[MrTea]

Hi all. Recently installed a MK18 handguard to my project gun to find that the outer barrel isn't aligned centrally.

I took a couple of pictures to display what the issue is. I've tried adjusting how many barrel shims i've used to no avail. Someone on some long forgotten forum post suggested nipping up the grub screw on the outer barrel so I tried that. It's almost eliminated the wobble in the outer barrel but it's clear it's sitting off centre of the handguard. Aside from the cable tie method mentioned in this video i'm drawing a blank on what else to do.

Google brings up a couple results for barrel spacers for MK18 style handguards but they're out of stock almost everywhere or won't ship to the UK. Can't find any aliexpress wares for this either.

Any advice appreciated.

 

[rm105]

Assuming it's a multi piece barrel (the 'barrel' inserts into a 'base' which slides into the receiver), here's how I handle this issue when it pops up.

First wrap the end of the barrel with 1 or more layers of masking tape until its a fairly tight fit in the base, then secure it with the grub screws. You do not want to angle the barrel in the base to center it as this can mess with your hop chamber seals.

Next install the barrel nut (threads onto the receiver, clamping the barrel base in place) and verify the barrel had no wobble when it's hand tight - if there's wobble, place barrel shims on the front of the base. Search for 'AR shims' on Amazon ot ebay, can usually find them. Possible to cut them out from cardstock, but tedious. Either way, also ensure the base doesn't protrude into the insides of the receiver when its hand tight- on most guns the back of the base should be flush with the face of the receiver where the hop chamber sits. It it protrudes, will need to place some shims between the base and the receiver.

Finally, install your handguard and check the centering with the barrel - if it's OK then you're golden, if not place one or several layers of tape or cardstock on the side of the barrel nut so when the handguard is tightened it tilts in the correct direction. doesn't take much to correct the centering.

If your handguard is a traditional quad rail instead of more modern monolithic design, need to place the tape/card shims on the face of the nut to accomplish the same tilt correction. If the receiver uses alignment pins, make sure they are the right size - if not, can cause the handguard to get angled. Make sure you are not over- tightening the handguard bolts, can warp the clamp and tilt the guard. Use some blue loctite to keep everything on place.

 

[Ben3721]

A lot of times the rail is actually straight and the front face of the upper receiver face where the threads are isn't flat 90° and it angles the outer barrel off as it rests on it. Put a long snug rod, barrel or arrow inside the outer and see where it aligns when it sticks back to the rear of the upper/lower. Outer barrels can be bent or warped too or if they are multi piece they can just be all kinds of off.

If that lines up then yes, it is the rail or the threading skewing it off.


Edit: also mk18 rails use bolts to tighten down on the rear. They can tilt stuff weirdly if they are off or if one is tighter than the others.

 

[aotsukisho]

Things to check

1. Upper receiver barrel face is true (example: Upper Receiver Truing-Upper Receiver Truing )
2. Outer barrel face (where the barrel nut tightens against) plus any spacers is true
3. Bolt Up system is torqued continuously in a star pattern, never all at once (like car wheel lug nuts)
4. Upper receiver and RIS II picatinny slots are aligned properly (straight line all the way down), could just be the outer barrel

If it really bothers you then you could just tug the outer barrel in whatever direction to try and straighten it out. Usually I only see this on longer 16"+ builds though not on a 10.3" Mk18 Mod 1.

 

[Bisqcateer]

I'm fortunate enough to have a 3D printer, so I designed my own spacer to shim the barrel muzzle-end perfectly for my M4 and it's now rock solid and literally cannot move. It's a super tight friction fit, but I added a place for me to screw it on to make extra sure it won't back out.

 

[MrTea]

Thanks for the replies everyone. Very helpful info from all.

After a couple afternoons trying out different options between making spacers for the bolts of the handguard and tightening the bolts in a proper pattern I appear to have accidentally fixed the issue by taking apart the outer barrel and reassembling it. I'm not exactly sure why it fixed it but it has. The outer barrel is now pretty much dead center and has zero wobble. Not going to complain but it would have been nice if there was a clear and obvious issue causing it.

Now I just need to find an extention that'll clear the handguard enough for my QD supressor.

Thanks again.

 

[Graybeard]

My experiences, usually when I find an issue of alignment, I take it apart and try again. Sometimes the alignment issue is caused by me; Especially when I can’t reproduce the problem consistently.

 

[MrTea]

Another afternoon of playing with the project gun and today I opened up the gearbox. The gearbox sticker was still intact. It had never been opened, ever.

The job today was re-shim, re-grease the internals of the gearbox, adding a Perun Hybrid V2, new inner barrel, bucking, nub and adding a functional sling-plate rather than the blank one that comes with the gun.

The Perun was a doddle to install minus a bit of dremelling required on a post inside the gearbox that blocked the trigger travelling all the way. Once that was dealt with, MOSFET was in quickly, tested and working.

Re-shimming the gearbox was a bit more troublesome. Had a couple of false starts with the shimming with one setup cycling halfway then locking up. Managed to get it right eventually. I probably should've got new bearings but totally forgot about it. For greasing the gears I used some Teflon grease designed for bikes as I didn't have time to get some LT2 grease. I used Silicone grease for the compression parts which are on their last legs. A new, upgraded, compression set should have arrived today but Royal Mail are on a go slow so they're getting here tomorrow. The current parts improved with new grease but they're still poor but don't have a chrono on hand to check how bad they are and how good it is after.

Reassembling the gearbox was a faff on, the issue being the tappet plate rather than the anti-reversal latch. The tappet plate wanted to keep jumping over the sector gear but was fixed with a long, small, flat screwdriver holding it down while I squeezed the top of the gearbox case on.

I added the new inner barrel and I thought it'd be a bit long (340mm) but it's the perfect length for my build. However, I have an issue with whichever factory makes/assembles the SA-C04. The grease/oil they use for the inner barrel/bucking STINKS of fish. I mean, not a little smell, it reeks! The bucking was well beyond it's expiry and went the journey to be replaced with a maple leaf Macaron 60 degree bucking and the nub was changed to a Prometheus flat nub. I cleaned the inside of the hop-unit the best I could with a cotton bud to remove the old oil/grease.

Once reassembled, I added the new sling-plate and put the the remainder gun back together. Programming the MOSFET was easy and with 3 levels of active braking and 4 of precocking, the piston is almost all the way to the rear and the trigger response is so fast.

Moving forward from here, i'm not sure where to go next. 13:1 gears? High torque motor? Brushless motor? Any and all advice/ideas appreciated here. I do think i'd go for a CNC/metal hop unit as the finishing on the Specna Arms one is poor as I had to clear off several sprues when changing the barrel & bucking. At the minute I have a new ambi charging handle in tan, dust cover and bolt plate arriving from AirsoftPro.cz to replace the worn/scratched/slightly rusted parts on the gun.

 

[Guges Mk3]

You should have used a match ML nub instead of the prommy...Prommy is not curved and thus the contact patch isn't matched to your nub.

Brushless motors are to early in Airsoft for general adoption. We are at an inflection point with motors...but that is a transition point still. Give it 5 years before you get a brushless motor. This is due to the industry having no clue on what is what and there being no standards with electronics and one brushless motor may not play well with another's ETU/Mosfet or other "electronics". Again...dud to no standards what so ever for "anything".

High Torque motor is entirely subjective. One company's HT motor is not even on the scale of HT for another company. Due yet again to no standards.

Honestly...upgrading nothing at this point except skill. Then after a season of many play dates...rebuild to your play style needs.

 

[MrTea]

You should have used a match ML nub instead of the prommy...Prommy is not curved and thus the contact patch isn't matched to your nub.

I was going to use an ML Omega nub but they were sold out at both retailers where I bought my parts from. I'll be heading through to my local airsoft shop soon so i'll see if they've got any sat around. I've used the prommy flat nub in my Krytac with the Macaron 60 degree and it's worked perfectly fine. Couldn't use an Omega nub in that AEG because the Krytac hop arm wouldn't accept it so I had to improvise.

 

[MrTea]

Another few hours working on the gun today. New compression parts arrived from AK2M4 and what a huge difference they are compared to the old set. I wish I had a chrono on hand to test the before and after. Had a bit of trouble installing the flat trigger (also from AK2M4) as the body pin for the receiver would block the selector going to safe and would bind the trigger. Took about 30 minutes of slowly dremeling material away from the middle third of the pin until the issue was resolved.

Put back together and tested. Working flawlessly and feeds fine with the new compression parts. Cannot wait to get this out to a field.

 

[Guges Mk3]

Krytac uses a captured nub so...you can place the nub and let it float under the arm for general use after trimming.

 

[Guges Mk3]

Many of the AK2M4 parts are not "upgrade" parts. They are just reselling various OEM parts as "upgrades".

These are all OEM parts.

This industry is an inverted pyramid for supply chain...know that and your part buying experience won't be costly...

 

[MrTea]

Many of the AK2M4 parts are not "upgrade" parts. They are just reselling various OEM parts as "upgrades".

Yeah I know they're standard parts. I changed the compression set as the gearbox still had the original one and the gun has never been services/relubed. When testing the old set, it could barely hold a seal, even with new lube. I wasn't too bothered about throwing £20-£30 on a new compression set because it's me A. learning how to do stuff myself and B. I know it's unlikely to fail in the near future, if ever.

 

[Guges Mk3]

You should have seen CA parts back in the day...new AEG out of the box 280-290fps tops...new o-ring on piston head...AEG shot up 100fps.

Seems their Japan models sported a bad seal to make if compley with Japanese Airsoft fps limits. But, if they sold the same AEG to other markets...they didn't care...let the end user deal with it...the people that ran it (Yip's) were terrible people.