Canadian Airgun Forum

This afternoon I did a bit of accuracy testing with my two .177cal Optimus rifles. These are the same rifles that I reported on before but at shorter distances. Nothing special was done to these rifles. One is a Canadian detuned model with a mid-power Crosman spring installed. The other is a full power version. Both rifles had the spring spacers shortened to reduce power. Moly paste to all friction areas and a mild polishing to trigger parts. Longer trigger adjustment screws. Factory guides & top hats, original crowns, OEM mainsprings, OEM triggers, no tube polishing, no barrel lapping.

Canadian Version
33 coils, .118" spring wire, 170mm non-vented piston
3/4" spring spacer for 1/4" preload
625fps with 7.9gr pellet

Full Power Version
36 coils, .122 spring wire, 150mm non-vented piston
3/8" spring spacer for 3/8" preload
800fps with 7.9gr

50 Yard Accuracy - 5-shot groups

Canadian Version
8.44gr JSB Exact - 2.49, 2.12, 2.98, 2.45, 2.96, 2.22 -- Ave = 2.54" ctc
8.18gr H&N Sport - 2.78, 2.15, 2.54, 1.61, 1.90, 2.38 -- Ave = 2.23" ctc

Full Power Version
8.44gr JSB Exact - 2.10, 2.24, 2.35, 2.10, 2.05, 2.48, -- Ave = 2.22" ctc

The 10m accuracy was previously tested at approx. 1/4" and 20 yard at 1/2" ctc for both these rifles.

I'm happy with the 50-yard accuracy for these cheap springers. Fitted guides might tame them down a bit and give slightly tighter groups, or maybe not. There was a mild but annoying breeze today... so groups might be better on dead calm conditions.

Good shooting! You can see where the wind died down a little for a few of your groups (1.6)
Dead calm would probably reduce your group sizes to 1.5-1.75.
Sounds like a candidate for soup cans offhand at 70 meters!

_________________
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 must have a crystal ball. Great prediction!

I got out shooting around noon today. This time I only took the 800fps version of the .177cal Optimus. The session started out with a light breeze and I managed 50 yard groups of 1.89, 2.29 & 2.22 for a 2.13" ctc average. This was a little better than before but not much. A few drops of rain fell and then the mild breeze went away so I could have some fun in dead calm conditions. This time I used a soft front rest and a rabbit ear bag on the butt stock. A very gentle hold was used with almost no shoulder pressure on the stock. Results...

50 Yards - 8.44gr JSB Exact (2016 lot)
1.45, 1.35, 1.29, 1.67, 2.08, 2.37, 1.30, 1.55 --- Ave = 1.63" ctc

50 Yards - 7.33gr JSB Exact
2.25, 1.64, 2.20, 1.35, 1.12, 0.90, 1.90, 2.41, 1.51, 2.48 --- Ave = 1.78" ctc

I adjusted my scope so all shots hit high. This way I could use blank printer paper above my targets and see all hits without a black bullseye. I roughly cut out the groups for a close picture.

Looking at the groups down the right side of your pic, there are three shot groups within the 5 shot groups. One has three shots touching! This tells me that the gun is capable of shooting better. The first gun-related thing that comes to mind is lockup. A stiff spring on the live detent, and a set of machined metal washers would be a good place to start. I'll have to take some measurements...
Second issue would be the breach face - compression tube - seal interface. Some guns shoot well with the breach seal proud such that the breach does not contact the face of the compression tube (the breach seal provides a "cushion" between the two faces).
I have had better lockup consistency (particularly for scoped rifles) by direct contact between the breach face and the face of the compression tube. It's a balancing act. My Fury Springer (the one with which you shot a .167" 5 shot group at 20 meters) is set up like this. I set up the breach seal by sanding the back side of the seal until it was too loose when the gun was shot. Then I added a few wraps of dental floss under the seal until it stopped leaking. If you look at the face of the compression tube on my Fury, you can see the clear outline of the breach face on the bluing.
Darn fine shooting, btw.

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

Good ideas Rick! I have some spares so can tinker with different breach seals when out shooting. In the past I have used the chronograph to ensure the best sealing at the breach but this doesn't necessarily mean the most consistent lock-up. I would give up some speed for better accuracy. Tinker, tinker, tinker...

Another thought is to be more selective with the pellets. Maybe I'll sort out some JSBs according to head size. I did try some RWS Superdomes, H&N Sports and Crosman HPs but the JSBs seemed to do best so far. The Crosmans showed some promise so I'll try them again. Once again, I think sorting would be worth while for top groups. I would still like to try H&N domes, 10.34gr JSB domes and maybe some new CPLs.

The detent spring seems about right, when compared to other rifles I have shot. I'll watch for horizontal spreads to identify the block washers as suspect.

Thanks!

I just finished checking the breach seal fit on the Optimus. I'll walk through the steps.

1 --- Removed the new seal and floss shim that was installed back during my lube tune (accuracy tested above).
2 --- Breach closed. Feeler gauges used to measure receiver-to-block gap. A .009" slips in all the way. A .010" just barely slips in but stops short. A .011" is no go.
3 --- Old spare seal sanded to .088" thickness and installed in Optimus. Same gap results as no seal. Velocity at 724fps with 8.44gr JSB Exact.
4 --- New breach seal installed. Measured at .094" thickness. Same gap results as no seal. Velocity at 748fps.
5 --- New breach seal installed with dental floss shim (multiple loops). A .012" gauge slips in to touch seal but a .013" is no go. Velocity at 753 fps. This is same arrangement that I previously tested for accuracy.

My plan is to test accuracy with the new seal and no shim. I could also do some testing with the new seal and less shim.

This Optimus rifle amazed me once again. This morning was great for group shooting. The air movement was minimal and the mild periods of breeze didn't last long. I packed up my gear and drove to my favourite shooting area. A 50 yard distance was measured out and my B&D Workmate bench and shooting rests were assembled. A total of 17 groups were shot with the 8.44gr JSB Exact but two had flyers that I caused so the remaining 15 were used for the average. I also shot 3 groups with CPHPs and then ran out of time.

The only difference from my last session was that I removed the dental floss shim from under the breach seal. You can read the previous posting for details.

8.44gr JSB Exact --- 5-shot groups @50 yards
1.47, 1.50, 1.56, 1.18, 1.15, 1.56, 0.73, 1.09, 1.11, 1.50, 1.49, 1.25, 1.05, 1.46, .139
Average = 1.30" ctc

7.9gr Crosman Premier HPs - 5-shot groups @50 yards
1.89, 1.65, 1.86
Average = 1.80" ctc

The JSB Exact were a 2016 lot. I picked the pellets from the tin and did not discard any.
The CPHPs had a couple of looser fitting examples that were tossed.

Here are the 15 cut out groups. I pinned the actual aiming targets below sheets of printer paper and adjusted my scope to hit high. This way I can see all shots clearly from the bench... and also save on ink.

I shot a few more groups today from 50 yards. Close to the same results.

8.44gr JSB Exact - 1.56, 1.07, 1.34, 1.17, 1.69 --- Ave 1.37" ctc