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 Post subject: Detuned .177cal Optimus
PostPosted: Wed Feb 01, 2017 2:03 am 
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Joined: Sat Sep 03, 2005 9:25 am
Posts: 3432
Location: Ontario, Canada
I finally broke into my Canadian detuned .177cal Optimus. I was expecting a .118" wire, 33 coil spring with a vented 150mm piston. Instead I pulled out a thin .098" wire, 34 1/4 coil spring with a non-vented 170mm piston. Interesting! The spring guide is the same .475" as on my full power U.S. spec Optimus. Same spring spacer too. Seals are fine. Out-of-the-box it was doing 497fps average with 8.44gr JSB Exact.

The Crosman web site indicates a B19-00-4B spring for the 495fps .177cal Optimus. I order this spring and a .118" wire, 33 coil spring arrived with this stock number on the package. I'm guessing that this medium weight spring is sometimes used with a vented piston for 495fps... but I'm not sure what vented piston length is used for .177cal.

My full power .177cal Optimus has a .122" wire, 36 1/4 coil spring with a 150mm piston. Original seals were damaged. With new seals it was doing 960fps with 7.9gr Crosman HPs (not dieseling).

So it looks like there are at least 3 different springs and 3 pistons used in the Optimus rifles.


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PostPosted: Wed Feb 01, 2017 3:48 pm 
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Joined: Mon May 26, 2014 1:08 am
Posts: 480
Location: Thunder Bay
That skinny spring (.098/34) you pulled out of your non-pal Optimus is identical to the spring I took out of my non-pal, non-vented short piston .22 phantom. Seems Crosman de-tuning is like a box of chocolates.
I'm going to try the .118/33 spring in my .22 phantom. The stock full power spring (.122/36) makes 17 fpe with a harsh shot cycle, even with a lube-tune and a shrink-tubed guide. I'm hoping the .118/33 will make about 12 fpe.

_________________
12 springers and a couple of pumpers.
2 lathes and lots of scrap metal.

I'm not multitasking. I'm doing something else until I remember what I was doing.


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PostPosted: Thu Feb 02, 2017 12:17 pm 
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Joined: Mon May 26, 2014 1:08 am
Posts: 480
Location: Thunder Bay
I put the .118 dia. 33 coil #B19-00-4B in my .22 Phantom. My non-pal phantom has a non-vented short piston.
With a full power (.122 dia. 36 coil) spring the gun made 17 fpe.
With the medium power spring power dropped to 13 fpe (CPHP at 640 fps).
It's a new spring so it still has to take a set. It should slow down a little. Shouldn't go below 12 fpe. I used the stock guide and spacer. There is still 1" of preload. There will probably be less preload after 100 shots or so when the spring takes a set.

I installed a Vortek "Docile" spring and a custom guide in a Ruger to de-tune it to 12 fpe. This medium power Crosman spring gives the same results with a short piston B18 and is a drop in fit using the stock guide and spacer. The Crosman spring costs $12 CDN + shipping($20 CDN total). Vortek is $18.50 US + shipping to Canada ($20) and exchange will push the bill over $50 CDN.

Hey Todd -sure would like to know what this medium power spring will do in your medium length unvented piston .177 Optimus :D
I'm guessing 650 fps. We should start a lottery...

_________________
12 springers and a couple of pumpers.
2 lathes and lots of scrap metal.

I'm not multitasking. I'm doing something else until I remember what I was doing.


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PostPosted: Fri Feb 03, 2017 12:26 am 
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Joined: Sat Sep 03, 2005 9:25 am
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Location: Ontario, Canada
I have the detuned Optimus in pieces right now. I'm finished with the trigger and just have a bit more polishing to do on the slots. They must have used SuperGlue on the hinge bolt. It won't budge! The hinge isn't sloppy so I will leave it be unless is wears loose. At that point I can dance a flame on the bolt and get it to turn. I don't want to ruin the synthetic hinge washers right now.

The .098" spring is a sloppy fit on the guide. I haven't decided if I'll sleeve the guide or just go with the .118" spring. Curiosity... yah... maybe .118".


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PostPosted: Fri Feb 03, 2017 6:30 am 
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Joined: Mon May 26, 2014 1:08 am
Posts: 480
Location: Thunder Bay
I had one hinge bolt I couldn't budge. I used a hammer blow impact driver with the receiver supported on a hockey puck.
Broke it free with no marring on the receiver or the screw. PM me if you want to borrow it.

_________________
12 springers and a couple of pumpers.
2 lathes and lots of scrap metal.

I'm not multitasking. I'm doing something else until I remember what I was doing.


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PostPosted: Sat Feb 04, 2017 11:17 am 
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Joined: Sat Sep 03, 2005 9:25 am
Posts: 3432
Location: Ontario, Canada
I re-assembled the Optimus with the .118" 33 coil spring installed with the same 170mm piston. Cocking effort was noticeably higher than with the .098" spring. The full 1.5" OEM spacer was left on the guide. After the initial dieseling routine, I shot about a dozen pellets that were quite consistent. Average velocity is now 745fps with 7.9gr Crosman HPs. My next plan is to reduce the spacer to 1/4" or 1/2" and test again. I'm looking for 600-625fps.


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PostPosted: Sun Feb 05, 2017 2:02 am 
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Joined: Sat Sep 03, 2005 9:25 am
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Location: Ontario, Canada
Update Optimus-500

I tried 1/4" and 1/2" spacers with the .118" 33 coil mainspring. There was no preload at all. I ended up using just over 3/4" of spacer that left me with approx. 1/4" of preload. Perfect! I'm now getting 630fps average with 7.9gr pellets.

Unfortunately, the accuracy with 8.44gr JSB Exact is far from acceptable. The Stoeger X-Field and H&N Sport are acceptable. Attached is a pic of 4 groups of 5 shots each. Two dimes were included for comparison. The middle target was 2 attempts with the JSBs. The JSBs look like 4-shot groups but there are 5 in each.


Attachments:
Opt500 002b.jpg
Opt500 002b.jpg [ 168.82 KiB | Viewed 411 times ]
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PostPosted: Mon Feb 06, 2017 1:44 am 
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Location: Ontario, Canada
I finished up the 10 metre accuracy tests with the tuned Optimus-500. As mentioned above, it's now doing 630fps with the 3/4" spring guide spacer. The spring is 33 coils of .118" with a 170mm non-vented piston.

Accuracy at 10m (5-shot groups)

H&N Sport – .21, .31, .16, .25, .32, .24, .30 --- ave .26” ctc
H&N Excite Hammer – .34, .33, .25, .40, .35, .30, .28 --- ave .32” ctc
Crosman HP – .36, .28, .33, .38, .45, .43, .45 --- ave .38” ctc
RWS Superdome – .31, .35, .43, .35, .27, .36, .26 --- ave .33” ctc
RWS Hobby – .36, .56, .47, .43 --- ave .46” ctc
Stoeger X-Field – .32, .36, .37 --- ave .35” ctc

RWS Diabolo Basic... JSB Exact 8.44gr... JSB Exact RS 7.33gr... H&N Excite Econ --- groups were 0.50” - 0.80” ctc

Oddly, this rifle doesn’t seem to like JSB Exact. I tried several different times to get them to group but no luck. My full power Optimus loves JSBs.


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PostPosted: Tue Feb 07, 2017 11:51 am 
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Joined: Sat Sep 03, 2005 9:25 am
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Location: Ontario, Canada
Crosman Optimus - 20 Yard Accuracy
I had some time to test the "long piston" Optimus at 20 yards. This rifle is still tuned to a little over 600fps with 7.9gr pellets. It has the 170mm piston, .118" 33 coil spring and a short spacer to give about 1/4" of preload.

Six pellet types were tested. Three pellet types averaged .62" to .67" over a minimum of 5 groups for each type.

The H&N Sport was the most accurate pellet at 20 yards so I shot 10 groups to get an average. The last group was shot at the aiming square to see if the target was easier for my old eyes to see.

Overall average for the 10 groups at 20 yards is 0.47" ctc.


Attachments:
Opt600at20sports 002b.jpg
Opt600at20sports 002b.jpg [ 229.97 KiB | Viewed 310 times ]
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PostPosted: Mon Feb 13, 2017 2:10 am 
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Joined: Sat Jan 25, 2014 9:16 pm
Posts: 1278
Location: United States
Ricksplace: The bolt head is tapered so it can lock kinda like a drill chuck on a drill press if you've ever seen that magic.
You can try to squeeze the forks around the screw to break the lock it has, but some people end up drilling the bolt out.
Otherwise be super careful when tightening that next time. I prefer to lightly snug it which is rekon is just a few ftlbs, but as far as locking up it all depends on the surfaces of the bolts head and the tapered hole it fits, apparently the better the surfaces the easier it'll lock, and of course the tighter you go the more likely. I've never had a need but I suppose you could alter the bolts surface to prevent locking, like really roughening it up.


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