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Technical Q: A&K M249 Hop Up upgrade


ECRRRainman

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  • 5 months later...
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I've installed several of these for my customers, both the PKM and M249 versions.

 

All but one had the Prometheus soft/purple buckings, the other was a G&G green. So far all the users have been quite happy. Most of the guns are around 350-400 fps w/ .20g bbs.

 

From what I hear, most are getting around 200ft/60m effective range. But that single gun that isn't doing 200ft/60m is only shooting about 300 fps w/ .20 bbs.

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  • 1 month later...
  • 1 month later...

I don't want to necro this thread, sorry if I do but its one of the best review/breakdowns on the bullgear hopup.

 

Out of the guys who have installed and used the Bullgear hopup.  I've read that it takes the standard hopup and buckings.  I also found one review that said the area for the nub is slightly smaller than normal.  I have the madbull red "shark" bucking and nub.  The bucking is currently installed in the stock hopup along with HS5's m249 hopup fix and works better (still have to get it dialed in better) than the stock. The reivew said that the h-nub that comes with the bucking is too wide for the hole on the bullgear.  Anyone have experience with this or can let me know if they have heard the same thing.

 

Thanks in advance.

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I know that in my Bullgear builds I've had no trouble using Prometheus purple nubs without modification. I know that the Madbull nubs are a bit larger in diameter than most, but I'm not sure about the width, so it's a possibility that those could require modification.

 

However, it might be possible to make the hop window in the unit larger with some careful filing. 

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You know, I have both the A&K PKM and the A&K M249 with stock barrels and hop units, and I had a CA M249 and an A&K M60. 

 

Given that they all have roughly the same hop design I found that the PKM was hitting out to 90m no issues at the same FPS as the M249 and the M60.  However the M249 and M60 have had random hooking of shots. 

 

I noticed the difference between the PKm and the M249/M60 and that the PKMs inner barrel does not move or bend within the outer barrel as the fitment is very good, while the inner barrel on the m249 and M60s rattled a bit within the outer barrel.  So I fitted "spacer" barrel between the inner and outer barrel on the M249 the random hooking disappeared, consistency of shots improved, and range increased.

 

Hence the hop up upgrade is not the root cause of the issue.

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  • 1 month later...

The stock CA hopup unit was starting to rotate freely in the receiver of my CA M249 Para, which was causing massive misfeeding issues. Part of the culprit was the broken hopup alignment tray (or whatever it's called), which was replaced with the equivalent part gutted from an A&K M249. Still, the rotation problem persisted, so I ordered the Bullgear hopup unit.

 

Fitting the Bullgear unit was a bit of a chore. Once installed on the inner barrel, I had to carefully hammer the C-clip into place and tighten the corresponding set screw. That part was a bit worrying, especially since it was being installed on a brand new Promy tightbore. I ended up pulling off the installation without rendering any damage, so I'll chalk that up as a win.

 

Making the Bullgear hopup unit fit into the outer barrel was a bit of a task as well. I used a Dremel to bore out the chamber of the outer barrel, periodically test fitting the hopup/inner barrel assembly as I went. After about half an hour of careful grinding, the hop unit slid nicely into place.

 

Now I had to see if the juice was worth the squeeze. I used two different springs, but the following airseal components remained the same:

Bullgear hopup unit (obviously)

SHS red aluminum M4 air nozzle

Prometheus 6.03 363mm EG inner barrel

Lonex 70 degree hard hopup bucking and nub, teflon taped

 

With a Guarder SP130, the gun clocked in at around 385-390 fps with 0.25g bbs (1.71-1.76 J). That was too hot for my local site's limits, so I swapped the SP130 out for a Guarder SP120. The SP120 pushed rounds out at 368-374 fps with 0.25g bbs (1.56-1.62 J). It looks like my airseal with the new hopup is good to go.

 

I wanted to get a feel for the range and accuracy this new setup would provide. I set my hopup to have a little over-hop, but not enough to lose track of the rounds when looking down the iron sights. Sight picture was held dead-on center mass on a man-size target. Ranges (measured with Google maps) are as follows:

SP130: 255 ft

SP120: 230 ft

The range was about on par with what I expected. The accuracy is what really surprised me. My previous setup utilized a stock Classic Army hopup unit, bic pen modded, with a Systema hopup rubber and stock Classic Army inner barrel. With that old setup, groupings at the extreme end of my range would open up to over 4 feet. My new setup is yielding groupings of just over a foot at the end of my usable range, which is a serious improvement. I'm running super cheap Goldenball bio 0.25g bbs right now, so I'm sure my groupings would improve further if I switched to higher quality or heavier ammo.

 

In short, I heartily recommend the Bullgear hopup unit. That said, if you don't have access to a Dremel, you'll have a tough time doing the installation.

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I ordered it and just dropped it in.  Haven't put bb's through it yet just a few dry fire to ensure the nozzle was moving properly.  The only issues I had was the barrel clip was too thick for the barrel.  I had to dremel it slightly to get it to clip in.  Also I had to take off the collar that the spring is on to get the barrel to lock into place.  No idea why but I couldn't get it to lock with it on.

 

For reference I am using the following:

Bullgear hopup

Madbull shark red bucking

Maple leaf nub

ASG 6.03 401mm barrel

Inferno hpa engine

 

Hopefully I can hit the side of the barn now.

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  • 3 weeks later...

Right, quick question around the BullGear unit - having been using it heavily over the last year or so, I've set about changing the hop rubber for something that hasn't developed a slight tear. I've got a TM bucking, however upon fitment, I'm getting quite bad feed issues, which I think are around the feed lips being too big. Also tried a Madbull blue to similar effect.

 

I did notice on Redwolf it says "is designed for the Prometheus Purple hop up rubber, or other lipless hop up rubbers" however, the last rubber definitely had feed lips. Also, I thought a prommy purple did have feed lips :S

 

Anyone else had similar issues? I did try reversing the c-clip that holds the barrel, which stopped the feed issues, but that just brings us back to our old friend, compression issues *facepalm* 

 

All else fails, I'll get an order for a prommy purple in ASAP, or get the sanding wheel on the dremel out for shaving the lips down...

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I have used the Madbull Red in both the stock A&K and the Bullgear hopup.  With slight adjustment the rubber worked fine with the madbull red.  I havent had a chance to put rounds through the bullgear yet but its designed to be used with lipped/standard m4 rubber buckings.  We'll see at the next open play I can get too.

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  • 2 weeks later...

As an update to my last comment - prommy purple is in the Bullgear unit and seems to fire / chrono OK again now. Taking it out tomorrow, so should be able to report back this week in case anyone else has had similar feed issues in the Bullgear.

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Double post, since I can't edit the previous one...


Took the 249 out this weekend with the new prommy purple rubber installed into the Bullgear unit - happy to report back that it worked without any issues. On a related note, the pairing with a Madbull Steel Bull barrel seemed to work quite well. After the first thousand rounds or so, the rubber seemed to bed in nicely and shots were firing straight and true.


I'm not going to try and estimate the total range - unfortunately I'm not good at that and any answer I give will be wildly out. Suffice to say though, that the range improved - massively over stock and marginally over the last rubber / bullgear pairing (we're talking prior to the old rubber tearing ofc)


As people start trying different rubbers, it might be worth keeping a list here of what works OOTB and what needs modification (and what the modifications are) for future reference.


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