saiga 12 4 port hole size question

[generalpetres 4]

I opened up my ports just a tiny bit a while back don't remember what size it was exactly but i recently talked with tac47 industries because my gun would only cycle with the auto plug being screwed all the way in with wally world winchester crap 12ga ammo.  this ammo functions fine with the default plug but when i switched it out for the autoplug it would hickup at least 2 times in 10 rounds. when i was on the phone with tac47 he recommended opening up the gas ports with a 41 drill bit which is .096 which seems like it might be a little to big. i was thinking about opening it up to a 48 or 5/64 which would be .076 or .0781 respectively.  ive sanded down the rails and tried polishing up the bolt a small about getting it smoothed out and that's about it on the internals that Ive modified besides the tapco trigger.  i don't want to have to take the gas block off again as i have a chaos titan rail installed now, so would running a bit larger port be fine with using the auto plug to tun the gas port so it runs 100 percent?

 

Edited October 23, 2015 by generalpetres

[gunfun 3,931]

Profile your hammer before going further. Not just polish. Profile. Look at the 'trigger job' link in my signature line for a picture and description of what I mean. (or video here:

) Those tapco hammers add a lot of drag, and are often the thing that makes the difference. This job is maybe 15 minutes with a bastard file, including getting the hammer in and out of the gun. 

 

For at .093" is generally as big as I would go. IMO, it's best to get an assortment of bits a few thou apart and drill, and test until you have perfect function rather than just pick a number and go to it. The friction varies from gun to gun, so you may as well optimize your ports to your actual gun. Suggestion: #46, 44, 42. However any drill bits a few thou apart will do to give you incremental increase.

 

But I would rather have 5 at .078" or at .082"... Look to see if there is room for a fifth in your pattern. There was for mine. Just be sure to punch, start vertical and then tilt to the desired angle so it doesn't wander. Practice first on a piece of pipe to test your skills.If you can keep your pattern still there, then you know what you can or can't do.

[JonWienke 131]

Optimal port size depends on the gun. It's a combination of spring strength, gas puck and plug geometry, action friction, etc. Mine would only run high brass stuff with 4x .094" ports with stock springs and the CSS or stock gas pucks, even after polishing and profiling the hammer, bolt, and carrier.

 

Obviously, the first thing you need to do is deburring, polishing, profiling, and break-in of the action and magazines. In addition to the hammer, bolt, and carrier, the bottom portion of the barrel that extends BEHIND THE CHAMBER can often use some deburring and rounding of the inner rear corner. If that area has a burr, 3" shells in particular will shave plastic off, snag, and jam while trying to feed.

 

(Hint: Lubricating the mating surfaces of the trigger, hammer, bolt carrier, and bolt with Remington 40-X Bore Cleaner will greatly speed up the break-in process. It contains a mildly abrasive polishing agent that does wonders on gritty triggers and actions in fairly short order. Just make sure you remove all traces of it when break-in is complete.)

 

Once all that is done, and you can hand-cycle 3" shells through the action smoothly without leaving any visible marks on the casings, then you can focus on the gas ports.

 

There's a scientific method you can use to determine the correct port size for your gun. Remove the dust cover from the action, and get a video camera. The higher the frame rate it will shoot, the better. Put a piece of masking tape on the side of the receiver, and use a sharpie or similar marker to mark 1/4" intervals from the back of the bolt carrier to the trunnion, so when you pull the bolt back you can see how far it has moved. Put the gun in a rest, and with the camera rolling, and with the gas block wide open (setting 2 with stock, 5 with MD Arms, 6 with CSS.DPH plugs), fire 10-20 rounds of your weakest ammo (wally world bulk pack, etc.). Review the video, and note how far back the bolt carrier traveled each shot. Calculate the average carrier travel distance.

 

The maximum carrier travel on a Saiga is just a hair over 5 1/4". Divide the maximum travel distance by the average travel distance, then increase by 10% to ensure reliability when the gun is dirty or not being held firmlywithout beating the crap out of it when it is not. In my case, the average travel distance was about 4 1/4", and my ports were .094" at the time.

 

5.25 / 4.25 = 1.24

1.24 * 1.1 = 1.36

 

1.36 is the factor by which the area (NOT THE DIAMETER) of the holes needs to be increased.

 

My holes were .094", so...

 

sqrt(.094 ^ 2 * 1.36) = .1095, which works out to either 7/64 (.1094") or #35 (.110).

 

(Note: multiplying and dividing by 2 and π when converting diameter to area and back cancel out, so I simplified the formula.)

 

When drilling out the ports, it's best to drill in 3 steps to minimize the burrs around the ports.Whatever size hole you need, start 2 drill sizes smaller, and work your way up a size at a time. Burrs around the gas ports will massively increase plastic and lead fouling in the gas mechanism.

 

This method can be applied to any undergassed gas-operated gun; the only difference is the maximum carrier travel distance is different between different gun types. Catching malfunctions on video is often very helpful when troubleshooting them.

[JonWienke 131]

One thing I forgot to mention: make sure the hole in the gas block is not blocking any of the ports in the barrel. Enlarging the holes in the barrel will do no good if they are covered and blocked by the gas block.

[poolingmyignorance 2,191]

Look. If Keith told you the specific drill size to use, why would you doubt it? Guy builds literally THOUSANDS of saigas, and extends a transferable lifetime warranty to them. He's not going to tell you to do something that will damage your gun.

Gun fun is right about the profile and that helps A LOT, and so does ensuring the ports won't be covered once you've enlarged them (I'd be really surprised if that wasn't mentioned in the conversation about what drill to use).

Point is, why ignore the pros advice and solicit random advice on the internet ?

Granted, I don't consider GUN FUN a random guy. His advice had always been based in logic and experience.

[JonWienke 131]

One other thing to consider:

 

If you set up a gun to run the light target loads, by definition it WILL be overgassed when you shoot magnum rounds. The whole point of an adjustable gas system (whether the autoplug, V-plug, or whatever) is to correct overgassing when heavier-than-minimum rounds are being fired. Overgassing can be easily adjusted away. But an adjustable gas system CANNOT correct an undergassed condition, which is what you probably have right now. If the autoplug is causing malfunctions even when the adjustment screw is turned in all the way, you're probably on the ragged edge of cycling properly with the stock plug on setting 2.

[gunfun 3,931]

I like the rationale of Wienke's method.

 

However there is one quibble. A 10% increase in hole diameter does not = a 10% increase in flow. It equals a greater than 10% increase. I couldn't tell you the math to calculate that, but this is one of the fundamentals of plumbing fluids (gas is a fluid).

[gunfun 3,931]

Look. If Keith told you the specific drill size to use, why would you doubt it? Guy builds literally THOUSANDS of saigas, and extends a transferable lifetime warranty to them. He's not going to tell you to do something that will damage your gun.

Gun fun is right about the profile and that helps A LOT, and so does ensuring the ports won't be covered once you've enlarged them (I'd be really surprised if that wasn't mentioned in the conversation about what drill to use).

Point is, why ignore the pros advice and solicit random advice on the internet ?

Granted, I don't consider GUN FUN a random guy. His advice had always been based in logic and experience.

 

Look. If Keith told you the specific drill size to use, why would you doubt it? Guy builds literally THOUSANDS of saigas, and extends a transferable lifetime warranty to them. He's not going to tell you to do something that will damage your gun.

Gun fun is right about the profile and that helps A LOT, and so does ensuring the ports won't be covered once you've enlarged them (I'd be really surprised if that wasn't mentioned in the conversation about what drill to use).

Point is, why ignore the pros advice and solicit random advice on the internet ?

Granted, I don't consider GUN FUN a random guy. His advice had always been based in logic and experience.

 

The difference is that pro builders are building to work and not wear out. They don't spend the shop time to dial each gun into exact balance. Instead they find a number that works for sure every time, in just about every gun, but might not be as smooth. That's a fine approach. A race build is typically tuned to exactly work based on that gun's individual friction, probably around a particular load. Very little extra margin of functionality.  IMO if I am spending the time on my gun, I'll potentially spend another range trip or two to get it exactly right. I am sort of splitting the difference between the race gun thinking and one size fits all production thinking.I want my gun to run with all normal ammo well, with absolute reliability. But I want to tune to the actual friction of MY gun, not a hypothetical "average gun + a bit for reliability". This gets me certain reliability and max smoothness. None of these methods are wrong.

 

I just figure I will spend slightly more time attention on my personal gun than will probably be given to a production build. The better pros also have the ability to control some of the other variables between guns more consistently than I can. Having a jig to do bolt profiles, the tools to check and straighten gas tube misalignment, slightly crooked or curved rails, or any of the myriad other things that affect the drag side of the balance makes it a lot easier to pick a gas port size and get repeatable results with it. Without those tools, a hand or 3rd party bolt profile plus a few step and checks will get as close to perfect as a DIY guy can achieve, and without a huge amount of work.

 

If you can take a cordless drill, and the bits with you along with the other tools to push the block out of the way, it can be done in a single range trip. [wood block+ brass or aluminum block. big hammer. small hammer. punches for the cross pins. a clamp or buddy to hold the gun upright while you drive the block on and off.] It comes down to being organized. Take the right ammo and mags with you. Have all the tools ready. Probably do the first step at home, so you know how it goes, and you know the block moves without a big shop press and press dies.

[JonWienke 131]

I like the rationale of Wienke's method.

 

However there is one quibble. A 10% increase in hole diameter does not = a 10% increase in flow. It equals a greater than 10% increase. I couldn't tell you the math to calculate that, but this is one of the fundamentals of plumbing fluids (gas is a fluid).

 

Which is why I said increase the AREA of the holes by X%, not the DIAMETER. Area increases by the square of the diameter, so once you figure out the percentage the cycling energy needs to increase, the diameter increase is the square root of the area increase. A 10% increase in diameter is a 21% increase in cycling energy (1.1 * 1.1 = 1.21).

 

I'm somewhat new to the Saiga scene, but I've built over a dozen AR-15s from scratch, and getting the gas system working right follows the exact same principles. The only difference is the max length of bolt carrier travel is shorter on an AR than on a Saiga.

Edited January 6, 2016 by JonWienke