Barrel consistency & chokes

[subscriber]

One might easily reach your conclusion, Ed.  I am still skeptical, and suggest that a happy accident turned into standard practice.  Something that no one wants to change now because it has worked for so long.

By the way, cheap barrels are not the same as garbage barrels.

What we have from Weihrauch is not positive affirmation:  It is like "not guilty", as opposed to innocent.  They did not state that the breech choke improves the system.  They told us that good barrels are important.  If the barrel was good, why do they need to knurl it

I own 7 Weihrauchs, and have given away three others as gifts.  I would not have bought 10 if I though they were junk.

[gloob]

You think any company would read this thread and think what a great idea to jump into the fray and just clear things up a little?

That would be like saying "YES, we support [abortion/right-to-choose]." You would be alienating a huge portion of your potential customer base. Just look how angry some of the members get over this.

[subscriber]

I am surprised that Weihrauch replied at all.

 

[gloob]

" I can't quite rationalize why HW makes the muzzle choke slightly smaller than the breech constriction."

To make sure the pellet that was "rattling down" the larger bore after the "leade constriction" is once again solidly stabilized at the muzzle before release???

Just because the pellet slips easily through the bore doesn't mean it's "rattling." It can slip through the bore without any room to tilt or yaw. And even if it was, the muzzle constriction could be the same size as the breech constriction or even perhaps a couple tenths larger, and the pellet would still get squeezed when it went through the muzzle constriction.

A partial constriction, still in the compression/elastic phase, would be plenty more than enough to stabilize the pellet. There's (seemingly) no need to actually plastically deform and size the pellet smaller at the muzzle.

[nervoustrigger]

Like subscriber, I am surprised they replied at all...even being the non-answer that it is.
 
But I don’t see why an actual answer is presumed to alienate or anger anyone.  They could word it however they want, spin it as a positive for any reason under the sun.  For example even if there is nothing to be said about it benefitting accuracy, all they have to do is say nothing about accuracy and instead say something positive about how it enhances reliability because it reduces the chances of a dry fire or because the barrel won’t work free from the breech block over time.  It’s just not clear to me how saying something positive about their product is a risky move.
 
However the notion that a breech choke is a trade secret is pretty silly.  It is a “feature” any layperson can detect with no special tools or training, and something trivial for any competing company to design an experiment to test it and then incorporate it into their own products if it is found to have sufficient merit.  It is a trade secret somewhat better guarded than the trade secret protecting two-ply toilet paper.

[gloob]

But I don’t see why an actual answer is presumed to alienate or anger anyone.

No matter what they say, some folks are going to suggest HW engineers drink poo water and they're just too lazy to improve. Crosman makes their rifles without any breech constriction, the pellet doesn't flip out when you close the barrel, and they sell these guns for $100. And if you get HW accuracy out of one, you're lucky.

[gloob]

What would happen if you put an older smooth twist barrel on a semi-magnum/magnum sproinger..?

...
The pellet would slow down as it passed through the rifled choke, just as it does with a PCP.  The fact that the muzzle pressure is lower with a springer matters not, if the pellet velocity achieved is the same. ...

In an unchoked barrel, a tight pellet would slow down as soon as the pressure subsided. So instead of slowing down in just last half an inch of crown, the pellet would decelerate with maximum drag for perhaps the last 6+ inches in a 22 or a 25 or a low powered 177. And if you selected a pellet that fit loosely enough to not drag much, then pellet-pellet variation comes into the picture, because the pellet hasn't been consistently sized by the breech constriction. The amount of drag now depends how consistent your pellet is. And even expensive JSB "Exacts" are nowhere near exact.

[gloob]

Your worry about too much friction down the barrel, in the absence of a breech choke is easily addressed:  Start with enough swept volume and enough spring.

This is why rifles like TX200 and Prosport don't need breech choke. They have enough swept volume and spring for the velocity and barrel length, so that the pellet exits while still under significant drive.

Some people might mistake the issues of swaging versus drag. Swaging is more of a momentum check than an energy drain. Example: After swapping my Ruger Explorer spring into my Hatsan Alpha, the pellet didn't budge from the chamber when you fired it. If you slowly increased the piston speed, you'd eventually get it to shoot. And it wouldn't start out at 1 fps. It would either not move from the chamber, or it would exit at a minimum speed. And it would hit that speed, consistently. You could shoot a decent group, just removing the pellets that didn't budge.

The drag steals velocity. In my tight-bored Buckmark, the gun had more than enough power to get the pellet started. But they were exiting at variable speeds.  Some didn't exit, at all. Some dribbled out and hit the floor before making to the target. And some shot out near the full 275 fps.

late edit: The swaging takes a higher peak force, but it's brief. The head of the pellet has a very small contact zone. Maybe a hundredth of an inch. That's why it works more like a momentum check. If you have enough torque, you'll make it over this hill. It'll be so brief, it won't hardly cost you a cent.

The drag from the pellet being under compression (because it's still larger than the bore by as much as a few tenths of thousandths of inches) continues on hundreds of times that long.

more: The Buckmark shows what a difference in accuracy a few tenths of thous pellet size can make at 275 fps, in an unchoked barrel. Pellets from the same tin were doing this (pellets other than just Gamos, to be clear). Group size... fps variation... from zero to infinity. Do you think this kind of pellet drag might affect your HW rifle enough to alter its ability to make 0.4" groups at 50 yards? It shoots a lot faster and harder, but every second of minute of angle matters at 50 yards.

[nced]

" I can't quite rationalize why HW makes the muzzle choke slightly smaller than the breech constriction."

To make sure the pellet that was "rattling down" the larger bore after the "leade constriction" is once again solidly stabilized at the muzzle before release???

Just because the pellet slips easily through the bore doesn't mean it's "rattling." It can slip through the bore without any room to tilt or yaw. And even if it was, the muzzle constriction could be the same size as the breech constriction or even perhaps a couple tenths larger, and the pellet would still get squeezed when it went through the muzzle constriction.

A partial constriction, still in the compression/elastic phase, would be plenty more than enough to stabilize the pellet. There's (seemingly) no need to actually plastically deform and size the pellet smaller at the muzzle.

LOL...."rattling down" is my attempt at humor since some emphasis centers on the FACT that HW bores do "open up a bit" after exiting the pivot block, are again constricted at the muzzle which has been determined by some to be detrimental to usable accuracy.
 
Anywhoo........this "bore map" (attached in a previous post) was determined by pushing a new CPL through the bore of my HW95 with a 4"ish "leade constriction", then 11"ish mid relaxation, and then a 1"ish constriction that was tighter than the "lead constriction".......


Here are a couple "pellet head measures" taken from a CPL pushed only far enough to clear the "leade constriction" and another CPL that was pushed past the "muzzle choke" showing that the CPL head was .03mm smaller than the CPL only pushed past the pivot block constriction. New "die B" CPLs from this die lot marked and dated 1250 count box measured from 4.54mm to 4.56mm with most at 4.55mm so those pellets could be "swaged" as much as .06mm simply by pushing them into the leade. The reasons for such constrictions may be a HW "trade secret" but it exists in all my .177 HW bores. While I've only "slugged" one HW95 barrel I'm guessing that such constricting does exist to some degree ........



 

[subscriber]

In an unchoked barrel, a tight pellet would slow down as soon as the pressure subsided.

No.  The pellet acceleration is reduced as soon as the pressure subsided.  Subside means to diminish.   Air pressure in a springer starts dropping after less than an inch of pellet travel, but is plenty high enough to accelerate the pellet for several more inches.  "Subsided" provides no information about absolute pressure, only that it is less than before and dropping; so your general statement is not very useful.  Subsided does not mean "zero".   

If you meant that if the pressure drops low enough, friction will eventually slow the pellet.  Yes, we knew that.  What happens in a German legal 5.5 FPE springer?  Isn't the pellet slowing down before it reaches the muzzle?  How can Germans possibly shoot those things competitively.  Especially with muzzle chokes?

If a .177 pellet has one pound of friction, all it takes to overcome that is 41 PSI.   From a peak pressure of 1000, 1500, 3000 PSI (pick a number), it takes a lot of barrel length before the pressure will subside to 41 PSI.  So even though pellet acceleration may be feeble half way down the barrel, the pellet is not slowing down.  It is just not accelerating aggressively.

If your "tight pellet" has 2 lb of friction, then it will take 82 PSI to maintain velocity.  Still not very much at all.

By the way; for a .177 airgun to generate 12 FPE, with an average pellet friction of 1 lb, requires the average pressure down the barrel to be 528 PSI, assuming a one foot long barrel.   528 PSI is very much diminished from a peak of perhaps 2000 PSI.  Yet, pellets make it out of the muzzle.

If pellet friction were double, the above 12 FPE springer would require an average air pressure of 569 PSI.   Also very much subsided compared to the peak pressure.

[subscriber]

Ken,

Dry friction is an interesting study.  Static friction is known to be higher than sliding friction.  What is less commonly known is that the transition from static to dynamic friction is not binary.    It is not a linear function, but more of a blended curve between static and dynamic friction - depending on the materials.

Manual transmission clutches are made of materials that are not snatchy as slip approaches zero.  Else, that causes and uncomfortable jerk to the vehicle occupants.

What you experienced with your Buckmark tells me that the primary problem is that it is underpowered.  The pellets are moving so slowly, that any variation in velocity generates a large variation in pellet to bore friction.  Slow pellet bog down, while faster ones slow less.  So, you are seeing a large extreme spread.   This would only affect pellet drop at ranges longer than 5 or 10 yards, but the timing of pellet release relative to the springe jump can cause groups to open up, even up close.

In my opinion, shooting pellets at less than 400 FS is begging to operate in the steep gradient where small velocity differences experience significant differences in friction.  Over 400 FPS, pellet friction is much closer for each 10 FPS variation in velocity.

Someone might argue that their P17 shoots rather well at 350 FPS.  I would say yes, because the SSP powerplant is good at velocity repeatability, and do not cause the platform to jump on the shot.

Even the German 5.5 FPE limit means a 7 grain pellet has a muzzle velocity of just under 600 FPS.  This is why the HW 30 still works well, despite its pellets probably slowing down near the muzzle - because they are moving fast enough in the first place.

Your Buckmark pistol is like a truck with single cylinder engine.  Interesting, but stupid.   Something that has too many aspects against it, to shoot well.  Starting with it being grossly underpowered.   You felt cutting the barrel shorter would improve it.  That may be, because its claim to fame is being a replica firearm.  That, over it being a capable airgun.  It is a novelty; not something with any data points worthy of inclusion in a serious airgun discussion.  Else it is like asking which vehicles land with most velocity, should you drive them off the north rim of the Grand Canyon.   Or if "choking" them on the way down would make a difference

[gloob]

If you meant that if the pressure drops low enough, friction will eventually slow the pellet.  Yes, we knew that.  What happens in a German legal 5.5 FPE springer?  Isn't the pellet slowing down before it reaches the muzzle?  How can Germans possibly shoot those things competitively.  Especially with muzzle chokes?

Because ze Germans know how to make a springer barrel with a proper breech constriction. The pellet doesn't experience significant drag once it's past the breech block. Now go out and buy a Ruger Explorer without any breech choke and see how it shoots. The muzzle choke slows the pellet some, but it's very brief, just what? Half an inch long? Less?

If a .177 pellet has one pound of friction, all it takes to overcome that is 41 PSI.   From a peak pressure of 1000, 1500, 3000 PSI (pick a number), it takes a lot of barrel length before the pressure will subside to 41 PSI.  So even though pellet acceleration may be feeble half way down the barrel, the pellet is not slowing down.  It is just not accelerating aggressively.

If your "tight pellet" has 2 lb of friction, then it will take 82 PSI to maintain velocity.  Still not very much at all.

So take a look at the graph you posted the other week. Reply #37.

https://www.gatewaytoairguns.org/GTA/index.php?topic=201294.20

Notice that the red line drops below 50 PSI at around 12". And it goes to nearly zero by 13". And before it reaches 16" it actually appears to go negative.

By the way, I checked one of my springers, and it took a bit more than 3 lbs to get it to go through the bore, once it has started past the chamber. I could support a 3 lb sledgehammer on the cleaning rod, without the pellet moving. So yeah, that's probably near the right mark.

What you experienced with your Buckmark tells me that the primary problem is that it is underpowered.  The pellets are moving so slowly, that any variation in velocity generates a large variation in pellet to bore friction.  Slow pellet bog down, while faster ones slow less.  So, you are seeing a large extreme spread.   This would only affect pellet drop at ranges longer than 5 or 10 yards, but the timing of pellet release relative to the springe jump can cause groups to open up, even up close.
...
Your Buckmark pistol is like a truck with single cylinder engine.  Interesting, but stupid.   Something that has too many aspects against it, to shoot well.  Starting with it being grossly underpowered.   You felt cutting the barrel shorter would improve it.  That may be, because its claim to fame is being a replica firearm.  That, over it being a capable airgun.  It is a novelty; not something with any data points worthy of inclusion in a serious airgun discussion.  Else it is like asking which vehicles land with most velocity, should you drive them off the north rim of the Grand Canyon.   Or if "choking" them on the way down would make a difference

Well, here's a couple points. The pellets that did shoot ok, they continued to shoot fine through the gun. I collected them from the pellet trap and shot them again. And again. And again. Probably shot some of them 4-5 times. They never got too loose. And they always shot fairly accurately.

But if a pellet got stuck and I pushed it through with a rod and reloaded it? It would get stuck again.

And after shortening the barrel from 6" to 3.2", all 7.4 grain pellets shoot a consistent 270-275 fps out of the gun. So it's not too weak. It works fine, now that it's been "TX200 HC-ized," meaning the barrel has been shortened to remove the dead weight.

[gloob]

A little slower than I remembered it.

Here's a 5 shot string with Econ 2's.

[Imgur]()
[Imgur]()

It won't one-hole. There's too much play in the lockup. But I can consistently snipe a piece of gravel from up to 12 yards away.

[subscriber]

Notice that the red line drops below 50 PSI at around 12". And it goes to nearly zero by 13". And before it reaches 16" it actually appears to go negative.

Ken,

I hope you realize that the red line in the chart you referenced was drawn in by hand, using a mouse curser, as an approximation.  The red line was not calculated.   It was drawn to illustrate a matter of principle.   Therefore no exact extrapolation should be made from it.

You must be the only person who reshoots pellets multiple times, from a rifled barrel, and then manages to achieve good accuracy.   The rhetorical question is, what is "good accuracy"?   10 MOA or 20 MOA?

[gloob]

Reasonable accuracy? See my next post. Hitting a piece of gravel from up to 12 yards. That's not shabby for a 255 fps springer with lot of play in the lockup.

I have 2 rifles shooting 425 fps. My Ruger Explorer (177) and my B5-1 (22) are both averaging 425-430 fps, now. They one-hole at 5 yards and have maybe 8 fps deviation. I'm confident both would hold on a dime to probably at least 20 yards, if I bothered to make a bench rest.  Neither are choked, but they've both been shortened to 6.5". I've held my 460 fps TR-5 to less than a dime at 16 yards with open sights. Also unchoked, but also shortened. Springers can still work fine at low speeds... if they have a breech choke or if the unchoked barrel is the right length.

But my main point in describing shooting the same pellets over and over is that the extreme variation in FPS and POI was not from variation in the powerplant or breech seal. It was 100% dependent on the pellet, itself. Small variations in pellet size created huge differences in speed and accuracy, because the barrel is both unchoked AND, like with many air rifles, the barrel was too long for the velocity.

It is clearly not the extra work of swaging the pellet doing the damage. A pellet that stuck in the last inch or two of the bore and pushed through with a rod was already swaged. But it still stuck on subsequent tries. The drag was 100% responsible for that.

Notice that the red line drops below 50 PSI at around 12". And it goes to nearly zero by 13". And before it reaches 16" it actually appears to go negative.

Ken,

I hope you realize that the red line in the chart you referenced was drawn in by hand, using a mouse curser, as an approximation.  The red line was not calculated.   It was drawn to illustrate a matter of principle.   Therefore no exact extrapolation should be made from it.

You must be the only person who reshoots pellets multiple times, from a rifled barrel, and then manages to achieve good accuracy.   

And as an approximation, you can see it is realistic for the drag to exceed the pressure. I think the reality is even more extreme and abrupt than you drew it. The pressure collapses suddenly, because the superheated quarter cup of compressed air in an HW80 rapidly cools.

what is "good accuracy"?   10 MOA or 20 MOA?

You can believe what you want. I can shoot 3 soft drink cans in a row from 50 yards with a Glock, open sights.

[subscriber]

You can believe what you want. I can shoot 3 soft drink cans in a row from 50 yards with a Glock, open sights.

Offhand?  Why only three in a row?  Can't get five or ten in a row?

There was a time when I could shoot 6 coke cans in a row at 25 yards, offhand with my Super Blackhawk.    That is only 10 MOA.  Now, at 50 yards, I might get half as many cans with my .22 Buckmark.

Next time you are shooting gravel on your driveway, using recycled pellets with your Buckmark, set up some paper targets and shoot some groups.  Then post them here.  It sounds like we should be impressed.

[gloob]

That's 50 yards sitting, two handed grip, arms and gun completely unsupported. Chair only for my @@@, because it's hot out here on Mars.

I'm not going to impress anyone with my air pistol shooting. My 1377 pistols have the potential, but I'm still working on the grips. The Glock 21/20 has a huge grip and a long trigger reach. It just works for me.

The point about the Buckmarks isn't the absolute accuracy. I already mentioned it doesn't lock up, well. Lots of side to side play, and the chisel only closes the breech partway before the o-ring compression stops it. The point is that because it doesn't have a breech constriction, a pellet that is slightly too large will ALWAYS be too large and have high drag all the way down the barrel. No matter if you push it through and load it again. OTOH, if it had a breech constriction in the first two inches of bore that was half a thous smaller than the rest of the bore, I wouldn't have had to cut half the barrel off to get it to shoot.


 

[HectorMedina]

Hello everyone!

Just back from a month of travelling, and catching up on things.

Long thread, with a lot of arguments and some oversights.

I'll comment the following briefly:

1.- Pure lead is a "dead" material. Once compressed there is no appreciable spring back. That is how bullet swaging works , whether jacketed or unjacketed bullets are made, the design of the die takes into account whether the CORE is going to stay put inside the bullet or not, or if the pure lead needs to be swaged to precise @@@-finished dimensions.
"Sizing" cast bullets is NOT an example of swaging pure lead in 90% of the cases, as most knowledgeable long range cast bullet shooters know, for real precision work, you cannot size a cast bullet more than a thou or two.
Pellets are, for all intents and purposes, "pure lead", even the high Sb Premiers have negligible spring back.

2.- The power output of a springer is highly dependent on the "release force" of the pellet in the breech, without some obturation by the pellet, the air inside the compression chamber cannot achieve "operational parameters" of temperature and pressure. Without the temperature buildup, the gun can change operational regimes and loose a lot more power than was expected.
This is the reason to want a tight breech.
Tightness can be overdone. A barrel can be inaccurate with some pellets at certain power level and then suddenly "come alive" at a slightly different power level.
Uneven, inconsistent, barrels will NOT shoot to a match grade acceptable performance no matter what the gunsmith does. They may be great at plinking, but long range precision work is the realm of uniformity and consistency in ALL aspects.

3.- One of the ideas behind the EMS is that by using a barrel that has a smooth/slight interference fit between barrel and breechblock, you do not have the long "breech choke" typical of most breakbarrels. Yes there is a slight tightness because the cylindrical section of the barrel is slightly larger than the hole in the breech block. The fork screw acts like an anti-rotation pin and prevents the barrel from turning in the cavity (which would cause galling and irreparably damage the barrel) when the rear nut is torqued to specs.
For the MOST part, EMS's are coming out of the line with good performance in the accuracy and power departments. Yes there are exceptions, but they can be easily remedied.

4.- Whenever anyone says that a gun is very accurate, you need to demand numbers. It is not the same to shoot at tin cans or clumps of dirt at 12 yards as shooting at a 40 mm's hole 50 meters away.
What is very accurate (and rightly so for his / her needs), may be totally inadequate to someone else. And it is not the same three shots in a once in a blue moon group as it is to shoot 10, 10 shot groups.
To each his own both styles of shooting can be entertaining and fun.

5.- The fact that most shooters use one brand of airguns, does not mean it is the only one to use. If you look at the World's Top Ten scores, you see a more even distribution among all the trophy winners than what the whole collective of shooters would seem to imply.
Out of the trophy/medal winners in Italy by Team USA, I can identify:
3rd overall.- HW97
5th overall.- TX200
10th overall.- Walther LGU
Veterans 2nd place.- D54
So, at some point where the guns (regardless of make or model) have been refined and fitted to the shooter's specific wants and needs, the rest becomes the shooter's experience and capabilities.

Thanks for the read!








HM

[gloob]

Here we go again. So many experts.

If lead is a dead soft material with no compression, then why does a pellet drag in the barrel?

After putting a break barrel with a uniform bore into a vice, I can get a pellet started in the bore and then support a 3 lb sledge hammer with the static friction of said pellet.

This is static. The dynamic friction might be say only 1 lb. But 1 lb of force on a 7.4 grain pellet is 830 g's of deceleration.

If lead had no compression, why did slightly too large pellets get stuck in the bore of the Buckmark? When pushed through and loaded again, they got stuck, again? (In the last inch or two of the 6" barrel, not in the beginning.) But a different pellet out of the same tin that pushes through easier (doesn't fall through) will shoot fine?

[subscriber]

Ken,

Hector is an airgunsmith, an airgun expert, a Field Target champion, and a Diana customer representative.

The reason why an oversized pellet keep dragging down the bore is because the contact length is increased, as the pellet diameter is swaged down.  Swaging down even soft lead takes considerable pressure and generates radial force on the pellet, and on the barrel.  The radial force springs the steel barrel open enough to maintain friction as is passes down the barrel.

If you doubt that contact length has anything to do with friction, push 10 pellets down your barrel, back to back; then measure the force.  They will probably wedge themselves until completely stuck, but then you can cut the barrel shorter.  A minor operation, that according to your experience should improve overall performance.