Kral Puncher Auto

[Racing]

Yeah well, this turned awkward..
Cause i ordered a 25cal gun and had a 22cal gun delivered.
Bought used as the only new ones in stock were 22cal ones.

Well, F it. It´s here at least. But.. with issues. It was used right, and someone had truly "leaned into" this one previous no doubt.



Have to hand it to Kral though. It´s a lovely gun no doubt.

To be clear right off the bat though.. Auto as in SEMI auto. Full auto guns are of absoltely zero interest to me. The purpose of shooting is to hit what you´re aiming at and i don´t care if the gun in case is a "no recoil PCP"..
A semi as it leaves that you can stay on target. Indeed the 12 shots of the mag can be dumped as fast as you can pull the trigger, but again.. to what avail?



Indeed. In black n white. Well.. Whatever. First thing i did though was rip the piece apart. For several reasons, as this thing turned out to have issues but mainly to see how Kral has handled that there with it being a semi auto gun, in essence being a Kral Puncher from the bottom up - they all share loads of build steps and features.

The gun sports a shroud right, as you can see. Now. Point here is that this shroud is indeed a shroud but it´s also the housing for a rather large aluminium "piston" that rides the outside of the barrel, being sealed off vs the shroud with what strikes at least me as a teflon ring. All good.
Up ahead of that piston per usual is that "shroud deflector setup. Ie; an adapter of sorts that seals off vs the shroud tube and carries in this case 4 rather large ports to deflect air into the shroud tube.
Or in this particular case.. pressure and volume vs that aluminium piston.

So. The other end of said piston resides a spring that rides the outside of the barrel as well and that spring sits between said piston and the receiver of the gun, excerting "return pressure" as gas pressure bleeds off.

At the very end of the aluminium piston there´s a threaded rod that runs the length of the receiver and actuates a sort of "slave piston" that is coupled to the bolt and.. the hammer.

Now. Someone had leaned into this gun alright cause that rod had been bent to hell and back and straightened. Numerous times making it look like a damn S.
The slave piston and bolt are linked via a pin and the absolute end of this pin runs the hammer... and that pin end...



..no doubt had been bottomed out a time or two. Explaining the bent rod too...

So apart from a number of other small jobs i turned a new such pin out of hardened steel (an old torx bit that i annealed and cut to size on the lathe before rehardening the thing again).



Uhu. A "minor" difference in protrusion to say the least. So.. that covered. I thought.

As i ripped the thing apart, these piece of kit i believe are claimed around the 40J mark stock, i about routinely opened various passages up while at it. Stock diameter being approx 3,5mm for the most part now ended up at 5,5mm.. which sure made for a difference, not all of it good as things turned out...

Anyways.



Kral being Turkish it only comes natural, also seeing their price point, to compare them to Hatsan for instance. In comparsion it´s like comparing ballet and brutal disco dancing approx. Kral in case carries NONE of that "harshness" and lack of fit of a Hatsan. Zero. This thing is not only well designed it´s also well put together.
Or..?
On a general whole, yes it it. More on that though..



Capacity of that there is a roomy 425cc´s. Limited to 200 bar by all means but still.. In the case of an aluminium tank better take notice of that maximum pressure however.



Uhu. Comes with a thread protector but.. you guessed it. 1/2" UNF. No extras or similar BS, it´s there from the onset.



"Scope rail" in turn is the typical Turkish solution. In other words a dual purpose one, both dovetail and Picatinny.



Shroud tube sure is of ample dimensions. We´ll get to that however...



Bolt stroke, as you can see, rather short - per usual for semi or auto guns.

So.
The shroud does help out a bit as far as muffling report no doubt. However, have in mind that the major parts of its innards are filled with a piston and so on.
40J.
Well. What that hands is that as i upped performance of the gun that auto load setup bottoms out it isn´t even funny, which AGAIN sheared that pin..
*sigh*.
Yeah well, i could have figured that out didn´t i?
But. The thing here is.. This is IMO a really lovely gun. However, we see pill weights and performance climb on a daily basis for PCP´s and this gun, in stock form, is basically dead set to running them 40J.
Why?

Cause what i plan here is to drill a number of holes in from the front of that there piston for the auto load thereby becoming able to bleed off what i don´t need as far as pressure and volume. This brings that by threading the holes i drill i´m able to close or open up them holes as i see fit, and i truly wonder, with a capital W, why Kral has opted to sell this design short by limiting it to said 40J.?
I don´t get it.
In turn, but drilling them holes and by bleeding of excess air into the shroud the gun will just become more quiet while at it. A win-win if ever.

Most of my 22´s are running shy of the 100J mark and i expect no less out of this Kral once sorted. Or more to the point, IF Kral would have set this gun up to be adjustable as far as this they could sure have made it work for instance at 12lbs too. What gives? Cause in contrast to where i live Britain sure is market enough? I mean, you guys buy PCP´s in comparsion to us guys like they were going out of style, so why not dial that setup in for 12lbs too? Or 7,5J for the German market?
I just don´t get it?

Cause as far as i´m concerned, again, lovely lovely gun.

Welp. As i then put the thing back together and pressurized it of course the valve leaked like crazy too. Apart.. and indeed the sealing surface out of POM or PEEK from the looks of it sure had seen better days why i handed it a shim cut where after i lapped the thing with the drill..
In turn the return spring for it stock is nothing short of insanely stiff why that was replaced with a WAY softer piece too.

Barrel in turn was handed a fresh muzzle crown and had its chamber and forcing cone polished out while on the lathe too.

So where i´m at is to balance that auto load out. Yeah, that and... the trigger.

WHAT IS IT WITH THE TURKS AND TRIGGERS OUT THE FACTORY DOOR?!?
Listen to this. There´s holes drilled in both the trigger and sear for adjustment grub screws. Hell, them holes are even threaded. But for some insane reason the actual grub screw were missing, handing me a trigger out of the box that was like trying to move a damn WALL!.
Two grub screws later and.. coarse adjustment we at least have something to play with. Absolutely certain that the trigger can be turned "ok" at least.

So?
My opinion on the gun? Neat piece of kit. WAY ahead of any Hatsan, that much is for sure but per usual.. a platform to build on. I hope and plan for this to come together asap, although.. no rush.
Need to adress that "balance" deal there and take it from there. In short, drill the damn holes for starters and nevermind if the gun won´t cycle, that can be done manual and hole after hole closed up until it starts to run as intended.
Yes.
Even at 100J (or 80 for that matter).

Across the FX radar it told me 25,4´s @ approx just shy of 900 already as is, and it´s a starting point i guess. Truth be told though it wouldn´t be a half bad idea with some sort of buffer there between the spring and the receiver to keep from breaking more of them pins evaluating what´s needed to make it run flawless.

But.. nah. We´ll get there.

Stay tuned.

[Shed tuner]

Interesting idea for the cycling mechanism.. gas piston... I guess they borrowed that from their firearms team

Can you also restrict the amount of air that enters the chamber to activate the piston ? Whilst bleeding it off ito the shroud is a good idea, having less getting there in the first place might be better / easier ? Or a combination of both apporaches ?

[rapidresponse1]

found that a interesting read

[Racing]

Thx guys!



A picture..and a thousand words. There you go.



To cover all bases i turned two spacers all in all. One out of aluminium and one plastic (POM). As it turned out none of them are needed however.
The setup of course needs the various pts to move freely and after a bit of wiggling around they do. The auto reload setup can basically, sans getting the probe through the o-ring of the barrel, be moved around with one finger.
Something that could NOT be said as i tore the thing apart..



Cover all bases. Indeed. I all in all drilled three holes into the front of that piston, of 2.5mm (0,1"). Truth be told though that in combination with that i drilled into the end of the shroud..a bit over the top. I´ve played around with it a bit today and where i´m currently at the auto reload happens like maybe 50% of the time.
Not good enough BUT.. and that´s a MAJOR but, this is depending on muzzle energy. As it turns out the probe o-ring was missing and as i installed an at least semi fitting one muzzle speed jumped a tad to 930fps. This then using 25,4 grain pills. In short where we´re at this thing is pushing like 65 Joules.
Certainly enough for rats and.. there´s a sort of side kick to it cause from these first tests DAMN this thing is accurate!

What i´m saying is that this needs to be evaluated further, and that no doubt starts with a bunch of fresh o-rings tomorrow for the probe to seal.



Uhu. So those spacers i turned for use out rear, no need. Right. That spring in the picture btw is the systems return spring. Not an overly stiff jobbie exactly..



The vent holes for the shroud. Seems that amounted to.. nothing too. Gun got a little more silent in operation though. Fit of that piston vs the barrel is so-so at best. To the point where i can´t but wonder how much gas is let to pass down that shroud/piston. Lose in the bore, yes Sir.



As such i´ve even gotten to shoot the damn thing a little. Trigger of it i set out to adjust, but that setup needs a more in depth approach to be all it can be. As is it´s JUST bearable, and that´s it.
That said though i can´t detract from the fact that the piece shoots like a champ. It really does, why it´s going to be interesting to see what happens and muzzle speeds approach like 1000fps+.

[Racing]

Uhu. WAY better. Considering adding a tad more red though ("cherry").

What´s more i got to have a look at the trigger assy. Polished the surfaces and reduced the back cut a tad. WAY WAY WAY better but far from what i expect so.. will revisit that.

[Racing]

...still pushing forward...





Given daylight it comes out a little better i´d say. The process of handing the stock that linseed/turpentine mix is a slow one, but hands results down the line and i´m very aware of that.



On this gun the shroud isn´t really used as a shroud but more so a "cylinder" for the reload piston to run in. Now. That got me thinking and as that piston carries two defined ends i said to myself that i ought to at least try..
So i cut a fresh piston pin groove at the REAR block of the piston this time on the lathe and with a rather anal approach as far as dimensions.



Being unsure as to how that air pillar would work on said piston.. but no need to worry as it turns out. Thus i cut the front block entirely off, the piece now run on the rear, with piston ring, piece only. The entity of the tube left in place though.



Per previous i had drilled a few "decompression" holes into the rear of the shroud and what this stunt brought was a shroud.. as in how WE regard it. Dual duty now in short.
Worked flawless to be blunt, and no.. no appreciable difference in reaction time to the piston. Now just a WAY more silent gun in operation.



Here´s one that´s come to make me wonder a tad though. First up, for some reason Kral has designed this valve with a 90deg seat. It even sports like a ledge/dimple for the plastic of the poppet to seal against.
All good and dandy, and the through hole i believe to be around the 7mm mark, which SHOULD be ample.
However.
Flow across them 90 deg is anything but cause what´ll happen is that the flow will "see" the hole in case way smaller than it is due flow restrictions. There´s a REASON "everybody" else runs 45deg seats..
What´s more.
The stock untouched head of the poppet is absolutely massive, to what avail i have NO idea. The pressure on that poppet is a direct function of area - within the pressurized cylinder, why i cut it down to approx 8,7mm diameter.
But.
Nah.
I´m going to put that valve on the lathe and bring an end mill out to fab a 45deg seat and then mod the poppet accordingly. I will in fact do ONLY that and we can see where we touch down on the two chronos i use. The FX radar and the LabRadar.
Currently, where we´re at, it´s shooting 25,4´s @ approx 930-940fps.
Seeing what´s been done to the valve block that number should no doubt be higher and as the idea here is to toss a regulator and a plenum at it down the road that brings that i need to get the speeds up there as with the reg and plenum it´s all downhill from THAT arrived upon number.



..and yes. She WILL shoot alright. Disregard the two "bouncers", they´re off of an adjacent target since previous. Thing here is that that hole there is 4 clips worth.
Ie; 48 shots.
So yeah. She shoots like a champ already and what´s more it seems she doesn´t really care if pellets or slugs. What i mainly use as fudder is either JSB 25,4 pellets or 25,4 Knockouts.
What´s more, yes. That´s in semi auto mode. So.. she works as intended and works well.. Distance is a mere 20 meters and indoors but.. shows promise no doubt.

[Shed tuner]

that shroud mod makes a lot of sense - nearly the whole shroud volume works now. I guess they had the sealing at the front to work at lower powers / lower air pressure & volume being vented into the shroud.

With the much higher power that you have, it allows for the option to have the rear seal only, and still have enough pressure to cycle.

BTW The fact that the vented air blast is doing some mechanical work shoudl actually make it quieter than a passive shroud of the same volume - are you seeing that ? hard without a direct comparison I know...

JB

[Racing]

Haven´t really thought about it that way but can´t but agree.

What i CAN attest to is that the gun turned much more quiet after placing the piston ring at the rear block, so i guess there´s merit to it.

On performance.



This is the SSG setup i made for this Kral (SSG= secured spring guide). Point being that it´s not really a performance mod if not so used why it sure can be a worthwhile setup for a 12 pound gun too, to save air primarily in that case.
None the less, simple yet very effective.
With a SSG you are free to alter spring-s for different spring force, able to adjust preload, able to set hammer free flight and what not. In this case all steel and based on a M5 screw. In short overkill for the app.
As you compress the spring that elongated M5 needs somewhere to go though why the stock hammer spring adjuster screw (which is still active by any means) has been drilled out. Pin thus expands rearwards the receiver why i´ve drilled into the stock to hand it room doing so.
Nothing that can be seen without lifting the hardparts of the gun out of there though so, no harm no foul.



Like stated Kral for some reason arrived on using a 90deg seat. Here the valve body already drilled out with a 12mm end mill on the lathe, and adjacent to it a new seat out of a rather specific acetal plastic.
I decided against that solution though, arriving on that i´d rather have the acetal riding the poppet why i made a seat out of very tough bearing bronze. What us guys call JM-7.
Installed with two comp and pressfit.

The "new" 45deg sealing surface than cut into the new valve seat out of bronze.



Poppet is two piece. The "head" unbolts as it´s threaded to the spindle. Brings that it´s very very easy fabbing a seat to ride that poppet, and be able to torq it down as you see fit (within reason of course).
No matter... what were the gains, if any?

Well. There were but less than i expected. Have to say. I tried a few different amounts of protrusion for said spindle (ie; what the hammer smacks as it comes rushing to open the valve). At first 6mm and that was very close in performance to 5mm, which is stock, but as i progressed to 4mm of pin sticking out i saw muzzle speeds drop.
At 5 and 6mm though with the exact same setup as before (simple to set with a SSG) i saw increases to the note of 10-15fps. In my book that means that the mod was NOT worthwhile, i expected greater benefits no doubt.
This was not the case though why.. it is what it is.
Then again a 45 deg seat setup sure can´t hurt why.. now it´s there right.? But. Truth of the matter, where i´m at right now, is that the gun simply screams for more hammer spring.
At this point it IS that simple.

Of course i could always come to dwell on a "balanced valve", but truth be told that´s overdoing it for this gun as i regard it. Thus.. The stock hammer/mainspring is wound on 1,0mm diameter wire and i guess what i´m going to ask for are different SPRINGS. As in plural.
Point here being that we´ve got the company that delivers most of the springs for FX here in town and they basically manufacture what´s needed in house.
A spring carries what we call a K value. This K value is the spring constant, which is what needs to differ here. Due that what affects spring outcome is diameter, No of coils per length and wire diameter as well as coefficient.
The neat thing about "Got springs" (companys name) is that they also house all that´s needed as far as tools to check what the original spring measures and thus what springs they carry that might be an alternative.

But. As far as i see it that´s where we´re at. Need to pick the valve apart again and add material to the spindle of the poppet and beleive i at that point will run with 6mm of protrusion.
As much as a stiffer spring will accelerate harder it also brings that more force is available at point of impact. In short not only will the poppet open up faster, it will do so further as well.
..and this can in turn all be balanced off via the SSG.

[eyebull]

In the original SSG thread on the yellow forum they were quantifying overall efficiency in an interesting way, by measuring the FPE per shot and adding up the total for all shots. So 15 FPE per shot for 20 shots would be 300 FPE per fill. If you toned down the spring and then got 14 FPE for 30 shots, you would be getting 420 FPE per fill so considerably more efficient.

I thought this was a good way to ascertain whether overall efficiency had been improved when FPE for individual shots may vary when you are trying out different spring set ups.

[Racing]

Have to agree with you on that one.
Reasonable and to the point.

This Kral has me a tad stomped tho.

In the search for more power i feel like i´ve tossed the entire book at it and it simply doesn´t respond as should.
Where i´m at, mod wise, this thing should be super sonic in my experience and.. it´s anything but. Something is eluding me here, it´s that simple and i need to have a sit to take this from A to B to get a grip on it.

Like i´ve mentioned above the only real peculiarity of the Kral is that the transfer passage within the valve block is offset. This means that both the valve exhaust port and the barrel transfer port have to be too, and.. yep. Have checked that in the most anal fashion thinkable.



Albeit it carries "the old" style poppet and these have been known to break it´s quite obvious to me at least that the reason for this is two fold. First up the dead stop of a 90deg shutter angle (vs a for insance 45deg where the poppet actually "takes a seat", which of course cushions the event) and second of all the use of a "top hat" (which is threaded on for these early style valves) that´s so pointlessly large in both diameter and weight that..
Nah.
Anyways.
That valve.. what´s left of it is the body really. As you can see there´s a "golden" piece in there, which is the 45deg angle seat out of JM-7 bearing bronze by me. The innards of the body/housing has been cut to 14.00mm flat now with an end mill on the lathe and that seat is press fit to the tune of approx 3/100mm as well as being installed with set glue.

Through hole for the poppet opening is now a full 8mm and the "pocket" below the seat just ahead of the exhaust port a full 8mm diameter too. Exhaust port in turn, 7mm flat.
Then the transfer passage within the valve block which is 6.5mm... Issue with that is that for this auto that brings that you run into the channel for the control rod, why this has been sleeved. Of course.



Just for "belt & suspenders" i handed the bottle fitting a go over too. The through hole is now thus 8mm flat and them smaller exhaust ports have been opened up from 3.5mm each to 5mm each.
My point being that i want "surplus" capacity available (idea is for a reg and plenum down the line as noted)



This also brought that i opened up the channel of the actual block, between the bottle and the valve. Now a full 8mm diameter, which ment that i "broke into water". Ie; the passage came to break through the wall to the world in general, and that of course needed to be handled. Yes, i own an AC TIG welder too, and in this case the parent material is rather poor quality cast aluminium that´s been anodized.. Brought that i had to "bondo" the piece, thus the looks of the weld.
No matter. Now it´s opened up as far as it´ll go and solid as far as integrity.

That done i again sat down to try the piece (hardpart of it only) using the FX radar. Remember that i´ve got a SSG installed and this for the moment holds a slightly tougher mainspring too.
No dice.
Doesn´t matter what the F ever i do, 950fps for those 25,4´s. It´s getting frustrating and it IS me that´s at fault here. I´m clearly missing something..
Dimensions involved here is such that the gun should be spitting them 25,4´s super sonic by now, or at least close to. I´m an EASY 100fps short..
Nope.
No leaks. It´s just like the piece stonewalls.

Due that offset transfer channel in turn i was adviced to "scallop" port the inlet for the barrel, which i did. Amounted to zip that too. Zero.

Poppet pin protrusion is now 6,3mm (1/4"). Which should be plenty. Whic IS plenty. But gun simply won´t take to it. Frustrated? Me? Naaaah... what´d make ya think that?
DOH!

I am missing something here. Most likely something obvious. I´m thus officially open to suggestions boys.

[Shed tuner]

we do like a challenge...

So where might the restrictions be hiding ?
Inside the bottle adapter - or it that 8m all the way through into the voide of the bottle with no restrictions ?
Is anything misaligning (valve / block / transfer port / barrel port) on assembly ?
Valve return spring too strong ?
Valve stem bottoming out (against return spring or some other stop) reducing valve opening ? Myabe mark the stem with some candle smoke and see how far it's being depressed when firing under pressure.
Valve duration too short - hammer too light ?
Hammer fouling on something stopping it fully depressing the valve stem ?

HTH - JB

[eyebull]

How about temporarily blocking the bleed off for the piston that cycles the action, to see how much pressure you're losing there?

[Shed tuner]

How about temporarily blocking the bleed off for the piston that cycles the action, to see how much pressure you're losing there?

maybe I misunderstood, but I thought there was no bleed - it just uses the muzzle blast ?

[eyebull]

maybe I misunderstood, but I thought there was no bleed - it just uses the muzzle blast ?

Reading back it seems you're right, bit of an odd setup and not well suited to running at peak efficiency if it relies solely on excess muzzle blast.

[Racing]

Right.
So frustrated it was about making me climb the proverbial wall and then.... this finally saw its solution.

Before that though i´ve ripped it all apart and put it back together like 10 times trying to get a grasp on what´s going on and.. solution was there all the time. Right in front of me.

As the intent here is to "ride the jagged edge" as the time comes ports have been opened up beyond sanity even. Valve and poppet reworked completely and what not.. So this thing´ll flow some air alright.

I´ve worked on the hammer too. Making the spring pocket deeper in the end and the hammer lighter. Started out at 68 grams, but seeing the rather limited stretch allowed for acceleration of it them 68 struck me as rather.. much.
The stock spring in turn, 8,5mm outer diameter and wound on 1.0mm wire. Spring is set in a SSG setup. Played around with some other, similar, springs but..
This thing had me beat. Until i opened the pocket of that hammer up to take 10mm dia springs and shoved an eeeeeeeever so slightly stiffer spring in there.
Bingo.
Still just about as light to cock, but muzzle speeds jumped an easy 60fps without even trying. Where i´m at at the moment that hammer weighs in at 50 grams flat, and truth be told i´m where i´m at now real pleased with that being done.
If we set speed vs weight speed will, as per the pills we use, win every time. So in short this was a matter of lack of hammer acceleration in short.

We´ve got the place that delivers all the springs for FX here in town so due that above there i´m going to pay them a visit come tomorrow. Since previous i´ve bought a few Impact springs from them for use as hammer springs on old French Mle 1866 Chassepot rifles.
Thus i´m all to aware that the spring i´ve got in mind, which is the stock piece for the "power plenum" upgrade, is wound on a 1,4mm wire and at 10mm outer.

Seeing the porting work done and so on i now honestly believe we´ll get this thing super sonic at will, which i have no interest in what so ever. Thus this thing will get tuned to "lick the wall" with 25,4´s for starters.
Then it´s regulator order time and as that piece shows i´m going to fab an approx 80cc plenum for it too. From thereon out in turn i hope i´ll "survive" for the most part on the porting already done as the idea here is to start shoving 34 grain 22cal pills down the throat of it.

Have actually ordered a box of the ZA made "Javelins" for my 22´s.. we´ll see where that takes me.

But. Finally arrived. Been a long time coming it feels like so.. kind of sweet "victory" to me this cause DAMN this has had me climbing the walls at the shop!
I´ll tell ya that much!

All well that ends well though.