Jump to content
Sign in to follow this  
panc8k3

FPS/BB Weight phenomenon

Recommended Posts

So I have a m4 (proper barrel to cylinder ratio and fully sealed) with a guarder sp 140. TN 455mm barrel with type A cyliner. The fps with .20 is ~475. Which is low in my opinion. But with .28 it's ~425. In my experience you will lose about 80 fps with .28. I have confirmed this with 3 other builds of mine. What is going on?

Share this post


Link to post
Share on other sites

An M140 spring should put out around 460fps. I have had a few Guarder springs in the past, and they never conformed to the idea that they are one level higher than usual I.e a SP110 performs like a M120. Dropping non Guarder springs into the same gun, the other springs performed as advertised. I don't buy into the Guarder "hype" and believe that their SP140 would do about the same as an M140.

 

Based on that 475fps with .20g is reasonable. Converting between weights, that energy level should give you 400fps with .28g.

The numbers you go with your SR-25 are consistent with what they should be which points to something with the gun, rather than with the chorno, however testing multiple guns on the chorno would be needed to confirm that the chrono isn't the issue

 

I'm not sure where the idea that the XCortech is inaccurate came from, but my personal XCortech shows consistent results along with field chronos from at least 4 different fields, along with our clubs XCortech. It is also a very common and recommended chrono by many of the well known techs over on ASM, which leads me to believe that they are more on the accurate side.

Share this post


Link to post
Share on other sites
I'm not sure where the idea that the XCortech is inaccurate came from, but my personal XCortech shows consistent results along with field chronos from at least 4 different fields, along with our clubs XCortech. It is also a very common and recommended chrono by many of the well known techs over on ASM, which leads me to believe that they are more on the accurate side.

I also have a XCortech, best investment I ever made in airsoft.

Share this post


Link to post
Share on other sites
An M140 spring should put out around 460fps. I have had a few Guarder springs in the past, and they never conformed to the idea that they are one level higher than usual I.e a SP110 performs like a M120. Dropping non Guarder springs into the same gun, the other springs performed as advertised. I don't buy into the Guarder "hype" and believe that their SP140 would do about the same as an M140.

 

Based on that 475fps with .20g is reasonable. Converting between weights, that energy level should give you 400fps with .28g.

The numbers you go with your SR-25 are consistent with what they should be which points to something with the gun, rather than with the chorno, however testing multiple guns on the chorno would be needed to confirm that the chrono isn't the issue

 

I'm not sure where the idea that the XCortech is inaccurate came from, but my personal XCortech shows consistent results along with field chronos from at least 4 different fields, along with our clubs XCortech. It is also a very common and recommended chrono by many of the well known techs over on ASM, which leads me to believe that they are more on the accurate side.

 

I've actually have begun to think the same of the guarder springs. So if 475 is reasonable with .20 how is it I get ~420-425 with .28 and I just confirmed this- 405 fps with bioval .30 bbs. It seems I'm getting higher numbers with the heavier bbs. I'm not complaining. Just wondering why/how.

Share this post


Link to post
Share on other sites

Guarder spring's higher power isn't "hype" its that their "SP" rating system rather than "MS" or "M" rating system is referencing your velocity in meters per second with .25s rather than .20s which is why you find your gun shooting hotter with guarder springs bearing the same number as compared to another brand's springs. Of course we've seen batch inconsistencies from Guarder as well as the odd broken spring, and given that its all dependent on your airseal and volume balancing, all bets are off.

 

 

As far as your specific situation goes an SP140 is supposed to put out 140m/s with .25s which is 2.45J which is 459fps with .25s, 513fps with .2s, or 434 with .28s.

 

How does your gun stack up? 475 with .2s is 2.1J and 425 with .28s is 2.35J. So you're a little low on power. Probably minor loss of airseal. You are however also seeing kinetic energy creep, so its likely you're also losing some to improper volume balancing.

 

 

Also anyone who is interested in being able to do these calculations themselves, shoot me an email. I got frustrated with existing calculator devices, so I did up a spreadsheet that gives you inputs and outputs in KE, M/S, and J and goes from .12s all the way up to 3.5g rounds. This is all pretty basic and important analysis, so you should have your own calculator of some kind to do calculations. ;)

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this  

×
×
  • Create New...