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Star M249 Para Examined...


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Hey Static... or anyone else who knows... The battery i use for the MK2 is 8.4v 3800 mah.  my Winstar farst charger however only charges 8.4v batteries up to 3000 mah.  what does this mean?  will i still get a full charge if i plug it in for the standard hour? or do i need to charge it twice??  i appreciate the help. thanks.

 

OFF TOPIC

If your battery is a Ni-Mh AND NOT a Ni-Cd you will be fine. Short explination Ni-Cd's have a "memory" and Ni-Mh's do not. So it will not "remember" that you short charged it if you ever get a charger that does allow you to fully charge it.

 

ON TOPIC

Gundrosen, thanks for the pic. That's just what I needed to know. :D

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OFF TOPIC

If your battery is a Ni-Mh AND NOT a Ni-Cd you will be fine. Short explination Ni-Cd's have a "memory" and Ni-Mh's do not. So it will not "remember" that you short charged it if you ever get a charger that does allow you to fully charge it.

 

ON TOPIC

Gundrosen, thanks for the pic. That's just what I needed to know.  :D

 

I have the same charger and it says:

AUTOMATIC

Ni-Cd Ni-Mh

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OFF TOPIC

If your battery is a Ni-Mh AND NOT a Ni-Cd you will be fine. Short explination Ni-Cd's have a "memory" and Ni-Mh's do not. So it will not "remember" that you short charged it if you ever get a charger that does allow you to fully charge it.

 

How is that off topic? The battery was reccomended specifically for this gun by static, who passed out the required information on this forum. My question affects the preformance of the gun and therfore belongs in this thread.

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Important Update Regarding FPS Discrepancy

 

I received an email today from a reader name Deki from Slovenia. Like many people he was motivated by the information posted by myself and others in this thread to get a Star M249.

 

He told me about an interesting discovery regarding the low FPS numbers that have reported. Like myself and others, he reports 315-320FPS stock. However, it seems the spring guide can be pushed in such that the catch engages the back of the retainer, rather than the normal notch. He refers to the normal position as 'Level 1' and the new position as 'Level 2' and so shall I. Frankly, I don't know how it didn't occur to me to try this myself sooner. I'm very grateful for his suggestion.

 

According to him when in the Level 2 position a given spring produces FPS results in line with what we would expect to see. With the stock spring in the Level 1 position he reports 320FPS as I mentioned. But in the Level 2 position he reports that the gun shoots 350FPS - the sometimes advertised FPS for the gun. In the Level 1 position with the same spring I have in my gun now, he reports a similar FPS to what I have observed. In the Level 2 position his results with the same spring are similar to and in line with what I would expect from that spring in any other AEG.

 

I have tried this with my gun and confirmed that I can put the guide in the Level 2 position and that the gun can properly cycle with the guide in this position. Also of note, I have a bering piston head installed and there are no ill effects when using the Level 2 position. The spring does not fully compress prematurely, something that was a concern for me.

 

I have not been able to chrono the gun yet, I hope to be able to do so on monday. I will report back after I have done this. I expect my results to confirm his findings.

 

One thing worried me, is the Level 2 position essentially 'overclocking' the spring or is it in fact 'underclocked' in the Level 1 position? In other words, is this just a band-aid which is compensating for a problem elsewhere by overly pre-compressing the spring or is the Level two position comparable to the level of pre-compression found in other AEGs? I decided to compare the Star gearbox in both positions to my easiest to access gearbox, the v3 found in my G&G UMG. Here are the results:

 

Here we see the Star gearbox with the spring guide in the L1 position. 'A' is the approximate end of the cylinders. 'B' is the approximate end of the M249's spring guide. 'C' is the approximate end of the UMG's spring guide. Note that in the Level 1 position the M249's spring is significantly less compressed than the G&G's. The difference is at least 1", probably more like 1.25" (the height of the UMG's spring guide is not known at this time).

IMG_7623.sized.jpg

 

And now the L2 position. Again, 'A' is the approximate end of the cylinders. 'B' is the approximate end of the M249's spring guide. 'C' is the approximate end of the UMG's spring guide. Note that in the Level 2 position the ends of the spring guides are nearly identical. The difference in compression is much less as a result, probably within .25". The difference between Level 1 and Level 2 is about .75".

IMG_7620.sized.jpg

 

Here's another angle showing Level 1. 'A' is the approximate end of the UMG's spring guide, 'B' the M249's.

IMG_7627.sized.jpg

 

And Level 2. 'A' is the approximate end of the UMG's spring guide, 'B' the M249's.

IMG_7628.sized.jpg

 

Based on this, I recommend using the Level 2 position to get the best FPS performance possible. Don't be afraid to use either a bearing spring guide or bearing piston head with the Level 2 position either. In fact, it's probably safe to use both if you wish to. On the other hand, if the spring you use ends up being too hot, you can easy decrease the FPS by switching to the Level 1 position.

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Important Update Regarding FPS Discrepancy

...the spring guide can be pushed in such that the catch engages the back of the retainer, rather than the normal notch. ...

This is spectulative:

 

I would be hesitant to do this.

 

The reason being that when you push the spring guide in in that fashion, the catch will be carrying the entire spring load as well as the percussive and concussive forces of firing. Also- the load on the mechbox then is tranferred at a point off center from the piston thru the relatively small catch pin axle. In the normal position, the stock itself is a supplemental support (I would say its the main support, from my looking at it) to the back of the spring guide itself, and thusly the receiver body takes some of the cycling load, and this load in addition is axially central to the cylinder/piston/spring guide.

 

The CA design is the same way and I personally view that catch as a retention mechanism for holding the spring in place while the stock is opened/folded down, and nothing more. I don't look at it as a load bearing member.

 

Just my two cents.

Edited by Hillslam
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hello,

please could you tell me wich spring guide with bearing can fit on star m249 para?

I'm not aware of any off the shelf options. However based on my observatipons you could use any v3 guide if you file the 'ears' down.

 

In the normal position, the stock itself is a supplemental support (I would say its the main support, from my looking at it) to the back of the spring guide itself, and thusly the receiver body takes some of the cycling load, and this load in addition is axially central to the cylinder/piston/spring guide.

This is not the case. There is only empty space directly behind the gearbox. The stock does not touch it at all. There is no difference between the L1 and L2 position as far as what's taking the load. It's always the catch. The force being applied back via the spring guide isn't significant anyway - it's only ever as much as the spring's energy in its fully compressed state or less. I don't think it's a risk (at least no more than using a stronger spring ever is).

Edited by staticzero
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Just push the spring guide further in so that the catch engages the back of the retainer instead of the notch in the retainer.

 

Here we see the positions on the spring guide retainer.

IMG_7299_001.sized.jpg

 

Here I've pushed the guide in further than L1 but not far enough to engage L2.

IMG_7298.sized.jpg

Edited by staticzero
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Just push the spring guide further in so that the catch engages the back of the retainer instead of the notch in the retainer.

 

Here we see the positions on the spring guide retainer.

IMAGE

 

Here I've pushed the guide in further than L1 but not far enough to engage L2.

IMAGE

 

Is it really that easy? I just press it further in?

Cool :) How many FPS would I be getting with this teqnique and my 140% PDI spring? :blink:

Edited by Gundrosen
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No idea, but it's probably over the forum limit. When in the L2 position it will likely yield similar results to the same spring in any other gun. Try it and see.

 

Ok, to bad we dont have a chrono in my club( :o ) But I will take the "coke" test tommorow ;)

Edited by Gundrosen
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hey guys got the gun working my para is great, i have a 9.6 2000mah and its great. rate of fire is scary!!!. but im worried about the lack of range for being at 330fps range is not so hot. i was wondering i have a spare M130 spring sitting around think it would be safe to use it for a few games? im just worried cause the 9.6 runs so fast with the stock spring have you guys been ahving any issues running them of 9.6? and do you think it is safe t run it on a 130 spring or shouldi try to find a m120. i know this is above forum limits just had to ask thanks for the great reviews STAT you are the reason why my wife bought me this gun for XMASS

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If your battery is a Ni-Mh AND NOT a Ni-Cd you will be fine. Short explination Ni-Cd's have a "memory" and Ni-Mh's do not. So it will not "remember" that you short charged it if you ever get a charger that does allow you to fully charge it.

Sorry but that's not correct.

 

http://www.batteryuniversity.com/parttwo-33.htm

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...im worried about the lack of range for being at 330fps range is not so hot.

This is may be a function of the para's shorter barrel not making use of all of the piston/cylinder's compression stroke. My bet is the bore+stroke on the Star's para and MkII mechbox's are the same in the interest of savings and commonality. I assume the color mechboxs soon to be sold are just going to be "m249 flavor" and not "para or mkii flavor". But (and I'm guess here) the inner barrel on the para will be much shorter than the MkII's. Much better to have a piston/cylinder volume matched to the longer barrel and have the shorter barrel shortchanged (pardon the pun) and lose some compression stroke than it would be to match the cylinder volume to the shorter para's inner barrel length and have the MkII owners really be screwed: Remembering its better to waste compression stroke than it is to have the piston reverse and start sucking in air to the cylinder before the previous bb cleared the end of the barrel.

 

I forget the url of thesite that had the formula to match cylinder volume against barrel length (took spring strength in joules as a parameter too), I have it at home but I'm at work now. Anyone remember that?

 

Can anybody confirm if the piston/cylinder volume on the MkII mechboxs are the same as on the para's?

 

There is only empty space directly behind the gearbox. The stock does not touch it at all. There is no difference between the L1 and L2 position as far as what's taking the load. It's always the catch. The force being applied back via the spring guide isn't significant anyway - it's only ever as much as the spring's energy in its fully compressed state or less.

On the CA the stock touches so the body of the gun takes the load. I don't think thats a good idea on Star's part, having a gap there so there's no option but having the catch bear the load off center. I'd look into finding some material (dense foam, wood, plastic) to put behind there. Or maybe buying/milling a heavier spring guide piston. But that's just me. The forces applied are more than the spring compression force. Its also momentum forces of the piston. At 1200rpm over a 4-6" stroke the forces acting on the piston won't be insignificant, but I can't tell you how much of that is translated back to the spring guide and catch. You're right: surely not all of it. Regardless, were it my gun, I'd find a way to support the rear center of the spring guide itself. It could be as easy as jamming a sock in there.

 

Rock on, fellow support gunners.

Edited by Hillslam
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BTW, I have ANGS heatshield in my gun. It fits almost perfectly.

 

OH OH pics pics! :)

 

To anyone who has added a rail for a red dot. Do you have to re-zero each time you open and close the back cover? Or does the cover fall into the exact same place each time it is closed. I can see even a slight variance throwing off the alignment of the scope. :blink:

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