Energy and pellet weight

no avatar
Archer50
Posts: 200
Joined: Mon Jun 20, 2016 5:06 pm
Location: Perth

Energy and pellet weight

Mon May 29, 2017 3:58 pm

I have just come across the idea on another forum that, if your gun gives a big difference between the muzzle energy of lighter pellets and heavier ones, the firing valve is probably staying open too long. So, not only is air being wasted when using the lighter pellet, lowering the shot count, but it is difficult to get a decent velocity with the lighter pellet and still stay legal with the heavier one.

Is this a useful measure for setting the firing pot in 400/500 series guns – ie minimum difference between, say, a JSB Heavy and an AA Field? Is it even true?

I’m particularly interested at the moment as there is a stonking 1.25 ft-lb difference between Heavies and AA Fields from my S400 Classic (.177) compared to the 0.5 ft-lb I'm used to from my HFT 500 and I’d like to get some views from more experienced Air Arms fettlers before I start tinkering (again!).

Alan

no avatar
Bezzer
Posts: 31
Joined: Sun Nov 13, 2016 11:15 pm

Re: Energy and pellet weight

Mon May 29, 2017 10:12 pm

Are you referring to what Tench/Simon Howarth was saying on STB forum? If so he was mainly referring to regged guns which all need transfer port, hammer spring and hammer weight tuning to get consistency and the optimum air "use" , and therefore with less air waste there is less power effect when using different weight pellets. All this is true for aftermarket regs, if already regged as standard you can still experiment with hammer strength etc to improve it.
Simon used to do a lot of AA work, making regs, setting up etc but has now moved on to other makes and more R&D work but lucky for me he's a member of our local HFT club so I have been bending his ear on what I can do to my 400. In basic form you're better off leaving the pot at it's standard 57.5mm and you can experiment with a shorter but stiffer hammer spring to give a quicker lock and valve time but in reality the standard 400 is as good as it gets for an unregged gun when you're in it's sweet spot.
I've got a Lane regulator ready to fit on mine, just waiting to find the time to fit and set it up correctly including reduced hammer spring, when Simon used to do them he cut the OE one down by up to a third or so.

no avatar
Archer50
Posts: 200
Joined: Mon Jun 20, 2016 5:06 pm
Location: Perth

Re: Energy and pellet weight

Tue May 30, 2017 4:06 pm

Thanks for that Bezzer, and yes, it was the STB post I was mainly referring to.

I understand that the post was referring to a regged gun, but surely the basic principle applies to any PCP: if the valve stays open longer than the lighter pellet stays in the barrel, the heavier pellet is going to 'benefit' from the additional air.

I have never seen such a big difference between a JSB Heavy and an AADF as I have currently in my S400. When the Heavy is clocking 11.53 ft-lb (709 fps) average for a 30 shot string centred on the max, the AADF is clocking 10.26 ft-lb (740 fps). It's not so much that I worship fps - far from it - but I just don't understand why this gun should be giving something like twice the difference I have usually found. And by the way, I have checked these figures over 3 different chronos, so I am very confident they are right.

Anyway, its 5 weeks to the next HFT competition up here so unless anyone can think of anything else it could be, I am going to try adjusting the pot and possibly playing with the hammer spring just to see what difference it makes.

Alan

Post Reply

Who is online

Users browsing this forum: No registered users and 28 guests