Canadian Airgun Forum

Hello everyone!
I'm a long time reader, first time poster

I have a Crosman Optimus .177 496fps (Canadian Tire Special) After downloading Chrono Connect for my Galaxy S8 and testing, I realized that the app is not working for my phone. I would consistently get around 130fps. Chrono Connect was setup properly.
I decided to go through with the mod anyways. I filled the piston limiter hole and added 2 pennies. I was able to borrow an iPAD from a friend and did the test again. This time it seems to be working (better anyways) and showing over 1800fps consistently. I'm not quite sure that this reading is very accurate. And without a real chrono meter, I'm kind of stuck and can't really tell of the app is off at all.
So, I'm wondering if anyone else out there did the similar mod, with the same rifle and either has, or can do a penetration test at 25 yards using crosman hunting (pointed) pellets? Or the same gun without the mod, a penetration test at 25 yards and original 495fps?
I'm almost going through a baking pan..

Any help or suggestions on estimating fps a different way or via penetration test would be appreciated!

Thanks very much!!

Well your APP is way off, like 1000 FPS off, Also don't trust them. Also if you don't have a PAL, shouldn't be modding.

Best to get a chrony......you should be getting between 950 to 1000 fps and 15 or 16 fpe with that setup....definitely not 1800.....that's 53 fpe by the way... ....…...that's PCP territory.....

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The cave you fear to enter....holds the treasure you seek

and breaks the sound barrier.

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I have some airguns.

Thanks for the replies!
I have my PAL and H1.. Now that we got the fact that the chrony app wasn't working properly, anyone have a penetration test I can compare with? or anyone here with a break barrel 495fps rifle we can compare penetrations on different objects? I'm not looking for exact numbers here. A guesstimate will work for me!

Thanks again!

Problem is yours not 495 anymore. I'm going to guess its shooting about 856 FPS with 7.4s and about 820 with 7.9. Because that is around what mine shot with 1 penny spacer and a blocked piston hole.

The BAM B18/19 platform, which is the basis for Crosman Quest, Phantom, Optimus, Summit, Benjamin Classic, etc is only capable of about 12 fpe no matter what you do (except add combustibles). So you should expect numbers like what leadslinger said. Phony chronys are not reliable!

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Iacio, ergo sum

Sorry about that....I seem to have over estimated your guns potential.I put a high powered spring in my phantom 500 and it now shoots an average of 933 fps with a 7.4 gr.(with no combustibles).....not 950 to 1000 like I thought you would get.If you're only getting 850 fps there's something wrong somewhere.....don't settle for less...

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The cave you fear to enter....holds the treasure you seek

Faster isn't always better. Also 850 FPS for a gun that wasn't full power out of the box is pretty good ( also tuned by pennies and JB weld ) But OP wanted to know how fast and well Im giving him the chrony numbers of my Vantage that I modded like his.

If I want faster and more accurate I'll haul out one of my 22LR. Or 850 FPS 22cal air rifles.

I agree leadslinger...but the the point of making 7.4 grain pellets shoot in the mid nines is only a reference for heavier pellets..obtaining 950 with a 7.4 means you'll get mid to high 800s with a 9 gr. which should provide good accuracy.Since he is using 7.4s.....shoot for the mid 9s when tuning.

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The cave you fear to enter....holds the treasure you seek

Well from my experience with tuning detuned guns. You don't fully get the same power as the assembled from factory high power ones. I never seen mid 900s on mine. Even deburred, polished, tuned etc.

What is the piston length on your detuned Optimus? I bought a .177cal 495fps Optimus last year from CanTire and it had the long 170mm piston with no vent hole and a thin .098" wire spring. This gave me a twangy 497fps with the 8.44gr JSB Exact pellet. I installed a 33 coil .118" spring and was getting 745fps with 7.9gr Crosman CPHP. The 36 coil (full power) .122" spring would likely give a bit more, as leadslinger posted. I ended up setting this rifle to 620fps for indoor shooting. It now has the .118" spring, 3/4" spacer and 170mm piston.

If you have the shorter 150mm piston with a vent hole then you would get higher numbers than I got with the 170mm, after you fill the hole. My 150mm piston Optimus with the .122" spring gave me mid 900s with the CPHP pellet from a new rifle. The rifle was not nice to shoot so I reduced the spring spacer length to 3/8" and settled on a sweet 800fps with the CPHP. A 3/4" to 1" spacer (rather than the OEM 1.5") with 150mm piston should put you into the mid to high 800s with 7.9gr pellets.

Here are some groups from 10 metres that I shot this week (from a rest). This is the 620fps Optimus. It's pellet finicky but still shoots okay.

170mm piston, no vent hole
33 coil, .118" spring
3/4" spring spacer
light barrel sanding, as per Chevota instructions

You can tune these rifles from 500fps to about 750fps with the 170mm piston. The 150mm piston, with a good set of seals, will take you up over 900fps when the spring is fresh. Find what spring combo gives you the rifle that you want.

Nice group....pretty accurate...mine too..I am shooting 885 fps with 8.18 stoeger wadcutters....full power spring with small shim..short piston... and switched over the breech seal to an o-ring style....to each his own I guess....

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The cave you fear to enter....holds the treasure you seek

Hellraizer: I think the only way outside a crony or app that works is to get some ballistic putty or similar that someone else has cronied against using the same/similar pellets. I remember Beeman used to sell putty and it came with a chart to estimate fps, but I haven't seen that or similar in a while. There are people here that use Duct Seal so maybe you can do a search for that? Crude but much better than your app that clearly isn't working. The app should be able to work but something is upsetting it. Maybe it's reading the shot and the shots echo rather than target impact. Or maybe the piston impact noise and shot? Or maybe your target distance is wrong, phone location wrong or who knows what. I'd check all the data settings and what not, plus shoot where there is no echo and see if it changes.
That app, or some app somewhere, will likely be able to see all noises, then from there you could ignore the wrong noises and do the math yourself. Lots of airgunners have a crony so maybe you could find someone locally? Maybe a local airgun club? Same with firearm ranges/clubs. Not sure how common those are in CA but they're everywhere in the US. If I have my crony out people often ask to take a shot over it.
I suppose another might be measuring pellet drop over distance, which is not very accurate but could at least tell if you're doing better or not.

Dukemeister: If a full power B18 is making 12 or less there is something very wrong with it. 15-18 is more the norm out of the box. My record is 20.4 for a .22 nitro version, after I tuned it. That's using all the oem parts, nothing special, no dieseling and using the spring that came with it. So while exceptional, it is possible, but not nearly as impressive as the 56 Hellraizer got
The lowest power I netted after a tune was 16.5 with a coil spring 177, which I discovered the source of the power loss was a bad barrel. Switching to another random barrel I had lying around instantly netted 18. Putting that bad barrel on another gun caused a similar loss. Imo the vast majority of B18 barrels are bad to varying degrees, so I almost always do a little work to them, or replace them.