Springer accuracy

[TonyL]

I but if I "pump" the spring full stroke (just short of cocking it) 3 or 4 times then the early inconsistencies are gone.........but try "pumping" yours a few times and see if your experience is like mine.

Sounds rude.

[Adam77K]

A tight piston seal can become a bit more flexible after a few shots, to answer your own investigations you'll likely need the use of a chronograph and a lot of patience _ ambient temperatures unlikely to influence that much (in UK) unless high summer (dripping in a tee shirt) / freezing winter ( al la cold snap a few weeks back)

You'd be surprised at how much a seal expands in small temp changes. I've had my zero shift while on FT courses. The most stark example was with my LGU before it was tuned. I was on a practice course and the morning had started quite cool. At first I was hitting everthing but it had got warmer, sun came out and I started missing targets. Suspecting seal expansion I left the rifle in the shade for ten minutes, fired a shot, bang on. Then I cocked the rifle and worked the lever back and forth vigorously a few times to warm the seal up. The next few shots went high. I can't remember exactly how much but enough to miss a 40mm kill zone at 45 yards. Left it again and it settled back, only to shift again after several targets with no shade around.

[WineRack 97KT]

There are a lot if things that can change accuracy or POI with temperature, but in the rifle I tested, velocity probably isn't one of them.

So I set up with a Diana 34, .22 cal. shooting JSB Jumbo RS, 13.43 gr. (0.87g) domed pellets. This is an unmodified rifle with a metal spring and synthetic piston seal, and it has always been maintained according to manufacturer's instructions. The rifle was stored, muzzle up, for at least 24 hours between shooting sessions.

The velocities were measured with an F-1 Shooting Chrony about 6 feet from the muzzle and the piston tube temperature was taken with an IR thermometer immediately before the first shot. Two more shots were taken within about 3 minutes.

Temperature 61.7F (16.5C)
Shot 1: 694.3 fps (211.6 m/s) Shot 2: 682.6 fps (208.1 m/s) Shot 3: 687.3 fps (209.5 m/s)

Temperature 42.0F (5.6C)
Shot 1: 688.6 fps (209.9 m/s) Shot 2: 700.7 fps (213.6 m/s) Shot 3: 704.6 fps (214.8 m/s)

Temperature 10.9F (-11.7C)
Shot 1: 687.9 fps (209.7 m/s) Shot 2: 709.2 fps (216.2 m/s) Shot 3: 705.2 fps (215.9 m/s)

As you can see, the velocity seems to climb slightly with a decrease in the temperature.

Rob

[TonyL]

Excellent stuff, Rob, and pretty much in line with contemporary expectations.. Keep going and thank you for giving this a go.

[Adam77K]

It's worth noting in the case I outlined above, the actual velocity did not change much with the temperature. Nowhere near enough to produce shots going an inch high at 45 yards. The change of seal friction changes the timing of the firing cycle so the pellet exits at a different point in the recoil.

[Muskett]

Some great posts.
I definitely need to "warm" into the rifle when I start shooting a springer. I wish it only took me three shots to get smack on. But I do get there and then good all day long.
Hold and cheek pressure are the two big deals, and always correct trigger pull. Frankly the full list of marksmanship and even then a shot or two to bed in.

[jjjohn]

I always thought it was residual gas /burnt fuel even on a microscopic level lingering in the cylinder after a few shots.
Not on the big bang crush your spring dieseling scale.

[WineRack 97KT]

It's worth noting in the case I outlined above, the actual velocity did not change much with the temperature. Nowhere near enough to produce shots going an inch high at 45 yards. The change of seal friction changes the timing of the firing cycle so the pellet exits at a different point in the recoil.

This makes a great deal of sense. I also have to wonder if the barrel harmonics change significantly with temperature.

Rob

P.S. Thanks TonyL!

[NickG]

The only temp testing I did was while trying to prove a synthetic piston ring wasn't temp sensitive. A friend had suffering extreme poi shift in high temp while shooting the world ft championship in I believe Portugal.
I tested from 15 c upwards to 40c, with very little change in fps. Never tried it cold though.

[Adam77K]

The only temp testing I did was while trying to prove a synthetic piston ring wasn't temp sensitive. A friend had suffering extreme poi shift in high temp while shooting the world ft championship in I believe Portugal.
I tested from 15 c upwards to 40c, with very little change in fps. Never tried it cold though.

I've shot my LGU with your 21mm tune in 3 winter league comps between about 5 and 10 degrees and not noticed any appreciable shift yet.

[Adam77K]

This makes a great deal of sense. I also have to wonder if the barrel harmonics change significantly with temperature.

Rob

P.S. Thanks TonyL!

I would need a lot of convincing that barrel harmonics aren't negligible for sub 12 airguns, certainly the underlevers I shoot in competition (97K and LGU) which have short stiff barrels that are damped by the lever being clipped to them.

[TonyL]

The only temp testing I did was while trying to prove a synthetic piston ring wasn't temp sensitive. A friend had suffering extreme poi shift in high temp while shooting the world ft championship in I believe Portugal.
I tested from 15 c upwards to 40c, with very little change in fps. Never tried it cold though.

Excellent input, Nick.. For some reason I thought you had tried it at very low temps as well?

[NickG]

Excellent input, Nick.. For some reason I thought you had tried it at very low temps as well?

It was summer time, so I went from indoors to outdoor leaving it in the sun, as I remember I had 4 fps change over ten shots, when cold , and 6/8 when 40 degrees pellets straight from the tin , not very scientific but I decided that was "temperature stable "

[NickG]

https://photos.app.goo.gl/tweUNbhy59uZSSsf9
https://photos.app.goo.gl/jmEAfSLgCknZ5pf98
https://photos.app.goo.gl/74B7R8ubBLZY8d9d8
Found these.

[Hsing-ee]

I know this might provoke some people, but can low temperature 'intial fliers' be down to additional layers of clothing?

If it be chilly then everyone will be putting on jumpers and fleeces and stuff under their sporting coats, and as you fire a few rounds off this material will naturally compress, given that you won't be holding a springer hard into your shoulder like you might do with a .303, 12-bore or PIAT.

Any thoughts on the 'textile' variable? The 'artillery hold' basically uses the human as it's recoil sledge, what if the sledge has less resistance? It will throw shots.