S510 Classic with bad grouping

[patratel]

Hi there,

I'm having an AA S510 for about four years now (bought it new in the shop), and it never really grouped better than 2-sigma (~34 out of 25 shots) within a circle with diam=40mm (or worse!) at 50m, even at windstill conditions, with regulated air pressure, pre-selected pellets, etc. In this state, I can forget taking part to any benchrest competition. I wonder: is this normal?

In any case, my shots (typically sets of 25, 30 or 35) very often feature a non-normal distribution, which hints towards a hidden root cause for my bad results.

I tried many variations along the way, without success (other pellets, pre-weighed, 5.51 or even 5.50; other pellet brands; with/without silencer; different pressures, different or no regulator; various sitting positions; manual/tray loading, and many other things). Then I had a friend look at the internals of my S510 and he said it all looks as new; also, he mentioned that the choke would be way too narrow. He said he never encountered such a narrow choke, in fact, and that he could barely push a pellet along this choke. He suggested to try another barrel, as this too narrow choke would spoil the accuracy.

Also, I glued the small ring at the end of the barrel onto the barrel, as it had started wondering around and wearing onto the barrel. Something other AA users suggested I should do.

Therefore a few questions for the experts:
1) am I too demanding to ask that I should be able to reduce the group size from >40mm to 15 or 20mm in a windstill condition at 50m, with regulated air pressure around 130 or 140 bars and JSB 16gr or 18gr from 2018 or newer pre-selected and weighted pellets?

2) are there other root cases that you can come up with, which could cause bad grouping? btw: expert shooters tried it too, and they confirmed it was not me.. Also I tried on some FX'es and obtained better results already from the first group of shots! So again, it is not the shooter..

3) Is there anything that AirArms Ltd could/should do about this, given the 4 years since I bought it, and given that a too narrow choke is a fabrication error and not something I could change myself for the worse with years? Our local importer says: 'no chance'... Yet I spent quite a lot of money on this product, and I've been looking for the root cause all along. Now, it is simply useless to try competition shooting, even with regulated pressure and in a windstill condition. ;-(

Who can help me out with some advice or hints, please?

Thank you, Michael

[bgaltd]

Which small o ring have you glued into place and have you tried a different barrel ?

[Zed.]

Which small o ring have you glued into place and have you tried a different barrel ?

+1

and...

theres too many variables to diagnose remotely,

have you shot a string through a crono?
what pellets?
what power levels are you expecting / using?
what caliber? (related to the above)
what condition is the gun & barrel in?
what is the temperature?
what optics / scope?
what is the sight picture like & do YOU have a reliable hold to accomodate this?
etc.

my s400's group well @ 50 yards
I DO NOT group well @ 50 yards

if the rifle is in 100% condition then have you tried clamping it in a vice (workmate?) for grouping tests?

Rich.

[patratel]

Which small o ring have you glued into place and have you tried a different barrel ?

To be more explicit: it is an Aluminium ring at the end of the barrel, which mechanically connects to the shroud and has one or two rubber O-rings on the exterior, to connect mechanically to the shroud. That small Al ring had started creating Al particles where it touches the barrel, so I glued it with onto the barrel (onto the barrel only, because the mechanical interface between the outer part of this ring and the shroud is assured by those one or two rubber O-rings); now this Al ring -- together with the barrel -- move up and down together inside the shroud.

As mentioned earlier, there was no positive/negative impact on accuracy before/after the gluing.

I haven't had the chance to try a different barrel so far, that would be one of the next steps, I presume.

[patratel]

and...

theres too many variables to diagnose remotely,

have you shot a string through a crono?
....

if the rifle is in 100% condition then have you tried clamping it in a vice (workmate?) for grouping tests?

Rich.

Thanks for the reply, Rich.

Oh, you don't wanna know how many things I've tried and diagnosed. Basically, I've made a whole document out of it that I could share if necessary. Each of the tests contains the 2D plot with the shots, some statistical analysis plots and also information that answers your questions and more. I even have histograms with weight buckets of various pellet types.

Not sure if I can attach pdf's, though, and (challenging remark ahead!) not sure anyone on this site has ever been that deep into statistics with AirArms.

For now, in short:
have you shot a string through a crono? --> yes, at multiple regulated pressures and with different pellet types; speed is very constant, typically within 1m/s and rarely 2m/s difference
what pellets? -> many types and batches, mostly JSB 16gr and 18gr, from 2017 (bad ones..) and newer (better); RWS; some Barracuda's and
what power levels are you expecting / using? --> 40J, measured with chrono (I've plots)
what caliber? (related to the above) --> 5.52 normally, sometimes 5.51 and 5.50
what condition is the gun & barrel in? --> sometimes I cleaned the barrel beforehand, then did some lead-in (10-15 shots) to stabilize it
what is the temperature? --> typically around 20C, sometimes around 10C
what optics / scope? --> Hawke 8x32 50mm
what is the sight picture like & do YOU have a reliable hold to accommodate this? --> sight picture I need to be able to share plots or a pdf & ; I would say I have a good hold, I tried multiple ways of holding with only minor differences in results.
etc.

[patratel]

1) Is it really a fact that the choke of AirArms barrels is a very narrow one (in contrast to barrels from other brands), so that one can barely push a pellet along it?

2) how good should grouping be at 50m, in windstill conditions, regulated, max, concentration (competition mode)? Can I reach the area of a thumb nail? Or of a pink nail? Now it is more like half a palm, in laymen terms.

[tonyc]

MV needs to optimised for the pellets you are using. Try at 850-880fps and see what grouping you get. Maximum MV will probably be low 900s but best performance may be lower.

You say you aren't getting a normal distribution, so how does it distribute? Any consistent deviation from normal distribution might give an indication of what else is going wrong.

I suggest you might check MV variation with a chrono and compute resultant vertical stringing. Chrono a full string so you can see if there are any variations and the reg is set correctly and not exhibiting cylinder-pressure dependency.

Don't believe windless conditions outdoors means no windage. Some places I shoot have unusual air movements so I'd only trust indoor results. Statistically, shooting 25 shots without human error is very unlikely so you need to factor in your wobble. When you've worked out the combined MV and human error you might reconsider your expectations.

With a sub-12 .177 I'd be expecting 2 sigma 25mm groups - maybe 10-shots in sub-20mm group on a good day - but only after I'd done a lot of work finding batches that work.

[patratel]

MV needs to optimised for

...
With a sub-12 .177 I'd be expecting 2 sigma 25mm groups - maybe 10-shots in sub-20mm group on a good day - but only after I'd done a lot of work finding batches that work.

Thanks for the reply. I fully agree with the definition of 'windstill outside', I can only acknowledge your findings. Amongst other things, I've done a series of real windstill measurements in a shooting bunker at 50m distance. In there, I also took groups of shots at different pressures (between 130-180 bar), with various types of pellets. And also here you are right, while I can get about 274m/s for a heavy pellet around 160 bars, I discovered that 130-140 bar gave a slightly smaller variation. Therefore, I've set my regulated pressure around 130-140 bar.

Also, I had some groups shot with a chrono in front and the barrel exit speed remained pretty constant for all pellets (for some groups below 1m/s changes, but mostly one digit change which is at most <2m/s). The exit speed is especially constant with JSB 16gr and 18gr, which are my best types from what I tested so far.

As per the distribution: it is hard to explain in words, but typically if I test the normality (or make box plots) of the dataset for x direction, y direction, and sqrt(x^2 + y^2), I get one or a few outliers at datasets of between 10-50 shots. And the distribution is sometimes not really gaussian for one or both directions. Sometimes I seem to see two instead of one peaks. Or a flat instead of gaussian histogram. And even when it is gaussian, sd is about 10mm in one direction, so my shots are roughly within a circle with a radius of 2 sigma, or about 20mm. Which is the half palm I mentioned earlier.

When you mentioned above: "maybe 10-shots in sub-20mm group", I translate this to a circle with radius of 2sigma, which would mean sigma~5mm which is half or less than my .22 best grouping ever, which has a sigma~8mm in the best case (windstill, regulated, selected pellets).

In conclusion, I'd say something is definitely wrong and it is not linked to the exiting speed.

Have you any idea of how arrow your choke really is?

[tonyc]

I can't help you much with the barrel or choke. I would just try loosening and carefully re-tightening the barrel band just to allow the barrel to centralise. Check the barrel crown and breech for any burrs, though I'm not aware LW barrels suffer in this respect. The other possibility is the magazine or loading is damaging the pellets. If you have the old-style magazine advance spring it could be slightly bent which can alignment for loading.

It's interesting you say there are possibly two peaks in the distribution. That could indicate something is moving in the barrel to line-of-sight alignment or possibly the stock or your technique. You haven't said in which direction the two peaks or flat distribution occurs, if this is constant direction or entirely random. It's also not clear if you are seeing 40mm groups from 10 shots or this is what you get if you shoot 25+ consecutive shots.

A concern at the moment is your adjustments to the reg pressure, If you haven't done so, I suggest you chrono a full string. Adjusting reg pressure between 130 and 160 bar I'd expect to see a change in the cylinder-pressure dependency. +/-2m/sec is not brilliant for a 10-shot string but if you also have a drift in moving average as the cylinder pressure reduces you may be seeing much larger variations over 25+ shots. +/-3m/sec could be giving a (near) vertical spread of 10+mm. If you also set the reg high, say 160bar, and run a few strings, each including at least 10shots on reg and 10 shots off reg. Look for shot-to-shot variation on and off reg. This may give an indication of erratic performance of the regulator (on-reg variation) or action (on and off-reg variation) . I'm getting typically no more than +/-2fps in a 10-shot string and <10fps spread over the full regulated profile - that's with sub-12ft lb .177 with Altaros reg, not the AA reg. Changing reg pressure by 20bar would easily push the spread to over 20fps.

If you know your regulator and action are consistent you can look at other mechanical causes. Have you changed your scope to eliminate that as a possible cause?

That's about all I can think of at present - hope it helps!

[poguemahone]

if the 510 has 2 little pads inbetween the cylinder and stock at the front, same as the 4*0 series, then float the cylinder
most guns are fine with the 2 pads, the few that arent wont shoot accurately unless you float the cylinder. mine was one of those guns takes less than 5 mins to do .