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uscmCorps : some more LM4 mods

charging handle ambi selector LM4 RS

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#1 uscmCorps

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Posted 13 July 2012 - 11:59 AM

Ambi Selector / Safety:

Leftover from my real ARs, I had some spare parts from my RS KAC selectors, so I modified the KWA safety and installed the KAC scalloped right side selector onto it.
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Not *quite* as flush to the receiver as I wanted, but it works great. To do this, you have to remove the selector, cut a channel which the back face of the right selector plate will key into, then drill and tap a hole for the hex screw to lock into. Sounds easy. Cutting the channel was in fact easy. Drilling and taping the hole perfectly straight into the selector proved a challenge given my pathetic drill press. Hence why the ambi-selector doesn't fit perfectly flat. It's not *that* noticeable, but it annoys me since it isn't perfect. It'll do for now though.

I have not had a chance to try out Crusader's B.A.D. selector for the KSC on this gun yet. Mostly because I'm not a fan of that particular safety since I used to have one on a real AR. Seeing that Guarder has steel KSC AR15 selectors out that work for the LM4, I'll probably buy some and get a machinist to do it properly now that I now it's do-able.


BCM Gunfighter (style) Charging Handle:

Next was the charging handle. Installed a replica BCM gunfighter latch onto the KWA charging handle. Works great. Minimal modification done to the latch. Rather than butcher a real BCM charging handle (which did cross my mind), I had some spare Crusader (VFC) parts, including their BCM Mod 3 charging handle latch. Installation was simple: using a small punch, pop the pin on the LM4's charging handle, and remove the old latch. Compare old latch to new latch. Old latch had a small notch/cut out to help the spring stay in place. Cut new notch on the Crusader BCM latch using dremel, or file, or both. Push the new latch in place and tap the pin back in. Done. I just wish Crusader had made Mod 4 versions (medium latches) as well as the Mod 3 (large latches) as I use the Mod 4 on all my real ARs.
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Left to do:
• Modify and install a Magpul ASAP plate. Thank you Akira. Gonna reference your guide.
• Modify and install a Magpul BAD.

Here's what my LM4 looked like right before these mods were done:
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* Midwest Industries Gen2 SS-Series 12" Rail
* Magpul Industries MOE Stock
* Magpul Industries MIAD with F4 strap
* KAC BUIS
* T-1 (4MOA) with LaRue mount
* LaRue rail panels and Handstop
* DYTac SF MB556K
* Troy Gas block

#2 aaps59

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Posted 13 July 2012 - 01:21 PM

A very, very cool build. Do you plan on doing any internal mods?

#3 uscmCorps

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Posted 13 July 2012 - 01:31 PM

Good question. I'm more in the camp of, if it ain't broke, don't mess with it. I may get steel trigger, mag catch, and selectors for it. Not entirely sure what other mods are needed. Curious about increasing the fps just a touch. Been reading about the flute valve modification and the NPAS mods people have been experimenting with. I'm cautious about modding the gun too much internally since in my experience with GBBRs in the past (granted it was other manufacturers) messing with the internals too much created more problems than solutions.

#4 aaps59

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Posted 13 July 2012 - 01:34 PM

I hear ya there man. If you want to raise your FPS a bit, you could always do the O-ring replacement people talk about on here. I hear that raises it about 10-20 FPS. If you want more, you could do the valve mod, or wait for a TBB to come and just do that.

#5 uscmCorps

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Posted 13 July 2012 - 02:16 PM

Not familiar with the o-ring mod. Got a link?

#6 Jatodude

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Posted 13 July 2012 - 03:11 PM

View PostuscmCorps, on 13 July 2012 - 02:16 PM, said:

Not familiar with the o-ring mod. Got a link?
It involves replacing the piston O-Ring (part number 191) for better compression.

Anyways, you have a clean looking gun. My favorite LM4 build that I've seen.

Edited by Jatodude, 13 July 2012 - 03:13 PM.


#7 uscmCorps

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Posted 13 July 2012 - 05:52 PM

View PostJatodude, on 13 July 2012 - 03:11 PM, said:

Anyways, you have a clean looking gun. My favorite LM4 build that I've seen.
Thanks! I'm quite happy with it. It *feels* just right. :)

#8 uscmCorps

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Posted 17 July 2012 - 11:01 AM

Last night I got a chance to modify and install a RS Magpul BAD Lever and RS Magpul ASAP Sling Plate. Big thanks to akiraspeedstar for the sling plate tutorial (I've done it before on other guns, but I'm glad someone was able to test it on this platform before I had to), and another big thanks to boobiem4h for the BAD Lever tutorial. The mod wasn't too hard. If anything, the only thing that gave me trouble was the castle nut. That thing was on there super hardcore. Almost destroyed the notches trying to get it off!

Frustratingly, I snapped the right rear trigger guard ear off the receiver trying to install a trigger guard pin. I chose to stick to the MIAD with the F4 front strap (integrated front strap / trigger guard one piece) and I glued down the broken piece. Not ideal but not really noticeable at the same time especially after I added some SuperBlack touch up paint. Silly rookie mistake all the same.

Pics to come once I get the last of the mods done.

#9 niko_gpsy

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Posted 17 July 2012 - 11:29 AM

I broke the ear off my LM4 too.  After gluing it back I use some JB weld putty and laid a thin coat over the area.  Then once it dried I sanded down smooth and then painted it.  Looks good as new.  Of course I will never be able to change my trigger guard again but I am not planning on it anyways. :P

#10 Jakeedaman21

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Posted 17 July 2012 - 12:06 PM

The metal quality on the LM4 is very poor.... And I hear you with the castle nut! Mine almost destroyed my castle nut tool as well as three of my notches on the nut itself. I had to use a hammer and steel punch to get the thing off eventually.

#11 uscmCorps

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Posted 17 July 2012 - 12:31 PM

Niko: good idea. I'm just too lazy / not enough time to do it. Ordinarily I would. But for me the LM4 is a training tool it doesn't have to be pretty. ;)

Jake: I'm wondering if the castle nut is a different spec from RS. One of my castle nut wrenches is specifically designed to interlock with three of the four castle nut notches. The LM4 castle nut appeared to be slightly just slightly wider in diameter preventing a proper lock up with the tool  I work on my real ARs a lot. Break them down. Build from scratch etc. It's not often I have this much difficulty doing a simple disassembly. Using a steel punch I eventually got it loose. Later I found one of my castle nut wrenches designed specifically for a one notch lock up and that did work much better.

Regarding the metal of the LM4, I think it's fine. I've seen RS trigger guard ears get broken in the past. It'd be nice to have an LM4 that's made to the same durability as a real AR15, but we're not paying real AR15 prices. The quality of this gun out of the box is still exceptionally high and relatively robust (IMO).

#12 uscmCorps

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Posted 20 July 2012 - 11:19 AM

Update: I've installed the last of the pieces I wanted to have put on the gun.

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* KWA LM4 Base Gun
* RS Midwest Industries 12" Gen 2 SS-Series Rail
* RS CQD Front sling mount (not pictured, on opposite side of the rail)
* RS LaRue Handstop and rail index clips
* RS Magpul MIAD with F4 front strap with integrated triggerguard
* RS Magpul CTR with enhanced buttpad
* RS Magpul ASAP (modified to fit)
* RS Magpul BAD Lever (modified to fit)
* RS Magpul Rail Ladder
* RS KAC Ambi-Selector plate
* RS KAC Micro BUIS
* RS Surefire M300A with SF Tape switch and HSP Dropwing Mount
* RS Aimpoint Micro T-1 (4MOA) with LaRue lower 1/3 co-witness mount
* RS Yankee Hill Machine Low Profile Gas Block
* DYTac SF MB556 MuzzleBrake
* VFC BCM Gunfighter charging handle latch

Gonna install the Guarder Steel mag release and Steel trigger this evening.

#13 BoobieM4H

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Posted 20 July 2012 - 11:36 AM

View PostuscmCorps, on 20 July 2012 - 11:19 AM, said:

Update: I've installed the last of the pieces I wanted to have put on the gun.

Posted Image
* KWA LM4 Base Gun
* RS Midwest Industries 12" Gen 2 SS-Series Rail
* RS CQD Front sling mount (not pictured, on opposite side of the rail)
* RS LaRue Handstop and rail index clips
* RS Magpul MIAD with F4 front strap with integrated triggerguard
* RS Magpul CTR with enhanced buttpad
* RS Magpul ASAP (modified to fit)
* RS Magpul BAD Lever (modified to fit)
* RS Magpul Rail Ladder
* RS KAC Ambi-Selector plate
* RS KAC Micro BUIS
* RS Surefire M300A with SF Tape switch and HSP Dropwing Mount
* RS Aimpoint Micro T-1 (4MOA) with LaRue lower 1/3 co-witness mount
* RS Yankee Hill Machine Low Profile Gas Block
* DYTac SF MB556 MuzzleBrake
* VFC BCM Gunfighter charging handle latch

Gonna install the Guarder Steel mag release and Steel trigger this evening.
Sweet set up!

Sent from my DROID2

#14 gcw360

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Posted 21 July 2012 - 04:55 PM

Can you write about the RS Midwest Industries 12" Gen 2 SS-Series Rail?  An modes needed?

#15 uscmCorps

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Posted 21 July 2012 - 06:14 PM

It was a pretty simple install. Following the instructions was straight forward (and not really needed since it's pretty self-evident). The *only* part that required a little extra effort was the barrel nut. I've installed RS rails on three LM4 uppers so far and they've all required varying degrees of brute strength to torque the barrel nut onto the receiver. The upper receiver's threading is non-milspec and just enough off-spec that RS barrel nuts don't screw on that easily.

So you generally have two options ...
Option 1: Use a milspec die and recut the threads on the upper to milspec tolerances. The die is about $60. Not cheap. It was a worthwhile investment for me since I've done more than a couple dozen receivers over the many years.
Option 2: Use the RS rail's included barrel nut to recut the threads. The RS barrel nut is (normally) made from hardened, often tool steel. The hardness of the of the barrel nut exceeds the hardness of material used in the upper receiver and as a result, when forced onto the upper receiver than barrel nut can and will cut (and to a small degree deform) the upper receiver's threads. This technique will work, but since the barrel nut's thread are not made for cutting unlike a true die, it requires more force and more time. Also since the barrel nut isn't designed to cut threads simply screw on, you need to exercise a degree of patience and care when torquing it down so as to make sure you're keeping the barrel nut inline with the receiver. You don't want to mess up the threads as it'd be hard to salvage it if you do.

Out of the rails I've installed so far, the RS Midwest Industries barrel nut wasn't too hard to do using the barrel nut itself rather than the die. The Troy was a fair bit of work though. Next time I do a RS Troy rail for someone, I definitely would use a die and recut the threads.

#16 gcw360

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Posted 21 July 2012 - 08:56 PM

View PostuscmCorps, on 21 July 2012 - 06:14 PM, said:

It was a pretty simple install. Following the instructions was straight forward (and not really needed since it's pretty self-evident). The *only* part that required a little extra effort was the barrel nut. I've installed RS rails on three LM4 uppers so far and they've all required varying degrees of brute strength to torque the barrel nut onto the receiver. The upper receiver's threading is non-milspec and just enough off-spec that RS barrel nuts don't screw on that easily.

So you generally have two options ...
Option 1: Use a milspec die and recut the threads on the upper to milspec tolerances. The die is about $60. Not cheap. It was a worthwhile investment for me since I've done more than a couple dozen receivers over the many years.
Option 2: Use the RS rail's included barrel nut to recut the threads. The RS barrel nut is (normally) made from hardened, often tool steel. The hardness of the of the barrel nut exceeds the hardness of material used in the upper receiver and as a result, when forced onto the upper receiver than barrel nut can and will cut (and to a small degree deform) the upper receiver's threads. This technique will work, but since the barrel nut's thread are not made for cutting unlike a true die, it requires more force and more time. Also since the barrel nut isn't designed to cut threads simply screw on, you need to exercise a degree of patience and care when torquing it down so as to make sure you're keeping the barrel nut inline with the receiver. You don't want to mess up the threads as it'd be hard to salvage it if you do.

Out of the rails I've installed so far, the RS Midwest Industries barrel nut wasn't too hard to do using the barrel nut itself rather than the die. The Troy was a fair bit of work though. Next time I do a RS Troy rail for someone, I definitely would use a die and recut the threads.
Thank you.  This is very helpful.

#17 Helix262

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Posted 12 August 2012 - 09:39 PM

so if you do use RS parts then its recommended to use a new thread die then? I want to buy a Knights Armament URX rail and it come with the nut. So do i need to by the die then?

#18 uscmCorps

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Posted 12 August 2012 - 10:30 PM

View PostHelix262, on 12 August 2012 - 09:39 PM, said:

so if you do use RS parts then its recommended to use a new thread die then? I want to buy a Knights Armament URX rail and it come with the nut. So do i need to by the die then?
A little hard to say. The current generation of URX 3+ rails use a barrel nut that is made from aluminum rather than steel which is what the older generation URX rails use. So if your rail uses comes with an aluminum barrel nut, either it will recut the receiver threads ... or the receiver threads will deform the barrel nut threads (if it's the latter of the two, that's probably not good).

#19 Helix262

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Posted 16 August 2012 - 08:56 PM

View PostuscmCorps, on 12 August 2012 - 10:30 PM, said:

A little hard to say. The current generation of URX 3+ rails use a barrel nut that is made from aluminum rather than steel which is what the older generation URX rails use. So if your rail uses comes with an aluminum barrel nut, either it will recut the receiver threads ... or the receiver threads will deform the barrel nut threads (if it's the latter of the two, that's probably not good).
So to be on the safe side you would recommend the die then?

#20 uscmCorps

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Posted 15 October 2012 - 02:07 AM

Honestly, you can try not doing it with a die, but with the aluminum of the URX barrel nuts, you're at greater risk of deforming the barrel nut than when compared to a regular steel type barrel nut. I would recommend using a die to recut the threads in this case.

ETA: Update for my gun:
Current status of one of my KWA PTS LM4's (US Edition). I have since moved the DBAL forwards, right behind the front sight.

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