Real Aliens M41A Pulse Rifle Build (Fully Functional SBR & SBS)

[NashuaGuns]

Being a huge gun enthusiast I wanted to build something different after building a few ARs. Being a child of the 80s the M41A Pulse Rifle from the movie Aliens always stuck with me.

So after about 2 years of tinkering, modding, fabrication, hunting down hard to find parts and two stamps later my fairly screen accurate live firing M41A Pulse Rifle is pretty much complete.

For this build you will need:

- HCG M41A Pulse Rifle Prop Replica (For the shrouds, stock and barrel vent) ($700-$1200 on ebay)
- A Semi Auto Thompson M1 replica model TM1 with a 16" barrel (MSRP $1300)
- A Remington 870 Wingmaster with chrome bolt. (used about $400)
- SPAS-12 Heat Shield and Pump Handle ($50-$80)

Various parts:
- Paint - Brown Bess (Humbolt Paint) Local hobby store helped me mix up this color because the color is no longer made.
- Resin casting kit to make magazine bases
- GI 20 round mags
- Black allen head machine screws
- Spare 870 trigger group with black shell spoon (Police Trigger Pack)
- Spare 870 Barrel
- Long charging handle for TM1

- $400 in NFA Taxes - $200 for the Thompson SBR & $200 for the 870 SBS.

- Time (didn't track hours)

Tools:

MIG or TIG welder
Dremel Tool

I wanted to thank Phil Steinschneider for his knowledge on building Screen Accurate M41A props and for selling me some parts needs to finish the project. He was a huge help throughout the past 2 years. http://props.steinschneider.com/pulser/prifle.htm

I wanted to Thank Eric and the awesome crew over at Old Glory Guns and Ammo in Mason, NH for helping me attach the 870 to the Thompson. I would have given up myself on making the 870 work if it wasn't for their help.

Also Thank you to Tom over at M41A.com His site was an awesome source of useful information.

To my knowledge this is the only screen accurate working version of the M41A not built by the movie armorers at Bapty's of London. I have seen a long barrel CA legal version without a working shotgun on a prop forum. Richard Lage of Lage Mfg made a subgun version using a M11 in place of the Thompson. It came out awesome but it was not screen accurate. Due to costs of a transferable M1 subgun and not wanting to destroy a real Thompson machine gun I opted for the semi version with 16" Barrel and went the SBR route. The factory SBR barrel would be too short for this to work.

I will be posting pictures of the build as I took a bunch over the past 2 years from the beginning

Note: All NFA rules were followed during this build. Check legality in your own state regarding ownership of SBRs and SBSs. Laws vary regarding magazine capacity state to state.

 

[NashuaGuns]

We'll Start with the SPAS-12 pump handle and heat shield. These are the hardest parts to find for the build. All cuts are made with a dremel cutoff wheel. The shell extraction port was radiused with a dremel sanding drum.

Pump Handle Mods:

The factory pump handle is cut down and flipped around from factory config. A notch is made to clear shell ejection port.

 

[TheCrowing]

Gotta say, that is pretty ****ing cool dude. Good job.

 

[warwickben]

Bad ass . I'm a huge fan of alien and predator .

Dose the round counter work ? I swear I read a build done one got it to work .

 

[NashuaGuns]

Thanks Guys. The round counter will display 95 rounds when the replica mag is inserted. I need to make it work with a real mag. The replica mag contains a 9v battery and makes contact with two pads on the bottom of the shrouds.

There is room in the shrouds to hide a battery...

 

[warwickben]

M41A Pulse Rifle Build (Fully Functional)

Thanks Guys. The round counter will display 95 rounds when the replica mag is inserted. I need to make it work with a real mag. The replica mag contains a 9v battery and makes contact with two pads on the bottom of the shrouds.

There is room in the shrouds to hide a battery...

More pics !

Have you thought about adding a sensor that the trigger or bolt taps to make the round count go down ? Since it's semi auto you could just use the trigger to tap a button etc . Could have it triggered when you pull you'll trigger or when you let the trigger reset .
A micro Arduino is a programmer able chip the size size of a stamp . You can have inputs (buttons sensors ) and out puts led screen .

Not knowing where or what space you have I'm just throwing ideas out .

 

[NashuaGuns]

The SPAS-12 heat Shield Mods

 

[NashuaGuns]

Now time for the cringe worthy part... you will need to take the HCG Pulse rifle apart for the shrouds, barrel vent and stock... HCG prop pulse rifles now cost at least 700 online. I got lucky and found mine cheap on ebay.

The Thompson and "Grenade Launcher" are resin on the HCG pulse rifle. They will likely not survive the process of removing the shrouds. They are hot glued onto the resin parts so a heat gun works wonders getting them off once you remove the glued in crap screws...

We will be saving the aluminum shrouds, the steel barrel vent and the steel stock...

 

[Rockrivr1]

Sweet! Nice build. How long did it take you to put all that together?

 

[Bob J]

So awesome!

 

[NashuaGuns]

Ok lets talk about the barrel vent...

Some minor mods are need so it will fit the Thompson Barrel. The barrel from the HCG PR is a piece of thin cheap tubing. It will NOT for the real Thompson barrel. There are two versions of the barrel shroud seen in the movie. There are 8 hole vents and a 10 hole vent hero version seen in the film. The HCG version has 8 holes.

Notch cut

Vent is attached to SPAS-12 Heat Shields using screws and locktite...

 

[NashuaGuns]

Sweet! Nice build. How long did it take you to put all that together?

Almost 2 years. I had to get the Thompson SBR'd to fit the "Grenade Launcher" part first and at that time form1s were running about 12 months. Now that I've done one I have all the measurements so I could do one much faster second go around. I know the barrel lengths and overall lengths by heart of each part.

 

[NashuaGuns]

Now the shrouds.....


This was the most unpleasant part of the entire build. The HCG shrouds do not fit the receiver of the real semi Thompson. I used a dremel to widen the receiver channel. A milling machine would have made this much easier. Also multiple mounting studs had to be ground off the inside of the shrouds to make things fit. Take your time and assemble and un-assmeble until the shrouds will fit around the Thompson. I did this over a dozen times or more.

Even though i was wearing a dust mask I was blowing grey boogers out of my nose for a day.

I went to a local hobby store to match the shroud paint color after making room in the shrouds. HCG pulse rifles come in two colors. Olive Drab and Brown Bess. Brown Bess is the screen used color but because of lighting in the movie they look olive drab.

Lets see inside the shrouds...

 

[NashuaGuns]

In the rear part of each shroud you will need to install an aluminum shim in each side of the rear upper receiver channel since a semi auto Thompson receiver is not as tall as the replica Thompson. This will prevent the shroud from wiggling once on the real Thompson. This may not be needed to a FA Thompson since I know the dimensions are different than a SA.


I didn't get pictures of this step.


The Thompson will need the stock removed along with removing the rear sights and front blade sight.... everything is tested for fit.

 

[NashuaGuns]

The HCG stock will need mods. Use your rear sight from your Thompson as a drill template for the stock. On the HCG pulse rifle the stock has a push button to collapse the stock. I found this rather challenging so I decided to make the stock permanently extended. It may have been able to be done with a collapsing stock but drilling into the Thompson receiver made me nervous.

yes the holes look off in this picture... but they fit perfectly.

A notch is made to clear the extended charging handle. I went with the extended charging handle to make manipulating the charging handle easier with my sausage fingers with the shrouds installed.

 

[NashuaGuns]

Quick test fit of shrouds.

 

[NashuaGuns]

The factory Thompson grip will be modified. It is re-profiled using a dremel sander. Slots are added on sides after sanding the palm swells flat. It is painted black then sealed with clear polyurethane.

 

[NashuaGuns]

Modded grip compared to factory Thompson grip....

 

[NashuaGuns]

Thats it for tonight. More to come soon. Including PR test video


With this project out of the way I have been thinking out the following projects:


1.) Working Terminator 1 AMT hardballer long slide with laser from movie.... (I'm already building movie jacket grey M65 replica)
2.) Working M56 Smartgun from Aliens using semi-auto MG-42 and stedi-cam rig.
3.) Working M240 Incinerator from Aliens
4.) Working T2 Endo rifle built from calico
5.) Working Auto-9 from Original Robocop built on Beretta 92 (semi)

 

[kingcrispy]

More pics !

Have you thought about adding a sensor that the trigger or bolt taps to make the round count go down ?

I was thinking the same. The first thing that came to mind was a hall effect sensor on the pump. Both segment displays driven by a single atmega8.

 

[warwickben]

Thats it for tonight. More to come soon. Including PR test video


With this project out of the way I have been thinking out the following projects:


1.) Working Terminator 1 AMT hardballer long slide with laser from movie.... (I'm already building movie jacket grey M65 replica)
2.) Working M56 Smartgun from Aliens using semi-auto MG-42 and stedi-cam rig.
3.) Working M240 Incinerator from Aliens
4.) Working T2 Endo rifle built from calico
5.) Working Auto-9 from Original Robocop built on Beretta 92 (semi)

I like the way you think .

 

[NashuaGuns]

I was thinking the same. The first thing that came to mind was a hall effect sensor on the pump. Both segment displays driven by a single atmega8.

feel free to share any info on better counter electronics. I'll see if I can make this count down from 20 rounds

 

[mclina]

feel free to share any info on better counter electronics. I'll see if I can make this count down from 20 rounds

Do you really want the aliens to know when you are almost out of ammo?

This is an impressive feat. I applaud your determination to pull off a project like this.

 

[warwickben]

feel free to share any info on better counter electronics. I'll see if I can make this count down from 20 rounds

How much room do you have ?
I think your best bet would be a Arduino micro (size of a stamp) and a button that gets triggered when you let off on the trigger to to the reset point . You could do it for under $30$.
Radio shack carrys them now.

 

[Kevin_NH]

There is a commercial shot counter made by RADETEC (Rade Technologies).

I seem to recall Instructables had plans for a "rounds remaining" counter using Arduino and a sensor to trigger on the shock of firing. You could go digital with a cellphone-type accelerometer, or low-tech with a micro mechanical shock sensor.

 

[NashuaGuns]

Thank you fellas. Will research this some more.

Lets talk about modding the 870...

we'll start with the trigger pack. I learned the hard way on the original trigger pack where to cut. I ended up cutting into the hammer spring pocket... so I ordered a nice police trigger pack with the black spoon. The wingmaster and the police 870 have metal trigger packs... the express does not...

Yup it fits like a glove....

 

[NashuaGuns]

Also note that the chrome bolt from a wingmaster has a NON-MIM extractor...

Now time to shorten the magazine tube.... you will need two parts from the replica prop master Phil....

"Grenade Launcher" Front block....

You will need to modify this part to make room for the barrel ring.. like this.

You will also need this from Phil or you can make one.... This is the modified pump action arm... note mounting holes from pump handle. you will need to cut off the front on Phil's version to clear the barrel mounting ring.

 

[NashuaGuns]

Now you can see how the pump handle mounts using two screws. I fit a small rectangle of Aluminum into the notch cut into the pump handle and counter sunk two holes into it.

I also learned that i had to make a spacer shim between that pump handle and pump arm... it made racking it smooth... you can see that piece in the top left of the next image.

 

[NashuaGuns]

Ok this isn't pretty... I had to cut off the barrel mounting ring from a spare barrel and weld it in place. i used a flux MIG but it got the job done. I left original mounting ring in place until this was welded so the barrel was straight. After welding the new ring on the mage tube can be cut down fter removing mag spring and follower.

 

[NashuaGuns]

Old ring is ground off the barrel. Front block is installed. Here's the hunting version of the GL assembly.