" and find the discussion "meaningless" and "doubt that there is much that can be concluded" then why, from your position as Super Moderator, do you contribute (and defend) a ":general description" that is flat (earth) wrong?

Please enlighten me.

Greg
 
Your question misstates my position. Answering it would seem to validate that inaccuracy. It is an old debaters trick that is often employed, misstate someones position as something that is easier to criticize. Most of the time, all that results is a harmless, if lengthy thread consisting of I'm right and you're wrongs. Personally, I think that if the participating parties view these sort of exchanges as illuminating tools of instruction, they flatter themselves. In short, when dealing with challenging subjects, it is possible for readers of the same material to materially disagreed as to what the "truth" is. It is also possible for someone who publishes to be right about many things, off on others, and still have produced a useful product. These issues will never be resolved here, due to the inherent limitations of this format. In any case, I think that using words as they are commonly understood is no fault, especially if one qualifies their use.
Buy or make some wind flags, and start using them. Take notes. I guarantee that they will do more to improve your shooting than this discussion has.
 
Last edited:
Boyd Allen said:
Al,
A little thought...we spend our time in consideration of elongated bullets, and the previous discussion has dealt with them exclusively. I understand that a bullet has a center of mass and a center area ( as viewed from the side. If these two were in the same place. I don't think that a cross wind there would have any effect on where the bullet was "pointing" relative to LOS, but I do think that the bullet would drift anyway. As an example of this situation I give you the round ball. Just because two things happen at the same time does not mean that one causes the other. Long pointy bullets have less drag so they slow down at a reduced rate. This means that they arrive at the target sooner than a round ball, and are thereby exposed to a cross wind for less time, so they are not pushed/pulled (take your pick) as far from LOS.

Boyd,

Sorry I misstated your position. Please forgive me. No trick intended. I thought from reading the above that you were explaining that time of flight, not lag time, is the factor that determines extent of bullet drift compared to LOS. Since this is not what you meant, can you explain your position so that I understand it?

I'm not trying to flatter myself as you seem to have suggested. I don't have much to work with on that front. Discussing these types of issues does seem to help me distill my own thoughts and make the models that I carry in my head more accessible to me. If the discussion helps someone else, that's even better. I do think that the actual, honest to gosh rocket scientists like McCoy and Litz (not to mention pilots like Beggs) have explained the physics to us,that is to say given us the truth. Now it's up to us to get our heads wrapped around the facts and put them to use.

I'm sure that you are correct that better use of flags could help my shooting performance. Thanks for the suggestion and especially the guarantee.

Sorry for the annoyance.

Greg
Click to expand...
 
Last edited by a moderator:
Oh heck Greg, It takes a lot more than that to annoy me. As it happens, over the same distance, with the same muzzle velocity, the the round ball has a longer time of flight and lag time. What I meant was that because it is exposed to the wind for a longer period of time, the wind has more effect (with the same starting velocity, over the same distance).
 
Hey Boyd,

Thanks for the reassurance that I'm not an annoying you. That truly is not my wish.

Here is something I want you consider. Even if you drive the round ball fast enough that its time of flight is shorter than the elongated bullet, it will still drift more, a lot more, than the elongated bullet. That is because it has more lag time even with a shorter time of flight. Punch some numbers into any ballistics program and test it for yourself. I "guarantee" you'll find it's true. Can't vouch for this truth improving your shooting though.

Best regards,

Greg
 
I would rather see it actually done. A while back, I came up to compare wind drift, nothing brilliant or complicated. You just set up on a windy day at the range with several shooters on adjoining benches, each with a verified chronograph. They all hold center of target. A friend who is not shooting watches the flags, trying to look for an extreme left, and an extreme right condition that he thinks will hold for a couple of seconds. On command, they all fire at the same time, first in the left condition, and then in the right.
This topic was discussed on this site some time ago. During the discussion Lester Bruno told of a similar test, after a match. He was shooting some sort of .22 caliber verison of a PPC. The other shooters were shooting 6PPCs. After looking at the targets, they accused him of holding into the wind. He had not. Sometimes results are not entirely what is expected. I don't mean that I disagree with what you have said, or that I have some fundamental mistrust of ballistic software, it is just that I feel even more confident of the results of an actual test. Sometimes I think that shooters forget that ballistic models have evolved....and may still be.

The most interesting thing that I have seen recently in this vein is a report that Lapua is offering free ballistic software that has been verified, for their bullets, using doppler radar. I like the idea that they checked their calculations.
 
Boyd Allen said:
The most interesting thing that I have seen recently in this vein is a report that Lapua is offering free ballistic software that has been verified, for their bullets, using doppler radar. I like the idea that they checked their calculations.
Click to expand...
It is also a bit interesting that that same Doppler radar study confirmed that the BC is not constant. Even throughout the flight of a single bullet - it varies with the velocity. This article references that same data.
http://en.wikipedia.org/wiki/Ballistic_coefficient
 
Ok, let me try this from a different direction.. :)

I hope that this is taken positively, not as just another argument :eek: I'm tempted to just drop the subject again because I can't seem to keep from creating an acrimonious atmosphere. PLEASE guys, lay it all at my door but lets not devolve to name calling. I can learn from Greg and Boyd.

The Alinwa "no physics" Description of Drag. (I'm sorry you physics guys, some of this verbiage is imprecise...)

Many will see this as overly simplistic but I'll try to explain how I picture the DRAG versus WIND conundrum.

We need to view this from the frame of reference of the bullet, the projectile. Since we're dealing with only one object, our "center of frame" can be the bullet, the projectile. We need to RIDE THE LIGHT'NIN'!

As I see it we give the projectile a velocity, (speed and direction.) NOW, if we're riding the bullet in a vacuum, we're motionless. The gun is gone, receding into the distance, we're just sitting on a bullet. For the purpose of discussion we'll ignore gravity. (until we crash! :eek:)

In a vacuum this projectile would travel with unabated SPEED and unchanged DIRECTION until the force of gravity caused it to collide with the earth. This would be its "vacuum trajectory." There would be NO CHANGE in any direction. In fact, given enough SPEED we won't even crash into the earth, we'll just assume an endless orbital path.......

BUT, we're actually NOT launching in a vacuum, we're riding through a viscous compressible medium, air.

In air the projectile loses SPEED rapidly, its rate of change of speed (acceleration) is quite high, in fact it's the dominant factor, far and away the largest component of change. Viewed from the frame of reference of the projectile, it's backing up. And it's backing up HARD. Be the projectile round or elongated it's backing up HARD, it's got a tremendous "rearward acceleration" because it's feeling a 2000mph wind in its face..... The projectile enters its trajectory with a speed of 2000mph. After only 1 second it's down to maybe 1500mph, or maybe clear down to 1200, it might even drop into subsonic range but let's just say it's a decent bullet so it only slows down to 1500mph.

From 2000mph to 1500mph is still a CHANGE of 500mph.... the bullet accelerated BACKWARDS from a dead stop to 500mph in 1 second. That 2000mph wind has accelerated the bullet from 0 to 500mph in one second. That's a ferocious WIND!

Now we add a little side force. We add a 10mph crosswind. Left to its own devices this weeny little 10mph wind can't do much, it can't impart much of an acceleration to the bullet in one second. But what it CAN do is change the DIRECTION of the ferocious 2000mph wind. Now we can "factor the vectors" and we can draw it all out numerically but all we're doing is quantifying what's going on...... what's REALLY going on is that that bullet is BACKING UP at a rate of 500mph with just a teeensy weeensy "side component" which is just a fancy way of saying it's backing up FAST with just a little sideways motion.

It's the BACKING UP that's dragging it out of line.... The backing up or "rearward acceleration" or DECELERATION is what DRIVES the thing we call wind drift. Give the bullet 10mph side and 500mph back and the result is an exaggerated sideward motion.

Now, as has been so gently pointed out, this really has NOTHING TO DO with the shape of the bullet and the fact that it's swimming like a fish in the apparent airstream. It's just that to the casual observer it "stands to reason" that if the bullet "turns into the wind" it should catch a little glide and kinda' plane one way or another, it doesn't. But IN RELATION TO IT'S INITIAL GIVEN TRAJECTORY it's sideslipping, the weird thing is, it's sideslipping THE WRONG WAY! For an elongated bullet it's "following its tail."

The only reason we elongate bullets is to pack more weight into the same frontal area.

And the only way to keep them pointing in the right direction is to spin-stabilize them. Spin stabilizing uses some weird gyroscopic forces which MAKE the bullet fight for stability. Anyone who's ever twisted a bike tire or raced motorbikes or otherwise tried to turn a spinning object has felt this weirdness. But the rifle bullet USES this weirdness to mechanically (mechanically?? I'm kinda' over my head here verbiagewise...) force the bullet into alignment.

The FASTER we spin them the FASTER they align themselves with the airstream... (well, almost....they don't align perfectly but 98%??? Yaw of Repose???.... that's nothing more than a SWAG) and the MORE ENERGY they have to align themselves. There is a price here, but it's not stability.....

Now...... on to the tipping over to follow the flightpath. IF IT'S TRUE that the bullet "balances" or centers itself on the apparent wind vector then it follows that the bullet WILL tip over in its flight path. Given enough stability.



At this point if anyone questions where the bullet is pointing then we need to understand that this is another discussion. If there are those who DO NOT agree that an elongated bullet points into the apparent wind then this need be approached separately IMO.


So, if we find that a properly stabilized bullet MUST keep its tip very nearly aligned between its CG and the apparent wind direction........ IF WE AGREE that the bullet aligns with the felt wind vector.......... then we can go back to the gravity thing.

We've been ignoring gravity but it hasn't gone away ;)

After that one second the bullet is feeling another "wind," it's FALLING......it's got a direct "UP"-wind of near 11mph, more than the crosswind. and after the next second this has climbed to triple that. My question then is, IF an elongated bullet is "forced" into alignment with the apparent wind vector, how can it not feel the "wind" generated by it's "falling through the air and center on it?"

I'll stop now lest I again stray into all sorts of peripheral garbage......

And my typical rabid inclarity! :eek:

CAN a stable bullet fly nose-high over yardage?

If so, HOW?

I'll check my books again to see if I'm reading incorrectly (or reading IN as the case may be!) I still can't wrap my head around the idea that a 3oz superball hits my head with twice the force of a 3oz lead sinker..... Maybe I'll go conduct some experiments :D

al
 
Vibe,

The reason that bc changes with velocity is because a drag model is for a particular bullet form factor and not identical to the bullet being tested. The commonly used drag model in hobbyist ballistics is the G1. That drag model is for a bullet that is much less pointed than the bullets we use in long range shooting. So the change reported in bc over velocity for a particular bullet actually describes the extent to which the model varies from the bullet. I read that the G7 drag model is a much better fit to the bullets we use but most available software and published bc's rely on the G1 model for historical reasons.

It isn't that the bc varies, we're just using the wrong drag model and have to adjust for that shortcoming.

Greg
 
You must log in or register to reply here.
Back
Top