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Discussion Starter · #1 ·
Hello all. I've been running a BBTac M62 (ASG M40A3 clone) for the past year, and wanted to share what I've learned about the gun so far, since there is a lot of misinformation regarding the platform (and scant correct info about it).

Stock my gun shot 450FPS the first outing, and quickly settled in the 410-430FPS range (1.6J). With hop up nearly maxed, the gun lifted both .36 and .4g bbs out to 200-220ft (laster straight), whereupon they'd fall like a rock.

The gun is easy to disassemble, and the stock hex screws are contained in the stock, making them impossible to lose. The stock is where much of the cost savings happened, and while it is certainly durable enough for play it doesn't feel high quality. Overall ergonomics are nice - to the point where I've gotten to quite like it. Interior part quality is sufficient for the price you pay - not top quality by any stretch, but not bottom barrel stuff either.

While stock performance was borderline impressive for an $80 rifle, I wanted my rifle to reach out quite a bit further. Given I was 1.2J lower than my field limit, I thought this would be pretty easy to accomplish. However upgrading has proven to be a challenge - not because there are not available parts, but because the gun is a mix of systems and no one really has figured out which parts are which. So, I decided to start this thread with my findings, so that others might have an easier time upgrading their rifles if they so desire.

Currently, my rifle is shooting accurately but still stuck at 1.8J - last tested with a Laylax SP170 spring. Seal is good everywhere except cylinder - best I can tell I'm leaking severely past the piston, causing my loss. I am about to purchase some new o-rings to hopefully address this issue.

Stock Specifications
Performance

.4g bb out to 220ft flat, then quick drop (hop up nearly maxed)

Spring
  • Length = 8.5in / 216mm
  • Outer Diameter (OD) .41 in / 10.5 mm
  • Seems to be VSR-10 spec
Piston
  • Length = 116mm
  • Diameter = 0.75 in / 19.05mm
  • Stroke length = 4.5 in
  • O-ring is 20mm x 3mm (maybe 3.5mm)
  • Inner diameter = ~12mm - does not accept 13mm springs
  • 45 degree
Barrel
  • Length = 456mm
  • Bridged (unbridge with dikes to install Maple Leaf Buckings)
Cylinder
  • Length = 9.5in (end to end, not including head nor bolt assembly)
  • Diameter = 7/8in / 22.2 mm
  • Estimated Volume = 44.34 cm^3 / 2.71 in^3
  • APS2 spec
  • Custom brass cylinder head (APS2 spec)
Hop Up
  • Hop Up unit is VSR-10 clone. Only difference is bucking slit is on opposite side
  • Maple Leaf buckings will fit, but will require shortening and removal of slit guide due to above.

Verified Upgrades
Springs

  • S&T Upgrade Spring for M40A3 - 500fps when new, quickly dropped to 410-430 range.
  • SSG springs do not work, as they are 13mm outer diameter and thus don't fit into stock piston.
  • Laylax SP170 Spring for VSR-10 - Fits, and had great power initially. Quickly dropped to 1.8J range with heavy bbs.
Cylinder
- SSG96 Cylinder Head - Seals well without teflon tape, and extends further into the bucking (perfect length).

Hop Up
  • Maple Leaf VSR-10 buckings - requires shaving off guide bar and shortening feed-size length. Mr Hop 2020 70 degree and 2021 80 degree work great.
  • Action Army Hop Up Chamber - Requires magazine modification, and removes ability to quickly adjust hop up.
Barrel
- Maple Leaf Crazy Jet 430mm

Trigger Assembly
- L96 Trigger Sear - Only the sear itself fits - sear assembly does not.

Possible Upgrades
- Type 96/APS2 Piston - Not 45 degrees, needed for stock trigger-assembly.

Helpful Links

T4nk's Build Playlist
SiliconeSword's Upgrade/Mod Guide
BlackDog's Compatibility List
Jeppe's Notes
 

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Discussion Starter · #2 · (Edited)
Reserved slot for future updates.

Update 1: The problem with this gun - and the cause of low power - is that it uses an APS2 chamber coupled with a proprietary piston. The trigger assembly (presumably to save cost) is 45 degree, instead of the 90 degrees usually utilized by APS2 systems. This requires the custom piston, which in turn doesn't allow normal APS2 springs (13mm OD) to fit. Since the VSR spec springs that do fit are too long, you can't get enough power out of them, even with ridiculously high ones such as SP170 spec.

Possible fixes include:

  • Finding a APS2 spec 11mm OD spring
  • Converting APS2 piston to 45 (heard some have done this), then installing APS2 spring
  • Conversion of trigger assembly to 90 degree, then purchasing APS2 piston + spring

There is supposedly a facebook group dedicated to this gun, if you have a FB account it is probably worth checking out.
 

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Nice work it's good to get some verified info on the platform and work out a good upgrade path as a lot of beginners pick up this rifle as it's cheap and iconic.

Possibly you might be able to use an Aps2 piston and 90' second sear?

Wonder if it's possible to drill new screw/mounting holes in a vsr trigger housing to fit the rifle. As they look very similar.

Also 44cm3 as the volume has to be wrong that's tac41/SRS levels of volume most aps2 stuff is around 30cm3 did you calculate it using the entire cylinder length or just where the piston head would sit from when cocked and the cylinder head?
 

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Discussion Starter · #4 ·
Nice work it's good to get some verified info on the platform and work out a good upgrade path as a lot of beginners pick up this rifle as it's cheap and iconic.

Possibly you might be able to use an Aps2 piston and 90' second sear?

Wonder if it's possible to drill new screw/mounting holes in a vsr trigger housing to fit the rifle. As they look very similar.

Also 44cm3 as the volume has to be wrong that's tac41/SRS levels of volume most aps2 stuff is around 30cm3 did you calculate it using the entire cylinder length or just where the piston head would sit from when cocked and the cylinder head?

Thanks! That was my thinking too.

Regarding the trigger - I believe one or two people have done this, although none of them went into detail on the process. I aware of a few people who bought an APS2 Piston and sanded it down to a 45 degree to work with stock trigger too.

Regarding mounting screws - I've wondered the same. It seems possible, but I'm not familiar enough with true VSR trigger assemblies to say for certain.

Regarding cylinder volume, I too thought this was too high. I used the stroke length and the inner diameter of the cylinder (so 4.5in and 20mm). I used an online calculator to convert and do it all for me. I was surprised at the number being so high so I ran the calc several times on different days. One would think if the volume is that high overvoluming the rifle would be trivial.
 

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Thanks! That was my thinking too.

Regarding the trigger - I believe one or two people have done this, although none of them went into detail on the process. I aware of a few people who bought an APS2 Piston and sanded it down to a 45 degree to work with stock trigger too.

Regarding mounting screws - I've wondered the same. It seems possible, but I'm not familiar enough with true VSR trigger assemblies to say for certain.

Regarding cylinder volume, I too thought this was too high. I used the stroke length and the inner diameter of the cylinder (so 4.5in and 20mm). I used an online calculator to convert and do it all for me. I was surprised at the number being so high so I ran the calc several times on different days. One would think if the volume is that high overvoluming the rifle would be trivial.
A quick Google comes up with 35.6cm3 volume which sounds more realistic but that still mean that extra volume must come from a shorter piston Bor longer cylinder.

I don't have access to my rifle right now so can't measure the stock type 96 parts. Might be able to get them for next Thursday though possibly to compare for parts support for cylinder and piston.

If the piston is aps2 spec with a 456mm barrel and a good enough hop rubber i would have thought it should be capable of launching .43 and possibly .45 bb's. But that's theoretical anyway let's stick to facts.
 

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Discussion Starter · #6 · (Edited)
Used a different calc and got 35.9 cm^3, which seems to be a lot more reasonable. At 430fps, the rifle - coupled with Mr Hop bucking - is able to send a .45g bb flat out to 230ft (maybe up to 250ft), but starts dropping hard after that. With hop dialed up to 60% or so, it can be overhopped to target at 280ft. This seems anomalous to me, especially given seal is solid everywhere past cylinder head. When cylinder head is covered, my gun leaks out the back (towards me), sometimes all at once and sometimes slowly over a few seconds.

When I first installed the Laylax SP170 spring, I had a flat trajectory out to 270ft with .45g bbs, as expected. However, in short order this reduced to 250ft, and energy was chrono'ed to be 1.8-2J with .32, .4, and .45g bbs. I got 2.2J with .2g bbs. Note this was with piston weight increased up to ~50g from the stock 15g, which only appeared to have deleterious affect on power.

Audio equipment Finger Gadget Trip computer Gauge


Shots 3-7 with .45g bbs, and 8-10 with .2g bbs. Laylax SP170 spring (seemingly defective?)
 

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That's about where we've settled I think.

I also recommend checking the O-ring groove for any weird spots, and smooth it down with sandpaper up to about 400 grit.
Also, what grease are you using?
At lower power its sometimes hard to overcome the friction of the O-ring, I've seen a power gain when using Tamiya CeraGrease.
You can use others like TechT, light weight silicone, light weight motor oil, and whatever everybody else says, but when rubbing Tamiya between your thumb and finger while pressing hard, they will fly apart more violently than any other lubricant I've tried.
 

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Discussion Starter · #9 ·
I'm hoping so. Proper sized replacements are in the mail to me as of today. Also going to run 2 - maybe 3 - for testing purposes. If it isn't that I've no clue what else it would be, unless I managed to get 3 different springs shooting 50-150fps lower than they ought to be.

I am using Ballistol as my lubricant as of right now.
 

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Discussion Starter · #10 ·
Full seal on my piston - in fact, it is so snug it doesn't want to go past threads. Have about 10g of weight on the piston and my new Laylax SP170 spring in. No chrono at the moment, but I'd be surprised if I made 2.3J based on how it's shooting.

Still only getting to 70m (with .45g) before starting to drop/over hop, depending on setting. Overhopped for decent consistency it drops at 280ft.
 

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Discussion Starter · #12 ·
Thanks for the kind offer, but I'm done with messing with it. I'm pretty confident everything past the cylinder is in good shape (the Mr Hop will overhop at will, it is just that energy is low).

Curious as to what it chronos - something about the cylinder/piston arrangement doesn't allow it to make much energy at all. Since the cylinder seems to be an APS2 system, it is strange that the power won't increase at all. I can only surmise that since the piston seems to be a one-off that something with it is curtailing the power production. It clearly doesn't like weight being added to it.
 

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Hmmm... so what is going on with your piston? Does it move freely in the cylinder with minimal friction with out the spring installed?
 

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So stock type96 plastic piston is 12cm by 19.5, so the m40a3 does use type 96 pistons.

You can get the type96 pistons in 7/11mm & 9/13mm spring versions depending on brand.

My type 96 piston is also 9.5 inches aka 24.3 cm (not including cylinder head or bolt handle/mount)

Type96 cylinder head is 20mm long (not including threads).

So cylinder and internals all appear to be aps2/t96.

Really it's only the trigger left to solve and I do wonder if drilling mounting holes in a vsr trigger could work in which case it changes the rifle from meh to a good upgrade base.
 

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The issue with the M40A3 is that the receiver is PLASTIC, hence why is has 4 trigger screws, 2 side by side on each end, so I don't think a VSR trigger would work out too well.

I'd maybe look at an ESC 90° conversion, but I believe you mentioned that the big sear and possibly trigger aren't compatible.

Maybe you could get a Mancraft SDiK for the APS2 platform lol, that would probably be best if you want hardcore performance out of a lame base, but that is likely not within a reasonable budget for you.
 

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The receiver is plastic? well that ruins it. Why do nearly ball Airsoft companies have to make at least 1 dumb design decision on every gun they make?

Could still potentially mod a trigger housing but than your waiting for the failure of the trigger housing and the gun is in the bin.
 

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The receiver is plastic? well that ruins it. Why do nearly ball Airsoft companies have to make at least 1 dumb design decision on every gun they make?

Could still potentially mod a trigger housing but than your waiting for the failure of the receiver and the gun is in the bin.
 

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Yeah, that was an extreme downer, same with the barrel being a slip fit with no threads at all.
Tbh the Double Bell VSR-10 I had for a week had the same slip fit outer barrel, but at least that had a metal piston, full piston seal, 500 FPS, and a nice bolt pull with a GOD DAMN METAL RECEIVER.
For the $130 or whatever it was, it's definitely worth paying the extra $30 for it due to the stainless cylinder and all the other things that made it better.
 
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