Barrel consistency & chokes

[Jim-in-UK]

Further to Scott's post, in the 2022 UK National HFT Recoil Championship, the top six places went to the TX200, the seventh to a Prosport, none of which had breech chokes.

[gloob]

The accuracy of the TX200 is not surprising, if you understand why.

The TX200 mk3 HC has a barrel that's way "too short" for its power, when using 8.44 grain pellets. There's no problem with pellet drag, because the 8.44 grain pellets exit while pressures are still high. This rifle is made for accuracy, and that's the direction they went with it. It works.

HW 97K has a fairly short barrel, too. Maybe this particular HW rifle would shoot as good or possibly even better if it had a uniform bore with no choke.

Most all of the other HW's and the majority of other spring guns would likely benefit from a choke, because the pressure is going dwindle while the pellet is still in the bore. It's mostly just the faster rifles in 177 that have barrels approaching as short as these two highly regarded target rifles, when adjusted for the velocity.


So perhaps more people will understand the reason why I have shortened many of my unchoked springer barrels to improve their accuracy, even if they continue to doubt my results. What works for a TX200 HC also works for a cheap, unchoked springer.
   

[subscriber]

The idea that a breech choke prevents pellets from falling out on loading, and that sizing pellets down uniformly so no pellets are loose is a good thing, could be satisfied by electing to make barrels with tighter nominal land and groove diameters.

Hard loading could be addressed by adding a shallow taper leade to the "chamber".
 
Geometry that works as well as this shape probably wears into the more abrupt conventional chamber after shooting many thousands of pellets in dusty outdoor conditions.  Images below showing added diametral taper of 0.002" over 0.08" depth - see red arrows.  Also, "worn" breech cone that would load tight pellets more easily.

What do you do if a given pellet loads too loosely in a give air rifle?  Find a pellet with a larger head diameter.  Starting with an air rifle that has a tighter bore amounts to the same thing.  Then you have hard loading to deal with, unless you cut a more friendly chamber, without it ever making any pellet sloppy at the head or skirt once loaded.

I think the Walther air rifle with the keystone breech block had such a compound taper leade.

[gloob]

You are still missing the point. The choke isn't to ensure that pellets aren't too loose. It's to ensure that pellets are exactly the right size, not too loose AND NOT TOO TIGHT.

Making the entire barrel tighter and adding a more aggressive leade on the chamber only addresses one half of that problem.

[Motorhead]

You are still missing the point. The choke isn't to ensure that pellets aren't too loose. It's to ensure that pellets are exactly the right size, not too loose AND NOT TOO TIGHT.

Making the entire barrel tighter and adding a more aggressive leade on the chamber only addresses one half of that problem.

Now that's ridiculous ...  you really think that ... WOW !!!

Think brother think .... Sizing a pellet down so they have it go into a larger bore that's NOT the same diameter but larger ..... NO that is INCORRECT !!!

[gloob]

We do that all the time in reloading and swaging.

If you push a 0.359" lead bullet through a 0.358" ID sizer, it won't come out to 0.358". It'll be larger by a few tenths. No matter how many hundreds of times you push it through said sizer, it will continue to drag the same amount where you have to force it through, but it will not get any smaller than it did after that first pass. To get the bullet to your desired size, you need to push it through a sizer that is very slightly smaller than your target diameter.

Subscriber's proposal of just making the entire bore smaller and adding a leade, that will just ensure that all pellets end up close but slightly too big, creating maximum drag of full compression fit, along the rest of the bore.

[subscriber]

Ken,  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.

Those in the know want accuracy and consistency over power.  How much force does it take to push a .177 pellet through a Weihrauch barrel at the breech block, once the breech cone has let go?  One pound?   If the remaining barrel is one foot long, then the extra friction of having the rest of the barrel at the same diameter costs you a whole foot.lb.  Start with 13 and you end up with 12.  For some, that is still too much.

If the pellet friction that occurs between breech block and choke is so vexing, what about the work done on the pellet at the muzzle choke?   

If you trust Weihrauch to engineer a perfect breech choke, why do you have an itch to cut off the muzzle choke?  Or doesn't Weihrauch know what they are doing when it comes to choking a barrel?  Surely the air pressure behind the pellet when it reaches the muzzle choke is "too low"; and that can't possibly shoot well. 

My attitude is that it only matters how well the airgun shoots.  With its preferred pellet, and with as wide a variety of pellets as possible.  What configuration achieves that matters less.  If a manufacturer has a lower cost formula to make this happen with less expensive barrels; more power to them. 

Looking at what produces acceptable accuracy, and comparing that to what produces top accuracy is nonetheless interesting.  Apparently the Lothar Walther barrels used by Air Arms work better without a breech choke.  But, they cost a larger proportion of the total airgun cost, and AA airguns cost more than equivalent Weihrauch products.

This discussion is a bit like arguing the ideal piston to bore clearance for performance engines.  More clearance increases power because it reduces friction.  But it also shortens the engine life, before piston slap become apparent and the engine sounds worn out.  At some point, piston yaw on turn around can also affect ring sealing, costing performance.  So, optimizing for one aspect can compromise others.

[Motorhead]

This HOPEFULLY will be my last post on this ....

These are AIR RIFLES and use a Diablo PELLETS which is what guns shoot in the context of this thread.

There points of contact with bores land / groove is a VERY narrow band on head of pellet.  WHY HEAD SIZE is so critical with ALL air guns shooting pellets !!!  And a thin skirt that slightly balloons ideally to help in a compressing seal.

IF THE HEAD OF PELLET is too small for the bore of a barrel IT WILL WOBBLE ( YAW ) being it's head is unsupported while in the larger bore beyond this crazily debated subject of a breech choke.   FACT FACT FACT !!!!
What your suggesting is that if one shot an under size pellet ( Too small a head diameter to get correct rifling support in a non breech choked barrel .... That it is going to shoot well ?  No it won't, never has, never will.  Another FACT supported by years of such shooting with air rifles and diablo pellets world wide.

Done 

[nced]

The idea that a breech choke prevents pellets from falling out on loading, and that sizing pellets down uniformly so no pellets are loose is a good thing, could be satisfied by electing to make barrels with tighter nominal land and groove diameters.

Hard loading could be addressed by adding a shallow taper leade to the "chamber".
 
Geometry that works as well as this shape probably wears into the more abrupt conventional chamber after shooting many thousands of pellets in dusty outdoor conditions.  Images below showing added diametral taper of 0.002" over 0.08" depth - see red arrows.  Also, "worn" breech cone that would load tight pellets more easily.

What do you do if a given pellet loads too loosely in a give air rifle?  Find a pellet with a larger head diameter.  Starting with an air rifle that has a tighter bore amounts to the same thing.  Then you have hard loading to deal with, unless you cut a more friendly chamber, without it ever making any pellet sloppy at the head or skirt once loaded.

I think the Walther air rifle with the keystone breech block had such a compound taper leade.

Problem is that pellets aren't especially consistent, even from the same tin so if the barrel were "set up" to acceptably shoot the "normal size pellet" it will be too loose to acceptably shoot undersized pellets. I always found that the hard lead die lot marked and dated boxed Crosman Premiers shot most accurately from my HW springers. I attributed this to the fact that most CPL head sizes ranged from 4.54mm-4.56mm so all were "swagged down" to a consistent size in the leade when loading. The supposedly 4.52mm JSB Exacts I bought.......not so much because the fit (even in my HW leades) was extremely variable. LOL....I even took the time to measure the heads of 8 tins of Exacts marked 4.52mm and one tin of Exacts marked 4.50mm. Some pellets from the 4.52mm tins had smaller head sizes than those from the 4.50mm tin and visa-versa. Here is a pic of the JSB Exact sort after the measuring..............
  

Anywhoo....I personally don't care about the exact size of a pellet head, only a consistent fit in the leade. The sorted size groups in the pic did indeed fit the HW leade consistently within the size group, the larger size groups fit the R9 leade "almost snug" and the smaller size groups almost fell into the bore without "finger assistance".

[gloob]

This HOPEFULLY will be my last post on this ....

These are AIR RIFLES and use a Diablo PELLETS which is what guns shoot in the context of this thread.

There points of contact with bores land / groove is a VERY narrow band on head of pellet.  WHY HEAD SIZE is so critical with ALL air guns shooting pellets !!!  And a thin skirt that slightly balloons ideally to help in a compressing seal.

IF THE HEAD OF PELLET is too small for the bore of a barrel IT WILL WOBBLE ( YAW ) being it's head is unsupported while in the larger bore beyond this crazily debated subject of a breech choke.   FACT FACT FACT !!!!
What your suggesting is that if one shot an under size pellet ( Too small a head diameter to get correct rifling support in a non breech choked barrel .... That it is going to shoot well ?  No it won't, never has, never will.  Another FACT supported by years of such shooting with air rifles and diablo pellets world wide.

Done 

If you put a precisely machined slug into a precisely honed bore, it can be airtight but with almost no friction. That would be a perfect slip fit. If you held the tube upright and blocked the hole, the slug would stop in the bore on a cushion of air. Then when you unblocked the hole, the slug would fall through, nearly as fast as the same slug dropped freely.

Or... you could take a slug that is slightly larger than the hole, and force it in. If you remove it, the slug is still the same size. The bore is still the same size. It fits, but under compression. That would also be airtight, but the slug would just be stuck there, unless you helped it along with a lot more force than just from gravity.

The added force from being under compression can multiply the amount of drag by a lot.

[subscriber]

Scott makes a very good point:  We are not shooting slugs in break barrel air rifles.
 The short total contact length of a waisted pellet head and skirt can't generate "too much" friction, even if it were a constant snug fit all the way down the barrel.   The yield strength of pure lead at 1000 PSI means the lead will flow, if you start with too a tight fit.  Then you have only a snug fit.

The idea that pellet friction would be constant in a parallel bore does not explain why the bore is coated with lead after a few shots.  If lead wore off the pellet, then the pellet must end up smaller in diameter at the far end of the barrel, because it lost material.  So, I contend that pellets push easier and easier, until you hit the choke.    That is how it feels to me.

Principle:  You can't think of any system as having only one variable.  In theory perhaps, but not in practice.

Ed, I think you are making the point that pellets should always be slightly larger than the land diameter at the head, and larger than groove diameter at the skirt.  You don't want them loose.  As in, the head must always make contact with the lands so it can't yaw.  This might still be possible with a small amount of breech choke, but zero breech choke guarantees it.

I see the chamber and leade as separate from breech block choke.  Chamber cone and leade can be cut to whatever the manufacturer deems to be optimal.  It is the chamber and leade that determine pellet fit on loading.  Obviously, if the land diameter is oversize at the breech, pellet heads will never load straight.  They will tend to load "easy", and fall out, if the barrel is inverted.

Muzzle chokes exist to tolerate variations in pellet diameters and to straighten them out before they leave the muzzle.  The idea that a breech choke will prevent the muzzle choke from working is counter the first statement in this paragraph.  So, the muzzle choke may let you get away with having a breech choke, but the system is not improved by the breech choke. 

Yes, you can have too much or too abrupt a muzzle choke.  In that case, cutting off the muzzle choke may shrink groups; despite a breech choke.  But "better" does not imply very good.  Our standard needs to be "very good"; or something more specific, such as 1 MOA, or half MOA.

How do 10 meter target air rifles get away with shooting "properly" at less than 600 FPS / 5.5 FPE?  Do their barrels have breech chokes?  Or are they short, parallel, with a gentle muzzle choke? 

The AA T200 does pretty well as a cheap 10 meter PCP at 5.5 FPE, despite its 19" long barrel.  The manual states that it has a "conical choke".  I assume this means it is gentle, and not a sharp transition crushed into the barrel in the last inch.

If breech chokes are great, why don't PCP barrels have them too...

[Bayman]

First, I'm not in the camp that believes breech chokes are absolutely necessary. I don't believe that they are necessarily bad either. My long winded posts were to point out that Weihrauchs springers all basically have the same barrel design. They shoot very well as is and I'm better off improving my self and other areas before I start fault finding the barrels.

That said I still believe that the possibility of it being deliberate and beneficial exists. Weihrauch may no longer rule FTT but the stuff is alot better than most.

Subs I believe that PCPs and PBs have a longer dwell time of applied power and that is why a breech choke would have no value for them. Although a waisted pellet has little contact area, the power a piston gun applies to it is considerably very short. The pellet is more burped out than pushed through like PCPs or PBs. Any unnecessary drag might be more detrimental to a piston gun. The breech  choke may be there to create a bigger burp 

As interesting as this stuff is my Weihrauchs all shoot very well. MOA or better when kept to power appropriate ranges. Of all the things, and there's many that can cause accuracy issues with these guns, the barrels are the least of my concerns. The barrels work fine as designed. Sure there's some barrels better than others and there's things you can do to tweak and care for them but the basic design must be sound or none of them would shoot well. Too many of them shoot excellent for the design to be bad. It may not be the best design but it definitely works very well. Too well for me to mess with.
You guys can have fun questioning the design but most of us (myself included) should focus our concerns elsewhere. I truly think that a AA rifle would make me a competitive shooter because of the barrel. Likewise on a day my 97 is running good with the right tin of pellets I might do better with it than a TX 200 with less than perfect pellets for the gun. There's so many other variables that we have better control over.

Be well all

[gloob]

True, I can't quite rationalize why HW makes the muzzle choke slightly smaller than the breech constriction. It obviously works fine, but I can't see how it is necessary to do that. It is possible that "too much" muzzle choke has very little consequences, as long as it is very short, so it just increases the tolerances a little.

In my experience, the muzzle choke is not even necessary, even with a good breech choke.

Yes, a little bit of lead will come off the pellet as it goes down the bore, for a good while. But once the bore is burnished and filled in with lead and lubed with the minute overspray from the compression chamber, this will go down to very little. You can also polish the bore yourself.

You can push a tight pellet through a uniform bore repeatedly, over and over, and the high drag will not lessen, noticeably. Or on your choked barrel, you can push the pellet back and forth through the choke repeatedly. Just don't let it fall out, so the rifling stays in the same grooves. Come back and post about it, when the pellet finally slips easily through the choke without any extra force. I'd like to hear about that.

IOW, I propose the breech choke is the more important one, and the muzzle choke is just for insurance in case the breech choke is too tight or the bore happens to loosen up near the muzzle.

[K.O.]

Me I just can not help but wonder...

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

[subscriber]

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

Assuming the liner is mounted in a tube that is strong enough to act as a cocking lever, I think a smooth twist barrel would shoot well enough.  This, provided the platform can drive JSB pellets at over 900 FPS - which is what FX used to engineer best grouping.  You would still have springer vibration and surge to deal with, so if you can't shoot a springer well due to its jumpy nature, the FX barrel won't help.

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.  The muzzle pressure on a FX PCP driving a 8.4 grain .177 pellet at 900 FPS is not very high either.  You could cut four inches off the barrel and the velocity would probably go up - because the choke is gone.  Obviously the pellet would not spin at all if you did that. 

Smooth twist barrels may have been rifled at 1:16 twist, based on the helix angle impressed in the steel.  But, due to the pellet skidding through the short rifled choke, the actual spin imparted on pellets immerging from smooth twist barrel have been measured at 1:36 to 1:48".  That amount of twist is actually enough to average out aerodynamic anomalies in the pellet.  Without inducing pellet spiraling at long range, as often seen with conventional rifling and twist rates, shooting "too fast".

Consider that FX dropped the original smooth twist barrel liners in favor of ones purpose made for the projectile used.  Now, FX can have any twist rate they want, using a conventional no-skidding in the rifling allowed approach.  So, slower twist liners for pellets, and faster twist for longer heavier slugs.   While FX may have sold their original smooth twist barrels as superior, the rifling method was developed primarily as a cost saving (in my opinion), that happened to work really well with specific pellets, at higher speeds. 

Now, FX has a low cost fully rifled liner manufacturing method, that provides more certainty over the projectile's actual spin rate, so that is what they use, exclusively.

[nced]

True, I can't quite rationalize why HW makes the muzzle choke slightly smaller than the breech constriction. It obviously works fine, but I can't see how it is necessary to do that. It is possible that "too much" muzzle choke has very little consequences, as long as it is very short, so it just increases the tolerances a little.

In my experience, the muzzle choke is not even necessary, even with a good breech choke.

Yes, a little bit of lead will come off the pellet as it goes down the bore, for a good while. But once the bore is burnished and filled in with lead and lubed with the minute overspray from the compression chamber, this will go down to very little. You can also polish the bore yourself.

You can push a tight pellet through a uniform bore repeatedly, over and over, and the high drag will not lessen, noticeably. Or on your choked barrel, you can push the pellet back and forth through the choke repeatedly. Just don't let it fall out, so the rifling stays in the same grooves. Come back and post about it, when the pellet finally slips easily through the choke without any extra force. I'd like to hear about that.

IOW, I propose the breech choke is the more important one, and the muzzle choke is just for insurance in case the breech choke is too tight or the bore happens to loosen up near the muzzle.

" 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???

Anywhoo, when I home chopped and choked a .177 R1 barrel used to replace the .20 R9 barrel I made sure the tightest part of the bore was at the muzzle after adding a choke. This was determined by pushing a new pellet from leade to exiting the muzzle using a .177 cal cleaning rod. While the R1 barrel home choke was the tightest constriction in the bore I did notice that my home choke wasn't as tight as a HW factory choke. Anywhoo....the R9 was very accurate with the home chopped and choked barrel as these two 50 yard 5 shot groups show  (shot sitting on a bucket resting the gun on cross sticks)...........

Anywhoo.....none of the bore constrictions in the chopped and choked R1 barrel affected the accuracy as far as I can tell when shooting "bucket and sticks" like this........

[subscriber]

Weihrauch replied to my query.  See screen capture of their email to me below.

I emailed them back with a follow up question.  Second attachment.

[nced]

Weihrauch replied to my query.  See screen capture of their email to me below.

I emailed them back with a follow up question.  Second attachment.

LOL.....now that clears up what we already know but doesn't completely address the actual question!

[subscriber]

It is a trade secret...

[nced]

It is a trade secret...

Well, that seems to indicate that the constriction is indeed "an intentional secret" and not just a function of HW springers being fitted with "garbage barrels".

Anywhoo, all of the dozen or so HW springers I've owned had "leade constrictions" and all shot a "proper fitting" die lot marked and dated boxed Crosman Premier into a 1/2"ctc (or less) "bucket and sticks" group at 30 yards after an initial bore clean and a couple dozen "seasoning shots".

Just like the Rekord trigger is a fine "sporter trigger" and not a true "match trigger", the HW95 and my other HW springers were/are fine "sporter springers" but not true "match springers" like the FWB300 that was triple the price. LOL....I'm perfectly content with my HW springers with "garbage barrels" when I can shoot consistent "minute of squirrel head" sub 1" ctc "bucket and sticks" groups at 50 yards!