FX barrel Slug vs Pellet port (air efficiency)

[Thach2264]

Hello-

can anyone explain to me why use S vs P port on the FX barrel is more air efficient than the other or they use the same amount of air?

if the reg is the same P port give you 900fps, and S port give 950fps. Why bother using P port?

and let’s say of we want to shoot lighter pellets, would lowering the reg be a better idea instead of changing to the P port?

Idk…just throwing this out. 

 

[douger]

i use the s port with a pin probe on my compact 22 seems to be better i picked up 30fps compared to p-port with a oem pellet probe same setting and accuracy was same went from power wheel 13 to 10 same reg presure

 

[nervoustrig]

can anyone explain to me why use S vs P port on the FX barrel is more air efficient than the other or they use the same amount of air?

Key ingredients for maximizing efficiency:

1. high pressure
2. low valve dwell (light hammer strike that barely opens the valve)
3. free flowing (large porting)
   [/LIST=1]
   
   The slug or pellet port influences #3. The higher the energy level you are tuning for, the more the slug port will be advantageous to efficiency.
   
   Just bear in mind that seeking to maximize efficiency as a primary goal by manipulating numbers 1 & 2 will negatively impact consistency because it puts the gun operating at a state of partial valve lock.
   
   

   and let’s say of we want to shoot lighter pellets, would lowering the reg be a better idea instead of changing to the P port?

   
   If the goal is higher shot count, yes. Generally speaking you would want to use the lowest regulator setpoint that will achieve your desired energy level. Or rather, about 10% over the desired energy level, that way you can dial back the hammer spring tension to around 95 - 97% of peak velocity. Doing so will place the gun at a balanced state of tune where it has good efficiency, best consistency (low ES), and is least sensitive to the inevitable little variations in pressure or hammer strike. 

 

[M0ist0ne]

@nervoustrig - you just got a +1 for that one! 

 

[ImpactX]

Think of a small hole vs a large hole. Yes it use the same reg pressure and air. But the smaller hole restrict the air going through the transfer port before the valve close. So you get less power/fps with the P hole. Fx made it that way so you can change from pellet to slug easily by just flipping the barrel around. Sure you can lower the reg and hammer, and use the S hole to get less power. But lowering your reg you have to degass/only turn 1/4 if have air in bottle. Which is more work than just flipping the barrel around. Your choose.

 

[qball]

Using the larger port will be more efficient. 



The smaller pellet hole is design to create a choke point for better consistency. Smaller port has physical limitation/restriction for amount of air that can get through at given pressure so your shot to shot consistency will be better with P port at lower power. Think of it as another regulator but with ZERO creep because it's not movable. The P port is also designed to be drill out a little at the time to fine tune your pellet or slug speed, the S port is to get you the MAX possible power. So if you want the ultimate sub 10 ES and SD of 2 then you will have to play with port size for extra fine tuning but not most people's cup of tea including me. Keep in mine that to get the best consistency the price is lost of some power and efficiency. 

 

[Thach2264]

Thanks all for all the explaining regarding S or P port. It make more sense now. 

 

[danjaz]

Great info...thanks to all!

 

[tor47]

There is also two holes to consider. If the hole in the pellet probe is smaller than the transfer port hole. Enlarging transfer port alone is just "wasted" volume for the gun to fill up. Idealy the pellet probe hole should be equal or larger than transferport.

 

[nervoustrig]

True, any unnecessarily large pathways beyond the valve seat can be viewed as a wasted volume that must be pressurized. However a narrow port followed by a wider one is not a preferred arrangement because it represents a restriction and produces a downstream pressure drop. 

Preferably the cross section of the pathway is either roughly equal all the way through or gradually decreasing:

throat -> exhaust -> transfer port -> barrel port -> probe

 

[Sanyulity]

Excellent info. Thank you all!

 

[Tom Strong]

I was very pleased to find this post. I've had my Impact MK2 700mm .25 cal for a couple of years. This year I decided to do a deep dive into tuning if. This forum, AEAC and others have been very informative. I'd never given the S&P ports much thought. The other day I discovered I was using the slug port and became concerned that I'd been chasing my tuning with a key variable wrong. I changed to pellet then took it out and shot it. Pellet speed had dropped significantly but extreme spread was very low. I also noticed my air efficiency was down. Next I did a search, found this and voila--concern solved. It's nice to have this group on hand. Thanks.

 

[tor47]

Think it is called pellet port, because usually the pellets are in a weight range where using the slug port is not benefitial. Think most would prefer a thigter spread, rather than a litle faster speed.

 

[Tom Strong]

Think it is called pellet port, because usually the pellets are in a weight range where using the slug port is not benefitial. Think most would prefer a thigter spread, rather than a litle faster speed.

From what I've read [here] the intent of the pellet port is to make a gun set up to shoot slugs to go back and shoot pellets without tearing down major aspects of the tune, which for the MK2 is a pain. I assume this would be a non-ideal setup for it appears is costs you shots per fill but I'm not sure why. My gun plus the thread I read suggest the pellet port on a higher pressure slug tune is less efficient; perhaps because of the longer barrel. I went back to the slug port. I'm thinking the gun came from the factory that way because I'm not far from the factory tune.

 

[tor47]

One probably has to try both, to find out what works best for the given setup. When I tuned my .22 maverick for 16 grain pellets only, the pellet port did work best, even I did loose some speed on the same hammer setting. It might had been the oposite had I used a 25 grain pellet, or a slug.
If you push the gun hard, you might not be able to achieve the desired power with the pellet port.

 

[Airgunmann]

Here is the weird thing I was able to get more power with the stock 30 cal port over the daul port which I thought was weird I had a daul port in and tuned and swapped it out for the stock port for some reason I can't remember why and speed went up by about 20 fps but the other calibers I've tried both for 25 and 22 and in those I found daul port had more power unless it has something to do with just shooting pellets I don't do slugs yet idk it was weird I thought

 

[Trucker3573]

I have found on my Maverick compact that the pellet port is utterly useless to me. I flipped it to the p port once. The 25.39 went from like 900 fps to 715. I was like….umm no I will never use that side. I guess I could see it being useful in the longer barrel versions of the gun when tuned to shoot heavy slugs. You could just flip it for pellets without a retune. It will be more air efficient because it is way more restrictive.

 

[Tom Strong]

Here is the weird thing I was able to get more power with the stock 30 cal port over the daul port which I thought was weird I had a daul port in and tuned and swapped it out for the stock port for some reason I can't remember why and speed went up by about 20 fps but the other calibers I've tried both for 25 and 22 and in those I found daul port had more power unless it has something to do with just shooting pellets I don't do slugs yet idk it was weird I thought

It may have been based on your tune. I would guess a lower pressure longer surge might get the pellet out the barrel and dump air behind it. Just a guess...