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Hooks law

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I've got a license of the spring design suite from the Spring Manufacturers Institute.
I don't have it installed on my own workstation currently, but can. How cool is your project?
 

warwickben

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I've got a license of the spring design suite from the Spring Manufacturers Institute.
I don't have it installed on my own workstation currently, but can. How cool is your project?

b66a3d0353b2673f389b808434c0c2a5.jpg

Just a bullpup I've been working on.
Uses standard ar bolts and barrels so you can swap cals easily.
Out side is a rough shape. I've been working more on the internals then fine tuning the out side shape.
 
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whatluck

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So gas piston then, since you don't have a buffer tube. You need to figure out spring rates to return the bolt and carrier to lockup at the barrel?
 

warwickben

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So what spring calculations do you need?

So gas piston then, since you don't have a buffer tube. You need to figure out spring rates to return the bolt and carrier to lockup at the barrel?

Nope it's di I'm using a ar15 bolt carrier cut down with a custom gas key .
Basically same idea as the sig mcx.

325585c3894e25c062318986d66512d1.jpg


Bolt moves 4.100 inches .
Guide rods are .25 od.

I have two options .
One is springs behind the bolt.
I forget the amount of room I have when the bolt is locked position the compress length of the spring when the bolt is closed .
I can get that number later . Take down would be easy this way . Pop butt pad off side out .

My other option it to have the guide rods hard mounted to the gas key . The springs would be over the barrel . Pushing the guide rods towards the muzzle .
This pic is setup as option two.
ca56c4e396fd6a1a28771d57a372acfc.jpg

Take down would require me to figure out a way to pop the spring end plate off at the front and be stuck with a reciprocating charging handle .

Ar180 springs should work but I don't know if they will need to be cut for uses in the rear, or how long they should be when compressed when used in the front location .
The gas block will be adjustable since my bolt will be fairly light, and with a standard ar15 barrel/gas block it will be over gassed .
 
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Sig MCX-way is probably better, because I've no idea how barrel heat will end up affecting spring steel. So what's the total reciprocating mass and length of travel? Is it only 4.1 inches or does it need to be longer for clearances/tolerances?
 

warwickben

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Looks like pistol buffers are short with a shortened BCG.

These guys have a mechanism with no buffer:
http://extarguns.com/

The pistol buffers add way to much length .
The extar systems is on top of the bolt so it makes it taller . Have the springs on the side doesn't raise the height .

Sig MCX-way is probably better, because I've no idea how barrel heat will end up affecting spring steel. So what's the total reciprocating mass and length of travel? Is it only 4.1 inches or does it need to be longer for clearances/tolerances?

8oz roughly .
4.1 inches is the stock length of travel. It moves back enough to clear the mag and load the next round .
 
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I'll have to ponder that for a bit. You're going to have a gradually reducing force acting back on the carrier group, which the spring has to counteract and stop in the distance of 4.1 inches.
 
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Hooks law is fairly simple... the force from a spring is proportional to some spring constant multiplied by the displacement. It makes the force from the spring linearly increase as you compress the spring.

You need to figure out the compressed length and these spring constants yourself, unless you have specs on it. If you need springs, start with McMaster..

http://www.mcmaster.com/#compression-springs/=1235oma
 

Mxracer239y

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This thread makes me wonder; has any firearm ever used a progressive recoil spring? They are used in some suspension applications, and I do not remember ever seeing one in a firearm.

Sent from my XT1575 using Tapatalk
 

peterthefish

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This thread makes me wonder; has any firearm ever used a progressive recoil spring? They are used in some suspension applications, and I do not remember ever seeing one in a firearm.

Sent from my XT1575 using Tapatalk

They sell variable rate recoil springs for 1911s/2011s. There may be others but those are the ones I know.
 
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