Which spring to use to stay under 350fps?

[FelipeFlops]

Hey guys,

I've just upgraded a couple of components in my DE UTR45, mainly the barrel (ZCI 6.02mm 363mm), hop up unit  (ZCI), and bucking & nub (Maple Leaf Super Macaron 60 degree and Omega nub). 

I unfortunately don't have access to a chronograph to find out myself, but I have an M100, M105, and M110 spring and I was wondering which one would safest to get me more or less to 350fps without going over?

Pre-upgrades it was shooting c. 300fps on .2g BBs, so I'm guessing the stock spring was an M90/95 combined with the original 229mm 6.03mm inner barrel and hop up setup?

 

[Colin Allen]

Buy a chrono!!!!!!!!

Until you know what the energy is, you cannot make an informed decision as to which spring to use.  However, I suspect that an M100 would probably be ok, or possibly not.  As you have  extended the barrel, did you also change the cylinder?  I am not sure which cylinder the UTR comes with, but, if the porting is wrong for the longer barrel, you might see a drop in power.

 

 

[FelipeFlops]

I have now ordered an AC6000, hopefully it'll arrive today!

 

[FelipeFlops]

So the chrono has arrived and I tested both the M105 and M100 springs in the UTR45. 

M100 - 346fps @ 1.12 joules

M105 - 366fps @ 1.25 joules

Looks like the M100 is the one for me!

 

[Rogerborg]

Nice!  Is that with or without hop for the weight of BB that you're using?  I'd assume not since you're quoting fps for 0.2g.  And do your local sites ask you to chrono without hop (I'd hope not, but some do)?

What I mean is that you might be under the site limit with the M105 and properly hopped BBs. Although it's best to have a bit of headroom to account for inconsistency between your chrono and the site.

 

[FelipeFlops]

That was with the hop completely off for the .2g BBs.

I usually use .25g BBs, the M100 is giving c.310fps @ 1.02j with the hop at its usual level at that weight. So yes, does feel like there's some wiggle room with the hop on.

 

[FelipeFlops]

OK so I put the M105 back in the UTR45. Hopped it using .25g BBs for a range of 40ish metres. Unfortunately, when I switched over to .2g BBs to chrono, I am still getting 358-360fps and 1.2j. So still over the limit of my local fields.

Re-hopped for the M100 on .25g, and with .2g am getting 344fps and 1.11j. I don't think I want to push it any further.

 

[Colin Allen]

OK so I put the M105 back in the UTR45. Hopped it using .25g BBs for a range of 40ish metres. Unfortunately, when I switched over to .2g BBs to chrono, I am still getting 358-360fps and 1.2j. So still over the limit of my local fields.

Re-hopped for the M100 on .25g, and with .2g am getting 344fps and 1.11j. I don't think I want to push it any further.

That seems reasonable.

 

[Cannonfodder]

I don't think I want to push it any further.

Good thinking. Trying to get closer to the site limit would be a waste of time as you could easily go over and that extra 6fps will make bugger all difference anyway