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 Post subject: Crosman Optimus Review
PostPosted: Tue Jan 17, 2017 1:37 am 
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Joined: Sat Sep 03, 2005 9:25 am
Posts: 3608
Location: Ontario, Canada
Crosman Optimus Review – Full Power Metal Spring Version

The spring-piston Crosman Optimus is basically the Chinese made Xisico B18 rifle with a bit of a facelift. We have seen Crosman market this Gamo copy with various stock configurations over more than a dozen years. We have seen it called the Quest, Phantom, Fury, Vantage, and a few other names. Even Remington grabbed onto the B18 with their nice looking Summit rifle. The metal work on the B18 platform is a design that seems to maintain adequate popularity. It’s a simple design that started many shooters into learning about airgun mechanics and tuning.

My .177cal Optimus started out with a few minor problems that were easily corrected. The rifle turned out to be a sweet little shooter with very reasonable accuracy. The original piston seal had a small gouge and the breach seal needed a bit of a shim to get it shooting up to par. Seals are only a few dollars so the expense wasn’t an issue.

The trigger on my new Optimus was typical and not something that was enjoyable. The pull was a little heavy and the creep was outrageous. It felt like a 1/2” movement was needed to get the rifle to fire. After a mild polishing, moly lube and installing a set of 4 small washers, the trigger became very acceptable. I’m not sure if I will leave the washers or remove them and install a longer trigger adjustment screw.

The rifle didn’t need much work to start shooting reasonable groups. It shot fine as a full power rifle but the twang was a bit annoying so I detuned to around 800fps with 7.9gr Crosman HPs. The twang pretty much disappeared... and accuracy improved. In full power form I averaged around 3/8” groups for 5 shots with a few ¼” ragged holes when everything went right. In 800fps mode the groups shrank up a bit and ¼” was more common with preferred pellets. Out of a dozen consecutive groups with 5 pellet types I only had one group that was over 3/8”. The average for the 12 groups was a reasonable .30” ctc.

The full power Optimus is a light rifle with relatively high power potential. My example weighed 7 lbs 7.8oz with a Leapers 3-9x32mmAO scope and mounts. The rifle length with 18 ½” barrel taped at an even 44”.

Here is all I did to the rifle. Nothing done was special, unique or difficult.

> Strengthened the stock screw areas with Super Glue. The areas inside the stock and under the screw heads were soaked with a couple of coats of the glue and allowed to dry.
> Sealed inside of stock with spar urethane finish to keep moisture stable
> Changed piston and breech seals
> Cleaned up cocking slot and piston slot with emery paper
> Cleaned out old lube from internals
> Polished end of top hat
> Bevel spring ends and lightly polished
> Changed spring guide spacer
> Lightly polished trigger sears
> Installed washers on trigger
> Moly to all friction areas including spring, guide, piston body, top hat, burnished into compression tube, hinge pivot, hinge latch, trigger engagement
> A mixture of moly paste and 30W-ND was applied to the linkage pivots
> Barrel cleaning with JB Paste
> Loctite hinge bolt threads and 3 receiver mounting bolts

Parts Measurements
Piston -- 150mm (5.91”) end to end, 145mm (5.71”) without seal post, 0.970” OD
Spring Guide -- consistent 0.476” OD, 4.450” length
Spring -- 36.25 coils, 0.122” wire, 0.485” ID ave, 0.734” OD ave

Velocity
My first velocity test was not long after removing the rifle from the box and cleaning the barrel. The rifle quickly settled down to 960fps with 7.9gr Crosman Premier HPs. Accuracy was fine but the spring twang was a bit harsh and annoying. Recoil was enough to cause the flip-open scope cap to pop off the scope’s eyepiece after every dozen shots.

A friend machined a set of spring spacers for me so I could experiment with preload. The factory OEM spacer measures out to 1.5”. My first step was reducing this to an even 1”. Velocity dropped to 900fps with the CPHPs but that’s still more than I wanted. The 3/8” spacer brought it down to 800fps with the same pellet. That’s about what I was looking for. Removing the spacer completely gave no preload and I prefer a small amount. The 3/8” spacer gave 3/8” of preload in the spring. Velocity consistency was still fine and the twang pretty much disappeared with the short spacer.

1 1/2” spacer = 960fps with CPHP ; 900fps with 8.64gr Stoeger X-Field
1” spacer = 900fps with CPHP
3/8” spacer = 800fps CPHP ; 760fps with Stoeger X-Field ; 770fps with 8.44gr JSB

Velocity Test (with short spacer)
Crosman HPs (7.9gr) – 795, 792, 799, 803, 802
Stoeger X-Field (8.64gr) – 754, 756, 754, 763, 764
JSB Exact – (8.44gr) - 774, 774, 767, 770, 769

Accuracy
One small difference that I noticed with the Optimus, when compared to my old Quest & Phantom rifles, is the tight breach pivot bushing. My older models had bushings that would easily slip into the barrel block and likely rotate during the cocking cycle. The Optimus bushing had to be tapped into position with a brass drift. I doubt there is any bushing rotation in the block when cocking this rifle. Possibly the characteristic contributes to accuracy when a scope is used but I’m not sure if this tight fit is typical. The Optimus is definitely more accurate than the other two Crosman examples that I tested many years ago.

Accuracy was fine when the Optimus was tested at full power. I was able to get most 5-shot groups measuring .35” to .40” ctc at 10 metres. The Stoeger X-Field gave a couple of ¼” groups so I knew the rifle was capable. Unfortunately the odd flyer would slightly open up quite a few groups that started off looking great.

The 800fps detune seemed to help rifle accuracy or at least made it easier for my shooting ability. The rear scope cap stayed in place for over 60 shots so recoil must be somewhat less. Less recoil + less spring twang = easier accuracy. Here are some groups from a rest at 10 metres. I shot 12 consecutive groups without any warm ups.

5-shot ctc groups
Crosman HPs – .30”, .36”
RWS Superdome – .26”, .42”
JSB Exact – .34”, .31”, .30”
Stoeger X-Field – .25”, .19”, .18”
RWS Meister – .30”, .35”

The overall average for the 12 consecutive groups was .30” center-to-center. The X-Field seems to be the clear winner, as it was when the rifle was unaltered at full power.

When the snow goes and the weather warms up I plan to test accuracy out to 50 yards. A few more pellet types might be added to the mix.

Overall Opinion
With a minimum amount of work the Crosman Optimus turned out to be a nice performer. With .20”-.25” accuracy and 750-800fps this rifle will be a useful addition to my collection. Pop cans at 30 yards should be no problem. It’s a lot of air rifle for the money.

Next I have to tinker with a detuned Canadian model to see how it does with some TLC. The Canadian 500fps model has a slightly longer piston, weaker mainspring and shorter 16 ½” barrel.


Attachments:
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Optimus 002b.jpg
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PostPosted: Tue Jan 17, 2017 5:06 am 
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Joined: Mon May 26, 2014 1:08 am
Posts: 566
Location: Thunder Bay
Nice review Todd. With accuracy like that, you're going to make the frauliens jealous!

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

Too soon old too late smart.


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PostPosted: Wed Jan 18, 2017 6:42 pm 
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Location: Ontario, Canada
Did some indoor 20 yard group testing with the Optimus this afternoon.

JSB Exact 8.44gr --- .70, .60, .54 --- .61" ctc average.
Stoeger X-Field 8.64gr --- .46, .60, .64 --- .57" ctc average

Poor groups with RWS Superdomes, H&N Sport, and Crosman HPs. The CPHPs did .91" ave and the other two were grouping a little over an inch.


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PostPosted: Wed Jan 18, 2017 11:14 pm 
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Joined: Thu Mar 24, 2016 7:33 pm
Posts: 319
Location: Yukon
Optimus, Crosmans best wood stock IMHO.

Did you remove the sights or did your version arrive without?

Can you maybe detune by using the longer Canadian version piston and slightly up gun the canadian with the 1000 fps piston?

Nice review, I have up-springed my Canadian version to the full power spring but did not measure the piston length. I suppose it should deliver slightly less FPS than your factory 1000?

thanks
tango


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PostPosted: Wed Jan 18, 2017 11:52 pm 
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Joined: Sat Sep 03, 2005 9:25 am
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Location: Ontario, Canada
Hi tango,

I removed the sights on the Optimus. I have a Crosman muzzle break but still have to put it on. I was waiting to decide if I was going to polish the crown first. The muzzle break is only about $5 from Gravel.

Yep, I could have detuned using the longer piston. It was easier and much cheaper to reduce the spacer length. My Canadian Optimus has a slightly longer piston and the weaker mainspring to give 500fps. The spring in my 1000fps is 36 coils of .122" wire. The Canadian version is 33 coils of .118" wire. A shorter piston in the Cdn version would give a bit more fps but I'm not sure how much.

I think some Canadian Optimus versions have the short piston (with hole) and the weak mainspring.

Your up-tuned Canadian Optimus should be sweet if you have the slightly longer piston. You didn't mention anything about a piston hole so I'm guessing you have the longer piston.

Cheers


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PostPosted: Tue Jan 24, 2017 5:36 pm 
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I did a pile of group shooting off the rest today. My OCD brain won’t be happy until I find the best pellet for this rifle...lol. Only then can I relax and shoot offhand without wondering if the pellet is the cause of less than desirable accuracy.

Here are today’s results:

5-shot groups @20 yards off rest
JSB Exact (8.44gr) – .62, .84, .79, .44, .65, .61, .68, .85, .45, .71 = .66” ctc average
Stoeger X-Field (8.64gr) – .75, .90, .53, .49, .63, .68, .72, .88, .80, .89 = .73” ctc average

My last 20 yard testing showed the X-Field as slightly leading (.57” vs .61”). Today the JSBs pull ahead. I’m guessing that the Stoegers are not the best of the H&N Field & Target Trophy selection. I’m guessing that H&N with a head size label would be a bit more consistent and possibly a touch more accurate. Gotta try some!


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