FPS variation in an HW100

[lensman57]

I recently chrono'd my HW100 over a whole fill of air, just to see what variation there was.

It showed me that the shot to shot output varies by around 3fps with the very occasional 5-7fps.

There is a gradual change across the whole cylinder of air, it starts slightly high, drops gradually, then climbs back up before dropping off again - more or less like a sine wave. I assume this is a characteristic of regulator. I don't think this gradual change is really very important, as long as it's not too big. On my rifle it's only 4fps change.

Worst case the spread between the fastest and slowest velocity shots out of 113 shots was 10fps. The worst spread between any two consecutive shots was 7fps.

What does stand out, is that the shot to shot readings nearly always go high, low, high, low. For example +2.8fps, -3fps, +1.6fps, -3fps and so on...

I was curious if this is a real effect or just random chance and if it's real, what causes it.

I have yet to compare FPS readings with pellet impact point to see if there is a strong correlation. In theory, if this was predictable and did have an effect on impact point, you could adjust for it with a slight change in point of aim, alternating high, low. Trouble is you'd have to synchronise with the changes in fps otherwise you could make the effect worse!

Lastly, does anyone know what's involved in bringing the FPS spread down on the HW100? Is it even possible? Is a shot to shot variation of 3fps as good as it gets? Is what I'm measuring more to do with variation in pellets than what the mechanics of the gun are doing?

The regulator is doing its job within reason. The spread is fine. The power fluctuation is probably indicative of an incorrectly set regulator but to be 100% sure the actual FPS read out against cylinder pressure is required. Unless you know exactly what you are doing I would leave it well alone. You have +- 1.5% variation which is nothing.
FYI my S400 unregulated has 27 ft/s spread from 190 bar, and my Huntsman just over 20 ft/s spread. Your gun is fine.

A.G

[RichardinDorset]

Thanks guys, some interesting thoughts there and leaving the internals alone is probably good advice!

Regarding my measurements, my Crony was hooked to my laptop, so I was rattling through the mags fairly quickly.


So given that I'm unlikely to improve the pellet velocity spread, is there anything else I should be looking at on the gun to improve grouping at longer ranges? (50 to 100M)

The new barrel shoots most pellets well, but the usual suspects group marginally better (AA/JSB).

I get 14 shot groups of 25mm at 50M, 50mm at 75M and 75mm at 100M.

This might just be as good as it gets with an HW100 of course! I know it can be an awful lot worse... it was with the original barrel...

[GrahamHenderson]

Is this leading up to a sales pitch??

[RichardinDorset]

Is this leading up to a sales pitch??

Curses, foiled again!




Sell my HW? Never...

I get very attached to my guns!

[lensman57]

Thanks guys, some interesting thoughts there and leaving the internals alone is probably good advice!

Regarding my measurements, my Crony was hooked to my laptop, so I was rattling through the mags fairly quickly.


So given that I'm unlikely to improve the pellet velocity spread, is there anything else I should be looking at on the gun to improve grouping at longer ranges? (50 to 100M)

The new barrel shoots most pellets well, but the usual suspects group marginally better (AA/JSB).

I get 14 shot groups of 25mm at 50M, 50mm at 75M and 75mm at 100M.

This might just be as good as it gets with an HW100 of course! I know it can be an awful lot worse... it was with the original barrel...

Wash the factory grease off the hammer/shuttle mechanism. This will improve the shot to shot consistency and cold weather performance. You do not need to dismantle the gunas it can be done with the gun out of stock and with the end cap removed. Spary as much of the Napiers air rifle oil in there as it taks to do the job, let it drain offand replace the end cap and the mechanism is already lubricated. Spray more of the same oil in there from time to time to keep it luricated. I use Napiers air gun oil as it is kind to the O rings.
Your group sizes are fine, beyond 60 yarsd and with a sub 12 air rifle it is anyones guess how the gun would group but your's are fine.
One more point, when target shooting use the single shot adapter. HW 100 regulator takes a bit of time after each shot to settle so if you fire off one after the other, chances are that you'd be firing before the pressure is stablised, single shot adapter will slow you down and give time for the Reg to settle.

A.G