Sig Sauer Inside the ASP20: Teardown and Specs

Jump to latest Follow Reply
Sqwirl57

Sqwirl57

Member
Apr 13, 2020
4,143
6,358
PA, United States
20240417_210415.jpg


Got bored and decided to see what the inside of the ASP looked like. Its really nothing too crazy. It does have a well made, big ol 30mm, 403g piston that rides on a synthetic bearing though. The piston seal looks like it may be interchangeable with an HW80 seal which would be great news (UPDATE: It does with very slight modification. See below for details). I'll start running part numbers on the gas ram to look for appropriate replacements if and when they start to fail. Worse case scenario a simple metal adapter should do the trick.

Tear down is pretty straightforward:

1: Remove both safety buttons

2: Remove front stock screws and front trigger guard screw and then remove the stock.

3: Pull the lock washer from the front tab that the trigger disconnect attaches to and then slide the disconnect off of the cocking arm

4: Gun in a compressor and punch out the end cap through pin

5: Remove end cap (careful not shoot trigger adjustment knob and spring across room)

6: Remove gas ram

7: Remove the trigger assembly. The sear that catches the piston may snag on the main tube. Slide it forward and off or you will not be able to remove the trigger unit.

8: Back out pivot pin set screws. 1 screw in the front of each fork
20240417_212741.jpg


9: Tap out the pivot pin. I THINK I went left to right here and I'm not really sure if that matters or not. It punched out with relative ease so if you are struggling, something isn't right. I will update this on reassembly.

10: Slide the barrel forward and lift the cocking arm and shoe through the cut out in the tube.

11: Remove the piston

As a final note a steel adapter to convert it to a coil spring would be easy enough to make if needed or wanted. I'll probably play around with this a bit soon.

SPECS (UPDATED AS WE GO)

Piston Outer Diameter: 30mm
Piston Inner Diameter: ~0.780"
Piston Weight (with seal): 403g
Piston Stroke: ~90mm
Transfer Port Diameter: ~3.4mm (falls between a 3.2mm and 3.6mm drill bit)

UPDATE 4/20 : I THINK I FOUND THE OE RAM. BARE WITH ME AS I FIGURE OUT THE DETAILS

PISTON SEAL:

The Vortek HW80 piston seal does work like a charm but the internal dimensions are a smidge off making the base sit proud of the piston. I am fortunate enough to have a lathe handy so I just sized it down a hair. Took a minute if that. I then installed it and found it to still be a hair oversized. The factory seal measured 1.178"/29.92mm and the Vortek seal was closer to 1.188"/30.17mm. Being as its a Vortek seal I am going to just put a tin through it and see if velocity rises as it sizes itself. Currently I'm only about 25fps slower than the factory seal which is no biggie. I'm betting it rises but if not I'll just size it down a hair. I will try to update this as I go as well.

20240425_204409.jpg
20240425_204448.jpg
Screenshot_20240425-203249_FX Radar.jpg
Screenshot_20240425-203347_FX Radar.jpg
 
Last edited:
  • Like
Reactions: MartyMcFly, Hold_Over, Kragman1 and 6 others
Nice! Have been super curious about what the inside of one of these babies looked like....appears pretty robust! Nit sure if I like the looks of die cast on the cocking arm, buy I'm sure something could be whipped up as a replacement if need be. Definitely would like to know when you find a suitable replacement for the gas ram, how cool would it be to have like a adjustable one in there like a theoben!
 
  • Like
Reactions: Sqwirl57
Upvote 0
zrman27500 said:
Nice! Have been super curious about what the inside of one of these babies looked like....appears pretty robust! Nit sure if I like the looks of die cast on the cocking arm, buy I'm sure something could be whipped up as a replacement if need be. Definitely would like to know when you find a suitable replacement for the gas ram, how cool would it be to have like a adjustable one in there like a theoben!
Click to expand...
I was honestly a little disappointed that the ram wasn't rebuildable. I wasn't really suprised though. I thought maybe with how much effort went into making the gun, Sig may have used something a little fancier there.
 
Upvote 0
Very cool and pioneering, Sqwirl57!

Some novel features in that ASP20:

A pivot pin that's locked in place by twin grub screws threaded through the stock front! Since a critical feature of breakbarrel pivots is the ability to tighten the joint laterally when needed, I wonder what SIG went for here? Pivot pins as opposed to pivot bolts are old tech, but pretty much discredited, too.

A gasram piston latch not made by cutting a slot through piston wall, but by grinding a massive groove through the piston rear circumference. The ASP piston must have a massive wall thickness, at least at the rear, for this. It is a heavy piston, for sure.

I haven't torn down gasram guns, but the gasram fit into the rear block by a pin looks curious, as well. It would seem a weak point, a pin waiting to shear, but I'm sure SIG made the calculations and the strength is there. If the gasram is fitted rock-solid laterally in there, the pin doesn't face much strain.
 
  • Like
Reactions: Sqwirl57
Upvote 0
Toxylon said:
Very cool and pioneering, Sqwirl57!

Some novel features in that ASP20:

A pivot pin that's locked in place by twin grub screws threaded through the stock front! Since a critical feature of breakbarrel pivots is the ability to tighten the joint laterally when needed, I wonder what SIG went for here? Pivot pins as opposed to pivot bolts are old tech, but pretty much discredited, too.

A gasram piston latch not made by cutting a slot through piston wall, but by grinding a massive groove through the piston rear circumference. The ASP piston must have a massive wall thickness, at least at the rear, for this. It is a heavy piston, for sure.

I haven't torn down gasram guns, but the gasram fit into the rear block by a pin looks curious, as well. It would seem a weak point, a pin waiting to shear, but I'm sure SIG made the calculations and the strength is there. If the gasram is fitted rock-solid laterally in there, the pin doesn't face much strain.
Click to expand...
The pivot pin is key to the ASPs greatness IMO. Cocking effort is basically zilch compared to guns of similar power. Its advertised as 35 pounds of effort but in reality it feels easier than an HW95 all because there is very little side to side tension on the breech block and instead uses a Keystone wedge system to keep the barrel lockup consistent. How does that affect accuracy? Here are two 10 shot groups at 32yds:

20240419_190844.jpg


The next one is actually only 9 shots. I threw one under that dime but all 10 shots still fit under that same dime.

20240415_191717.jpg
 
Upvote 0
Sqwirl57 said:
I was honestly a little disappointed that the ram wasn't rebuildable. I wasn't really suprised though. I thought maybe with how much effort went into making the gun, Sig may have used something a little fancier there.
Click to expand...
Definitely think they don't want anyone messing around in there...as far as I know, you are the first to take one apart, the soaring value on these rifles right now is just getting crazy! Only complaint I have with mine is I don't like the shape of the trigger blade, I'd be all over a metal replacement blade from someone. Also wish I had the wood one instead of synthetic, but out of the few rifles I own that are synthetic, the sig is by far my favorite.
 
Upvote 0
zrman27500 said:
Definitely think they don't want anyone messing around in there...as far as I know, you are the first to take one apart, the soaring value on these rifles right now is just getting crazy! Only complaint I have with mine is I don't like the shape of the trigger blade, I'd be all over a metal replacement blade from someone. Also wish I had the wood one instead of synthetic, but out of the few rifles I own that are synthetic, the sig is by far my favorite.
Click to expand...
I've always been a fan of flat blade triggers although I do agree this one is a bit funky and metal definitely would have felt better. When I had it apart I chopped a coil and stretched the spring some. Now it's 1lb 3oz with a clean wall and break. I may have to see about cloning the trigger to aluminum next because it would be bar far my favorite rammer trigger if it was
 
Upvote 0
Sqwirl57 said:
I've always been a fan of flat blade triggers although I do agree this one is a bit funky and metal definitely would have felt better. When I had it apart I chopped a coil and stretched the spring some. Now it's 1lb 3oz with a clean wall and break. I may have to see about cloning the trigger to aluminum next because it would be bar far my favorite rammer trigger if it was
Click to expand...
Well if you do.....I will gladly pay whatever one costs! Nice to know it can be made to go that light, I'll have to throw my gauge on mine and see where it is, although I don't really have a complaint with the feel of the trigger, just the shape, not so much that it's flat, but just too wide for my liking.
 
Upvote 0
zrman27500 said:
Well if you do.....I will gladly pay whatever one costs! Nice to know it can be made to go that light, I'll have to throw my gauge on mine and see where it is, although I don't really have a complaint with the feel of the trigger, just the shape, not so much that it's flat, but just too wide for my liking.
Click to expand...
Now that you mentioned it the width may be what throws my too. Something a little thinner and slightly rounded off on the face would probably feel great.

Time to start looking for a CNC machine I think 😆
 
  • Like
Reactions: fishing43
Upvote 0
You must log in or register to reply here.
Top Bottom
Back
Home
Forums
Resources
Menu