Tuning Continued Confusion with Reg pressures

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I have a .22 Mk2 with power plenum and 700 mm barrel and upgraded to the dual port and pin probe. Then noticed that the 21 and 23 gr slugs tends to tip when the magazine advances. When it reach the point where it is next to enter the breech, it is presented at an angle. The pin probe then pushes it into the breach while it is not strait.

One cannot see if the slug straitens out when it enters the breech, but that made me change back to the original tube probe and opened the air-hole up to a similar size as the dual port.

My reasoning is the the tube probe will straiten the slug out as it pushes it all round the edge into the breach. It should theoretically give better results.

Some makes and weights of pellets or even slugs, have hollow bases with variable depth. The pin probe will push these in to the breech at different depths, making it so much more difficult to find the correct settings. I have lugs with a very deep hollow base, and found that the pin probe does not push the skirt all the way past the transfer port. The powerful blast of air coming through the tp will definitely upset the alignment of the projectile and decrease accuracy. The tube probe seat them all to the same depth and pushes the skirt past the tp, presenting the blast of air in the middle of the projectile.

I don't know if my reasoning makes sense?
 
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I have a .22 Mk2 with power plenum and 700 mm barrel and upgraded to the dual port and pin probe. Then noticed that the 21 and 23 gr slugs tends to tip when the magazine advances. When it reach the point where it is next to enter the breech, it is presented at an angle. The pin probe then pushes it into the breach while it is not strait.

One cannot see if the slug straitens out when it enters the breech, but that made me change back to the original tube probe and opened the air-hole up to a similar size as the dual port.

My reasoning is the the tube probe will straiten the slug out as it pushes it all round the edge into the breach. It should theoretically give better results.

Some makes and weights of pellets or even slugs, have hollow bases with variable depth. The pin probe will push these in to the breech at different depths, making it so much more difficult to find the correct settings. I have lugs with a very deep hollow base, and found that the pin probe does not push the skirt all the way past the transfer port. The powerful blast of air coming through the tp will definitely upset the alignment of the projectile and decrease accuracy. The tube probe seat them all to the same depth and pushes the skirt past the tp, presenting the blast of air in the middle of the projectile.

I don't know if my reasoning makes sense?
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A litle off topic but there is a guy here (Orion I think he call himself) who is selling 3d printed mag inserts for the impact. Lighter slugs tumbling in the high capacy mags, is a known issue. Those inserts should allow you to use the pinprobe.
 
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JohanG what you say makes a lot of sense to me. I did wonder about the pin on the back of a slug. If it’s just the slightest bit off then the slug advances at an angle and could scape as it seats in the bore. That could explain why groups are more consistent when I switch to an Impact with the standard probe. Pellets don’t seem to be affected I guess because of the skirt

Im going to go back to the standard probe on the MK2 to see if that makes a difference. If it does then I’ll either open up the standard probe or buy the Huma Probe. 
 
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I have a impact with 700mm barrel. When I switched out the standard probe with a pinrobe, it gave me 10 aditional fps, everything else stock. I have custom made inserts in my mag, so the JSB knockouts turning sideways is not an issue. But if you suspect issues with the probe, and/or mag, the pinprobe is probably not needed to shoot slugs. When using the pinprobe the gun will not work with pellets anymore, as it is not possible to adjust it enough forward to get pellets clear of the transfer port. So it doeas limit the gun for slugs only. 
 
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Here is a link to one of the threads by Orion, with pictureshttps://www.airgunnation.com/topic/ive-fixed-the-fx-magazine-for-slugs/#post-819605

Since I live in europe I bought theese: https://www.oh-snap.dk/vare/magfx/

Think they work the same way, just different makers. Since you live in US, you can probably contact Orion if you want to buy one.

Regarding the pin probe working with pellets or not, I did mark where the end of the barrel was on the probe. And when I took the probe and barrel off the gun, and pushed a pellet in the same distance, the skirt would stick out obstructing some off the transfer port in the barrel. It does not push the pellet enough in to the barrel to get it all clear of the transfer port. But if you tried it, you would know, but I would believe there is a risk of damaging the skirt when the air enters the barrel. 

If you look at huma air website, they also say it is not suitable for pellets: https://www.huma-air.com/FX-Impact-Slug-Power-Kit
 
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Mine was at 100 Bar and last night I tried at 110 Bar for 915 FPS on power wheel 4. 
at 30 yards w no wind I was getting POI shift galore. Just can’t explain it. With my MK 1 Impact and my Kalibrgun Cricket at 30 yd I’m getting one hole groups but that’s w pellets. I know pellets are better at shorter distances but it’s the POI shifts that I can’t get over. 
Going to try and contact FX
 
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I was able to shoot yesterday but with the weather and time of year the time window was only a little less than two hours. But I have not changed the 125bar or hst so instead of max I turned my power wheel to #4 @810fps so I could spend more time shooting than filling. But my results are very good consistent speeds and accuracy is moa accurate @75yrds . It seems to me that the springs have settled in and not as loud but again that’s on power #4 at this point I just enjoyed shooting groups and did not shoot on max power. But overall I am very content and do need some more nice days and spend more time with the gun, today is too cold and windy. But some better days are ahead.
 
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You really have to make sure the barrel is clean. There can be lead build up, often near or at the choke. If you use regular patch pulling (the fishing line method), you may not be able to remove it. If in doubt take the barrel of the gun, remove shroud, and inspect it with a flashlight shining from the breach end. It should be visible with naked eye, if there is lead present.
 
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Mine was at 100 Bar and last night I tried at 110 Bar for 915 FPS on power wheel 4. 
at 30 yards w no wind I was getting POI shift galore. Just can’t explain it. With my MK 1 Impact and my Kalibrgun Cricket at 30 yd I’m getting one hole groups but that’s w pellets. I know pellets are better at shorter distances but it’s the POI shifts that I can’t get over. 
Going to try and contact FX
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I think it is the barrel liner being too sloppy withing the barrel tube. This can be remedied by a couple of things, aside from installing the carbon liner. The first is locating the o-rings evenly on the liner and the second is with the lock nut being modified to hold the liner centered.

As to the liner o-rings, put a couple of wraps of tape on each side of each of the o-rings so they stay located in the tape grooves when sliding into the barrel tube.

The lock nut wabbles around on the liners with a lot of play. The barrel tip jumping around in there is a dramatic shift down range. (Heat shift would explain day to day differences in accuracy, as temps rise the barrel gains length and tension changes.) To fix the nut slop, wrap the end of the liner with a couple of wraps of teflon pipe seal tape, or a single layer of clear Scotch tape. This permenantly locates the barrel centered in the nut, and even if the nut becomes loose the liner won't shift around.

Another experiment to do is test the grouping without the moderator end cap on. If the groups tighten up then the moderator at the shroud is not machined true and the slugs are coming close to clipping the end, inducing some turbulence in the projectile as it leaves the moderator.
 
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Airgun Hobbyist. Some good tips there. I have my liner set up with four o-rings in the middle secured with some teflon tape and then on each end there are 2-3 o-rings also secured with T tape.

Actually they aren't at the very ends but a third of the way in from the ends. I measured the liner and divided by 3 and I put the 0-rings at 1/3 points on the barrel. If there is a better way then I'll try it. I had another liner set with one o-ring at 1/3 intervals then tape was put o each side of the o-ring.

I'll try the tape on the ends.

Thanks
 
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Airgun Hobbyist. Some good tips there. I have my liner set up with four o-rings in the middle secured with some teflon tape and then on each end there are 2-3 o-rings also secured with T tape.

Actually they aren't at the very ends but a third of the way in from the ends. I measured the liner and divided by 3 and I put the 0-rings at 1/3 points on the barrel. If there is a better way then I'll try it. I had another liner set with one o-ring at 1/3 intervals then tape was put o each side of the o-ring.

I'll try the tape on the ends.

Thanks
Click to expand...

I also had to re-crown my liner the other day to get it to group tighter. You can't really see it well in this picture, but it doesn't take much to do and then polish it and then the bore. (The end is wrapped with the Teflon pipe tape, and the barrel nut in the picture for reference.)

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IMG_20210124_185919211_BURST000_COVER_TOP2.1611998412.jpg

 
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