An interesting one for you...

[Pricey]

I recently acquired a CA Scar H and went to Chrono it (as I do with all new AEG's). When I chrono'd it I was impressed with the first round: 344... but not so much with the rest.

Over ten .2's (Marui bb's) I got: 344, 254, 256, 340, 339, 251, 254, 256, 340, 251.

At first I thought it was the chrono, so I pulled out my trusty TM MP7 and run that using the same BB's: it was around the 250 mark (as it should be), I then tried my P226 on green gas: around the 250 mark as it always has been. Which made me think it wasn't the chrono.

The thing that's confusing me is, despite the Scar shooting at 250 fps, it sounds like it's hitting my target (a cardboard box) a damn site harder than the MP7 (considering they're box supposed to have the same FPS...

I also tried this test on myself (seemed like a good idea at the time) with the help of friend. We loaded the MP7 and he fired a couple of rounds into my leg. The rounds hit and I pretty much shrugged them off (250fps is hardly a hard hitter). Then we loaded the Scar and by my reckoning the impact should feel the same if they are firing at the same FPS? Was I correct? No... It F*cking hurt :P

Has anybody got any idea as to what could be causing this low FPS and then Random spike of 90ish FPS? I've checked the airseal and everything appears to be fine! Should I try a new rubber and see if that helps?

Cheers

Pricey

[Figjam]

Re: An interesting one for you...

One thing that would give you those results would be accidentally mixing up the weights of BBs in the mag you are running through it.

I dont mean to sound condescending, but I did it myself a while back and I did my nut trying to sort it until i realised thats what was going on.

[Pricey]

Re: An interesting one for you...

One thing that would give you those results would be accidentally mixing up the weights of BBs in the mag you are running through it.

I dont mean to sound condescending, but I did it myself a while back and I did my nut trying to sort it until i realised thats what was going on.

I see what you mean, but it's impossible. The TM BB's came from my P226 box and were sealed until I opened them to test the rifle.

[mcwimbo]

Re: An interesting one for you...

have you tried turning the hop completely off? see if that stabilises it, could prove an airseal issue if it does? maybe that you have a build up of grease around the nozzle causing an inconsistent seal? unlikely but possible?

[Figjam]

Re: An interesting one for you...

Normally I'd be putting my money on the hop rubber as most likely candidate, either a tear or its rucking up in some what, but that would give you either consistently down, or all over the place. I still look at those numbers and think BBs, you were getting either 340 (+/-) or 250 (+/-), nothing in between. And the seemingly consistent impact energy can really only have that explanation unless you were mistaken in your "human target test". I know it seems unlikely given what you say about them coming straight out of a bag, but maybe try with some totally different BBs from a different source just to be sure, as its an easier check than the next things on the list of possibilities.

If not, hop rubber, nozzle, spring guide, piston head, tappet plate was the order I was given of things to check when FPS is down.

[Pricey]

Re: An interesting one for you...

I'll try the hop rubber then and report back with my findings!

[a_flea]

Re: An interesting one for you...

Yeah, bunching hop rubber or a glooped up o-ring on a vented piston head... Not sure if a spring twisting up could make a 90fps difference?

[Pezza]

Re: An interesting one for you...

I had a similar problem with my Stoner a while back. Turned out to be the air nozzle wobbling slightly and breaking the air seal every few shots, new nozzle sorted it out

[Figjam]

Re: An interesting one for you...

I had one where it was a notch in the tappet plate, meant that it was moving the nozzle forward erratically. Was a right old pain as it was the last thing I checked!

Any results on this yet?

[sYan]

Re: An interesting one for you...

If not, hop rubber, nozzle, spring guide, piston head, tappet plate was the order I was given of things to check when FPS is down.

Agree with this. My money is on hop rubber or a dodgy/broken nozzle. If you don't have any success with that, you might want to check your piston head and it's air seal to the cylinder just to make sure it's working properly.

Keep us up to date either way!

[Pricey]

Re: An interesting one for you...

Well, ordered a madbull blue last night, so when it lands I'll get it in and report on the results! If its still shite i'll refer to Figjams check-list and go from there

[No1_sonuk]

Re: An interesting one for you...

I suppose you have checked if the inner barrel's clean?

[Pricey]

Re: An interesting one for you...

I suppose you have checked if the inner barrel's clean?

Of course mate, it's the first thing I did when I got it. Don't suppose it would matter but the barrel appears to be a Prommy Tightbore... would that factor into it at all?

[No1_sonuk]

Re: An interesting one for you...

Just making sure. You'd be surprised the number of people that don't think of that.

WRT the barrel: You might be having BB size tolerance problems. In a tight bore, you could get a big swing with a wide size tolerance.

I'd suggest trying some precision BBs. Any weight will do - You're having consistency problems, not absolute fps, so any consistent result, no matter how high or low, is what you're needing.

[sparrowhawk]

Re: An interesting one for you...

its your nozzle not completing a perfect seal on a consistant basis, which is normally down to an erratic cycle, or any other of the issues connected to the nozzle mentioned already