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PostPosted: Thu Dec 08, 2016 1:15 pm 
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Joined: Sat Sep 03, 2005 9:25 am
Posts: 3432
Location: Ontario, Canada
I picked up a full power .177cal Crosman Optimus to have some fun comparing to our Canadian detuned .177cal version (model CO1K77X vs CO5M77X). The rifles look almost identical on the outside. Same stock, sights, and receiver tubes. But the barrel on the Canadian version is 16.5" while the full power model is 18.5". Not sure why.

The detuned Canadian Optimus seems to have a slightly longer piston which gives a shorter power stroke. My old original Crosman Quest had a piston that was so long that the barrel only cocked to 90* with the tube. The Cdn Optimus definitely has a longer stroke than the old Quest. This Canuck Optimus is quite accurate and enjoyable to cock and shoot. Dime sized groups at 10m are typical.

The detuned Optimus gives a very consistent velocity. The rifle has seen a few hundred shots and recently tested at 489, 488, 487, 487, 491 fps with 8.4gr JSB Exact. It was about 10fps faster out-of-the-box. The rifle has seen no work other than a barrel cleaning. Eventually I'll give it a lube tune.

My full power Optimus has only seen about 20 shots and clocked at 760, 762, 760, 770, 750 fps with 8.4gr JSB Exact. I'm guessing that this is a bit low. I'm suspecting piston seal damage so that will be where I look first. It's louder to shoot than the detuned model but velocity is also 50% higher.

Cheers


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PostPosted: Thu Dec 08, 2016 6:12 pm 
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Joined: Sat Jan 25, 2014 9:16 pm
Posts: 1278
Location: United States
I'd imagine the barrel length is about power. The full power one needs the 18.5, the 500 probably needs less than the 16.5 but they gotta factor the leverage needed to cock it.
I imagine the 500 model has both a longer ~170mm piston and weaker spring. Your older gun must've had the 190mm piston. I like to hear about what's inside so if you can please post the piston length and spring wire dia, OD and coil count :) Helps others better figure out their guns too.
Good call ordering new seals, but I suspect something else is also hurting you because that is very low. First thing I'd suspect is breech seal leakage, but there are lots of things that can hurt it so I always go thru it all and fix everything. Assuming I haven't already, I can send you my guide which covers all the classic issues/fixes plus misc outside the box fixes like sanding the seal and barrel. Also how to adj the scope parallax, centering the scope, making the spring quiet, trigger mods etc. chevota at hotmail if you want it. Altitude is another that can hurt you but if the 500 is kissing 500 then I'd guess you're <300M?.


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PostPosted: Thu Dec 08, 2016 6:42 pm 
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Joined: Mon Jan 20, 2014 10:32 pm
Posts: 758
Location: Burlington ON
Chevota wrote:
Assuming I haven't already, I can send you my guide which covers all the classic issues/fixes

You should pm him, this guide is well worth having (Chevota - you should tidy it up and get it published as a book!)


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PostPosted: Thu Dec 08, 2016 6:45 pm 
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Joined: Thu Oct 04, 2012 10:27 am
Posts: 1108
Location: Thunder Bay,On.
My full p. Optimus now shoots 8.64 gr h&ns @885 fps.....if that helps you any....original seal had a slice in it so changed it out of course....

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PostPosted: Fri Dec 09, 2016 4:00 am 
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Joined: Mon May 26, 2014 1:08 am
Posts: 480
Location: Thunder Bay
Chevota wrote:
Altitude is another that can hurt you but if the 500 is kissing 500 then I'd guess you're <300M?.


This is interesting. Lake Superior is approx 600 feet or 200 meters above sea level. I live rural, but 300 meters higher than Lake Superior. When Todd chronographs my guns, his readings are consistently higher than mine.

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PostPosted: Fri Dec 09, 2016 11:46 pm 
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Joined: Sat Jan 25, 2014 9:16 pm
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Location: United States
It's not something a lot of people think about. I noted something to the effect of 12fps per 1000' with a Crosman, but hardly a good test, just a few guns at a few diff altitudes between ~500 and 8000'. The guns internals like spring, stroke and condition are no doubt factors, and I know other brands/models can be very different. The pumpers will suffer too obviously, but I never checked by how much, plus they too would be different by design and condition.


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PostPosted: Sat Dec 10, 2016 12:12 am 
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Joined: Fri Jul 01, 2016 7:47 am
Posts: 711
Location: Bradford
You can also convert it to nitro piston and do away with the spring entirely.

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PostPosted: Mon Dec 12, 2016 6:12 pm 
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Joined: Thu Mar 24, 2016 7:33 pm
Posts: 246
Location: Yukon
My Quest 1000 came with the longer barrel. I then swapped it for a Optimus stock so pretty much have the same rifle as your Optimus 1000. The Optimus is a very nice looking rifle. Even nicer once you remove the front site.
I need to spend more time (once I have a better ammo selection) to dial this rifle in. 20 meters targets are not so good just yet.


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