A&K Masada SPR - DMR Theory Crafting

[MrTea]

Nice thread by the way, found it really helpful just reading through.

That's also funny that the right side on yours is worse, on mine the left side binds and feels coarse but the right side is really easy to to move. Is there anything you found that helped with getting it working smoothly?

I didn't do anything special honestly. I just re-assembled it and left it how it was. Sorry I can't help more.

 

[Leo Greer]

Thanks for the insight. I've gotten a M160 spring in prep for modifying and testing the ML MR Hop 70 degree bucking but I seem to have misplaced that hop rubber... somewhere??? Not sure how i've lost it but i'm on a drive to consolidate all of my spare parts + tools into something that I can carry onto an airsoft field (due to a recent crappy experience) and work with so it may turn up in a random box when I break everything down.

I put together an “Airsoft Medkit” that’s basically a briefcase filled with tiny plastic shelving units. I can carry all my tools, adhesives, and enough spare parts for a complete internal rebuild of two RIFs. It’s saved my butt a few times. Just make sure you include the essentials; super glue, emergency crackers, a backup to your backup screwdriver…

 

[MrTea]

@grumio Have you found a hop rubber that will work properly with this hop unit design or are you still using a standard/stock one?

 

[MrTea]

Actual progress this time around but additional confusion.

I tried sanding down the Maple Leaf MR hop rubber feed lips. No matter how little I took each time, I could never get a rubber that resulted in consistent FPS readings - at one point I got an FPS reading of ~800 so IDK ?

I've been messing with different hop rubbers trying to find one that consistently works especially when the stock hop rubber ended up splitting when changing it over. I was going to try the a ML Macaron 60 degree as i've never had an issue with them before and they just worked. During the process of installing it I noticed that the hop unit wasn't applying hop evenly, it was applying too much pressure on the right side resulting in uneven hop. I think this is simply due to the way the hop unit is designed that makes the hop arm slightly off center. Happily I managed to remedy this quite quickly by using a small o-ring that I had lying around which I think is for a MOSCART fill valve? All I did was just put this between the body of the hop unit and the hop arm. Before anyone mentions it, yes the screw is in the wrong side of the hop unit and no, this isn't what was causing the issue with the misaligned hop arm

View attachment 131979View attachment 131980


Now that I had sorted that I moved onto changing the hop rubber. I have a prommy purple I was going to try out but for some reason I just wanted to try a Maple Leaf Macaron yellow/60 degree just because they've worked flawlessly on everything I've put them on. I also installed the bucking with the Gearparts Omega 70 nub from AK2M4 and it worked. I am so mad. I am confused as to why this works. Before I tested this, i'd bought and installed a SHS M160 spring to creep up the FPS. The spring is very twangy (if that makes sense) and it's pretty annoying.

View attachment 131978

Since starting this build, i've changed which outdoors site I go to and they allow 450fps for DMRs so i've still got a bit of headroom that i'd have to buy an M170 equivalent to get to. Is a SP160 the same as a M170?

Could it be the MR hop bucking didn't work as the hop window on the inner barrel is too small causing inconsistent contact?

I am at a loss as to why this suddenly works... I want to buy another ML MR hop rubber and try it but I feel like if I disturb the hop rubber in the slightest it's gonna throw a fit and not work anymore.

 

[Lozart]

Since starting this build, i've changed which outdoors site I go to and they allow 450fps for DMRs so i've still got a bit of headroom that i'd have to buy an M170 equivalent to get to. Is a SP160 the same as a M170?
 

For the love of GOD don't start chasing FPS limits.

Use it, see if it's actually lacking in range/accuracy first.

As for your other question, yes absolutely if the window on your barrel is too small or if the rubber hasn't gone on properly then an MR hop will catch on the edges.

SHS springs can be quite wide tolerance. Pick a spring brand you like and trust (*coughs* XT @ak2m4 *cough*) and stick with it.

 

[Colin Allen]

SHS springs can be quite wide tolerance. Pick a spring brand you like and trust (*coughs* XT @ak2m4 *cough*) and stick with it.

XT springs are great; they are very consistent.

 

[MrTea]

SHS springs can be quite wide tolerance. Pick a spring brand you like and trust (*coughs* XT @ak2m4 *cough*) and stick with it.

That was what I was going to do initially however it appears his XT springs don't go past M150. Up until this point, it's exactly what I was using.
 

For the love of GOD don't start chasing FPS limits.

Not yet. Now i'm closer to the limit, and have it chrono-ing consistently, i'm going to give it a test on 0.36g BBs to see how it's performing.

 

[ak2m4]

M160 are arriving in a few months however what's going on with that build?  Never worked on a Masada personally but why so low power ?

 

[Lozart]

M160 are arriving in a few months however what's going on with that build?  Never worked on a Masada personally but why so low power ?

I was wondering the same, my MK12 is doing 420 FPS on a M120 spring!

@MrTea just to go back to basics, I assume you've checked that you're actually getting good compression with all the new cylinder/piston parts?

 

[MrTea]

I was wondering the same, my MK12 is doing 420 FPS on a M120 spring!

@MrTea just to go back to basics, I assume you've checked that you're actually getting good compression with all the new cylinder/piston parts?

That's annoying. The air seal was perfect when I originally changed out the stock compression parts but I can definitely go back and check again when I get the time.

 

[ak2m4]

@MrTea what's the inner barrel length, is it 6.12mm?  what's cylinder type is it? 

 

 

[MrTea]

@MrTea what's the inner barrel length, is it 6.12mm?  what's cylinder type is it?

6.12mm yes, 360-ish long IIRC and a full/non-ported cylinder.

 

[ak2m4]

6.12mm yes, 360-ish long IIRC and a full/non-ported cylinder.

I've never run a 6.12mm so can't comment, however I'm guessing it loses a fair amount of power.   I'd love to test one and get my borescope down one.

However I suspect the issue is you're using a full cylinder with a 360mm barrel, you should be using either a 4/5 or 3/4.  You should be able to hit you're required power with a M120 spring. (Unless there's something else I'm missing).  I've not the time to read through the whole thread, so don't know the whole story.  The 6.12mm however does introduce more unknown variables.

 

[MrTea]

I'll take the current setup and use the stock barrel and see what happens to the FPS. Should give an idea as to whether the barrel is causing significant FPS drops.

If this turns out to not be causing large FPS drops, i'll test the airseal afterwards.

Sound good?

 

[Colin Allen]

I've never run a 6.12mm so can't comment, however I'm guessing it loses a fair amount of power.   I'd love to test one and get my borescope down one.

However I suspect the issue is you're using a full cylinder with a 360mm barrel, you should be using either a 4/5 or 3/4.  You should be able to hit you're required power with a M120 spring. (Unless there's something else I'm missing).  I've not the time to read through the whole thread, so don't know the whole story.  The 6.12mm however does introduce more unknown variables.

I went down the wide bore rabbit hole with an SVD I had many years ago; the drop in power was significant compared to a tight bore barrel.

 

[ak2m4]

I'll take the current setup and use the stock barrel and see what happens to the FPS. Should give an idea as to whether the barrel is causing significant FPS drops.

If this turns out to not be causing large FPS drops, i'll test the airseal afterwards.

Sound good?

Yeah give it a try, I'm fairly confident it's your cylinder type.  What cylinder type did the AEG come with?

 

[MrTea]

Yeah give it a try, I'm fairly confident it's your cylinder type.  What cylinder type did the AEG come with?

Funnily enough, it's a full/non-ported cylinder. I 100% sure of this as I kept all the parts/spares from this build in it's own box so I didn't get them crossed with anything else.

 

[ak2m4]

Funnily enough, it's a full/non-ported cylinder. I 100% sure of this as I kept all the parts/spares from this build in it's own box so I didn't get them crossed with anything else.

The stock inner barrel is 509mm though right?

View attachment 132053

 

[MrTea]

@ak2m4 Measured at 480mm. This doesn't mean the person who owned it before me changed anything but why would they go for a shorter brass inner barrel?

 

[Lozart]

@ak2m4 Measured at 480mm. This doesn't mean the person who owned it before me changed anything but why would they go for a shorter brass inner barrel?

Because they're stupid?

Don't assume that anyone that worked on your gun before you knew what they were doing!