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45Bretired

Puck Keeping Carrier from going into full Battery?

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I measured my setup. It is as follows:

 

Op rod face to front of gas block: 1.378"

Auto Plug depth from front of gas block: 0.760"

 

Difference of those measurements: 0.618"

 

Thickness of my CSS puc: 0.642"

Thickness of my factory puc: 0.591"

 

The CSS puc is slightly marred on its face around the ring of where it contacts the Auto Plug. I need to check my carrier closely for cracks, I guess. I need to take off .024" for a flush fit plus about 0.015" - 0.020" of extra clearance or so for clearance? Can anyone tell me if 15 or 20 thousandths is a SAFE minimal SAFE clearance? Until I get this done, I will use my factory puc.

 

Thanks a lot!

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The best way to tell if there is a problem is to simply unscrew your gas plug with the bolt closed. If the carrier moves then you will have to modify the puc. We designed the puc so there is only a very small amount of space which is why it works so well.

We allowed for many variances in the guns and have only had a few that needed to be modified out of many thousands.

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When you designed it, was there a nominal clearance that is optimum for puc operation? I don't want too little or too much gap. I'm pretty sure I need to shave a little bit off the tail of the puc. Thanks CSS!

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When you designed it, was there a nominal clearance that is optimum for puc operation? I don't want too little or too much gap. I'm pretty sure I need to shave a little bit off the tail of the puc. Thanks CSS!

We wanted it as close to gas adjustment knob as possible and still to allow the bolt to lock up tight.

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I really hope 45 does not mind my commandeering this thread... I can move to my own if it would be better. Someone let me know.

 

 

In trying to find the optimum gap for the puc/ op. rod ("piston" or "carrier extension" if you prefer) interaction surfaces, I have done some ROUGH thermal expansion calcs for a CSS puck and estimated 5" steel rod. I assumed a 5" steel rod and assumed a 70 degree F ambient temperature with a maximum internal temperature of 650 degrees F. If someone has accurate numbers for the maximum temperature an S-12 gas block can reach under sustained heavy fire and a closer length of a factory op. rod from dimples to tip (I'm at work right now), I could refine my calculations. I have come up with the following estimation/ calculation for a maximum operating temperature of 650 degrees F:

 

CSS Performance Puc: Thermal coefficient of 6.6x10^-6 in/in*F and length of 0.642" >>>> 0.0025" Thermal Lengthening

 

5" op rod (*estimated): Thermal coefficient of 9.6x10^-6 in/in*F and length of 5" >>>> 0.0278" Thermal Lengthening

 

Auto Plug (threads to valve face): Thermal coefficient of 9.6x10^-6 in/in*F and length of 0.760" >>>> 0.0042" Thermal Lengthening

 

This leaves a total expansion sum of 0.035"

 

The sum of these three should, theoretically, be the perfect gap to have between the puc and the op. rod. so as to be capable of non-damaging sustained fire. However, these seem unlikely. I believe the max temperature I used is too high and the estimated op. rod length is too long. The thermal expansion coefficients I used for the Auto Plug and the rod are also conservatively estimated. Perhaps results would make more sense if these few things were corrected. I also did not account for debris in the gas system, which would necessitate further increase of this gap!

 

Please chime in, and tell me if you know a better set of numbers or see something I missed. Thanks a lot!

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I'm good. Just kinda astonished at where this thread has gone. Really was looking for, sure I had that issue filed down all good. This has gotten pretty technical here. I'm afraid we may scare off some new comers or those with absolutely no machinist style measuring back grounds. I got my answer along time ago and thanks CSS for making a great puck. I recommend them all the time.

Edited by 45Bretired

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How much length are you guys having to remove from the tail? I just got my puck yesterday and had to remove so much material, the CSS puck ended up just a c-hair longer than the stock puck. I'm using an MD Arms gas plug, is this really supposed to be normal?

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I'd say as much as necessary to let the bolt & carrier go fully forward but not so much that the puck is sliding back and forth with the plug in.

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Every Saiga is dimensionally different.

 

I have been using the Piston/Puck in all my conversions/builds for over a year, and it is rare that I need to remove any of the extension. If I do, it has never been more than .020 and that is with a stock plug.

 

Some of the aftermarket plugs may have an interference fit with the new piston and if that is the case, make sure the new plug is not extending too far into the chamber/cylinder and partially blocking the ports.

 

I would remove some of the materiel off of the clean out plug (MD Arms) if it was interfering, rather than the piston/puck.

 

Jack

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