TargetTalk

Hi! I recently had the chance to get the compensator of an dysfunct fp10, which i want to try on my toz. My problem: whats the distance between muzzle and the "insert"? And is this distance of any importance?
Thanks in advance!

flolo wrote:Hi! I recently had the chance to get the compensator of an dysfunct fp10..e distance between muzzle and the "insert"? And is this distance of any importance?...

Beyond marketing bling, what is the need for a compensator on a 50-meter pistol? The bullet is long gone before muzzle lift, and there is no second shot.

zoned wrote:Beyond marketing bling, what is the need for a compensator on a 50-meter pistol? The bullet is long gone before muzzle lift, and there is no second shot.

They can (not always) improve grouping. I tested mine in a machine rest with and without, and the groups with the comp were better, especially with the cheaper ammo. Maybe my results were a fluke but that what I found.

I am always curious when people say the bullet is long gone before the flip. But that contradicts physics which says equal and opp action. and so the flipping woudl start happening as soon as the bullet is ignited in the chamber. It could be another case in AP as the recoil in AP is much less combined with 10 meters that the difference is probably not noticible. I would like to think it would matter at 50 meters. I dont know the answer but my school level physics tells me a more recoiling gun is a worse one than a lesser recoiling one. Didnt the AP springers have worse accuracy than the PCP APs.

John -

You are correct that the recoil starts when the projectile starts to move. I have had a very hard time convincing some people of this, but Sir Isaac will not suspend the laws of motion just for shooters.

The compensator serves two functions: allow the gun to come back to shooting position more quickly in rapid fire, and allow some of the muzzle blast to dissipate rather than kick the projectile in the butt.

The first is of no consideration to single shot pistols, although with higher power guns reducing perceived recoil may help consistency.

The second occurs because as soon as the projectile leaves the barrel it begins to decelerate. The propellant gases still in the barrel may be moving faster than the projectile and for a short distance beyond the muzzle the gasses can provide a bit of a shove which may be destabilizing. Of course, the effect depends on the characteristics of the particular gun, projectile and propellant combination. If a compensator has any effect on the accuracy of an air pistol, it is through this mechanism.

IMHO, of course.

Roger

john_almighty wrote:I am always curious when people say the bullet is long gone before the flip. But that contradicts physics which says equal and opp action. and so the flipping woudl start happening as soon as the bullet is ignited in the chamber.

High-speed photography of bullets leaving pistol barrels always look like the bullet is gone before the pistol moves. As you point out, that seems to contradict basic physics. I always figured there was some very small amount of movement before the bullet leaves but that it's just so small that we don't see it in the videography.

No matter. It doesn't make any difference. Whatever movement occurs before the bullet leaves cannot be corrected by a compensator because the compensator only begins to work after the bullet leaves. Mostly, the function of compensators is to reduce felt recoil and pistol movement so that followup shots may be placed more quickly and accurately. That's a very big deal in the run-n-gun sports but it's not a concern for any single-shot firearm.

Compensators may also have some impact on the state of mind of the shooter. That's not something I can address.

Compensators may also help by extending the sight radius, though there are certainly other ways to accomplish that goal.

Roger makes an excellent point about propellant gas turbulence adversely impacting bullet flight as it exits the muzzle. Look at this:

http://www.youtube.com/watch?v=otpFNL3yem4

I haven't a clue how a compensator could deal with the problems that video shows such as the blow-by of gases preceding bullet exit and the great puff of destabilizing gas that impacts the bullet immediately after it clears the muzzle. That video is of a pistol that would have more problems of this sort and I'd hope that high-level 50M and air pistols are better. At minimum, that gas blowby that indicates insufficient bullet-to-barrel seal simply shouldn't be there. Compensators may help with all that stuff.

One thing that folks around here seem to ignore, however, is that compensators clearly impact accuracy. As pointed out by j-team, sometimes pistols group better with a compensator in place. In those cases, the compensator is not acting as a compensator but as a barrel tuner. Hanging a weight off the muzzle of a pistol or rifle can greatly improve (or destroy) accuracy by changing the way the barrel vibrates while the bullet is still in the barrel. Benchrest rifle shooters who are chasing group sizes approaching 0.00" at 50 and 100 yards make extensive use of them. (And yes, 100-yard benchrest group sizes in "the zeroes", with center-to-center measurements of 0.09" or less, are common under fully controlled test conditions.) They can be as simple as a couple of nuts on a threaded rod clamped near the muzzle or they can be nice little things with marked, repeatable adjustments. The world of real accuracy nuts has been greatly changed by the general adoption of these things. It's amazing to see group sizes change (sometimes radically) by just screwing a weight hung on the end of the barrel in and out.

I don't know if tuners are legal under ISSF rules. I also don't know if they're needed. Are 50M pistols sufficiently inaccurate that, at the highest levels of competition, increasing their grouping ability by 0.10" is a worthwhile goal?

It's clear to me that compensators impact accuracy on 50M pistols since they also act as tuners. Whether that impact is positive or negative takes a lot of experimentation to understand. Frankly, since I see no 50M pistol compensators that are easily adujustable, it's my guess that it's a total crap shoot whether they help or hurt accuracy as they are currently implemented.

Surely someone has done some proper testing involving a typical 50M pistol and a proper barrel tuner. If they have, I encourage them to speak up.

Anyway, some pictures:

Great replies.

Ben, that youtube video was amazing. I had heard about the gasses moving faster inside the barrel like Roger mentioned. That video shows it so clearly. I agree with your comments on benefits of using a compensator.

Now I am wondering if those barrel holes in a steyr lp10 are the solution which lets the gasses escape through the barrel and most of what is left is diverted by the compensator. I am guessing a barrel with lots of holes all over without hazarding the barrel strength would be the answer for free pistol where you hope the gasses start escaping as soon as created and as less as possible come out if the barrel.I would like to hear about some research as well.

Well, let's not get too enthusiastic about letting those bad old gasses escape as they are the reason that the projectile is accelerating for the full barrel length of the pistol. Venting near the muzzle doesn't cost much so there's only a little trade-off to get less gas mass impacting the bullet heel.

I think it is possible under some conditions (which may not apply to FP) that the projectile is subsonic but the escaping gases are supersonic and produce a shock wave. A slight reduction in the gas pressure may get it down into the subsonic regime, significantly reducing the effect on the projectile. Ballistics gets complicated quickly and I'm quickly going beyond speculation and into blowing smoke, so I'll just leave it at that.

Ben - I wonder if the shorter length of the pistol vs. rifle barrel makes tuning less of an issue. Despite all the fanatical precisionists out there, I've never seen any sort of tuning mechanism on a pistol. Perhaps because the shorter barrel is be stiffer, ceteris paribus, and has less scope of movement from breech to muzzle?

BTW, nice video. Impressive blow-by - I also wonder if that is a problem or typical.

Roger

So, to get on the topic again: could somebody who owns an fp 10 please measure the distance from the muzzle to the insert or from the fixing screws to the muzzle?
I just want to mount the comp on my toz properly, and the guys at SAM( didnt know that company still exist) are, according to their page, on vacation til september.

And in terms of accuracy:
It's, in my opinion, totally nonsense to put an compensator on a freepistol to improve grouping! None of us mere mortals is built like a vise, and therefore nobody can hold the pistol in a way that could make any improvement visible.
So, what are the benefits then? First of all a steadier sight picture( depending on the mass of the comp), therefore a more confident execution of the shot. And second: because of less recoil an easier follow-through and shot-calling. Depending on the comp, also a longer sight radius( if you can profit from this). Disadvantages: your gun gets heavier at the muzzle.

Barrel harmonics: theres a good article on the issf-page!

So: as long as we can't ( mathematically) integrate the human factor in our calculations, a comp will be nothing more than a barrel weight.
Last year, when batch testing my cm84e with the new compensator installed, i ended up with eley team, with a ten shot group of 11x9 mm at 50 meters. But: my scores are significantly higher with federal 711b, which grouped about the size of a postcard!

flolo wrote:And in terms of accuracy:
It's, in my opinion, totally nonsense to put an compensator on a freepistol to improve grouping!

Once you have won or lost a match by 1 point, or a final by 0.1 of a point you might change your mind.

"Didnt the AP springers have worse accuracy than the PCP APs.", asked John Almighty.

No, if you're referring to the very popular FWB65 series.

@j-team:
Take a look at the olympics, we're not talking rifle prone.
In freepistol nearly everybody shot morini. So, if they all got the same gear ,it for sure doesnt depend on the pistol. If the discipline would been called "50m clamped pistol" you were right, but if you see, especially at worldcups and finals, what happens if the 75 seconds are running, then you can't come to any other conclusion. If you're batch testing ammo, you'll see that with nearly any ammo you get groups that hold the ten-ring. The crap begins just behind the grip!

flolo wrote:@j-team:
Take a look at the olympics, we're not talking rifle prone.

I watched the final. 0.5 points difference between gold and silver. That's after 70 shots.

So, if just one shot in the 60 qualifying shots had been 1mm outside a scoring zone due to poor grouping ammunition, the gold medal is lost.

But, if you are happy with postcard size groups then that's fine.

It' the shooter, not the pistol!

flolo wrote:It' the shooter, not the pistol!

It's a combination of shooter and equipment. Do you think any of those FP finalist from the Olympics would be there using ammo that shot postcard size groups?

Great equipment can't make a crap shooter better, but crap gear can hinder great shooters.

Yeah, but dont you think worldcup-shooters already have(!) the best possible equipment? So it's up to them!

RandomShotz wrote:A slight reduction in the gas pressure may get it down into the subsonic regime, significantly reducing the effect on the projectile. Ballistics gets complicated quickly and I'm quickly going beyond speculation and into blowing smoke, so I'll just leave it at that.

I have some small experience with subsonic pistol accuracy and can't address your question without unfounded speculation. If anecdotes will suffice, though, I can attest to the fact that many pistol shooters have found that certain highly efficient cartridges working in the subsonic range seem to be incredibly easy to make shoot well. It sometimes seems that with a good barrel, you can just put a pinch of any powder behind any bullet in, for example, a 300 Whisper and get breathtakingly good accuracy. In that case, the relative mass of the bullet is so much larger than the powder charge that everything works to minimize the problems with supersonic gasses buffeting the bullet just out of the muzzle. You pose an fascinating question and I hope someone with the instrumentation necessary will look into it.

RandomShotz wrote:I wonder if the shorter length of the pistol vs. rifle barrel makes tuning less of an issue. ... Perhaps because the shorter barrel is ... stiffer ...

Indeed. All else being equal, pistols are more accurate than rifles and shorter barrels are more accurate than longer ones.

I get a kick out of making that statement, flat-out like that, since it seems so wrong to so many people. Back in the late 1970s and early 1980s, pistol silhouette shooters found that their pistols were, on average, so much more accurate than similarly engineered rifles that it wasn't even funny. Rifle shooters thought we were crazy but when you see pistol shooters calmly and consistently shooting snuff boxes (laid flat, so that only the smallest side is visible) off target stands at 200 meters with iron sights, you tend to get the idea that something is going on. At the time, I found rolling 8" plates at 400 yards to be simple enough to be boring.

Eventually, rifle shooters started thinking about harmonics and barrel lengths (and using tuners) and everyone came to realize that if you take a barrel of whatever thickness and cut the length in half, it suddenly becomes much stiffer. Those mini-rifles with 14" barrels are easy to make shoot; the ratio of thickness to length has been so radically altered that they easily achieve stiffness that makes rifle shooters green with envy.

How well does this translate to 50M pistols? I have no idea. Most have relatively thin barrels and I'd dearly love to see someone do up a lightweight prototype tuner and test.

Come to think of it, I have a Hammerli 120 that I could fuss with. I like experimenting and I have a nice, indoor, 100 yard range nearby for testing. I have rings and good pistol scope lying about, unused. I could cobble together a clamp-on tuner with a minimum of effort, though extending testing to include a barrel held in tension (another method to damp barrel vibration) is probably beyond my capabilities.

Instead of trying to formulate a pithy conclusion to this thought, I'll go off and ponder a while. Sometimes I hate becoming really curious about odd things. Surely someone has already run tests like this and published the results, haven't they?

RandomShotz wrote:... video. Impressive blow-by - I also wonder if that is a problem or typical.

I deliberately chose that video because it showed a worst case. The pistol appears to be a service-type weapon where the barrel may not be of the best quality. The projectile is large and may be jacketed, both of which would mitigate against the obturation we expect to create a better bullet-to-bore seal.

I sincerely hope that 50M pistols show this behavior much less or not at all. They get soft lead projectiles and (presumably) the best possible barrels.

An aside: Do any 50M pistol makers choke their barrels? Some of the most accurate rimfire barrels have a small choke in the last 2 or 3 inches before the muzzle. (No, I won't veer off into those long-choked barrels that swage a .22 projectile down to .17 before it exits the muzzle.) There are a variety of ways to help a projectile seal well in the bore and I hope 50M pistol makers use all the best practices in that regard.

I find it endlessly fascinating the way that experience in the shooting sports translates from discipline to discipline. Thanks for your thought-provoking post.

flolo wrote:Barrel harmonics: theres a good article on the issf-page!

Google searches for "harmonics site:issf-sports.org" and "harmonics site:issf-academy.com" turn up no results.

Can you point me to the article? I'd love to read it. TIA for any help.

Didnt find it on the issf site either. It was from one of the former issf-mags
Pm me your email address, i can send you the pdf.
Summarized, its about the invention of a barreltuner, and naming the patent number for further research.