Accuracy...differences?

[Racing]

K guys.
So i´m currently working on, and developing, this Reximex Throne Gen 2.



Slug use primarily and in doing so it really made me lift my eyebrows.
Why?
Cause of the massive differences in accuracy from very very minute differences in pill diameter.
It´s a 22 right and i guess the "standard" is 25,4 grainers and what´s used is regular JSB Knockouts.

Using 0,217" pills i get decent results on target, while using 216"s i don´t even HIT the d*mn thing 
I mean, to the letter.
At a range of 10 meters even i don´t.

Barrel has been "modified" for slug use (read - have had the major part of its choke cut off. Minute amounts remain though.)

Now. I shoot mainly powder burners and doing so am well aware of the importance of "slugging" barrels, and always do. Altough the 216´s barely gets prints from the rifling, it DOES do it..

Yes. Muzzle has had a fresh crown cut, polished and the full 9 yards - all according to the book, and what´s more this is certainly not my first time either.

Run them at approx 1020fps but due what i experienced i´ve actually done the testing from approx 650fps up, and the result remains.

Mark. I´d be puzzled for ANY pill to behave this bad, let alone the exact same design and weight. Have tried the barrel using 218" Patriot Javelins too, with results on par with the 217" Knock outs.

Ditto. If i use pellets it of course won´t print as would it with the choke intact, but it at least prints - and decent at that. This ranging from 18 grain ones to 33,9 grain ones.

How can the end result vary to THIS extent?

[nervoustrigger]

A couple of possibilities that come to mind:
 
1.  The faint rifling marks on the 0.216” diameter slugs…is that an observation from pushing them through?  If so, it may be that firing produces something different, perhaps accelerating it so forcefully that it is skidding over the rifling and failing to pick up the spin.  ->  Try recovering one fired into water or a soft medium and inspect the rifling marks.
2.  Could be getting enough blowby through the grooves that the turbulent air is upsetting the slug at the critical instant it is released from the crown.
 
And of course it could be some of both….or neither

[Racing]

The latter seems reasonable at least.

Airgun pills are normally made out of dead soft lead correct, why I wonder is there any obturation what so ever going on at the pressures involved?
I guess this would also be a matter of how stiff the pill is to shove through the rifling and of course pill weight will have an effect as well?

[ranchibi]

Jesper, finding the slug your barrel "likes" (contacts the lands properly for optimal spin stabilization) is usually the most time consuming part as well as the speed it needs as well as weight and length. If you can, I would start with an NSA sample pack of .22. Start with speeds of around 950fps for each slug weight and diameter, you will see right away which ones your barrel likes, they will group better, then tune from there. Once you find the diameter, weight and length of slug your barrel prefers, you can then try other brands like Griffin, AVS, FX...ETC....have fun!

[nervoustrigger]

JSB uses soft lead, yes.  However unless they’ve changed something about the base geometry, the hollow is much too shallow and thick to promote obturation at such modest pressure which is why I questioned the possibility of it skidding across the rifling.  Generally I would not expect a true 0.216” to be capable of skidding in most bores but some choked barrels have fairly large nominal dimensions.  For example LW’s spec is 0.215” land, 0.221 groove.

[Racing]

All to aware and can´t but agree.

I just found it..kind of flabbergasted by that massive difference. I mean, let´s say the 217´s hand us a MOA group. I could then see as a worst case scenario that them 216´s would end up say at 4 MOA.
But where we´re at the boolits miss the entire target.

FWIW in turn said target is of course air rifle ones (ie - small ones) but there´s "three in a row" each direction.

Many a PCP hands me downright fantastic results.



This for instance is the performance of a Hatsan Nova i handed the full 9, a full clip worth (10 pcs) @ 20 meters. The Throne will hand me approx double that, and on occasion then some, using said Knock out slugs.

Yes, i use chronos when tuning. Both an FX "brick" and in turn a LabRadar. As i do work as sorts of a shade tree smith around here that focus on black power arms the LabRadar became a no brainer to be honest. Thus no Magneto speed or similar, the LabRadar does all i could ask for.
However the FX brick is way more handy. To note though is that i NEVER hang it off of the barrel, stand alone only..

As for practical accuracy i guess we can go on an on but the fact remains and that´s that the exact same boolit, in essence, with a difference of a thousand of an inch makes for all the difference in the world.
As i shoot and develop both loads and guns for ppl in general i´m by no means a newcomer to it, but this.. never seen the likes of.

Anyways.
I tried her out using 218´s and that indeed handed me even tighter groups, so that she seems to crave the larger fudder i guess is arrived on.
Going to order a bunch of the "newer" generation slugs by H&N as well as Patriot Javelins and what not. The Knock outs seems to be available as 218 as well so actually ordered three tins worth earlier today.

Thing is though that this particular gun is sorts of a mule to me. Idea is to push on it performance wise to see how far it´ll go, for a more "simple" setup than for instance the Impact and what not.
Already as is i´m pushing 90 Joules but have no intent what so ever so stop at that. So i fabbed a fresh much larger plenum for the unit out of seamless high pressure tubing.



Uhu. Thus far only tacked together as there´s more to come within the plenum as far as surfaces for sealing and what not. The thing is though, the offset is there to make the thing fit the unit within reason and it´ll hand me approx 100cc´s worth, vs the stock 34cc´s.
From what i´ve been told there´s a few guys that have gone down this path with the Throne, albeit the "Gen 1" version, telling real good results from it.

Thus i expect to touch down using pills ranging somewhere between 30 and 40 grains, most likely 34´s all said and done.
That said it then of course pays dividends knowing what THIS particular barrel seems to crave as far as dimensions.

Different. But hey..
Reximex Throne is an offspin on the Kral brand from what i´ve understood and in all honesty here in Europe the Turkish made PCP´s... vary in Q.
Just sorted a BT-65 in 22cal for a cust that had a barrel that turned out to lack choking, at all. That kind of set the scene i guess, and we came to a rest using slugs for fudder, and then for starters running at approx 850fps, which handed at least decent accuracy all said and done. Of COURSE to be improved upon.
I guess what i´m saying is that i´m all to aware that barrels are individuals and should be regarded as such.

[customcutter]

I'm wondering if it's possible that the slugs are spiraling, or even turning sideways.  Is it possible to use a larger piece of paper or cardboard to see how they are printing?  Are they grouping off of the target you have, or a shotgun pattern?

[Racing]

JSB uses soft lead, yes.  However unless they’ve changed something about the base geometry, the hollow is much too shallow and thick to promote obturation at such modest pressure which is why I questioned the possibility of it skidding across the rifling.  Generally I would not expect a true 0.216” to be capable of skidding in most bores but some choked barrels have fairly large nominal dimensions.  For example LW’s spec is 0.215” land, 0.221 groove.

This IS interesting, which leads to yet another question on my behalf.
Obturation i guess shouldn´t be regarded as the end of all ills but has anyone tried using a wad to seal behind a PCP pill? Within the black powder crowd we about do anything but.. Wads are used all the time, for various reasons.

This is just me thinking out loud mind you..
Still though. I guess a chrono would tell real fast if and what is handed using SOME sort of "sealing aid". This being PCP it might even suffice with a carton disc? Thinking milk carton here..

Has anyone out there gone that route, in any sense or manner?

[Racing]

I'm wondering if it's possible that the slugs are spiraling, or even turning sideways.  Is it possible to use a larger piece of paper or cardboard to see how they are printing?  Are they grouping off of the target you have, or a shotgun pattern?

Shotgun, from what i´ve gathered. Hard to "see" though, but they sure as *(&^ do not group. I can tell you that much.

Ditto. When it comes to keyholing et al this if often a matter of misjudged need of pill diameter coupled with lack of pill speed IME. This becomes even more evident as pill weight increase.
For instance. Got an old original Whitworth rifle, with it´s hexagonal rifling, where if i use boolits of "the wrong dimensions" and/or to short and/or not enough gun powder = key hole.
Same rifle with fudder it craves OTOH we use out to 2000 yards.

[JimD]

I'm certainly no expert on slugs.  I never found one my Avenger 25 likes.  My P35-22 shoots 25 grain H&N Slug HPs, the bigger diameter pretty well but not quite as well as the Baracuda Match it really likes.  I ordered some 21 grain but got the smaller diameter H&Ns and groups were about 1 inch at 25 yards.  It's more like 1/4 inch with the 25 grain or the pellets.  I also tried some 13 grain Slug HPs in my P35-177 and got about 1 inch groups with it too.  It does much better with pellets.  So I suspect I need different diameters with slugs in both guns but I don't know if the larger 22 slugs in 21 grain will work in the P35-22.  I may order a tin sometime I am ordering other projectiles but it isn't high on my wish list.  Pellets work fine for what I want to do.

I have noticed a pretty strong diameter preference in pellets for the P35-177.  I tried H&N Baracuda Match in 4.52 and Baracuda Power - only available in 4.50 - initially and the Power shot much better.  But then I wondered if it was the copper plating or the diameter.  So I tried the Match in 4.50 and they shoot even better than the Power.  Most recently I tried Crosman 10.5s not expecting much but they shoot as well as the Match in 4.5!  Really nice when cheaper pellets work well in a gun.  I mention this only to relate that even in pellets, one of my guns has pretty strong head size preference.  My P35-22 doesn't seem to care (at least in pellets, possibly it does care in slugs) but my P35-177 definitely cares. 

It's still somewhat surprising to me that all 5 of my airguns are most accurate with particular pellets and/or slugs.  My P35-22 is the least picky.  I guess my powder burners liked different ammo better too but there you have a velocity and a projectile difference.  Handloading for my powder burners showed velocity certainly was part of the accuracy equation.  But in my air rifles I have not found velocity to be a strong factor for accuracy at all.  In powder burners the pressure pulse is MUCH stronger setting off vibration in the barrel.  Airguns act like the main factor in friction of the pellet in the barrel or something like that. 

[Racing]

Again just thinking out loud here...
Could it be worth the hazzle to pick the cheaper 22 molds up say from LEE and cut those down to approx 30-34 grain pill weight,  turn a 219 sizer on the lathe and take it from there?

Thinking as such thqt the stock barrel was thought for heavy choke n use mainly with pellets.

[customcutter]

Again just thinking out loud here...
Could it be worth the hazzle to pick the cheaper 22 molds up say from LEE and cut those down to approx 30-34 grain pill weight,  turn a 219 sizer on the lathe and take it from there?

Thinking as such thqt the stock barrel was thought for heavy choke n use mainly with pellets.

I've never tried casting conventional slugs or pellets.  I did cast some lead slugs to put into .22 casings to make .223 ammo.  When I get caught up on other projects I'm going to try making a mold to drop slugs for a couple of calibers.  Might be a waste of time, but I'm retired.

Make a D-reamer to cut the shape and nominal diameter.  Then take a very small boring bar to cut the larger ring sizes.

[Racing]

@ Jim D
I hear ya, but truth be told that there as far as speed affecting accuracy, i´d say it depends.
Just take that cylinder bore Hatsan BT-65 i did for a cust the other day. Set to approx 600fps, regulator installed n all. This using 18 grain pellets and the thing wouldn´t hit a sky scraper if its life depended on it.
Enter..slugs.
In this case what he had with him were 216 diameter Knock outs and i told him seeing the cylinder bore and so forth we needed to up exit speed.
In short by going from approx 600fps using 18´s we were seeing silly difference in accuracy upping that to have them 25,4´s out the snout at approx 850fps. Like.. night and day.
I´ve seen this for several rifles i´ve worked on, so albeit that cylinder bore "mistake" by Hatsan in THIS case it is by no means a fluke by any measure.

On a general whole i´d say most nod at keeping pellet speed at a maximum of approx 900fps while slugs need to pass like 800 AT LEAST to start working as intended.
At that then that SOME barrels just frown at you trying to use slugs, and no wonder.

Like you i´m mainly into powder burners and this whole deal with PCP´s is a latter offering to me, a very interesting one however.
But.
As you note amount of powder, COAL, set height, free flight and what not needs to be taken into consideration with the powder burners. *(&^, there´s half an industry making their living from making sure the brass is uniform enough, and still most of us reloaders prefer to pull that off ourselves. Down to measuring rim thickness of 22LR´s before use even..

But. The use of "sluggin´" a bore i´d say is universal no matter if powder or HPA. It comes down to that we need to know the dimensions involved to be able to interpret what results are telling us as we vary the setup.
Common sense really. Thus.. a pen and a piece of paper is a more valid tool than any if you ask me, and indeed different brands and makes vary their dimensions to a greater extent as far as rifling than the equivalent powder burners. Might be off on that but.. i stand to be corrected in such a case scenario.

So. What i have in mind here is to produce pills of varying diameter catering to THIS specific barrel.

Here´s what i did today. I really took the time to sit down at our in door to evaluate a bit, starting with using them 216 Knock outs.
Indeed. There was no point even trying to get an idea of any "group size". Just fugedaboutit...
Exit speed was between 1010 and 1020 fps, and pill weight of course the fabled JSB 25,4.

I´ve pushed both the 216 and the 217 down the bore and they BOTH engage the rifling, the 216 if ever so slightly. Plz keep in mind that my barrel is modified to work better for slug use, and that the stock offering choking action of THIS barrel was out of this world. INSANE in a word.
So. I cut back on the choking action by both cutting like 15mm off the end of the barrel and then turn to lap what was left using a brass mandrel i turned and valve lapping compound. I´d say i´ve made away with like 90% of that MASSIVE choke, which translated to a more "normal" choked barrel for air gun pellet use would be along the lines of maybe 65-70%.
Reasoning as such that all guns to shoot mainly leaded ammo benefits from an ever so slight choke.

Anyways.
Time for the 217, exact same setting and voila.. grouping. Say along the lines of 15mm @ 20 meter. In other words not exactly stellar for a PCP but at least reasonably usable for scaly tail hunting no doubt.

I then sat down with the micrometer and indeed both them pills were within reason on the money. So all good on that count.

Now. The idea here down the creek is to push the envelope for a Throne Gen 2. Due that i´ve already started "cheating" using heavier pills, and we these days see them offered mainly by H&N and Patriot Javelins for the moment. I´m sure others are to follow.
But.
In this case i have a tin of JSB 33,9´s pellets in 22cal at my disposal and i´ve reported on the effect of that previously. A bit impressed that with the same tune used for the 25,4´s i see like 930 or so out the nozzle with these 33,9´s. In short, potential to grow.
I then took the micrometer to them and the head is about on par with the 216´s while the skirt, which is REAL thin, comes all in at like 223 or so.
This of course gives way as the pill is introduced to the rifling, but the imperative part here is that these 33,9s exiting at approx 930.. i was to the letter stacking them at 20m.
IF i got me an ever so slightly larger group than bore diameter approx it was me. On my behalf, not the guns.

So. Lesson learned, but that also brings fresh question marks as i regard it. This tho.. for the next post ment for Customcutter...

[Racing]

@ Customcutter.
All to aware. Cutting a "master" to cut a mold sure isn´t the end of the world when we´re talking old school mech machinery, but i´ve got some fairly die hard CNC machinery at my disposal so..
But. That all adds up and i´m all for the KISS principle.

Thus. What i´m after is a CHEAP mold that´ll hand me what i need to TRY.
Thus this all starts with compressing a few of them Knock out slugs ever so slightly to be able to get a definitive reading on land vs groove diameter for THIS particular barrel. Ie; shove it down the barrel up UNTIL what remains of the choke and then very carefully shove is out the same way it came in.

What i don´t have a clear cut answer to is what is considered "bottoming out" with PCP guns as far as running clearances, if any, vs the grooves.
I mean, somewhere we´re going to see the point of diminishing returns no doubt.

Setting one of them dirt cheap LEE molds up on the lathe or the mill and mill off what we presume is reasonable to end up with pill weights between 30 and 40 grains is all good as i see it and as the stock LEE pill is of 55 grains total to start with and second up cut to handle a gas check.. well..
What i´m after, as sub sonic is the ONLY alternative as i regard it, is a flat base jobbie that hands me reasonable accuracy and power to boot.
25,4´s as weight we´ve obviously already outgrown for THIS gun so no point beating that dead horse anymore is it.?

Hm. No matter the next batch of Knock out to show up IS the 218 25,4´s and i guess that´ll be a neat experiment to conduct none the less. Will it suffice or not?
Y/N?

Then. Where i´m at right now, just for the idea, is at least 30 grains. Be adviced that to run the JSB 33,9 pellets i had to put the one mag that came with the gun on the mill, and removed like 1mm from the floor of it and in turn 1mm of the top lexan part. This tho made me end up with dire clearance and then some, and indeed this let the mag spring move the carousel freely.

Nah. Right now i could really do with some advice on what to aim for as far as boolit diameter for a given profile and ditto thus height as well as due that weight.

We´ll get this thing to perform. Make no mistake.

[Racing]

In an effort to try and give credit where..



It might very well be i´m kicking in open doors here, in such a scenario just tell. As i told i keep an original Whitworth 451 Military match. Yes, the old fabled one with a hexagonal bore, where "modern" accuracy was arrived on/invented in the mid 1850´s Britain.
Now.
Although many shoot just as well using regular ogive boolits in these i´ve come to get die hard on evaluating the hexagonal offerings.
To my knowledge ALL Whitworth molds on the market are multi piece, to cater to that the bullets have the rifling twist cast into them.
Thus said twist has to "roll" with the mold as well.

Enter CNC.
As you can see what we arrived on, and which has cut down on machining time MASSIVE, was to simply cut the parting plane of said 1 turn in 20 inches. Uhu.. the parting plane of the mold follows the rifling twist.
This hands that we per normal get away with just cutting yet another 2 piece mold.

Yes. We´ve produced a number of swaging dies for it as well, but truth be told it´s WAY WAY WAY more involved (these are 3 piece with a 4th as lock ring).
Casting vs swaging? Mm. Most claim you´ll never arrive on the same "accuracy" weight wise with cast pills.
Might be.
There´s this thing known as a scale see..  So let´s say i cast 200 and out of those i get to keep 130. All good in my book.

In turn. Turning a calibration eye.. you know as well as i do that just noodling along at the lathe having a cup of coffee we do that at the drop of a hat.
So..

[Scotchmo]

I would not expect such a huge accuracy difference. Have you tried both .216 and .217 without any baffles/moderator or shroud? You could then rule out clipping.

[JimD]

Just for a point of reference, my P35-22 shoots H&N Slug HP 25 .218 grain slugs at about 750 fps - accurately.   I shot a 171 at the AGN 30 yard challenge (which I shoot at 33 1/3 yards) with these slugs at that speed.  Later that day I shot a 183 with Baracuda Match pellets and my best is a 194.  171 is an average of between 8 (1/2 inch ring) and 9 (1/4 inch ring).  So it's kind of like keeping 20 shots within around 1/2 inch at 33 yards. 

This didn't make me want to switch this gun to slugs but it did make me want to try some lighter ones it could push quicker.  But they were smaller and didn't group nearly as well.

I keep looking for a situation where more or less velocity improves accuracy in my guns but I haven't found it yet.  I accept that it happens for other people with their guns. 

[Racing]

I would not expect such a huge accuracy difference. Have you tried both .216 and .217 without any baffles/moderator or shroud? You could then rule out clipping.

Me neither, but the fact remains.
Yes. Have tried both with and without, no difference.

Mind you. Shooting the JSB 33.9 grain pellets in 22cal it´s accurate and then some. Plan is to push on using "heavier" slugs. Will take it from there, cause where i´m at and that´s without the fresh plenum installed it tosses them 33,9´s downrange at 920fps. Which tell where this is going i guess seeing we´re talking 22cal.?