American Air Arms Low powered Evol Mini tune

Dairyboy said:

Anyone tune the Mini down to a lower power than the usual 28-30fpe they come at? I'm getting close to tearing into mine and tuning for the 12-14fpe range and was curious of anyone has a good reg setting for that. Doubtful anyone has but thought I'd ask. And if not I'll be letting people know lol. Mines at 2050psi at the moment and shooting at 30fpe. I'm thinking at least 1500psi would be where I should aim for. If not less.

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Extrapolating 30 fpe from a 2050 psi .22, I would say 1550 psi for 20 fpe, and, 1100-1200 psi for 12-14 fpe (1100 12, 1200 14, or 1150 for the best of both), provided you're trying to tune to the knee / 97% of the plateau.

Removing 800~ psi from the valve = 60-80 lbs less holding force, depending on the poppet diameter, which is a lot so you may need to add a stiffer valve spring (or pre-load it more with shimming) AND a lighter hammer spring, both not too difficult or expensive to figure if you tear into and do some simple calcs, and very reversible if you hang onto the stock units.

The OTHER option is just adding a choke to the transfer port. Say if you're currently ported to .165" or 75% of bore, you could somehow choke the port via transfer path with obstruction down to .085"-.09". No reg change + spring reconfig needed then, and no de-gas either more than likely.

-Matt

I'd choke the transfer path personally if you don't care for the shot count lower reg setting would provide, more work for the latter, but more shot count as well, less work for former, and no re-springing needed.

Your quest is why I modded my marauder to have a quarter turn valve, the VMS screw doesn't do enough with .225" porting and isn't super convenient requiring tools, where a quarter turn valve I was able to knock my power down from 40 fpe to 15 fpe in .22 on the fly without tools, I just lose the benefit of shot count which I don't care for on lower power.

-Matt

I don't know the math, but mine (.22) is shooting a nice solid 800+/- fps. As I recall, (it's been a couple of years) I may have done a small regulator adjustment. I have a barrel removal tool, and that's the only reason to have that. But without a gauge, I know that if I did that it was a "small" adjustment, so I didn't go too far, and have to pick it up again.
I should get it out, I haven't shot it in a while.

MIke

MikeVV said:

I don't know the math, but mine (.22) is shooting a nice solid 800+/- fps. As I recall, (it's been a couple of years) I may have done a small regulator adjustment. I have a barrel removal tool, and that's the only reason to have that. But without a gauge, I know that if I did that it was a "small" adjustment, so I didn't go too far, and have to pick it up again.
I should get it out, I haven't shot it in a while.

MIke

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800 Fps with what weight projectile? 15.89 puts that around 23 fpe, and 18.1 around 26 fpe, a bit higher than Dillon is interested in afaik.

-Matt

There's no valve return spring...
I had to go to a reduced transfer port(needs to be made), a lighter hammer, lighter spring,, AND lower the reg to get down to 20 ft lb and later, 12 ft lb.. For mine to run well, 12 ft lb is 1400 psi... 20 ft lb is 1700 psi...
This is for 177. For 22, a lower pressure might be necessary but the valve depends on this pressure for closing...
You might be able to get close to 20 ft lb by reg and hammer spring adjustment alone but I'd be very surprised to see you get below that.
A query to Tom might yield some parts or info or both if he has a moment to respond..
Bob

Arzrover said:

There's no valve return spring...
I had to go to a reduced transfer port(needs to be made), a lighter hammer, lighter spring,, AND lower the reg to get down to 20 ft lb and later, 12 ft lb.. For mine to run well, 12 ft lb is 1400 psi... 20 ft lb is 1700 psi...
This is for 177. For 22, a lower pressure might be necessary but the valve depends on this pressure for closing...
You might be able to get close to 20 ft lb by reg and hammer spring adjustment alone but I'd be very surprised to see you get below that.
A query to Tom might yield some parts or info or both if he has a moment to respond..
Bob

Click to expand...

The more you choke a port, the more the power can be reduced to the point of 0, so you don't HAVE to run less reg, it is very much an option, but definitely a good one for increased shot count.

-Matt

Seems like I remember a post a while back that someone de-tuned their .22 (not a mini) to a high shot count and settled around 1650 psi.

Dairyboy said:

Lol so not as simple as I thought. Don't think I can do the TP that's a complicated piece. Guess I'll need to think about it more.

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You can add a restriction into the existing tp with a very mild adhesive that heat would remove. Just need a tube with the same OD as the current tp ID and then have the new tube ID be around what I suggested above, give or take.

-Matt

Just to add a few other ways to skin the cat....

1) Limit poppet travel, throat then becomes the choke as the poppet can only lift so far off the seat, cutting dwell and possibly air flow
2) Assuming balanced valve, check if the vent is adjustable, if not (Tom would know), scrap the idea.
3) Severely reduce the plenum volume
4) Choke at the valve inlet

All the above can be done while being reversed if the approach is mindful enough.

-Matt

It's not hard to get into these to change the regulator setting. Simply de-gas with the burst disk, remove the barrel while it's exhausting the air, and take off the front cylinder cap. This gives easy access to the regulator adjuster with a long tool. I used a hex bit attached onto an aluminum arrow shaft for a permanent adjuster tool. I also drilled out an access hole behind the rubber butt plate this allowed me to get at the hammer spring tension adjuster without having to remove the chassis each time I want to make a hammer spring adjustment. The same arrow shaft has a bigger 5/16" hex on the opposite end for this.

I did, at one time, have an Evol Mini I tuned down like that. I don't remember the exact fpe, but I tuned it for Crosman 14.3s at around 700fps, IIRC. I recall dropping the reg down to something like 1400 psi and then just adjusting the hammer spring. I didn't muck with the TP and my recollection is that it was quite consistent. The one problem I ran into was that I had to back the hammer spring WAYYYYY out and it made getting the lower frame back on tricky as it was hard to get past the hammer spring screw sticking way out the back of the receiver.

So it's all possible, but a lighter hammer spring is recommended.

I have had my regulator down under 1000 psi just playing around. Was able to get some lower speeds but they were not consistent at all.

Stubbers said:

800 Fps with what weight projectile? 15.89 puts that around 23 fpe, and 18.1 around 26 fpe, a bit higher than Dillon is interested in afaik.

-Matt

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Matt -

While I use varying pellet weights during any given session, I do my adjusting on all of my adjustable guns with 18.1 gn pellets. Either FX or JSB.

Wow, slower than 800fps. That's getting down there. Seems that most of the high end shooters comment that below 800fps is getting below any good accuracy with most all pellets, in most all guns.

Mike