Power increase with no mods?????

[helpimonfire]

Hey guys.

Just recently I'd built a gearbox from scratch but used an old TM spring I found as my budget ran out. It chrono'd at 210fps which was poor but the range was still rather good. I decided to speed up the time to target as people were seeing rounds coming at them and moving out of the way.

So! New spring then.

I dropped a JBU M100 in and the results were good - 348, 348, 348, 348, 349, 348, 348. Consistent, is the word I'd use.

Anyway, I've skirmished this a few times and it's been brilliant. I thought it'd settled down a touch, but with there being a weekend game for us this weekend, I checked all my guns last night. This gun inparticular came in at a staggering 385fps! I thought it was a bit odd. So I put a few more rounds through the chrono. 385, 385, 384, 385, 383, 380, 386 etc...

What would cause this massive hike in power? Airseal settled? I thought the airseal was brilliant when I built the gearbox, now all of a sudden I've gained 38fps since last sunday? I'm changing the spring tonight and I'm going to take a selection of springs with me when I go this weekend, but I'm just curious as to why I'd suddenly get a massive increase?

Would turning the cylinder round down the power? Currently the vent/window is at the back (spring guide end). Would putting it to the front cause a massive loss in power? Or would it make no real difference?

[jagillham]

Re: Power increase with no mods?????

Same chrono?

All others same as last week?

You can't turn cylinder, won't work!

[helpimonfire]

Re: Power increase with no mods?????

Yes and yes.

I'll just put the old TM spring back in then, hopefully with the better airseal (i presume) it'll bump up the power a touch.

(Just so you all know, I'm not too worried about power, I know the hop is the more important part)

[richardy]

Re: Power increase with no mods?????

chronoing with hop on first time and hop off second time can make that kind off jump if there was enough on and ond standard m4s its hard to tell where its at.

You cant blame the gun, physical components just dont change that kind of amount in a heart beat.

Also this time off year youll see a drop in fps with the cold it will also take longer when adjusting hop for it to take affect. Down the workshop its like 1 degree... guns are cold....

[helpimonfire]

Re: Power increase with no mods?????

When I chrono'd the first time around, I had no hop set at all, last night the hop was set for .25's.

I'm hoping the chrono was misreading, but everyone elses guns were reading a sensible level. I'll still change the spring though, purely to be on the safe side!

[richardy]

Re: Power increase with no mods?????

yeah chronoing with 0.25s originally and chronoing with 0.20s now would also do it.

If its none of those things then im afraid we will never know, it is what it is .. just roll with it and either clip the spring or fit the next spring down.

No its not common for this to happen nor should you see it again, just take your time and make sure you chrono with 0.20s. I did it the other day i had a bottle of 0.20s and sure enough they where 0.25 in weight so its easierly done.

[helpimonfire]

Re: Power increase with no mods?????

As an update to this, last night I stripped the gearbox down, swapped the cylinder to a polished cylinder and a new cylinder head, along with a vented piston head. The problem came with springs next, as I had the JBU M100 and a Guarder M100 (Which in my ates G&P M16 gave out 365fps, so that came out sharpish!), but other than that all I had were old and soft TM springs (We're talking original springs from 6 or 7 year old guns!).

So... A plan was devised. You all know the little metal block that sits inside the piston so the piston head can be screwed into it? Well I put and extra one in to give the old TM spring a fighting chance (Previously chrono'd at 210fps). That extra 10mm with the "upgraded" parts gave me a very respectable 290fps with the hop set for .25s.

I'm happy with that One day I'll drop an M90 in or similar, but for now, this will do!