Physics of a compensator

[little_kahuna]

I don't mean to question the magic, because LimCats run! I'm just curious about the physics of this.

Please refer to edited image for the following:

1. How does having ports (8) before the main exhaust/expansion chamber affect recoil control, and how does it affect your load? Do you have to load (too much) hotter to make it feel different? Are these ports necessary?

2. How does integrating the Comp into the barrel by cutting back a 5" slide like that affect the feel of the gun? Does it fee faster? Does it make it feel like a shorty? What is the advantage other than simply slapping the comp on the end of the barrel/slide?

3. These ports look like they are raised (outward) to increase the volume of the last chamber, does this more effectively vector gasses out, how does this affect recoil/recoil control and stability? Does it straighten the dot tracking?

4. What is the function of that (looks like 1/8") of barrel at the end of the comp? Does it contain the gasses for longer? What does that do?

Not to pick apart the gun, because i'm not a physicist or a mechanical/exhaust engineer or technician. I'm just curious. How do these things affect the shooting and handling of the gun?

Thanks. (please move if this isn't the right place for this?)

I decided to make this a new thread because it's not exactly relevant to the other one. Anyone got answers?

Just gotta be curious. Thanks

Edited May 4, 2009 by little_kahuna

[little_kahuna]

A lot of people have something that looks like this. How many "side bleeder" ports do you need? What is there advertised function, and what is their actual function?

Does the shape/size of the chambers make that big of a difference, how is the gas affected when being exhausted out of a square port rather than a round one?

More, smaller chambers? or fewer larger ones? How does a comp like this recoil compared to one with fewer larger chambers?

What is the advantage of differently shaped or angled chambers? Why are some short and some long? This one is exremely long, is that necessary? What is the functionality of a long comp vs a shorter one?

This looks pretty plain-jane, how effective is something like this compared to something elaborate, such as a limcat?

How does a ported barrel compare versus a dedicated compensator?

These chambers look very square, like they were hogged out, to maximize internal volume. Other than weight, what is the effect of very square chambers vs rounded ones?

These chambers progressively shrink. They reduce in size to accomodate lower gas pressure? Why are some "progressive" while some maintain consisntent chamber volume/size/shape?

Sorry if these are questions for a physicist or an exhaust gas engineer. lol Thanks anyway!

[CJDOUBLETAP]

For question # 1 in the first post.

Some people believe that you have to load very hot to get the comp to effectively work, that's not the case. In my testing of loads through my STI Trubor I have found that the powder type is the difference maker. I only used two powders, IMR 4756 and VV N105, but I can really tell the difference between them. I think that the slower burning powders that require more powder per case work the comp better because they produce more gas than fast burning powders. On a plate rack I can cut off about .3 seconds per run with VV N105, it works the comp a lot better and is slower burning. My steel load with 4756 is 6.2 grns. and with N105 it is 7.7 grns. VV N105 is really hard to find though...

Thats my thoughts.

BTW- Congrats on A class Nick.

Craig

[little_kahuna]

I see, Thanks Craig. How does a slow burning powder affect having huge or small chambers? because the Trubor comp's chambers aren't really small, but some of the other's are. When dealing with small vs large chambers, what type of powder would you load? and how would that affect recoil?

Edited May 4, 2009 by little_kahuna

[CJDOUBLETAP]

I see, Thanks Craig. How does a slow burning powder affect having huge or small chambers? because the Trubor comp's chambers aren't really small, but some of the other's are. When dealing with small vs large chambers, what type of powder would you load? and how would that affect recoil?

Well, I'm not an expert on this stuff but I would believe that slow burners would work best in any situation because of gas. I have also heard, I forgot from who, that the more and the bigger the ports the better.

[uscbigdawg]

Nick - All you need to know are two things. One is the Venturi jet principle (this will take care of all your port design questions). The other is that in open guns, you need to go against some old reloading mantra. The old adage in reloading was to burn the last kernel of powder when the bullet is at the muzzle. This (theoretically) made the load more efficient and you were not wasting components. In open guns, we want slower powders as we want as much gas as you can get (personal preference) in order to have some combustion out in front of the muzzle. More gas being created = more gas that engineering in the pistol can use to reduce muzzle rise and torque.

As for #2 - where Johnny cut back the slide it is a simple thing for a guy that shoots a Fat Free. If you reduce reciprocating mass the gun will shoot a little faster and flatter. So, by having more comp and less slide he's dropping the weight of the slide as well increasing the non-moving weight out at the muzzle (i.e. the furthest point from your hand and having a greater overturning moment [physics] to reduce muzzle rise).

Hope that helped.

Rich

ETA: As for the little nub at the end of the comp, some folks think it helps to stabilize the bullet.

Edited May 4, 2009 by uscbigdawg

[double_pedro]

Here's my approach to the "physics" of the problem (the rest is "engineering"):

When firing a projectile:

1. Linear momentum is conserved which means something (the bullet + exhaust gas) goes one way and something else (barrel, slide, frame, shooter and re-directed exhaust gas) goes the other....think equal and opposite.

2. Angular (rotational) momentum is also conserved. This comes into play in two ways....the first is the spin of the bullet imparted by the rifling will cause the pistol to twist the opposite way. The second is a little harder to conceptually grasp, but there is also angular momentum associated with the linear motion of the bullet + exhaust gas (relative to some reference point). Offsetting this is the angular momentum imparted to the barrel+slide+frame+shooter which is perceived as muzzle flip. Re-directed exhaust gas will also carry angular momentum and this may reduce the rotation of the pistol due to recoil.

So, the way a compensator fits into all of this is that the without a compensator, the exhaust gas can only work against you (which is why loads using a heavy bullet and fast powder use less gas for a given bullet power factor and this yields less recoil in a non-compensated pistol). If you have a compensator, the ports re-direct some of the gas backwards, upwards and sideways). Gas that is re-directed backwards, can impart up to 2x its momentum to the thing (compensator) that re-directed it - this results in a net redcution in the recoil momentum of the barrel+slide+frame+shooter and ends up as more momentum in gas molecules that are now directed backwards (which is why someone felt the need to invent blast shields). Similarly, by re-directing some exhaust gas upwards and sideways, you end up with exhaust gas off-setting the angular momentum carried by the bullet - as a result twist and muzzle flip is reduced.

Now, all of the above essentially allows you to make gains on the contributions to recoil from the gases themselves. For example, suppose the residual gases carry 10% of the bullet's 170 PF. In this case, uncompensated you'd have a 170 PF bullet + 17 PF of gas going one way and the net recoil of the pistol would be 170 + 17 = 187 PF going the other. If all of the exhaust gas could be re-directed backwards, it would impart a momentum kick forwards of 2 x 17 = 34 PF, reducing the net recoil of the pistol to 187 - 34 = 153 PF (you'd have a 170 PF bullet going forwards offset by 17 PF of gas that has been re-directed backwards; the net recoil of the pistol would be 153 PF).

The last point to make is that by using a slow powder you end up with gas generated after the bullet leaves the barrel. This results in a larger fraction of momentum carried by the residual gases which allows you to gain more from the compensating effect of the compensator.

Edited May 4, 2009 by double_pedro

[notasccrmom]

I'm looking forward to see some responses in this thread, especially from some open gun builders.

As a mechanical engineer, I understand the physics behind it, and how they work. When it comes to some of these designs, I really can't help but think that most of what you see is artistic expression more than actual analysis driven design. Most of the wild designs that I see look as if they kept putting holes in it until they ran out of places to put more holes.

My take is that the simpler the comp, the better. More isn't always better when it comes to fluid flow.

[Kingman]

Wil Schueman was an engineer at ATK rocket facility at one point. I know his barrels were designed with rocket nozzle principles and calculations based on pressure tests me did.

As for comps, it seems as long as you have a decent size comp with room for expansion it works. Some work better than others. I have never shot a limcat gun or so.

[little_kahuna]

Thanks!

Rich, i can really see why someone would cut back into a slide/barrel like that. You could maintain structural integrity as well as the 5" recoil system, but also significantly (safely) lighten the slide (and add weight to non-reciprocating mass/barrel). That is pretty smart haha.

Pedro that actually made a lot of sense. I can really see the reason for all the different designs. Through unique designs, people are attempting to maximize the amount of re-directed gas to further reduce felt recoil.

Another question. Is the barrel really non-reciprocating mass? It does move, but it moves at a different time, and it doesn't move much. What is the advantage of having a heavy barrel/comp versus a light barrel/comp? Other than overall weight, saying you could choose to put the weight somewhere else besides the barrel/comp, would you have a heavy or light barrel, and why?

So, comparing efficiency/effectiveness, I won some parts. I have a Schuemann ultimatch .355 SS threaded bull barrel as well as a BCG ThunderComp2. People have said to trade it for a Straight barrel and a cone-comp, or to get a Trubro T1/T2 comp. Will the Thundercomp+Schuemann barrel be too heavy/slow/ineffective compared to a Trubor or a cone-comp/barrel? What would fluting the Schuemann barrel do? What's the best combo of barrel (straight/bull) and design of comp (bull/cone/Ti/SS/Trubor etc.)

[little_kahuna]

I'm loving this feedback. Does anyone have any responses to the images/captions?

[uscbigdawg]

Nick - I'll tell you this from my Open gun, to probably the other extreme, our buddy Mike's. I have a 4 port hybrid barrel, 3 port comp and 2 side ports through the slide (i.e. a Rusty Kidd 5" Viper). It's awesome, but needs gas in order for it to run happy. It was designed under the old power factor and shot like a dream. When they dropped the power factor, the gun ran sluggish with 124's and N350 loaded down to 168 PF. I then switched to 115's, increased the powder charge, dropped the recoil spring weight and it was a LOT better. The thinking there was to increase the gas volume by pushing a lighter projectile at the same speed. After going back and forth, the reality is that my gun likes 124's (more accurate with them) and I just load them at 173-174PF. I don't ever worry about making major and the gun still feels "light" compared to the old PF. The gun is VERY loud, powder is burning every where (ask anyone that's RO'ed me) but it's flat.

Now...Mike's pistol is a 5" gun with only a 3 port comp. He shoots either 115's or 124's (can't remember) and N105. The gun is VERY smooth and the dot tracks great. If I were to build a new gun, I'd be hard pressed to not consider this as I can tell you that in using his pistol, I could call my shots cleaner and had better accuracy and follow through. Less violent than mine. Why don't I switch to something similar? I like how fast my gun cycles.

So...with what you have, talk to Mike and he'll guide you down the right path. At the end of the day, go with what feels right. You know what you like/dislike. Try out every open gun you get your hands on. We talk theory, design, etc. 'til the cows come home, but ulitimately, it's what you prefer.

Rich

[little_kahuna]

Very True. Thanks Rich. I shot a 5" open gun w/ a conventional Trubor comp/barrel for an entire match this weekend and I enjoyed it. I've heard a good argument against hybrid ports or popple holes. Like notasccrmom said, simplicity seems to work all the time. I'll test things and try all kinds of stuff. Thanks for the info guys. It's all speculative as of now anyway, because i'm broke. So until i have the $$$ yall need to keep telling me why yours is the best. haha

Edited May 4, 2009 by little_kahuna

[Davidp1911]

I shoot a 5" open with a Shuemann 4-port barrel and Bedell 7-port steel comp shooting a 115 gr. Montana JHP using AutoComp (168pf) - this is by far the best combo I've ever tried to date. It shoots amazingly flat and soft! I've tried other powders over the years like N350, N105, 7625 and LongShot but so far the AutoComp is working out great.

Edited May 5, 2009 by Davidp1911

[Shay1911]

I don't know much, but this is my experience. We shot a Millennium Custom 9mm major (MC comp, like the one in your pics), a Brazos Pro-SX (4 popple holes, 4 port comp with side ports, short slide), a shorty 9mm major (with all kinds of popple holes and comp ports), and a stock STI competitor with a 3 port comp.

First, the STI chronoed a whole 100 ft/s faster than the Brazo's. The longer Millennium custom gun chronoed a whole lot faster than the shorty 9mm. The combination of longer barrel, no popple holes probably did that.

Second, I was very impressed with how nicely the STI tracked. There was a tad more side to side dot movement, but very little if any vertical dot rise.

In my humble opinion, based on shooting them and not knowing anything else, the longer slide guns with the simple 3 port comps shot much softer and tracked much better for me. Again, this is not based on science, just a personal feel.

If we look at rifle comps, my favorite is the rolling thunder from Benny Hill, three progressively smaller holes, nothing fancy.

I am in the KISS camp, three progressively smaller chambers on longer barrels.

[RickRak2000]

Here's my 2 cents worth.

The largest component of muzzle flip occurs when the slide hits the end of it's travel (either open or limited gun). Slo-mo video clearly shows this. It follows that the primary function of the compensator should be to reduce the rearward energy/velocity of the slide so that it impacts the limit of it's travel as softly as possible. There is only a short time interval available for the compensator to do this work since once the slide unlocks from the barrel+comp, any remaining gasses exiting the compensator cannot affect the energy that has been already imparted to the slide.

Compensator ports that divert all the gasses upwards can cause the locked slide+barrel+comp to begin to dip downward a bit just as the bullet is transiting out of the compensator... and this may contribute to the overall perceived flatness of the gun. Once the slide unlocks from the barrel though, the compensator has pretty much done it's thing. Any remaining gasses exiting the comp may serve to impart some momentum to the barrel, but I don't think that they do too much.

Side ports are rumored to momentarily freeze the barrel laterally as the gasses are ejected... kind of like 2 rockets opposing each other. The opposing vectors upposedly "pin" the gun in space... ->O<-

I believe that most of the useful comp effect simply comes from the supersonic gasses moving forward and acting on the compensator plates to push the still locked slide+comp+barrel forward in order to counteract some of the rearward momentum imparted to the slide by the fired bullet. The more gas that pushes the comp forward, the better the comp works.

Once the slide unlocks from the barrel, the only thing that the comp can do is add an impulse in a direction opposite to the jet(s).

At Area2 a couple years ago, I noticed that the comp on Match Winner Chris Tilley's open gun had no upward facing ports... only side ports. It worked quite well.

Another minor contribution to dot movement happens after the slide hit's the stop an begins to accelerate forward. You can observe this by locking the slide back, watching the dot and releasing the slide from slide lock. The dot will rise slightly at first and then dip down as the slide goes into battery. When actually firing the gun, I don't think it's possible to see this slight rise effect, but you can usually see the dip at the end of the cycle.

As for what comp works best on any particular gun... It's just VOODOO, I think.

[jjanglin]

I think Wil Schuemann told me about a test done overseas some years ago, The comps that top the list then were

Sti then EGW's design.

I find that the Egw comp that Brownells sells works really well with the 9mm open guns.

Comps with small chambers tend to let the gas go out by the bullet drawing it with it.

Comps that have a fairly large 1st port let the gas diverge thus letting it work somewhat better.

Four years ago I tested several comps including the ones mentioned above using a video camera

and a home made scale, the differance wasnt much.

Ive also found that comps that are real noisy lets some shooters think thay are shooting flatter.

Popple holes throw a lot of the gas back towards the shooter and some think thay make the comp shoot

flatter . In the tests Ive done popple holes sometimes push the front of the gun down.

THE COMP THAT WORKS THE BEST IS ONE YOU PICK AND THEN SHOOT HECK OUT OF IT, IT

SOON BECOMES THE ANSWER TO ALL THE COMP DEBATE.

Jim/Pa

Sailors

[notasccrmom]

Side ports are rumored to momentarily freeze the barrel laterally as the gasses are ejected... kind of like 2 rockets opposing each other. The opposing vectors upposedly "pin" the gun in space... ->O<-

I follow most of your post and most of it makes sense, except this part here. Two opposing forces from the side will only cancel each other out. They will do nothing to pin the gun from front to back.

[Gregory_k]

after 200 rounds it does not matter.

[norbs007]

Here's an excerpt from the STI website about Limcat's work back in the days when the power factor is a lot higher. Make-A-Wish

THE GUN

It's a beauty, isn't it?" says Johnny Lim from his shop in Fremont, California. Limcat Custom has long been known for it's "no holds barred" custom guns. When offered a chance to create a masterpiece to be auctioned off for the Make-A-Wish match. Johnny Lim jumped at the chance. "I'm thinking of calling it the Panther Turbo Twin Side Port LRI." he says, "It's cool."

And cool it is.

Lim started with one of STI's already trick polymer-framed Commander length .38 Supers. After making sure every part of the gun was perfect, he started his own work. First, he added a new version of his acclaimed Turbo compensator, the Turbo 3. The six-port comp has an enviable reputation of being one of the most shootable, fastest-handling comps for full-blown raceguns. The new comp is "a lot lighter, which results in better pointability."

To that Lim added a pair of side ports, cut into the slide and barrel just before the comp. "I've always been pretty amazed at the way the side ports on AR- 15 compensators worked." he says. Even without any ports in the top, the side ports seemed to have a major effect on recoil and muzzle rise."

The result is a racegun that shoots really soft, with a resulting loss in muzzle velocity of only 20 feet per second (based on a 125-grain VV-based load; it clocked out at a power factor of 183 before the side ports were cut, then 180 pf after the cuts).

"I like using the Commander length gun," he says, "even though you're going to get a little more kick. It makes up for it in the way the gun handles."

Here's one about the Turbocomp.

Doesn't exactly give you the science behind it but tells you what it does.

[little_kahuna]

The more i see Johnny's guns, the cooler they look lol. Thanks for all the info guys, i'm diggin it. Since i have hardly any experience in open to begin with, it's all just academic for me. I know that anything will work with practice. I think that poppleholes or hybrid-comp ports may just be extraneous. It seems that people who are in the know (gunsmiths and engineers) dont seem to value them too highly. I like the 3-chamber progressive w/ side ports more and more. I also can really see all the time and thought behind the LimCat turbo "under-the-comp" bypass system.

Just on a side note, how important is it to clean out your comp? How do you clean a Limcat comp, if at all?

For prize-table parts, I think i'll like the stability of the scheumann bull+BCG thundercomp. It would seem to be to be a "solid" and soft-shooting gun, due to the weight of the barrel, and simplicity of the comp. Does that sound at all right? lol

I know that Mr. Johnny Lim himself just joined ( ), so how many other really active gunsmiths are here on the forums?

Thanks for the input everyone. It's rad. Keep it comin'!

[RickRak2000]

Side ports are rumored to momentarily freeze the barrel laterally as the gasses are ejected... kind of like 2 rockets opposing each other. The opposing vectors upposedly "pin" the gun in space... ->O<-

I follow most of your post and most of it makes sense, except this part here. Two opposing forces from the side will only cancel each other out. They will do nothing to pin the gun from front to back.

"freeze the barrel laterally" means the left-right plane of motion. I agree that the opposing left - right forces cancel each other out and they have nothing to do with the front to back plane. The "pin" reference meant hold the barrel from moving left or right. (I find it interesting that some of the so-called star wars type devices use modulated opposing thrusters to manuver and hold lateral positions/attitudes in space.)

Another bit of voodoo seems to be that positioning side facing ports higher on one side of the compensator and lower on the other can impart a twisting moment when the gasses vent. Depending on the direction of twist of your barrel you might be able to counteract some of the torque by tinkering with the side port placement.

Most of these mental gymnastics are probably a waste of time though. Sometimes just changing your grip will make a large change in perceived flatness. Get an accurate and reliable gun and spend the time practicing, dry firing... shooting on the move... working on footwork. That will pay bigger dividends than having a perfectly flat gun. ;-)

[uscbigdawg]

Nick - Nothing wrong with a Trubor. Frankly if I were to have a "bare bones" entry level Open gun, I'd go with probably one of Brazos SC pistols. Maybe 2 ports through the top, but that's a big maybe.

Next time you see him, ask Max to see his pistol. Pretty basic and he does alright.

Again...it's personal preference.

Rich

[double_pedro]

...Here's a little more thought regarding geometric details. It may shed some light on the reasons for popple holes, side ports, finding the "right" load, etc.

Geometry Considerations

Each partition of the gas (x, y, z) will carry the same momentum. Depending on where the gas molecules exit the muzzle and the angle at which they exit, some gas molecules will encounter (collide with) the compensator and some won't. The resulting compensation, depends on the specific (geometric) details of how the exiting gas molecules collide with the compensator. If the angular distribution of the exiting gas molecules is (approximately) known, it would be fairly straightforward to use a computer simulation to follow the bouncing gas molecules to determine the expected compensation for a given compensator design.

Rather than going into such a full blown analysis, let's take a look at some back-of-the-envelop estimates of the most critical features. Taking the z direction as the barrel axis, the x and y components normally cancel out and the exhaust gas carries a net momentum in the z direction. As in the above example, we will parameterize the z-momentum of the exhaust gas as a fraction, f, of the bullet's PF (f will primmarily depend on the bullet weight and burn rate of the gas). Now, depending on the geometry (mostly the length and caliber) of the compensator, only a fraction, F, of the exhaust gas will encounter the compensator, the rest will exit through the muzzle of the compensator and have no effect.

Vertical Compensation (muzzle rise/flip)

One of the primary objectives is to compensate for muzzle flip. Muzzle flip arises from the torque produced by the accelerating force of the gas acting along a line of action (the barrel axis) that is off-set from the axis of rotation of the recoiling. Exactly where this axis of rotation lies is a matter of debate and depends on the shooter, grip, etc. For this discussion, it will be taken to lie just under the beaver tail. In this case, the lever arm yielding the torque produced by the accelerating gases is about 1 cm (vertical distance from the bore axis to just under the beaver tail); the lever arm yielding the compensating torque from the exhaust gases is about 20 cm (distance from just under the beaver tail to the compensator). The longer lever arm of the compensating exahust gases is important because it enables a small fraction of the exahust gases to more fully compensate for the torque produced by all of the accelerating gases (acting via a shorter lever arm). For simplicity, we will use a relative lever arm of 20, but this may vary somewhat depending on the pistol, shooter, grip, etc.

The simplest way to compensate for muzzle flip is to port the top of the compensator but not the bottom (or use something like an AK47 muzzle brake where the entire top is milled off). It is worth noting that a large initial port allows the higher angle components to escape vertically - these carry more of the off-axis momentum and most effectively compensates muzzle flip. In the limiting case, we end up with a net fraction F of the exhaust gas exiting upwards. As before, the vertical (y) momentum carried by the gas is the same fraction f of the bullet's PF resulting in a compensating torque of 20 * f * F * PF relative to that produced by the accelerating gases of (1+f) * PF. To perfectly compensate for muzzle flip, we need to have:

20*f*F = 1 + f or f = 1/(20F - 1)

This is just a "ballpark" relationship to illustrate the balance between the load and the design of the compensator. As mentioned above, f will primarily depend on the bullet weight and burn rate of the gas, while F will depend on the geometry of the compensator. The relationship above amounts to "finding the right load" (bullet and powder) to achieve the best compensation for muzzle flip. Using rough numbers, if F is 30% (i.e. 70% of the exhaust gas exits through the muzzle of the compensator), we find f needs to be about 20% to achieve full compensation for muzzle flip. This is a reasonable value for the momentum fraction carried by the exhaust gases of a slow powder. If a different compensator design was able to encounter (i.e. use) a larger fraction F of the exhaust gas, a faster powder would be required. Note that the design of the compensator may be such that it selectively captures a certain fraction of the exhaust gas for vertical (flip) compensation and a different fraction of the exhasut gas for horizontal (push) compensation (e.g. by using side ports as well as top ports).

Horizontal Compensation

As discussed above, muzzle flip should be possible to completely compensate due to the larger (20x?) lever arm of the re-directed gases (distance from the comp to the beaver tail versus the distance from the bore axis to the beaver tail). When it comes to horizontal (rearward recoil impulse) compensation here is no such "mechanical advantage" for the effect of the re-directed gases. Therefore, relatively speaking, horizontal compensation (rearward recoil impulse) is going to be less effective since the gas only carries a fraction (10-30%?) of the bullet PF to begin with, and only a fraction of that gas (less than 50%?) will encounter the compensator. By re-directing all of the encountered gas rearward, you may be able to reduce horizontal recoil by roughly 5 - 15% of the bullet PF - e.g. reducing recoil to 145 PF for a 170 PF bullet. Further, since the pistiol requires a certain amount of recoil to operate reliably, there will be a practical limit not far below this.

It is worth noting that the longer the compensator, the better it will compensate horizontally because it will encounter (use) more of the low angle near-axis directed gas. This would be my guess as to the idea behind "popple holes" in the barrel - the comp sort of starts way back in the barrel.

What does it all really mean?

Having now thought about the details a little, I can imagine some designs may achieve a little more horizontal compensation than others, but that probably has relatively little practical effect. I think the biggest difference you may encounter is more likely to be in how well a load is matched to the requirements of that particular design to eliminate muzzle rise. Since the choice of bullet weights and powder burn rates are limited, there is no guarantee that you can find a "perfect" load for every compensator design. Hopefully there are enough options to be able to get close enough.

[Raudi]

Disclaimer: I am not an expert.

But IMHO the logic doesn't add up. The muzzle rise when shooting comes at a different time than the downforce the comp generates. I.e. until the moment the bullet passes the muzzle, flip is pretty much negligible, or else, we would all shoot WAY high. But at the moment the bullet passes the muzzle, there is a sudden drop in pressure, that would render the comp unoperable. This means, that in order too outcomp the flip, the gun would have to down first, in order to compensate for the flip, that happens later on, as the slide drains it's energy into the spring and ultimately makes contact with the slide.

But why then, does the gun stay flat instead of going down first and then jumping up from the down position like an uncompensated gun? The only answer that I can come up with is: The comp does not push the muzzle down that much. What it does is take momentum out of the slide. (Which would also be an explanation why side ports work.) Basically what happens (according to my logic) is this: We take a slide and mill it down to be much lighter, we take an extremely light recoil spring. Both makes the slide go back extremely fast. Now we use the gas to brake the slide/barrel assembly down to the slowest speed it will function with. And voila, we have a gun that shoots, as if it were shooting at a much lower PF, since the momentum in the slide is lower.

I am very probably wrong, but let me know, where my logic got out of line...

BTW an interesting experiment would be to take an open gun and determine the slide speed. (For example via hi-speed cam.) Now assemble a load that will give you the same slide speed, with the same slide, the same springs, etc but without the comp (or ideally with some kind of weight equivalent to the comp at the muzzle) and shoot that assembly. Now you would have to look for any difference in the handling of the gun, and we would know, what the comp really does apart from braking the backward movement of the slide.