Anyone remember the Evolution 9 with ASAP Nielsen/piston booster?  Time frame was early 2000s.

The piston spring—any ideas on a replacement spec or source or how one would measure compression spring values other than ID, OD, height & coil #? It looks like an engine valve spring, but this could be a costly guess….

Yes, I asked AAC & they don’t know.

I got u fam… gimmie a few min to measure.

I have the spring so I can measure what I posted—I need a compression value & alloy type.

Note, this spring is 12+ years old, dirty, used (probably 2-3k rounds), stored in an assembled state and it’s a sample of one.  As such some measurements may not represent nominal values and some dimensions (like the free length and installed preload) may have taken a set.

6-Coil closed and ground
Tests as Stainless, magnetic (likely 17-4 or 17-7)
Coil ID .660”
Coil OD .846”
Wire Dia .093” (3/32”)
Free length 1.200”
Installed length 1.025”
Installed preload ~7.75±.5 LB

For what it’s worth… I’m 90% sure the Evo9 spring is the same spring as the AAC Illusion 9 and TiRant9 and Gemtech Tundra.  Try searching for those springs as replacements as they’re all newer than the Evo9.

This may be of some value. Half way down the page there is a compression spring calculator. Also the springs are searchable by your dimensions I believe.

Century spring

Whoa!  Awesome!  Thank you!

ETA: you had me at your disclaimer!  The world needs parameters because they matter!  I’ll check mine vs yours & post so our N = 2; then our correlation of 1.0 means more!

Before I forget—let’s do the controls later, after the experiment to save time!



Oh yea—as noted below, “biz boys” wouldn’t commit to interchangeableness, but good idea—that was the original guess, but no commitments were to be had.

Thanks man!

Thank you, too!

I was on Lee Springs doing the same.  

I would guess 17-7PH.

But there’s Elgiloy which is cool because it was used in the SR-71, which as everyone knows has been scientifically proven is the coolest jet ever made.

Like the Steyr AUG is the sexiest bullpup & AR15 sexiest semi rifle….

But…thank you.

As an aside, nobody “in the biz” would commit to other springs from current production.  Probably a liability issue.

I was concerned AFT went full-retard & “springs” are only exchangeable when silencer parts…


Yea, I know…write AFT a letter asking, then send 87 more which will be irrelevant when they change their minds again…but their changed minds won’t work any better.

I think Hanson bothers sells AAC springs

I’m probably counting coils wrong?  I got 5-1/2…So, 6.  I didn’t know how to include the ?half coils? at the ground/squared ends.
Right hand coil
Magnetic
Free length 1.204”
ID 0.655”
OD 0.855”
Wire is 0.0.097”, 0.098” & 0.099” (3 different readings, I mean)
Piston OD is 0.620” (mine is metric 13.5, because the 1/2x28 would shoot loose)
This was bought in 2007 & they changed the piston vents holes from round to oval as an update, but were thoughtful to make me buy the “Gen 2” because…AAC “blamed” ATF saying it was designed that way.  It was a lame excuse.

https://hansohnbrothers.com/shop/hansohn-brothers/accessories/mounts-and-pistons/hansohn-piston-springs/

I could be wrong but I believe the Ti-rant 9 first gen and Evo 9 used the same springs.

Great idea & am currently in contact with Chris.  They’re “old school” customer-oriented folks I’ve purchased from before & gave him the specs.

I’m going to sound like the ol’ Boomer yelling at clouds…but I kinda doubt AAC, back in the day, had a custom order of unobtanium booster springs made & it’s probably COTS that my ol’ Boomer ass cannot figure out.

So, some young whipper-snapper is going to say:

Sir, it’s this.

And, I’ll be the sullen ol’ man shuffling OTD

I don’t want to risk damaging the can & have no idea if the wrong compression weight or unboxed ends would do that.

Spring steel vs aluminum, etc.  I would guess the piston is stainless & there appears to be a liner in the piston chamber.

There was an interweb rumor back in the day these springs could be obtained at a local auto parts store, but that’s not as sexy as unobtainium, limited production run of vaporwear that isn’t available after an hour passes—but I’ve never tried to replace it before.

ETA:  as the French say: Violá!

Thank you Chris at Hansohn Bros!