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PostPosted: Mon Nov 14, 2016 2:06 pm 
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Crosman Optimus – Detuned 495 fps

Canadian Tire recently had the detuned .177cal Crosman Optimus on sale for $118.99 so I scooped one up to play with. Many years ago I had a detuned .177cal Quest that was pretty much identical to the Optimus on the exterior, except for the stock contours. The Vantage model also seems to looks similar, except for some stock contours. Same metal, different handles.

Cocking effort with the Optimus is very mild. I would compare it to the Weihrauch HW30S (aka Beeman R-7). Long shooting sessions would be no problem with this plinker. The rifle only weighs 7.2 pounds with the 4 power CenterPoint scope mounted.

Although I have had a FAC/PAL for over 35 years, I may even leave this rifle as a 500fps basement shooter or maybe “adjust” it to 600-625 fps.. It will likely see a lube tune, some trigger work, maybe a crown polish... and possibly new optics.

The new Optimus hasn’t been disassembled yet but right away I noticed that the cocking stroke is longer than my old Quest. The stroke might be close to a full power rifle, while the Quest only cocked to where the barrel was 90* to the compression tube (long piston). This Optimus definitely has a shorter piston length but I’m not sure if it’s identical to the full power version. It might be a tad longer.

Here are a few bits of piston & spring info that I gathered from the Crosman web pages.

.177cal
495 fps Quest >>> Piston B19-4-04-100 >>> Spring B12-1-00-4A
1000 fps Quest >>> Piston B18-04-100A >>> Spring B18-00-4D

495 fps Optimus >>> Piston B19-4-04-100A >>> Spring B19-00-4B
1000 fps Optimus >>> Piston B18-04-100D >>> Spring B18-00-4D

.22cal
Quest 800 >>> Piston B18-04-100A >>> Spring B18-00-4D
Optimus 800 >>> Piston B18-04-100D >>> Spring B18-00-4D

The .177cal-495fps Optimus seems to have unique piston & spring numbers. The original .177cal-495fps Quest had a mild B12 spring but the 495fps Optimus has something that appears to be different.

The rifle that I tested was unaltered, out-of-the-box. All I did was clean the barrel and mount the included CP scope. I’ll do the tests again after the tuning.

--- VELOCITY ---
JSB Exact (8.44gr) - seated pellets - 497, 500, 495, 497, 495 --- Ave = 497 fps

--- ACCURACY ---
10 Metres – From a rest at 10m I was averaging .40” to .45” ctc for 5 shot groups with JSB Exact 8.44gr, JSB Exact 7.33gr, RWS Hobby, and Stoeger X-Field pellets. The rifle seems to like the pellets seated so I use a Bic pen cap to push them slightly below flush.

30 Yards – From a rest, 5 shot groups.
JSB Exact (8.44gr) - 1.85”, 1.51”, 1.63”, 1.53” --- Ave 1.63” ctc
The 1.85” group included a flyer. The group was under ¾” ctc without the flyer (4 shots).

The untuned rifle has a lot of spring twang that can be greatly reduced with the tune. A lube tune, better fitting guide and a fresh barrel crown should all help squeeze the groups down a bit. I don’t expect HW30 accuracy but a little improvement should be possible.

--- OVERALL OPINION ---
The Optimus seems to be a nice rifle for the price. It’s the typical Chinese B18 with another facelift but I knew that before the purchase. We all know that the B18 gets dressed up often but maintains the basic common foundation. It shoots fine, parts are cheap, a power upgrade is easy, and the trigger is not too difficult to improve.


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PostPosted: Mon Nov 14, 2016 2:24 pm 
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The 5-shot, 10-yard groups can be covered by a dime. Here is a pic of the 30-yard target from yesterday. The 1.85" group has a definite flyer. The remaining 4 shots formed a sub-3/4" group.

I adjusted the parallax on the 4X CP scope but I think better optics might help... especially with my aging eyes.


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PostPosted: Mon Nov 14, 2016 6:00 pm 
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Location: Nova Scotia
Cool review. My nephew Toner has had his Optimus for a few years now and is still loving it.

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PostPosted: Tue Nov 15, 2016 5:16 am 
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Location: Bradford
Thanks, your post reminded me I have one of these somewhere :)

Low and behold i just found it buried under a bunch of other rifles in cases that I have no room in cabinets for LoL.

Has to be 4 or 5 years old I guess and unfired, at least I dont ever remember shooting it.

Very likely dry by now, so another small project for this weekend! Thank you again for your write up.

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PostPosted: Thu Nov 17, 2016 1:56 pm 
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Location: Yukon
In my personal opinion the Optimus is the nicest looking Crosman of all.
The slim stock has an elegance not found on most of the bulkier Crosman wood stock models. I bought a used at a pon shop and up-springed it.

Kick myself for not buying one 2 years ago when CT had them for 99 bucks scoped.


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PostPosted: Fri Nov 18, 2016 5:07 am 
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Location: port colborne. ontario.
tango wrote:
In my personal opinion the Optimus is the nicest looking Crosman of all.
The slim stock has an elegance not found on most of the bulkier Crosman wood stock models. I bought a used at a pon shop and up-springed it.

Kick myself for not buying one 2 years ago when CT had them for 99 bucks scoped.

your;e right it is a very nice looking rifle. I got one a few years ago when they were on sale and i just got back into shooting. i sold it very shortly after tho because of that hard twang. kicked like a mule.


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PostPosted: Tue Jan 17, 2017 5:34 pm 
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I just bought a non-PAL (I have a PAL) Optimus from another forum member who had only fired around 200 pellets through it. It looked brand new when I opened the box so I'm sure that's accurate.

By the time I got to try it, it was evening, so I just fired a few pellets in my garage firing range.

Pete's remark "kicked like a mule" rang true.

The cocking effort was the heaviest of any of my non-PAL guns and the barrel went past 90 degrees to cock.

It was LOUD, and felt like the piston was hitting the end of the cylinder, so I stopped shooting and took it apart. (I wish I'd Chrony tested it, but by the time I thought of it, it was too late.)

I took it apart without a spring compressor, and the spring had only about 1/2" of pre-load. It took it out, and it looked fine. I suspected the seal had a chunk out of it from the factory assembly causing the hard kick, but as I looked at it, it looked fine too.

Then I looked at the end of the piston. WOW :shock:

There was a hole drilled (obviously a factory job) through the dove-tail into the interior of the piston. That's why there was no air cushion to stop the piston at the end of its travel. What there was, was the seal 0.042" proud of the dove-tail. That was the "cushion" for the piston.

I drilled out and tapped the hole to take a M3x0.5 bolt bedded with JB Weld, cut and sanded flush with the dove-tail.

While that set, I sanded 0.030" off the face of the seal leaving 0.012" cushion.

I made a Pepsi bottle piston liner, and those were the only three things I did to the gun. No shims or anything.

The trigger I replaced with one I had modified with the two screw mod some time ago.

I put the whole thing back together, and it fired a lot smoother.

This morning I put it over the Chrony.

Crosman Premier HP 7.9 grain

10 shots, avg 813.95 fps, Max Spread 19.8 fps, SD 6.26

JSB 4.52, 8.44 grain

10 shots, avg 783.74 fps, Max Spread 8.6 fps, SD 2.86

I'm going to disassemble it again, and do a full lube tune, de-burring, piston buttons etc., but I'm pretty happy with the way it shoots right now. If I remember, I'll take some measurements (piston/dove-tail/spring), and I'll see what happens to the Chrony numbers.

Peter :D


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PostPosted: Tue Jan 17, 2017 10:16 pm 
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Thanks for posting Peter! It sounds like your non-PAL Optimus was detuned differently than mine. It sounds like you might have the full power mainspring and shorter guide spacer (1/2" vs 1.5" preload). It will be interesting to hear if you have the 150mm piston or slightly longer. I posted a pic below showing the open barrel angles on my Optimus-500 vs Optimus-1000.

Mine non-PAL Optimus has the weaker spring and slightly longer piston. No piston hole. I could probably cock the rifle with one finger. I'll post piston and spring sizes when I finally get around to tearing it down.

Thanks,
Todd


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PostPosted: Wed Jan 18, 2017 12:30 pm 
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Well I did the lube tune and took some measurements. I de-burred it, buttoned the piston honed the cylinder etc., and it is now even smoother. I didn't think to measure the spring guide spacers but I will next time. I have extra spacers and washers, but I'll probably leave them out for now.

Piston diameter 24.6mm (1")
Piston length without dovetail 145.27mm (5.719")
Piston dove-tail height 4.55mm (.179")
Spring length 22.8cm (9")
Spring OD 18.8mm (.75")
Spring wire dia. 3mm (.119")

The Chrony test today was disappointing regarding fps as it went down and that's the first time that's ever happened after a lube tune.

Average with JSB Exact 4.52, 8.44 grains was 760.7, max spread of 24.7 fps but a really good SD of 1.16 over 20 shots. (One shot about 10 above average and one about 15 below average. The rest were close.)

When I disassembled the gun the first time, I realized that the piston seal was not very tight, so after I sanded so much off the face, the diameter may have reduced slightly. Then when I honed the cylinder a tiny amount more "clearance" was created, thus the decrease in velocity.

In the next few days, I'll probably put an un-sanded seal in the gun and see what it does to the numbers. It'll leave more "dead air" inside the cylinder, but it may fit snugger.

Accuracy at 10 yards seems to be excellent using the open sights. I prefer a different open sight set-up so I'll change it when I get another rear peep sight, meanwhile I'll put the included scope on it, and see how it does with that.

Having fun with air guns.

Peter :D


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PostPosted: Wed Jan 18, 2017 6:00 pm 
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Thanks Peter. It sounds like you have the standard 150mm piston... but it had the hole for detuning. Your spring is a bit thinner than what came in my full power Optimus (.119" vs .122"). You would likely see mid 900s with the heavier spring. I'm not after the power so I detuned my full-power version to 800fps with 7.9 grain. I plan to keep my Cdn version at 500-600fps. Now I'm curious as to what spring and spacing they used in my detuned Cdn version. It's likely the .118" spring with very little spacing and a slightly longer piston.

I recently purchased a full power and a detune spring from Gravel. Full power is 36.25 coils of .122" wire. The detune spring is 33 coils of .118" wire.

Cheers,
Todd


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PostPosted: Thu Jan 19, 2017 1:52 pm 
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Just a note that I solved the fps puzzle.

The surface by the transfer port where the breech seal presses, had major machining swirls on it. During the lube tune I sanded it with 400 up to 1500 grit which made it a lot better, but I forgot to change the breech seal.

New (slightly thicker) seal, (there was already a shim underneath it) and the gun is back where it was fps wise.

It really is a very nice gun.

Peter :D


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PostPosted: Tue Mar 14, 2017 6:00 pm 
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I updated the review with 20 yard accuracy tests. Once the warmer weather arrives I'll do 30 and 40 yards.

---------------------------------------------------


Crosman Optimus Review – Canadian Detuned 495 fps

Our local Canadian Tire store had the detuned .177cal Crosman Optimus on sale for a reasonable price so I picked one up to tinker with. Many years ago I had the Canadian detuned Crosman Quest that was pretty much identical to the Optimus, except for the stock contours. The Vantage model also seems to be the same rifle with a different handle. This Chinese B18/19 rifle wears many handles and name tags.

Cocking effort with the detuned Optimus is very mild and can easily be accomplished with only two fingers on the barrel. Long shooting sessions would be no problem with this mild plinkster. The rifle only weighs 7.2 pounds with the 4 power CenterPoint scope mounted.

The Optimus shoots great as a 500fps basement shooter but my preference was for a little more power to bring it up to 600-625 fps with average weight pellets. The added power will help flatten out the trajectory for 30-40 yard plinking shots.

After a complete teardown, the factory detuning method became obvious. This Optimus-500 has a non-vented 170mm piston whereas the full power version uses a shorter 150mm. The mainspring was 34 coils of light .098” wire whereas the full power version uses 36 coils of .122” wire. The shorter cocking stroke with the very mild mainspring drops velocity down to the non-PAL level. My old non-PAL Quest used an even longer non-vented piston with a thicker wire mainspring. Other versions of the non-PAL Optimus/Phantom have been reported as using a short 150mm vented piston with the thin wire spring. All versions seem to be using the 1.5” spring guide spacer.

It was interesting to notice that my detuned Optimus did not have the B19-00-4B mainspring, as indicated by Crosman for this model. My shipment of spare Crosman parts arrived with a 4B mainspring and it turned out to be 33 coils of .118” wire. There are at least 3 different springs and 3 pistons used for these rifles.

Here are a few bits of piston & spring info that I gathered from the Crosman web pages.

.177cal
495 fps Optimus >>> Piston B19-4-04-100A >>> Spring B19-00-4B
1000 fps Optimus >>> Piston B18-04-100D >>> Spring B18-00-4D

495 fps Quest >>> Piston B19-4-04-100 >>> Spring B12-1-00-4A
1000 fps Quest >>> Piston B18-04-100A >>> Spring B18-00-4D

.22cal
Optimus 800 >>> Piston B18-04-100D >>> Spring B18-00-4D
Quest 800 >>> Piston B18-04-100A >>> Spring B18-00-4D

--- VELOCITY ---
The rifle was first tested in unaltered form, out-of-the-box. All I did was clean the barrel and mount the included CP scope. A couple of dozen shots were taken to distribute the OEM lube.

JSB Exact (8.44gr) - seated pellets - 497, 500, 495, 497, 495 --- ave 497 fps


--- ACCURACY - unaltered rifle ---

--- 10 Metres – 5 shot groups ---
From a rest at 10m I was averaging .40” to .45” ctc for 5 shot groups with JSB Exact 8.44gr, JSB Exact 7.33gr, RWS Hobby, and Stoeger X-Field pellets. With the mild .098” spring, the rifle seemed to like the pellets seated in the barrel so I used a Bic pen cap to push them slightly below flush.

--- 30 Yards - 5 shot groups ---
JSB Exact (8.44gr) - 1.85”, 1.51”, 1.63”, 1.53” --- ave 1.63” ctc

The untuned rifle has a lot of spring twang that could be greatly reduced with a tune. A lube tune, better fitting guide and a fresh barrel crown should all help squeeze the groups down a bit. I don’t expect HW30 accuracy but a little improvement should be possible.


--- MODIFICATIONS ---
I broke into the detuned .177cal Optimus to do a bit of polishing and lubrication. As mentioned above, the spring turned out to be a 34 coil with thin .098" wire. The spring guide is the same .475" diameter as used in my full power U.S. spec Optimus. The skinny spring was a sloppy fit on the guide which allowed the spring to bend into a mild s-shape. The spring maintained this double cant when removed. This sort of poor fit resulted in the typical metallic twang noise when shooting.

The piston seal and breech seal looked fine so replacements were not required. After the typical polishing and moly paste treatment, I re-assembled the Optimus with a 33 coil .118" spring and the same 170mm non-vented 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 was now 745fps with 7.9gr Crosman HPs. Unfortunately, this was much more than my desired 600-625fps with 7.9gr pellets.

The next modification was to reduce the spring spacer length and test again. I tried 1/4" and 1/2" spacers with the same 33 coil .118" mainspring. There was no preload at all with these spacers. I ended up using just over 3/4" of spacer that left me with approximately 1/4" of preload. Perfect! I'm now getting 625fps average with 7.9gr pellets.

Trigger work was very minor. The return spring was over-bent to reduce tension, engagement surfaces polished, moly paste to all friction areas, and a longer adjustment screws was added. I adjusted the trigger engagement so it still had a little creep. The feel is much better than prior to the work.


--- ACCURACY – modified rifle ---

--- 10 metres – 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 – groups .50” to .75” ctc
JSB Exact RS 7.33gr – groups .50” to .75” ctc
H&N Excite Econ – groups 0.50” to 0.75” ctc

--- 20 yards – 5 shot groups ---[/b]
H&N Hammers – 1.22, .83, 1.06, 1.05, .56 --------------------- ave .94” ctc
JSB Exact – .74, .40, .38, .80, .84, .53, .69 --------------------- ave .73” ctc
Crosman HP – .70, .76, .41, 83, .76, .57 ------------------------ ave .67” ctc
RWS Superdome – .54, .71, .58, .77, .49 ------------------------ ave .62” ctc
Stoeger X-Field – .60, .62, .62, .74, .67, .61, .75, .50, .50 --- ave .62” ctc
H&N Sport – .63, .50, .54, .40, .39, .50, .34, .55, .48, .40 --- ave .47” ctc

The Crosman HP did better than expected at 20 yards. I was careful to throw away a few fat pellets that seemed a bit difficult to start into the barrel. Now I’m curious to see how these Crosman HPs do at 30 and 40 yards.


[b]ACCURACY - after 500 pellet break-in period


--- 10 metres – 5 shot groups ---
JSB Exact 8.44gr - .21, .35, .22, .36, .18, .34, .31, .34, .21, .28 --- ave .28”ctc

--- 20 yards – 5 shot groups ---
H&N Sport - .63, .50, .54, .40, .50, .39, .34, .55, .48, .40 ----------- ave .47”ctc
JSB Exact 8.44gr - .55, .64, .69, .35, .46, .75, .36, .45, .64, .70 --- ave .56”ctc

--- 20 yards – 5 shot groups ---
H&N Sport - .67, .62, .41, .58, .56 ------------- ave .57”ctc
JSB Exact 8.44gr - .57, .38, .48, .71, .58 ---- ave .54”ctc

Note: JSB Exact 8.44gr were a new lot from 2016

--- OVERALL OPINION ---
The Optimus seems to be a nice rifle for the price. It’s the typical Chinese B18 with another facelift but I knew that before the purchase. We all know that the B18 gets dressed up often but maintains the basic common foundation. It shoots fine, parts are cheap, a power upgrade is easy, and the trigger is not too difficult to improve. I’m looking forward to testing accuracy at 30 and 40 yards.


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PostPosted: Wed Mar 15, 2017 11:10 pm 
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Thanks for sharing, nice groups at 25!

Sent from my LG-H812 using Tapatalk


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PostPosted: Thu Apr 06, 2017 9:20 am 
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PeterG wrote:
I just bought a non-PAL (I have a PAL) Optimus from another forum member who had only fired around 200 pellets through it. It looked brand new when I opened the box so I'm sure that's accurate.

By the time I got to try it, it was evening, so I just fired a few pellets in my garage firing range.

Pete's remark "kicked like a mule" rang true.

The cocking effort was the heaviest of any of my non-PAL guns and the barrel went past 90 degrees to cock.

It was LOUD, and felt like the piston was hitting the end of the cylinder, so I stopped shooting and took it apart. (I wish I'd Chrony tested it, but by the time I thought of it, it was too late.)

I took it apart without a spring compressor, and the spring had only about 1/2" of pre-load. It took it out, and it looked fine. I suspected the seal had a chunk out of it from the factory assembly causing the hard kick, but as I looked at it, it looked fine too.

Then I looked at the end of the piston. WOW :shock:

There was a hole drilled (obviously a factory job) through the dove-tail into the interior of the piston. That's why there was no air cushion to stop the piston at the end of its travel. What there was, was the seal 0.042" proud of the dove-tail. That was the "cushion" for the piston.

I drilled out and tapped the hole to take a M3x0.5 bolt bedded with JB Weld, cut and sanded flush with the dove-tail.

While that set, I sanded 0.030" off the face of the seal leaving 0.012" cushion.

I made a Pepsi bottle piston liner, and those were the only three things I did to the gun. No shims or anything.

The trigger I replaced with one I had modified with the two screw mod some time ago.

I put the whole thing back together, and it fired a lot smoother.

This morning I put it over the Chrony.

Crosman Premier HP 7.9 grain

10 shots, avg 813.95 fps, Max Spread 19.8 fps, SD 6.26

JSB 4.52, 8.44 grain

10 shots, avg 783.74 fps, Max Spread 8.6 fps, SD 2.86

I'm going to disassemble it again, and do a full lube tune, de-burring, piston buttons etc., but I'm pretty happy with the way it shoots right now. If I remember, I'll take some measurements (piston/dove-tail/spring), and I'll see what happens to the Chrony numbers.

Peter :D


Just looking back at this post and wondering what does keep the piston from slamming into "wall" at the end of its travel? Especially since the relief hole described is in fact non existent on all the US models and only used to detune canadian models.

i am especially interested as I purchased a used Optimus detuned with a relief hole in a short piston. I simply JB welded the hole on the front face (the quick cure variety) and then a smaller amount on the inside of the piston. When I took it out to shoot the retort was extremely load, like a rimfire at least and persisted through 5 shots. I decided to tear it down before shooting any more and could find no trace of the weld on the front of the piston though the hole was still effectively plugged by the inside weld. All the material from the weld had obviously exited the barrel.
I am now concerned that the top hat will soon destroy the inside weld too. I have now purchased the full strength JB weld and want to replug from the front face but want to first understand what how the piston face was designed to be cushioned.
Anyone else attempting to plug a piston be aware of the different types of JB weld out there. I didnt realize there are 3 or 4 grades.


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PostPosted: Wed Apr 19, 2017 9:56 am 
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UPDATED

Crosman Optimus Review – Canadian Detuned 495 fps

Our local Canadian Tire store had the detuned .177cal Crosman Optimus on sale for a reasonable price so I picked one up to tinker with. Many years ago I had the Canadian detuned Crosman Quest that was pretty much identical to the Optimus, except for the stock contours. The Vantage model also seems to be the same rifle with a different handle. This Chinese B18/19 rifle wears many handles and name tags.

Cocking effort with the detuned Optimus is very mild and can easily be accomplished with only two fingers on the barrel. Long shooting sessions would be no problem with this mild plinkster. The rifle only weighs 7.2 pounds with the 4 power CenterPoint scope mounted.

The Optimus shoots great as a 500fps basement shooter but my preference was for a little more power to bring it up to 600-625 fps with average weight pellets. The added power will help flatten out the trajectory for 30-40 yard plinking shots.

After a complete teardown, the factory detuning method became obvious. This Optimus-500 has a non-vented 170mm piston whereas the full power version uses a shorter 150mm. The mainspring was 34 coils of light .098” wire whereas the full power version uses 36 coils of .122” wire. The shorter cocking stroke with the very mild mainspring drops velocity down to the non-PAL level. My old non-PAL Quest used an even longer non-vented piston with a thicker wire mainspring. Other versions of the non-PAL Optimus/Phantom have been reported as using a short 150mm vented piston with the thin wire spring. All versions seem to be using the 1.5” spring guide spacer.

It was interesting to notice that my detuned Optimus did not have the B19-00-4B mainspring, as indicated by Crosman for this model. My shipment of spare Crosman parts arrived with a 4B mainspring and it turned out to be 33 coils of .118” wire. There are at least 3 different springs and 3 pistons used for these rifles.

Here are a few bits of piston & spring info that I gathered from the Crosman web pages.

.177cal
495 fps Optimus >>> Piston B19-4-04-100A >>> Spring B19-00-4B
1000 fps Optimus >>> Piston B18-04-100D >>> Spring B18-00-4D

495 fps Quest >>> Piston B19-4-04-100 >>> Spring B12-1-00-4A
1000 fps Quest >>> Piston B18-04-100A >>> Spring B18-00-4D

.22cal
Optimus 800 >>> Piston B18-04-100D >>> Spring B18-00-4D
Quest 800 >>> Piston B18-04-100A >>> Spring B18-00-4D

--- VELOCITY ---
The rifle was first tested in unaltered form, out-of-the-box. All I did was clean the barrel and mount the included CP scope. A couple of dozen shots were taken to distribute the OEM lube.

JSB Exact (8.44gr) - seated pellets - 497, 500, 495, 497, 495 --- ave 497 fps


--- ACCURACY - unaltered rifle ---

--- 10 Metres – 5 shot groups ---
From a rest at 10m I was averaging .40” to .45” ctc for 5 shot groups with JSB Exact 8.44gr, JSB Exact 7.33gr, RWS Hobby, and Stoeger X-Field pellets. With the mild .098” spring, the rifle seemed to like the pellets seated in the barrel so I used a Bic pen cap to push them slightly below flush.

--- 30 Yards - 5 shot groups ---
JSB Exact (8.44gr) - 1.85”, 1.51”, 1.63”, 1.53” --- ave 1.63” ctc

The untuned rifle has a lot of spring twang that could be greatly reduced with a tune. A lube tune, better fitting guide and a fresh barrel crown should all help squeeze the groups down a bit. I don’t expect HW30 accuracy but a little improvement should be possible.

--- MODIFICATIONS ---
I broke into the detuned .177cal Optimus to do a bit of polishing and lubrication. As mentioned above, the spring turned out to be a 34 coil with thin .098" wire. The spring guide is the same .475" diameter as used in my full power U.S. spec Optimus. The skinny spring was a sloppy fit on the guide which allowed the spring to bend into a mild s-shape. The spring maintained this double cant when removed. This sort of poor fit resulted in the typical metallic twang noise when shooting.

The piston seal and breech seal looked fine so replacements were not required. After the typical polishing and moly paste treatment, I re-assembled the Optimus with a 33 coil .118" spring and the same 170mm non-vented 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 was now 745fps with 7.9gr Crosman HPs. Unfortunately, this was much more than my desired 600-625fps with 7.9gr pellets.

The next modification was to reduce the spring spacer length and test again. I tried 1/4" and 1/2" spacers with the same 33 coil .118" mainspring. There was no preload at all with these spacers. I ended up using just over 3/4" of spacer that left me with approximately 1/4" of preload. Perfect! I'm now getting 625fps average with 7.9gr pellets.

Trigger work was very minor. The return spring was over-bent to reduce tension, engagement surfaces polished, moly paste to all friction areas, and a longer adjustment screws was added. I adjusted the trigger engagement so it still had a little creep. The feel is much better than prior to the work.


--- ACCURACY – modified rifle ---

--- 10 metres – 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 – groups .50” to .75” ctc
JSB Exact RS 7.33gr – groups .50” to .75” ctc
H&N Excite Econ – groups 0.50” to 0.75” ctc

--- 20 yards – 5 shot groups ---
H&N Hammers – 1.22, .83, 1.06, 1.05, .56 --------------------- ave .94” ctc
JSB Exact – .74, .40, .38, .80, .84, .53, .69 --------------------- ave .73” ctc
Crosman HP – .70, .76, .41, 83, .76, .57 ------------------------ ave .67” ctc
RWS Superdome – .54, .71, .58, .77, .49 ------------------------ ave .62” ctc
Stoeger X-Field – .60, .62, .62, .74, .67, .61, .75, .50, .50 --- ave .62” ctc
H&N Sport – .63, .50, .54, .40, .39, .50, .34, .55, .48, .40 --- ave .47” ctc

The Crosman HP did better than expected at 20 yards. I was careful to throw away a few fat pellets that seemed a bit difficult to start into the barrel. Now I’m curious to see how these Crosman HPs do at 30 and 40 yards.

After 500 pellet break-in period

--- 10 metres – 5 shot groups ---
JSB Exact 8.44gr - .21, .35, .22, .36, .18, .34, .31, .34, .21, .28 --- ave .28”ctc

--- 20 yards – 5 shot groups ---
H&N Sport - .63, .50, .54, .40, .50, .39, .34, .55, .48, .40 ----------- ave .47”ctc
JSB Exact 8.44gr - .55, .64, .69, .35, .46, .75, .36, .45, .64, .70 --- ave .56”ctc

--- 20 yards – 5 shot groups ---
H&N Sport - .67, .62, .41, .58, .56 ------------- ave .57”ctc
JSB Exact 8.44gr - .57, .38, .48, .71, .58 ---- ave .54”ctc

Note: JSB Exact 8.44gr were a new lot from 2016

--- OVERALL OPINION ---
The Optimus seems to be a nice rifle for the price. It’s the typical Chinese B18 with another facelift but I knew that before the purchase. We all know that the B18 gets dressed up often but maintains the basic common foundation. It shoots fine, parts are cheap, a power upgrade is easy, and the trigger is not too difficult to improve. I’m looking forward to testing accuracy at 30 and 40 yards.


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