Tuning to 11.5 FPE

[JP806TX]

Chrono my main TX recently and it was toooo close to the 12 FPE threshold for WFTF. The next logical step was to tune it down to 11.5 FPE (to legally get below the WFTF power requirement). Did a google search and talk to my shooting buddies about my options. Was told the easiest way was to leave the gun cocked for extended periods of time and then check with a chrono. I was told trying to lower springer power by 30-50 fps is not going to be easy.

Welcome to the world of voodoo spring magic. I wanted to do this conservatively soooo...First session left it cocked for 3 hrs-no change in FPE. Second session left it cocked for 6 hours-no change in FPE. Third session another 6 hours-STILL NO CHANGE IN FPE (I think I'm starting to see a pattern). Fourth session 24 hours-checked today no change. Gonna try one last session for 48 hours...after that, it's time to get out the power tools and start cutting spring. I hope I don't mess up.

 

[iAMzehTOASTY1]

Chrono my main TX recently and it was toooo close to the 12 FPE threshold for WFTF. The next logical step was to tune it down to 11.5 FPE (to legally get below the WFTF power requirement). Did a google search and talk to my shooting buddies about my options. Was told the easiest way was to leave the gun cocked for extended periods of time and then check with a chrono. I was told trying to lower springer power by 30-50 fps is not going to be easy.

Welcome to the world of voodoo spring magic. I wanted to do this conservatively soooo...First session left it cocked for 3 hrs-no change in FPE. Second session left it cocked for 6 hours-no change in FPE. Third session another 6 hours-STILL NO CHANGE IN FPE (I think I'm starting to see a pattern). Fourth session 24 hours-checked today no change. Gonna try one last session for 48 hours...after that, it's time to get out the power tools and start cutting spring. I hope I don't mess up.

Coooouldnt you find a smaller spring?*a different spring, I would personally swap out for another and keep the regular one in case you want to switch it back?just a thought

 

[JP806TX]

That's a good suggestion. Except this is a Tony Leach Skirtless piston set up. So trying to find a spring here in the USA that fits his top hat and guide...is a pain. Trust me I've tried. Maybe a look thru the spring bin to find that unicorn spring before I cut.

 

[beerthief]

Maybe a different pellet heavier, will shoot slower and crono lower ?

How far down do you need to tune ? if your saying 12 down to 11.6 then the pellet trick might work .

 

[jccams]

Maybe a different pellet heavier, will shoot slower and crono lower ?

How far down do you need to tune ? if your saying 12 down to 11.6 then the pellet trick might work .

As long as the heavier pellet meets accuracy requirements.

 

[JP806TX]

Maybe a different pellet heavier, will shoot slower and crono lower ?

How far down do you need to tune ? if your saying 12 down to 11.6 then the pellet trick might work .

Another great suggestion. Except the suggested pellet is JSB express at 7.87 grain. I've tested other pellets for WFTF competition accuracy and the JSB express is the go to pellet for accuracy (with this Tony Leach set up). I will retest with a heavier pellet for power level and accuracy.

 

[Mycapt65]

Heat up the end of the spring until it glows and collapse the last half coil or so. Some people let them air cool slowly others quench them in oil to re-temper them. I've always let them air cool slowly and haven't had any problems. This is the easiest way to drop a little power

 

[iAMzehTOASTY1]

Heat up the end of the spring until it glows and collapse the last half coil or so. Some people let them air cool slowly others quench them in oil to re-temper them. I've always let them air cool slowly and haven't had any problems. The is the easiest way to drop a little power

I've learned so much on this website!
I will definitely remember this tip

 

[JP806TX]

Heat up the end of the spring until it glows and collapse the last half coil or so. Some people let them air cool slowly others quench them in oil to re-temper them. I've always let them air cool slowly and haven't had any problems. This is the easiest way to drop a little power

Thank you Mycapt65
I think that will be my next step if this 48 hr cocking scheme doesn't work.

 

[thumper]

If your spring loses it's "spring" by any appreciable amount in several to 48 hours, it was junk to start with.

You need to lose preload by cutting a 1/2 coil and closing and squaring, removing shims if there are any, or heating and collapsing a coil.

The BEST way, would be to reduce the stroke just a touch by unscrewing the latch rod in the piston. If you can get away with this with Tony's piston design, I'd try that first.

 

[JP806TX]

Heat up the end of the spring until it glows and collapse the last half coil or so. Some people let them air cool slowly others quench them in oil to re-temper them. I've always let them air cool slowly and haven't had any problems. This is the easiest way to drop a little power

I know 48 hours are not up yet. But I think Thumper is right. Some of these quality springs just does not easily take a set. They just bounce right back again and again.

SO onward to -----Operation coil collapse.-----

Pulling that coil spring off the Delrin guide was a B I T C H. I now found an easier way to get those tight springs off. But that's another posting.

Tools needed, heat source (in this case ...gas stove top...wait till the wife is out of the house), needle nose vice grip, and the old OEM steel guide and bottom washer. (maybe an oven mitten cos this stuff gets F....ing hot).

heat up the end of the spring till it's slightly red. Take off heat, put spring on steel spring guide and collapse with needle nose vice grip. (while trying not to get a 3rd degree burn...that would be bad).

Will post pics when I successfully chrono this spring/gun. (Tech difficulties, will try later)
---

Pretty happy with the results (3 shots... average to around 11.6 FPE. ) I'm sure it'll settle in and stabilize at a lower FPE as I also changed out the breech seal.

Thank you to all those with helpful suggestions.

--
After 60 more shots. We are averaging 11.48 FPE (according to my cheap China Chrono..woo hoo). Hope it stabilizes at this power...till after the AZ Sonoran Desert Grand Prix in March 2023

 

[brownhipower]

congrats on solution

 

[JP806TX]

Update after collapsing 1-2 coils, back in Jan 27, 2023
Shot a local match on 2/19/23
score was 45/62=72.6% (didn't bother to chorno the gun thinking ...it's stable)

Was shooting in Arizona. March 3, Friday at sight-in, chrono the gun and it was shooting 820 fps (shooting JSB express at 7.87 grain, this works out to 11.75FPE. Right in the sweet spot).

Arizona, Saturday shot a 27/60 = 45%, damn??? what happened? shooter/operator error? Gun was chrono during the match as required 787 fps (10.8FPE...hmmm, low but not low enough to make changes)

Arizona, Sunday shot a 28/60 = 46.6% double damn?? shooter/operator error? Gun was chrono during the match as required 813 fps (11.5 FPE...hmmm ok maybe the reading on Saturday was not accurate?, looking more like shooter S U X)

Shot a local match on 3/19/23
score was 49/64= 76.5%, I noticed during the match that after 16 shots, the TX started shooting 1 mil-hash lower (took 3 misses to figure that out. Thank gawd there was no wind only rain). Shot the rest of the match aiming 1 mil-hash low...Still S U X. Came in last place again.
chrono the gun post match at 10.2 FPE. OMG...maybe we need to do something.

Tore the gun apart: the spring looks good. Breech seal looks ok.

Added a washer at the end of the spring guide, new breech seal just in case. Chrono the gun, it's back up to 11.4 FPE.

I think there's probably 4-6 months of stability left in this spring (maybe less?).

So what is the morale of this story?
I S U X at away matches (and most of the local matches...someone suggested PCP...isn't that spendy and addictive?) and when you heat and collapse coils, keep a very very close eye on your FPE. With high volume use, 2-3 months of stability is probably all you can milk out of your spring.

 

[Mycapt65]

What I find interesting is your power increased at one point. I'm not familiar with the TXs but I would think that if heating and collapsing coils was the culprit of the power loss, the power might settle, but I can't see how it would return.

I'd be more inclined to look at atmospheric conditions or lubrication. I've had springers with uncut springs go up and down a half pound with no changes but the weather. My HW50 is 11.5 fpe some days 12 other days. That's with the same tin and inside my temperature steady basement. Most of my other springers vary daily as well but its closer to a quarter pound. I believe both atmospheric pressure and humidity affect springer outputs.

Also where I live is basically sea level but if you have significant altitude differences there in your AZ locations that could vary your power.

Also my experience is springers shoot significantly hotter initially and then slow down a bit as they are shot for long periods of time. They eventually plateau but it's usually a fair bit slower than the first few shots. If you test your power when you first get to a match, the power will likely be higher than if you test it after a lengthy practice session.

Just a few things to consider.

 

[JP806TX]

Good points. Just to add more data to confuse the issues (sorry)
my home gun range after some research is around 400 feet above sea level.
I was using a cheap Chinese chrono at home.
Home range chrono readings were all done post match.

Rio Salado gun range at Mesa Arizona was around 1,500 feet above sea level
I think, it was an Airchrony? and I believe the same one was used for all 3 days.
Chrono readings on Friday were after sight-in (gun was warmed up)
Chrono readings on competition days (Saturday and Sunday) were during the match. (gun was warmed up during sight-in and during the match)

According to limited Google search. Spring gun power tends to go down with increase in elevation. Most don't notice a power drop until around 2000 feet.

The fact that multiple chrono (at least two or more) were used may have tainted the actual readings.
Elevation may have robbed some power (didn't record or research weather conditions. That may play a role).

It's possible that spring behavior may not be totally linear after "alterations". Meaning it may "bounce" around till it stabilize.

Plus using match results is not the best method of gauging spring behavior. This shooter at least historically s u x shooting springers (regardless of spring condition.)


Edited: If you ignore the Arizona Chrono readings (at different elevation and with different chrono). The home chrono trend was 11.6, 11.48, to 10.2 (from Jan 27 to march 19, 60 days, with heavy use). The 10.2 FPE had correlational supporting evidence for the observed POI drop.

Eliminating the Arizona chrono readings seems to reduce the noise in the data and provide a potential explanation for the (rogue?) increase in FPE. This supports our shared experience that over a "longish" time frame, spring performance tends to degrade over time and a high probability that in "this" case the change in power is most likely spring performance related and not due to environmental conditions.

 

[Mycapt65]

1000 feet of elevation makes a significant difference. At least according to this formula found on Vortek's website. When practically applied my HW50 which makes 11.99 fpe at sea level would only make 11.28 fpe at 1000' above sea level. That's a significant difference.

Also using two different chronos can lead to different results. They shouldn't in a perfect world, but we don't live in a perfect world.

I'm not saying there wasn't some instability in your spring modification. I'm just saying there's a lot of other stuff to look at. I've never had a rifle spring increase power after initial installation. I've had lots of gun's wander around as the parts break in. Seals, guides, hones, barrels all contribute to the power equation. Anytime I've had a freshly tuned gun increase power there was a practical reason other than the spring got stronger.

Like I said earlier I've also had well broken in guns go up and down in power for internal temps and atmospheric conditions. It's totally normal for springer power to vary a bit as conditions change. Sometimes its noticeable to the layman, sometimes it's not. It will always be noticeable to someone who shoots competitively. I don't shoot competitively so I doesn't bother me to occasionally reset my zero at the beginning of a session.

In any event when trying to diagnose anything you have to minimize variables. Testing at two different altitudes with different chronographs could easily F with your head. I think its more important to learn to work with the power you have for that day and ignore the actual number. If the guns average power level isn't working for you after it settles, then change it. Then you'll have to expect some temporary instability again.