Massive fps increase

[Glen666]

Hi Im curious to know how on earth my m4 fps l has jumped so high. It's a classic army m15a2 cqb so an entry level rifle which when I purchased was running about 310-320 out the box. I had it chronoed yesterday and it's now kicking.out 360 fps average. Highest was 362. Which obviously a bit awkward as most have a 350 limit. The only mods I have had done is a tight bore and longer barrel and a harder hop rubber. It was chronoed with 0.20g ammo the Marshall said.could be because.of the cold.the rubbers were harder. Was just curious if.this was the case and if there.are any tweaks I could make to bring it down??

Cheers

 

[kungfumonkey]

i know increasing the length of the barrel will increase fps thats why alot of guys who build dmr's fit longer barrels with mock suppressor's not sure about the harder hop or the cold what bore is the barrel 6.03 or 6.01?

if its a 6.03 i read they can give upto a 15% increase in fps so 315 fps with stock barrel would then increase by upto 47.25 fps with a 6.03 tbb which would give you the 360fps it was reading on the chrono

 

[rschris]

Tightbore will increase FPS to an extent but not that much....by any chance did you release the spring after you last game??

If it has sat in the coiled up waiting to go then this will increase your fps for a little while - get a few shots through it and will soon be back to normal.

 

[kungfumonkey]

ahhh right cheers for putting me straight chris i was just going off the fire support website as im looking for a tbb at the mo cant decide on 6.01 or 6.03 as im building a dmr and from what i read one guy says 6.03 gives better fps increase and accuracy then the next guy says no 6.01 is better lol

 

[rschris]

ahhh right cheers for putting me straight chris i was just going off the fire support website as im looking for a tbb at the mo cant decide on 6.01 or 6.03 as im building a dmr and from what i read one guy says 6.03 gives better fps increase and accuracy then the next guy says no 6.01 is better lol

6.01 allows for no mistakes of BB etc...

Plus as its a metal it will contract in the winter making it tighter....potentially to the point a BB will no go through...in summer with will be a tiny amount wider aswell.

I run a 6.03 Madbull TB and cannot fault it.

 

[kungfumonkey]

looks like im going for a 6.03 then cheers mate

 

[Glen666]

Cheers fellas, didnt think that a barrel could make that much difference, and no I didnt release the spring, didnt know you could tbh haven't been doing this for long il run a couple of mags through before my next skirmish as after I had it chronoed I used a different AEG for the day, thanks again for the info

 

[Liam Porter]

When I installed a tightbore in my M16, the FPS went from 335-360 (+25 FPS). This tightbore was 0.05mm tighter (went from 6.08 - 6.03mm) and the same length.

As you've increased the length too, this could also increase FPS, if your cylinder volume is bigger than it needed to be for the stock barrel.

The extra length means the air is behind the BB for longer, and there's an excess of it, so therefore the BB is accelerated further, meaning an increase in FPS.

I've noticed a 10-15 FPS difference between different barrel lengths in my L96; 363mm - 509mm was +10 FPS and 509mm - 650mm was +15 FPS.

Include both of these increases (+25 +15 = +40), means you can get from the 320 stock to the 360 with a new barrel.

There may be tiny changes in the hop up too.

As you've installed a new barrel, it may have a very slightly different outer diameter, meaning slightly different airseals.

The hop may not have been adjusted the same; a longer barrel may not require as much hop as the BB has more time to stabilise before leaving.

 

[Tariq]

The new barrel will also be cleaner.

My FPS jumped 20 after a good old clean.

Longer and tighter barrel will increase fps, and you probably have a better air seal now.