Home Forums Hunting & Shooting Ask The Gunwriters Muzzle brakes.

Problem with my 788, doesn't have a flat butt plate. It's been nicely modified to a curved checkered steel butt plate. When recoiling the top and bottom are brusing my shoulder. Another, I don't have much recoil tolerance built up. Pretty much a nooby when it comes to hunting and shooting.

Mark

Robrobinette.com has a simple calculator and I just ran some numbers for my 7mm Wby mag with a 175 gr bullet and 72 grs of powder. If total’s don’t add, it’s because of rounding.

Total recoil energy: 40 ft lbs
Recoil due to bullet weight: 21 ft lbs or 52%
Recoil due to gas: 4 ft lbs or 11%
Recoil due to jet effect: 14 ft lbs or 37%

Can’t do anything about the ejecta (weight of bullet and powder gasses) of a given load, but the brake comes into reducing the jet effects. How much depends on efficiency of the brake.

I shoot a 6.8mm Rem SPC AR. No "brake" needed!
My "range" is about 200 feet from my front door, surrounded by 80 acres of "mine all mine"!

Etoh,

I know two makers of muzzle brakes very well, and they performed a number of experiments that actually measured how much a brake of certain design affected not only how much the brake affected rifle movement backward during recoil, but how much a brake with holes only on top of the barrel behind the muzzle affected muzzle rise. The experiments included "hanging" the rifle like a ballistic pendulum, and in all instances the differences between brake and no-brake were measurable--despite your claim that all recoil effect takes place while the bullet is still inside the barrel, so can't be affected by powder gas released at the muzzle.

The U.S. Army has also conducted considerable experimentation on artillery brakes for a long time, some of them very recently. You might try Googling some of those.

Unfortunate he doesn't separate out the recoil and the torque vector but groups them under one category of recoil. He also doesn't include the calculations for the increase in volume the "jetted" gasses have which according to the he gas law PV/T=PV/T equation the reduction in pressure caused by their expansion. Its pretty easy to adjust his basic math to include the gas law equation in Matlab or MathCad and have done that having read his site before, to get adjusted answers more in line with the events.
He does give some credit to added weight. Not enough, and particularly where you place the weight.

Just a note on the yellow flame coming out. Its traditional to equate flame color with burning, we've been taught that since children. However consider that the kinetic energy hill in the reaction has already occurred and the system is on the down side of the energy hill, Nitrated oxygen has already been converted to end products, CO2 and ammonia. and the visible light band seen is the remaining electrons have already dropped from their higher energy state to a much lower state and emitting in a wavelength visible to the eye.
What happened to the ones you can't see? Im just burning to hear some answers. Perhaps you can see that most of the terminology is outdated in a lot of gun stuff on the net today.

Didn't/don't have time to go to PrecisionRifle to see what their set up was, if it was "in vivo" or calculation driven.

Yes Ive seen those studies, and methods also. Muzzle exciting gases do have an effect, which is determined by the total surface area of the barrel diameter, as I stated early. Most of the studies and conclusions fail to factor in the gas law equation that PV/T = P'V'/T which simply states that because the temp. has fallen and the volume has increased the pressure has dropped considerably. All Im saying is that any effect caused by this comes after the main recoil vector has been transmitted.

Neither a human or a ballistic pendulum can see that small of a time frame. The system is a non-linear 3rd order. In mathematical terms the iteration level of the differential (difference) equations is not set small enough for the bifurcation to occur and show the new state of the system.

As a side note -- the several muzzle devices Ive used with smaller holes, whether they are on top, or sides. plug up so fast they are operationally useless. Really hard to beat TRG devices.

Mark, I’m pretty sure that Pachmyar makes a Decellerator recoil pad that is a bolt on swap for your 788…..unless the previous owner modified the stock! The Decellerator will really tame felt recoil…..though it will increase the LOP (length of pull). If it makes the LOP to long for you …..that opens a new can of worms. If you cut the stock to get the proper LOP…..chances are your new “custom fit” Decellerator won’t fit any more. I usually get a pad larger that the stock pad area…..cut the stock (careful to keep proper butt angle) then fit the pad to the new butt dimensions!

Good Luck with making that 788 comfortable to shoot! memtb

Stock has been modfied to fit the recoil pad. Here's a photo of the rifle. Who ever did the stock work did a half decent job. Steel butt plate has nice checkering with a widows peak. Has a nice metal grip cap. Kind of dressed up a otherwise plain stock.

I have a local gun guy that has a 243 barrel. Really good advice on this thread that I'm going to use toward adding a brake to my 300 win mag LH carl gustaf

Picture of the 788
788

I thought the bolt handle had fallen off at first..

Mark, an attractive stock….looks like the previous owner worked pretty hard to give it some “curb appeal”! 😉

So……I gather that you’d like to keep the attractive steel butt plate! Beauty often comes with a price! memtb

Yeah, it's a nice stock I think I'll be able to keep the steel butt plate, going to be rebarreling to 243.

I use to think the same thing until I tore up my shoulder and had a plastic/metal one put in . Without it I would have had to either quit shooting the rifle I liked to use or go to a smaller caliber that I was not comfortable shooting an elk with.

We all get old and and parts wear out. We have to make compromises. You will be there some day.

Seems to me that using an 18” barrel and then adding a brake is an odd way to go. A normal length barrel, say giving an OAL the same as the braked shorty, with maybe a slightly heavier contour, might reduce the recoil, and not lay the daisies low with the blast. A Limbsaver slip-on would help, and let the LOP be instantly adjustable for say, cold weather clothing.

I’m in the Don camp on brakes, certainly for regular rifles. If my shoulder wears out, I’ll just use the left one, or a smaller caliber. Lots of pretty big stuff gets slain with 6mms.

The number of braked rifles at my range far outweighs the unbraked jobs, Hell I have even seen them on .223's!
The interesting thing is, many shooters think ypu absolutely need a brake, and I get told often I would shoot better with one.
My answer is always the same.
" my disciplines I compete in do not allow braked rifles , and with the number of rounds hunting that I need to accuratley shoot even out of a .375 H&H M70 , there is no need for me to shoot a brake on them."
My high volume range shooting is done with rifles in .223 , 6mmBR, and 308.
These are rifles weighing in the vicinity of 10 to 12 pounds .
If a person wants to shoot with a brake , that is up to them

PTG builds a good brake.
Cat

ETOH.

Usually your posts here are well thought and reasoned. But in this case you are mistaken about the effectiveness of the muzzle brake.

I am comfortable in stating this, only having fired one, about four hundred times, on a 26 inch 340 Weatherby mag shooting 225's and 250's at maximum velocity. Muffs and plugs!

Were brakes not effective, they would not be fitted to most tanks, and artillery pieces, and shoulder fired 50 BMG. In the case of the 340 Wea, it recoiled about like my 30-06 with 165s. I had a couple friends with home built 50 BMG rifles. They were equipped with remote triggers. The difference in recoil with or without brakes was obvious.

As to the physics involved, it is a matter of force vectors. Any forces directed against rear facing structures of the rifle, are removed from the sum of recoil forces. I doubt any would deny that force exits the perpendicular ports on the brake. If one doubts, he could wrap his hand around the brake as the gun is fired.

The ignition of the powder charge pushes backward against the rifle at 50,000 - 60,000 PSI times the surface area of the rear of the combustion chamber, for a brief moment and then diminishes. That rearward force is mitigated by the force pushing forward upon the interior of the shoulders of the chamber so the only relevant net force is the diameter of the bore.

That force is further mitigated by subtracting the pressure against the base of the bullet, until the bullet exits the barrel. And also mitigated by forces pushing forward against baffles in the brake as gases are redirected to the side.

If the brake has cuts in a non uniform pattern, or a compensater with only a cut in a single direction, the muzzle will be pushed away from the cuts. Not by escaping gases, but by the pressure in the vessel pushing in the opposite direction from the cut or cuts. The brake would work identically if the gun were fired in a vacuum.

These forces are often called rocket effect, misnomer or not. It is the same force which lifts a Saturn V off the pad. If the flame of the rocket were redirected to the sides, as with a muzzle brake, that rocket would sit on the pad.

The comparison is made to ejecta mass of bullet vs powder charge. But that comparison does not take into account ejecta velocity. Energy is equal to mass times velocity squared. Gases are ejected at much higher velocities than is the bullet, and do contribute to recoil at that square factor.

Most misunderstand the manner of "rocket effect". Rocket gases, do not drive by pushing against air, or a wall behind them. They work by pushing forward on the container in which they are held. We all know a rocket functions as well in a vacuum.

The fuel of the rocket pushes out of proportion to its mass as well. It takes advantage of heat developed during burn and exits the combustion chamber at high velocity.

That is a damned nice looking 788.

Thanks

Thanks for the compliment, except for the qualifier.

First, I want to apologize for hijacking the thread.

Look up the definition of non-linear dynamics. Your explanations are a repeat of the mantra repeated time after time. Ive shot all the guns you talk about with and without a brake. Shoot 50 Barretts and Desert Techs in Desert on occasion still. Except for one, which I refused to, without the break, it was a 20 mm. single shot owned by Jack Tomilson who was a military surplus dealer in Tooele Utah. Jack also had a 105 howitzer, and all the license need to make explosives etc. etc. one could image. Local law enforcement didn't care if Jack shot the howitzer in the desert just as long as he didn't shoot over highways. I hung out there is my spare time. He also had a amphibious World War II Duck him and his buddies had in England/France and every year they would meet and celebrate the landing at Normany by getting in the Duck and repeating it. So pleeeeeez don't bust by ass with a bunch of hunter stuff.
The devices used on howitzers and tanks weigh several hundred lbs. How does that change the torque moment/ Which is never brought up

My backround which I really didn't want to bring out is post-doc. work in an area called non-linear dynamics, the lay terms for this is chaos theory the correct term is bifurcation theory. Regular engineering analysis loves linear systems. By setting the time frame, or the dimensions small enough they can ignore the irreguarites in the computations. This works especially will in control systems analysis all the time. TL3 in SLC does this,, until they had to finally look at fuzzy logic systems. This method is called LTI--Linear
Time Invariant. Getting to the point is -- this is what vector analysis is. As a side note Tensor analysis should be used but it would loose people doing calculations in pi*rads.

The shooter is just a ballistic pendulum. But unlike a block of wood, (except the IQ part) it changes with every shot. Thus a different resistance against the gun each time. Its amazing how the systematic errors can be magnified and the random errors cancelled out.
Got to wonder if EP and SD is load problem, chronograph, or shooter gun hold.

Sorry, lets get started with the basic model.

The Robrobinette model is a good place to start as it sort of explains why the jet/rocket effect is given so much weight. (pun intended) . The rocket effects folk through in a J-factor to make their calculations come out. They attribute more wt. to the gas ejecta than the wt. by a factor of 1.7. While the escaping gases do have a momentum. They do it at the sacrifice of velocity. No where in these calculations, is the results for the reduction in velocity due to the increase in the volume according to the Universal gas law PV/T=P'V'/T. This is one of the problems as far as using linear analysis type approach.

I have to laugh as he used a Microsoft worksheet, from the early 2000 to make his site. Could of at least used something like Matlab.
Next problem: When a reaction occurs, and most are chemical, its because the activation energy exceeds a certain value and the right hand side of the equation, products are formed. You get them in this hobby - powder companies called them flame retardants, in my former line of work they were enzyme inhibitors. Part of this analysis is building a graph, (picture is worth a 1000 word stuff)
and part of that is what formulas are used to fit the data to the curve, because the data, is stepped. Natural log curves, are some exponential e is one type, Heaviside, Dirac, and transforms are other curve fitting tools. Rob uses 1/sq rt. of. e

The kinetic energy equations is second order. which means its not linear. The term v is squared because when it was invented folks had no idea there was a fractional derivative. It took difference equations and very small iterations steps to see the differences in fast events. When this started to come out, about 20 years ago, engineering, math, and created a non-linear systems analysis.
This means that not all KE=1/2mv*2. it can be KE=1/2mv*2/3. Ill leave this here.

The gun firing is a 3rd order system, barrel, (closed thermodynamic system), device (opera thermo system) and kinetic (gun recoil)
The time frame duration of the whole event goes over at least 6 orders of magnitude form at least .0001 to 3.0000 (shooter wakes up). During the overall event I see 2 bifurcations, smaller iterations on a computer may show more.

If you don't understand some of the concepts or math here, ITS NOT MY PROBLEM.

Gotta go ---- Working up some loads today, got a great price on 16 lbs of Superperformance, No loading info. for 300 win mag.and 175 TMK or 178. Not looking for highest velocity, just good consistency to 1700 yds. Using my TRG 42 with the compensator.