s400 consistency

[lanky mk]

I recently did a crono string for my S400 MPR after fitting some new bits.

The following pics are from a 170 bar fill with unweighed pellets, i get good results even with the last one which i fired to make sure it was off pressure.

Im getting 75 shots around 10fps variation (excluding the last shot) with nearly the last 40 being the best spread. Came off around 110 bar.

Mark

[wezdavo]

Hi Mark,

That is very impressive, do you by any chance know what the internal differences between the mpr and s400 are? valving? cylinder size? hammer weight?

[wezdavo]

Hi

Here's what it looks like on my spreadsheet. Orange lines are 20fps apart. I reckon filling to 160 Bar should yield another 3 or 4 shots within that 20 fps band.

Mark

S400_Curve.jpg

I have just tried 160 bar fill and it returned 60 shots 18 fps spread

I have being reading up on pellet weight variation in the same tin and came across some very interesting info... I am going to buy some scales! Any recommendations??

Here are some links to interesting discussions in regards to pellet weight consistency ...

Mods please delete this link if it breaches forum rules

http://www.airgunbbs.com/showthread.php ... onsistency

http://www.airrifle.co.za/threads/11441 ... bservation

http://www.airgunforum.co.uk/forums/arc ... 66584.html

[lanky mk]

Hi Mark,

That is very impressive, do you by any chance know what the internal differences between the mpr and s400 are? valving? cylinder size? hammer weight?

Hi mate

Don't quote me but as far as i know the internals are identical between mpr and s400.

Pellet weight variation will make a big difference, i used unweighed pellets for the MPR but I've got an air ranger and with unweighed pellets was getting just over 10 fps spread but with weighed pellets that dropped to just under 3 fps spread.

Mark

[wezdavo]

^^^Mark, you are right about the MPR, I cross referenced the internals and they all share the same part numbers...^^^

I have been doing a little more tinkering

I have removed the small preload spacer from the hammer and compensated for power via decreasing the choke in the transfer port, firing pot is still set to 57mm..

This time to find the curve I left the rifle connected to the divers bottle after filling so I could read directly off the gauge on the bottle for a much more accurate set of figures..

After quite a bit of fannying around I found a very good sweet spot, strangely a little lower than I expected.... I think this is because of the lack of preload which is obviously reduced the striking force...

I also bought a good set of scales (On Balance CT-250, 0.001g) and proceeded to weigh out some jsb exact 4.52.... Out of the 400 or so I weighed they ranged from 8.28-8.69!
I managed to find 60 ranging from 8.40-8.50 so I decided to use these for the test..

140 bar fill!!!!
1. 777
2. 777
3. 778
4. 777
5. 780
6. 779
7. 778
9. 781
10. 780
11. 781
12. 781
13. 780
14. 782
15. 781
16. 781
17. 781
18. 783
19. 781
20. 781 (128 ish bar)
21. 782
22. 781
23. 783
24. 783
25. 780
26. 783
27. 783
28. 780
29. 781
30. 782
31. 782
32. 782
33. 782
34. 782
35. 782
36. 780
37. 782
38. 782
39. 781
40. 784 (112 ish bar)
41. 783
42. 784
43. 784
44. 784
45. 780
46. 783
47. 783
48. 783
49. 784
50. 781
51. 782
52. 780
53. 781
54. 780
55. 779
56. 779
57. 778
58. 779
59. 778
60. 776 ( 98 ish bar)

I stopped at 60 shot because that's all the pellets I had weighed, besides by looking at the figure I think is was on the drop anyway..

I ended up with 60 shots with a spread of 8fps, I think this is as good as it is going to get and to be honest I cant face taking it apart again!!! I have used around 2 tins of pellets and nearly 7 litres of air!!

I have also polished the trigger sears, fitted crinkle washers and adjusted it to within an inch of its life, it feels very nice, very positive with a crisp predictable break..

I am going to the club on Sunday to see how my handywork fairs down range..

[Mark112]

Hi,

A bit of a transformation in the consistency of the shotstring. Here it is using the same scale etc as your previous shotstring results:-

S400_Curve2.jpg (149.14 KiB) Viewed 9287 times

previous string:-

S400_Curve.jpg (153.26 KiB) Viewed 9287 times

Mark.

[wezdavo]

Cheers Mark.

I think its all down to weighing the pellets..

I have just worked out what the fps variation would be on those 400 jsb pellets I weighed the other day if I picked them straight from the tin...

Based on a constant energy source of 11.4 ftlb and the jsb pellets ranging from 8.29-8.69 the variation due to pellet weight alone would be 19 fps..

[panman3]

Hi guys,
As a relative newbie to the sport I've been devouring all the info I can to help me improve. I've done my own testing with a chrono on my s400 MPR ft with similar results (fps rises as fill pressure goes down - still haven't got my head around that one!) I''ve also read a lot about washing/weighing/lubing pellets so did a little test myself (all pellets weigh between 8.42g - 8.46g)
Dry (tested first of course!)
742.9 at 170bar rising to 762.7 at 160bar

Oiled (Napier pellet lube)
747.7 at 170bar rising to 769.1 at 160bar

Result - wasted £7 on lube!

Next,I'm wondering what difference pellet weight makes to fps so I weighed a tin of jsb match 4.52s (over several days - nearly lost the will to live!) and found that most were between 8.40g to 8.48g with one exception being 8.28g and at the other end one at 8.88g!

When I have time (I have a life y know) I will post the results if anyone is interested?
I'm not expecting massive differences in fps as - after all - we are only talking tenths and hundredths of a grain. Unless someone has already done this and found out different?

Cheers all

[wezdavo]

Hi guys,
As a relative newbie to the sport I've been devouring all the info I can to help me improve. I've done my own testing with a chrono on my s400 MPR ft with similar results (fps rises as fill pressure goes down - still haven't got my head around that one!) I''ve also read a lot about washing/weighing/lubing pellets so did a little test myself (all pellets weigh between 8.42g - 8.46g)
Dry (tested first of course!)
742.9 at 170bar rising to 762.7 at 160bar

Oiled (Napier pellet lube)
747.7 at 170bar rising to 769.1 at 160bar

Result - wasted £7 on lube!

Next,I'm wondering what difference pellet weight makes to fps so I weighed a tin of jsb match 4.52s (over several days - nearly lost the will to live!) and found that most were between 8.40g to 8.48g with one exception being 8.28g and at the other end one at 8.88g!

When I have time (I have a life y know) I will post the results if anyone is interested?
I'm not expecting massive differences in fps as - after all - we are only talking tenths and hundredths of a grain. Unless someone has already done this and found out different?

Cheers all

Based on what I have found during many hours tinkering is with a constant energy sauce of 11.4 ftlbs every 1/10 of a grain results in around 5 fps difference in velocity with jsb exact in my setup..

I used this formula to confirm my findings (calculate velocity section)

http://www.airgunsofarizona.com/energyc ... grains=8.4