Tuning Pellet probe - Tube/Cylinder(standard) probe versus Pin probe

Yes, mine does that also, but worse with flat base slugs than with pellets. I almost always single load the slugs. If you pull back all the way, pause for a second, then quickly load the ammo it usually doesn’t get stuck or have a rough load. But with the pin probe, single loading is best. 

If you have ported your barrel, instead of buying a dual ported barrel port, it could be far worse than a rough cambering. I installed the pin probe in my gun and a few shots later it shoved a slug down the barrel port. It was very difficult to get it out to say the least.

Since I had already done power mods to my gun the pin probe did nothing for the velocity on my .25 700 slug A Impact either. I was expecting to be able to adjust where my pellet/slug was chambered in the barrel but that also did not happen. Although with a dual port barrel and singe shot loading it would be possible. The one good thing the slug kit did for me, and I had to go through the extra step of drilling out my valve adjuster knob and screw on my MK1 to make it happen, was to allow me to change the valve spring externally. This is an excellent thing for tuning when changing calibers or making massive velocity adjustments.

https://www.airgunnation.com/topic/the-infamous-slug-power-kit-on-my-gen1-impact/

Alternatively, clean up the leade with a rubberized abrasive bit and polish it so there’s nothing to snag the projectile as it is chambered. Using a hollow probe does circumvent it to a large extent but is also masking a more fundamental problem.

I was having the same problem so I installed a huma dual port and solved the problem. Plus, between the two I gained almost 60 FPS. 

I just came across this same issue with mine today. I was group testing NSA 26.8 gr slugs. I have the factory brass transfer port and the slug pin probe. I had two of the slugs get stuck on the tp hole as they were being chambered with the muzzle pointed slightly down as I was shooting from a prone position out to my 100 yard gong. Had to hold muzzle up, and shake it a few times to get the mis-chambered slugs back out. If I kept slightly muzzle elevated and fast cycled there were no issues. If I went kinda slow it would stick. But this also points to why I sometimes feel a rough chamber when shooting pellets. 

Just further cements in my mind that the “huma” style bridged transfer port has merit on helping to keep this from happening. Can’t wait for Ernest to get his dual, dual ports back in stock as I will be getting one.

When I installed my dual port, I halted when I saw something on the pin probe.

(English is not my native language, excuse me if I get my grammar or my tenses incorrect) 



There are a variety of slug bases, from flat based to deep hollow based as can be seen in the picture below.



So obviously the pin probe will seat a flat based slug deeper into the breech than a hollow based slug.

Flat based slug



Hollow based slug.



This was confirmed when I took some measurements of the penetration depth on the pin probe. The pin probe is adjustable and was adjusted to clear the magazine by about 0.5 mm when it is inserted.

While the flat based slug was pushed all the way into the breech, the hollow bases slug did not go all the way in.

In fact, the edge of the base protruded into the passageway of the port.



This cannot be good for accuracy. I am not an engineer, but common sense can tell that a blast of air coming through the port will upset the alignment of the slug in the barrel and cause all sorts of accuracy issues?????

The original probe will seat all these types of slugs to the same depth and should give better overall accuracy. Even if one uses only flat based slugs, some of those slugs tips sideways in the magazine, and is not correctly aligned when they are pushed in by the pin probe. The pin probe will not correct this, and the slug can enter the breech misaligned.

The conventional probe however, pushes all around the outer edge of the slug and will correct any misalignments when the slug enters the breech.

Eventually I enlarged the opening in the probe to match the port in the dual port and got a 40 fps velocity increase from this and the dual flow port.

Some 50 meter results below. The flyers are due to the changing to different slugs without first shooting a couple of settling shots off target. 

I shoot mostly pellets and have noted that the pin probe negatively affects things for me. I went back to a standard probe with the hole enlarged to match the Huma dual-port TP.

When I do shoot slugs they are H&N 21gr .218, out of a slug A at 960 ish, the pin probe is excellent, insofar as I can lower my reg pressure by about 10 bar for the same performance compared to the standard probe. I am not really overpowering things in the first place, but if I shot heavier slugs then I guess the probe is essential?

I shoot every day and slugs are for fun, the pellets are for practice and I enjoy practising as much as I can so the choice was easy for me. For the price, I am still glad that I have one and can recommend that one try it if using slugs.

I used the pin probe and took it off almost immediately, not because it didn’t work but there were no gains in fps over a well made modified bolt probe for me. The modified bolt probe has a more concentric area to push the projectile evenly and the seating depth is the same every time with a variety of projectiles as Johan pointed out. I had a few slugs that were tight and the pin probe almost couldn’t push them in the barrel because there is such a tiny surface area contacting the slug. My experience is that a well made, modified probe is smoother, gives you the same gains in performance.

Stoti

I’m with Stoti, I built an adjustable pin probe last spring when the Huma TP came out. Went back to lightly modified OEM stuff. Minuscule gains were not worth the hiccups.

watched a video by Ernest on the pin probe. If the pin is too long, it causes most of the issues you are talking about. I shortened mine a touch and no longer have the problems mentioned above.

I am not an engineer by trade but I came to the same conclusion as JohanG early on as well. I had equal gains with my lightly modified stock probe and the pin probes by FX and NSA. Differences was noted by JohanG in his pin measurements. The main difference for me was the consistency of loading pellets or slugs with the modified FX probe, consistent depth chambering of all projectiles by using the skirt of the projectile.

Am I understanding this correctly? You have 2 absolutes that hinder "pin probe adjustability" to any extent that would support said adjustability? #1 would be the magazine block has an absolute back edge. Adjust your pin to this edge for unobstructed magazine loading and this depth IS as far in as the pin can push ANY projectile to the lead. As the variations in projectile bases is huge so will be the seating depth. What adjustability is there here? Less? What is the point of this?

#2 : The probe body length. As shown in JohanG's photo. If it is to long it encroaches into the TP area potentially negating any gain by the probe. Again, what is the point of this? A shorter probe body might not engage with the TP O-ring to seal and cause additional problems.

The main benefit I found with my slightly modified stock FX probe was it's consistency loading any projectile, regardless. 

Tinkering and modifying is great, but to what end? This might solve 1 problem with 1 slug. Not my cup of tea.

I could be missing something here and would appreciate insight if so.

Definition:

"Slightly modified FX probe" is taking only <50% of the diameter of the probe barrel down and polishing all the surfaces. This allows most all slugs and pellets to load without issue and give a slight increase in FPS.

For me, The "pin probe" could work for a particular projectile, but, not all.

Hmmmm...A retractable probe??? Now were talking.