Canadian Airgun Forum

I picked up a .177cal Optimus 1000 from Pyramyd Air and the initial velocity numbers seem a bit low. The rifle was just unboxed yesterday. After a barrel cleaning and a few "warm-up" pellets I got 760, 762, 760, 770, 750fps with 8.4gr JSB Exact. I plan to shoot about 50 more pellets and then tear it down to check the piston seal. I'm expecting some damage so I ordered some spares, along with some springs. Piston seals are only $2.39Cdn for these rifles.

Many thanks

Hey Todd.
Sounds like my Remington Express. The piston seal was gouged at the factory. Unlike Crosman, the seal was $18. The Remmy now shoots at 15fpe with a fitted seal.
My Fury springer (same B18) ran 16fpe with a new full power spring. I detuned it down to 14fpe by cutting the large spacer at the rear of the spring guide in half, thereby reducing the preload by 50%. It seems to be a "sweet spot" for that gun. It shoots different pellets to relatively the same poi, and the shot cycle just seems a lot less stressed, and quieter. The spring should last longer too. Cocking force dropped a little. I sure don't miss the fps lost.
If you would like to try the detune method I used, I'll make a half-sized spacer for you. I'd rather not take down my fury to measure the dimensions of the spacer as it is buttoned up and loctited. (Guess I should have written the dimensions on the wall of my shop like I usually do). Call me with dimensions when you have it apart.

Rick

_________________
Theory is when you know how something works, but it doesn't.
Practice is when something works, but you don't know why.
In my shop, Theory and Practice are combined!
Nothing works and I don't know why.

Two lathes and too many projects

Rick, the spacer is 1.5" or 38mm. Removing the spacer took my 18ftlb gun to 9, so I guess people could use that to better estimate what length they want. Cocking effort dropped in half as well, only 12lbs at peak!
I also attached a pix of the Rem Exp seal from my gun so everyone can see. It's the worst I've ever seen and others tell me theirs look more or less the same, Five major divots cut out of the sealing edge, four appear as flatish spots and the worst is the mangled mess on the left. Plus the seal was made of some nasty stiff plastic that has no business in there imo. I've seen it in some ultra low end chinese guns but I didn't expect this to have it. The 28mm Diana seal will fit it since it is a Diana 34 clone, minus the nice trigger.

The seal on my .177 Remmy had a 1/16" gouge right through the side of the seal like somebody carved it out with a knife along with the various smaller nicks and gouges like yours. The OEM Diana seal I installed had to be turned down a little to get the right fit in the tube. The new seal works a treat. Very smooth shot cycle with the Diana seal.
Strangely, the gun likes RWS basic 7.0 gr at 960fps. I tried a few pellets just to see how fast they'd go. The ES was <5! I tried them on a target and was really surprised. Basics aren't supposed to shoot well at these speeds! The Remmy gets a steady diet of them now.
I think my P17 is getting jealous 'cuz the Remmy is eating all its food.

Edit: I tried a stock full power spring in my Fury with the spacer removed. The spring had barely 1/16" of preload. Thumb pressure was all that was needed for re-assembly. Velocities were all over the place on my Fury, probably due to uncontrolled piston bounce. ES was over 100fps without a spacer. With the half-size spacer, ES is 3fps. However, that's just my gun. Another B18 may (and probably will) behave differently.

_________________
Theory is when you know how something works, but it doesn't.
Practice is when something works, but you don't know why.
In my shop, Theory and Practice are combined!
Nothing works and I don't know why.

Two lathes and too many projects

I think I figured out the problem. It was my bad! I did some experimenting with my Optimus-500 and found that the velocity and accuracy were very consistent when I seated 8.44gr JSB Exact pellets. I mistakenly assumed that the Optimus-1000 would digest the same diet with good results. I never considered that a "magnum" air rifle would prefer the added initial resistance from non-seated pellets.

I replaced the Opt-1000 piston seal with a Quest seal that I had from long ago. It had a small gouge but it seemed to fit the compression tube better than the original Opt seal. The original seal was discoloured and slightly damaged on one edge.

The Optimus still only shoots seated JSB Exacts at 800fps, which is slightly better than before. When I shoot them without seating I get 905fps. The Crosman 7.9gr HPs do 960fps. I have plenty of other pellets still to test out... then I'll shoot some groups.

105 fps difference between seated and non seated? Seems to me the seated pellets are so far in the barrel you've created extra space for the compressed air to fill....resulting in less pressure and less fps.

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

I seat them with the cap of a cheap BIC pen. They are seated barely below the surface, maybe 1/32". It's just enough to get the skirt squeezed down into the barrel. This old trick sometimes brings more consistency and accuracy from certain airguns. My Quest-500 does very well with seated JSBs and shoots 490fps. I didn't expect so much velocity loss in the Opt-1000 but experimenting is how we find these things out.

The JSB Exact have thin skirts. My guess is that the seated pellet starts to move before the compression builds up to as high a level as with non-seated pellets. The tighter fitting, non-seated pellet, allows more compression stroke before they get a run down the barrel.

Yeah....I used to use a plastic "seater" too but soon discovered the fps drop....although it was only 30 or 40...... and now I prefer a snug fit.....good fps....a satisfying sound upon firing and no more wasting time wiith seaters.

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

The Optimus 1000 is showing some accuracy potential. I shot about 50 pellets this evening to check group size at 10 metres. The Stoeger X-Field performed quite well. Four consecutive groups of 5 shots each measured .39", .41", .40", .34" for an average of .38" ctc (approx. 3/8" ctc). A couple of groups would have been nice one-holers if it wasn't for the flyers. With some tuning and a break-in period I'm hoping to get the group average down to around .30" to .32". I also tried the 8.44gr JSB Exact, RWS Superdome, and Crosman Premier HPs but they didn't perform as well.

All I have done to the rifle is clean the barrel, change the piston seal, do the common trigger mod with the washer, and add a 3-9x32AO scope. Nothing else has been done. I haven't even checked the pivot bolt. I plan to do a polish & lube tune... and detune to around 12-13 ft-lbs. It's currently running at 16 ft-lbs.

I shot a few more 5-shot (10 metre) groups with the Optimus 1000. The Stoeger X-Field seems to be the performer so far. Crosman UltraMag shoot well but I find lots of peewee or large head pellets. The group labeled "A" has a peewee head that I shot to see POI (flyer). I also shot a 6th pellet for that group and excluded the peewee for group measurement.

The rifle seems to be capable of 1/4" ctc accuracy at 10 metres. Once the spring is tamed down and the rifle detuned, I'm hoping that all groups hover around 1/4" ctc at 10 metres. Careful pellet sorting seems to help a lot too.

Nice

The seating problem is likely to be about power imo, the more powerful the gun the more cork effect it'll like. If the gun is weak it may have trouble breaking the pellet free and they will no doubt break free at different times so the pressure curve the pellet rides will be off. Deep seating will solve that. Same with the coil spring w/ no spacer, it makes a more gentle lower pressure gun that will have more trouble with resistance. My gun w/o a spacer has a very smooth breech and bore compared to the nasty oem setup so the pellets have less problems and are more consistent. Say you have a tight breech and the classic tight spot at ~4", it will have a bigger effect in killing the power than it would at full power. I suppose this is why Crosman chose to short stroke the guns and/or use holes rather than use super light springs.
Mine works fine so know it can work if the flaws or whatever are fixed.