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Sear Carbine Writeup

writeup snap sear spring

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#1 Aeromech

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Posted 24 July 2016 - 10:34 AM

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The idea of using some type of sear to lock a bolt in place has been used on real-steel firearms since the advent of the machine gun, due to the simplicity and self-locking action of the mechanism. In the homemade Nerf market, this is a relatively new field, first being implemented on the ESLT some years ago. This is my attempt to marry SNAP style redneck engineering with the aforementioned locking mechanism.

 

RULES:

-No McMaster/Online ordered parts (Barring a [k25] spring, Good luck finding 11" long springs at a hardware store).

-No special tools required (No long-shank countersinks, holesaws, or any of that)

-No 3D printing

-Keep weight as low as possible

 

TOOLS:

-Rat-tail file

-Pocket knife

-Electric Drill with standard bits (no larger that 1/2")

-Woodsaw

-Hacksaw

-Screwdriver

-Sandpaper

SUPER HELPFUL BUT NOT NECESSARY

-Belt sander

-Drill press

-Table saw

-Vice

 

For this Writeup, descriptions will be BELOW the photos they reference.

 

4_zpsyhqpbuso.jpg

This was the original idea, using 3D printed components. I wanted to do the same thing without limiting myself to 3DP parts. But this is the idea. Borrow an ESLT/submachinegun catch and use it in place of the fickle SNAP nail and clothespin catch. Insert anecdote of "my SNAP shoots like 150 feet and I've never ever lubed it or replaced anything on it ever" but I have built three and they have ALL failed within 100 shots. Stop trying to convince me. Unless there is some kind of drastic improvement in the design I will not endorse SNAPs as being consistently war worthy. Moving on...

 

The actual catch mech can be seen here. a slot through the body tube and bolt allows a catch finger from the sear to rotate upward and extend into the bolt slot, blocking the bolt from moving forward, when the trigger is pulled, it pivots the sear downwards and the catch finger moves out of the bolt slot, and the bolt flies forward under spring force.

 

20160723_223928_zpswe3vfru2.jpg

This is the bolt. It is made of 1" PVC, with both ends capped off by cutting board. Get the fat kind, from Walmart, It's $6 and is like 1/2" thick, really great stuff. This bolt is about 7 inches long.

 

20160723_223932_zpslx5wydar.jpg

Superlative plunger head screwed into the front. Actually provides a really good seal on this thing.

 

20160723_223940_zps3vpeydo1.jpg

The back shows a 1/2" dowel sunk into the tube, with the rear cap held on by a screw into the dowel itself. I cut the bolt too short so the cutting board is sticking out, but yours shouldn't stick out.

 

20160723_223953_zpsdyqzztgb.jpg

Pretty standard at this point. Gooped in front bushing, with a slot cut 6.5 inches away from the front, running all the way to the back.

 

20160723_224142_zpsd8tiwehq.jpg

This is an anti-kinking device (1" PVC pipe beveled internally at one end) duct-taped directly to a 1" to 3/4" bushing.

 

20160723_224251_001_zpsuqgyj7pq.jpg

We've all done the thing where we reach into the hardwre store bin without looking and get home with a 3/4" bushing and not a 1/2" bushing. Now is the time to use it.

 

20160723_231936_zpsbv7bqzyi.jpg

Now we need to make some decisions. Decide the orientation you want your bolt to stick out. It should probably be at least 45 degrees up from the horizontal. Drill holes all around to lighten it up, but do not drill holes on whatever the "bottom" side is. On the bottom, make a slot about 2 inches long right at the front of the bolt. This is where the catch will lock. Make it wider than it needs to be, it will be much less finicky if this hole is oversized.

 

20160723_232331_zpsvusoazgh.jpg

Test fitting with the [k25].

 

20160724_084538_zps21nppuxk.jpg

Testing with the new handle. I used a 1-1/2" PVC "half piep" (really more like a 2/3 pipe) to snap directly onto the barrel. Note the stylish wooden handle that SNAP users seem to love. You can also just barely make out the hole in the bottom of the body tube; this should match up with the slot that was cut into the bottom of the bolt, so the catch can have access to the bolt slot and lock in place.

 

20160724_093535_zpstrlzo9pm.jpg

This is the guts of the catch, with cutting board sideplates holding everything in. Basically, the trigger is pulled, which rotates the catch itself downwards and out of the way of the bolt. The catch itself is triangular shaped and really just has a piece which pops up into the body tube and locks into that hole in the bolt. Just like an ESLT, make sure you made a slot in the body tube as well that lines up with the bolt slot.

 

20160724_103529_zps6njn2wel.jpg

 

20160724_103533_zpsn5axy9mh.jpg

 

20160724_103541_zpsto2nro2f.jpg

 

The 3/4" bushing in the rear makes it almost trivially easy to throw on a stock, and the 3/4" pipe is much stronger than the 1/2" pipe. Rubber bands act as the catch restoring mechanism, and create a spring loaded trigger too. The front of the sideplates are held on simply by zip ties.

 

This baby is pretty asymmetrical, but I kind of like it that way. The spring kinks up a little, but the anti kinking mech fixes that without using any guide rods. The spring is not reaching full compression (need to chop another half inch off the back) but has like an inch or so of precompression, gets 5.25 inches of draw with the [k25], and rocks roughly 200 FPS based on just ear-analysis, I want to test it at APOC and get hard numbers.

 

The blaster without a barrel and hopper weighs 1 pound, 15 ounces, so with a barrel and hopper probably around 2.5 pounds, and even that weight can be brought down if you used wooden sideplates or went ham on lightening holes, particularly in the rear where the anti-kinking tube is.

 

Overall, I am mildly impressed with the blaster. A hardware store hitter that can play with the SNAPs with sear reliability and without the need to order anything. Get a pack of springs from spiderbite and you're set.


Edited by Aeromech, 28 July 2016 - 09:24 PM.

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This is so ghetto but so awesome.


#2 CaptainSlug

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Posted 24 July 2016 - 02:23 PM

This is delightful. I think the only thing lacking now are templates and a shopping list.


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#3 Snoop Doggy doge

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Posted 24 July 2016 - 09:54 PM

So it's official, you don't need your PCSR back lol.
Thanks for ripping my lightened bolt bro, 
13177196_883317518457835_2287153634396097300_n.jpg
(newest itteration has more holes, this is mk2)

So, some notes. First, what the fuck happened to your writeup quality? I know how to follow this but no noob can. Hope this is revised.

Some criticism
Alright so, Bolt. You need to countersink the screw going into the dowel. Don't cut off the screw, get a knife and countersink it. The wood dowel can shear off (happened to me at CPNO) and it is a bitch to get off. leaving it friction fit is gonna sheer after a few wars, even with that back cap (tried it too) 
ALSO, don't out speedholes on the exposed part of the bolt, that's how dirt and shit gets in there,  I tried it on of my older bolts. it's really easy to get dirt and grass in there, I would just leave that part covered and put holes in the rest of the bolt. 
Second, You also don't need the anti kink device or the cutting board plate inbetween the "bolt" if you just use a k18 spring. Save more weight and just secure the damn bolt with a flathead. That's what I use in my SnapCarbine. If you're gonna use a spring from Mcmaster, may as well use k18. (I got some and can sell. K18s also nest over [k26] very well)

When I get home, I'll upload pics of my carbine revised (yet again after mechout) of what I'm talking about, and a conversion to a ucup or skirt seal you can add on to the front (because I fucking can) and U-cups work really well in these things. 

Compliments
Wow you built a blaster for your own competition! Did you even get a winner or are you rating it NH style really late?
Second, this thing be damn compact. shit bruh it looks realy cool and easy. I'm gonna make like 3 of these and use these as loaners with whatever blasters. I probably have enough time before APOC lol.
Once you release the templates for the sear catch, no reason for SNAP triggers for noobs IMO since they're too damn finicky for me. Maybe it's just me, but they're hard to get to work.
Great job, I hope more new people can see this, and that it's not that hard. It'll be like the sten/grease gun of the hobby
If you want to lighten the thing even more, drill more holes in the stock, rear end of the blaster, fuck I'll make one with a ton of holes to cut the weight down to liek 3/4 a pound.


Questions
How far does this hop?/FPS?
How long did it take to build?
How much did it cost?
The cutting board plates in the rear and front, those look like they were made using a hole saw cheater
WTF are the exact dimensions? I'm building this rn, I have like a 14 in pipe of 1-1/4 and I think that may be too short. RIP lmao


Edited by Snoop Doggy doge, 25 July 2016 - 01:46 AM.

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#4 Meaker VI

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Posted 25 July 2016 - 09:09 AM

So, cool as this is, I'm missing something: What makes this a carbine? Is it the length? The action? It seems like it should be longer than a SNAPoid or redirect, since you've got that big plunger/bolt in there.


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#5 The2ndBluesBro

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Posted 25 July 2016 - 09:27 AM

So, cool as this is, I'm missing something: What makes this a carbine? Is it the length? The action? It seems like it should be longer than a SNAPoid or redirect, since you've got that big plunger/bolt in there.


It's just a SNAP Carbine with an ESLT catch. That's where the name comes from, and ACE (inventor of the SNAP Carbine) got it from the fact that the blaster is self-contained and doesn't get any longer when you pull the plunger back like a regular SNAP does.
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#6 Meaker VI

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Posted 25 July 2016 - 12:34 PM

It's just a SNAP Carbine with an ESLT catch. That's where the name comes from, and ACE (inventor of the SNAP Carbine) got it from the fact that the blaster is self-contained and doesn't get any longer when you pull the plunger back like a regular SNAP does.

 

I figured that part out, but I suppose I don't get what makes the SNAP Carbine a carbine either. What makes this a carbine? How is it better than a pullback or pump action?


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#7 The2ndBluesBro

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Posted 25 July 2016 - 03:36 PM

 
I figured that part out, but I suppose I don't get what makes the SNAP Carbine a carbine either. What makes this a carbine? How is it better than a pullback or pump action?

A carbine is just a real steel term for any derivative rifle that is shorter than the original design (M4 carbine vs. M16). The original SNAP design starts about the same size as a SNAP Carbine but when you cock it because of the rod coming out the back it's much longer. The Carbine version stays the same length even when cocked and therefore is "shorter" than the original. Mostly I think it was done just because the name sort of fit and was an easy and quick designation for the design. There isn't really anything that makes it better than pullback or pump action, it's just different. Time for my question to OP: To be honest I don't see the advantage of the 45° bolt handle as opposed to the 90° one on the original. Is it easier to pull back?

Edited by The2ndBluesBro, 25 July 2016 - 03:37 PM.

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#8 Meaker VI

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Posted 25 July 2016 - 04:46 PM

A carbine is just a real steel term for any derivative rifle that is shorter than the original design (M4 carbine vs. M16). The original SNAP design starts about the same size as a SNAP Carbine but when you cock it because of the rod coming out the back it's much longer. The Carbine version stays the same length even when cocked and therefore is "shorter" than the original.

 

Ah, ok, now I get it. The carbine has no plunger rod sticking out the back. I knew the real-steel term, but felt like any given redirect blaster would be shorter overall than the 'carbine' styled blasters I've seen (The barrel being within the frame of the blaster on a redirect instead of sticking out the front) so wasn't sure what the connection was.


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#9 Snoop Doggy doge

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Posted 25 July 2016 - 04:59 PM

 

Ah, ok, now I get it. The carbine has no plunger rod sticking out the back. I knew the real-steel term, but felt like any given redirect blaster would be shorter overall than the 'carbine' styled blasters I've seen (The barrel being within the frame of the blaster on a redirect instead of sticking out the front) so wasn't sure what the connection was.

I have a PCSR and an ESLT. Currently making one of these and I have a SnapCarbine from Alfatrooper. Without the barrel, the carbines are smaller, and can be compacted. Granted, both ESLT and PCSR can fit in my bag too, but they need more dissasembly and reassembly. The snap carbine just needs the screws put back in if you take the stock out, though it can be a bitch to do so sometimes. Currently, I have the body tube finished (hopefully right length BECAUSE CHRIS DIDN'T PUT ANY FUCKING SPECS ON LENGTH but also fits in a backpack and wouldn't need much to put in a stock.

Carbines are extra compact and don't have facerape, usually unfuckable for a noob and easy to make are the plus sides of them IMO.
If you put a u-cup or skirt seal on one of these, lube it the fuck up, add speedholes, you can put a wye on it and make it hop very nicely. 
Why would you ever pick this over a regular rifle that you can learn not to fuck up? Carbines are great loaners to noobs that are easy to make. I spent like an hour making half the blaster already, may as well make one that kinda works and just have a loaner IMO. 


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#10 CaptainSlug

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Posted 25 July 2016 - 06:31 PM

 I spent like an hour making half the blaster already, may as well make one that kinda works and just have a loaner IMO. 

This is what I like about the design most. The time and material investment is so low.

 

If Aeromech doesn't have the time to make templates or drawings available it wouldn't take me very long to throw a set together.


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#11 Snoop Doggy doge

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Posted 25 July 2016 - 07:03 PM

I'm literally tracing my ESLT lower and I'm just gonna replicate it out of cutting board lmao. 
I mean, I know it wouldn't be hard for Chris to upload it all and info, but I know that he's working OD right now so I can't uphold him to these standards.

I'm gonna hate myself for cutting up the only cutting board I have, 
I'll make dinner on the remains of the board after I'm done with this because I really want to finish this.
I spent half this day dicking around, and the other half trying to replicate this, trying to make it better, (fuck superlative seals, and fuck the 1/2 in speed holes) 


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#12 DICE134

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Posted 25 July 2016 - 07:45 PM

I'm a little confused why the anti-kinking device is so long. Is the [k25] sitting inside it or resting on it (I've never used a [k25] so I'm not sure of the dimensions)? If it's resting on it, than I feel the entire blaster could be shortened by a couple inches. 


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#13 The2ndBluesBro

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Posted 25 July 2016 - 08:54 PM

I'm a little confused why the anti-kinking device is so long. Is the [k25] sitting inside it or resting on it (I've never used a [k25] so I'm not sure of the dimensions)? If it's resting on it, than I feel the entire blaster could be shortened by a couple inches. 

It's sitting inside it. I believe it's like that because without a rod through the spring it kinks much worse without the long support at the back.
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#14 Snoop Doggy doge

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Posted 28 July 2016 - 01:28 AM

ITS ABOUT TIME I MAKE A QUALITY POST AGAIN!!!

Preface

Spoiler


My Build goals
Spoiler



RESULTS

IMG_9271.jpg
I have no fucking clue what this would be called. IDK, call it the practical innovated sear carbine?
Enough with the stupid names, if you build it like I did I don't care, it doesn't need a name, it's a different approach to a similar concept which is the sear carbine

IMG_9270.jpg
Pic from the rear

IMG_9272.jpg
Pic of the lower near bolt. I attatched a tek 6 spring with a nerf screws because it looks better IMO. any return style spring should work. 

IMG_9273.jpg
Notice the skater tape on the black bolt, I would do this just cuz, tactics?

IMG_9275.jpg
most of the right side was flush. But because I built this all in my lap, I accidentally drilled too high making the catch connection point on the reciever. So I used deez nuts to help kinda secure it. The other screw is a trigger block to prevent from pullign the trigger all the way

IMG_9276.jpg
SNAP Carbine size compraison. (Alfatroopers Mk2 heavily modded and repaired by me)
The SNAP is longer because the stock isn't removed, but it can be shorter since it has a shorter bolt than the Sear Carbine
However it is taller, which kinda feels weird at first.

IMG_9277.jpg
Fits in a backpack great. Just the bolt handle is a bit akward but I tape my barrel and wye assembly on the left side so it 's not just the charging handle jutting into something


INTERNALS

IMG_9278.jpg

IMG_9279.jpg
My bolt has a lotta 3/8 holes because I drilled 2 bolts with 1/2 in drill bit and they came too close. Fuckit, this pisses off OCD and will fuck with you if you have trypophobia. Sorry

IMG_9280.jpg
oversized but where the sear, locks into to "catch" the bolt

IMG_9281.jpg
U-cup seal because I'm cheap. You can totally adapt this to use a Skirt seal if you're R I C H

IMG_9282.jpg
Attatchment method + shitty explanation
Spoiler


IMG_9283.jpg
Lower reciever. Pieces of 1-1/2 in PVC clamps well over 1-1/4, so I have a large piece on the front clamp on pretty tightly so it doesn't wobble and a rear piece that's kinda loose and secured with screws. 

IMG_9284.jpg
Reciever attatchment method

IMG_9285.jpg
less than 5 minutes to open up and reassemble while taking pictures using a multitool DX gave me.

IMG_9286.jpg
Size comparison, in case you wanted to see

END THOUGHTS
Spoiler


Edited by Snoop Doggy doge, 28 July 2016 - 01:29 AM.

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#15 DjOnslaught

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Posted 28 July 2016 - 04:47 AM

Hey snoop, what did you make the shell of your lower receiver from? Is it polycarbonate sheeting? If so can you provide a template or at least some dimensions?
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#16 The2ndBluesBro

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Posted 28 July 2016 - 11:21 AM

Hey snoop, what did you make the shell of your lower receiver from? Is it polycarbonate sheeting? If so can you provide a template or at least some dimensions?


He used cutting board like Aeromech. Cutting board is low quality HDPE (High Density PolyEthylene). It isn't as strong as polycarb but it is suitable for larger pieces like the sideplates because it's dirt cheap. I think Aeromech is going to release some templates, but for now as Snoop said you can copy an ESLT's for the lower section and you should be good.

Edited by The2ndBluesBro, 28 July 2016 - 11:22 AM.

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#17 Snoop Doggy doge

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Posted 28 July 2016 - 12:19 PM

Lmao did I hijack the thread?

the lower reciever is cutting board. I would love to make a template or give out dimensions but I don't have anything to make a template with, and dimensions for the sear need a template. This is an ESLT lower, if you can copy the lower reciever of an ESLT you're good to go. I'd change the trigger to be an L though. Look up ESLT build guide and copy that reciever


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#18 Meaker VI

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Posted 28 July 2016 - 02:22 PM

Lmao did I hijack the thread?

the lower reciever is cutting board. I would love to make a template or give out dimensions but I don't have anything to make a template with, and dimensions for the sear need a template. This is an ESLT lower, if you can copy the lower reciever of an ESLT you're good to go. I'd change the trigger to be an L though. Look up ESLT build guide and copy that reciever

 

If you can scan the pieces on a piece of paper with a line marked at a specific length, I can make templates from it. Shoot, if you take a good dead-on picture of them on a flat monochrome contrasting background with a ruler, I can make templates.

 

Alternatively, use Sketchup or Inkscape. Both are free, both are up to the task. Fusion is also free and up to it, but overkill and possibly trickier to use.


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#19 CaptainSlug

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Posted 11 August 2016 - 11:44 AM

The wood dowel did end up breaking during APOC. I'm not sure if he was using the pine dowels or oak. Oak dowels are a bit stronger than the cheaper pine ones.


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#20 Meaker VI

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Posted 11 August 2016 - 03:49 PM

The wood dowel did end up breaking during APOC. I'm not sure if he was using the pine dowels or oak. Oak dowels are a bit stronger than the cheaper pine ones.

 

Yeah, Oak is usually *way* stronger than the pine/birch/poplar that is cheaper.

 

The downside with wood is that you *do* need to take care to select good specimens and work with the grain, otherwise you compromise most of the available strength.


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#21 The2ndBluesBro

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Posted 11 August 2016 - 03:57 PM

The wood dowel did end up breaking during APOC. I'm not sure if he was using the pine dowels or oak. Oak dowels are a bit stronger than the cheaper pine ones.

If you put a ridiculously long wood screw through an oak dowel you'd probably be fine.
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