Inconsistent FPS

[Liam Porter]

I've recently got a chrono, so thought I'd just test my M16 and L96 out to see what they're shooting at (also a nice excuse to shoot the garden a bit ).

The L96 has FPS ranging from 480-520, averaging 509 over 25 shots.

The M16 has 320-350, averaging 326 over 25 shots.

What's causing the inconsistent FPS?

My M16's relatively new, the barrel's been cleaned, as has the hop rubber.

I've had the hop apart to swap the nub with the sniper one as an emergency last time I skirmished.

I haven't touched the gearbox at all.

For my L96, the whole bolt was replaced about 6 months ago, including piston, spring, etc.

The hop has been apart quite a lot, and I've recently changed the barrel for a shorter one.

No air should be leaking from the hop, as it's got tape around the barrel/hop and the rubber fits in nicely etc.

What's causing this? And how can I solve it?

Not really wanting to take the M16 gearbox apart as it will void the warranty.

Thanks.

 

[RR01]

The M16 probably just needs to settle down a bit. Put a couple 1000 more rounds through it then check it again to see if there is any difference, although a 30 fps difference isn't that much to worry about with an AEG.

The L96 is probably a different matter. When I had mine I had a shot to shot consistency of around 10 fps max, sometimes follow on shots were the exact same fps for 5 or 6 rounds, although because of site limits I kept mine to just over the 400 fps mark. Have you changed the inner barrel, hop unit / rubber / bucking from new or is it still the OE ones in there? If it's the original, they're not the best so maybe replacement is due. If you have changed it then you may be getting a bit of air leakage even with the tape, and of course if you are firing fairly rapid follow up shots then the air in the cylinder will heat up from the friction of the shot, so could affect the readings.

Try taking a shot every minute, allowing things to cool in between and see what the consistency is like then. If it's still all over the place then try stripping, cleaning and re-greasing the cylinder / piston and try a new hop rubber & nub. In a lot of cases it's just trial and error. I spent hours on a gun club range getting my L96 to shoot consistently at 50 yards, but even then hitting the target was only about 60 % accurate (hitting a 10in square steel plate). My Air Arms S400 air rifle could put a pellet on the same point of aim nearly every time but what is basically a smooth-bore musket (the L96) is never going to be able to achieve that sort of accuracy without spending a whole heap of money on it, if ever. So long as you can hit your man sized target at anything up to 60 yards I wouldn't be worried how consistent the fps was or if it was hitting the exact same spot, as BB's will anyway be more affected by wind conditions than a lead pellet would at the same distance.

 

[Liam Porter]

I'll use the M16 a bit more to see what happens. Haven't really used it much, probably only put about 2000 rounds through it since I've had it.

I've replaced literally everything in the L96, only stock parts are externals.

I'll try with a minute or so between shots, to see what I get.

If they're the same then I'll take it all apart and clean it again :L, I seem to do that quite often though.

Another question, how can I lower FPS without changing the spring/removing the tight bore barrel?

When I first upgraded it, it was a pretty consistent 510, so I couldn't use at my local site, so had to put the old bolt back in it, shooting about 440.

I've used it a lot since then, and even left it cocked overnight (my brother was playing with it..) and now it's ranging from 480-520, I definitely won't be able to use it there because of the shots over 500.

 

[RR01]

Without changing the spring I doubt you will get it down where you want. Changing a spring in the L96 should not be too difficult if you have the special cylinder head spanner. I changed mine regularly as I used to use it at Dragon Valley where they had a blanket 350fps limit for all guns. Still got the spanner but not the L96.

 

[d_loydy00007]

Just a thought but how accurate/consistant is the chrono??

its abit unusally for a spring FPS to vary as much as you have stated and with if happening on both just seems abit odd. get one of your buddies round with a gun that has previously been verified and see what your chrono shows. it might save you worrying about parts and repairs on your armoury :blink: