Max gas port size?
How short can you go without mods?
...you can pretty much cut the port(s) as big as you want. However, the larger you go, the more fouling you will get.
I can tell you though; the largest factory port I have ever seen was on the early .410 guns.....they used a single .169" port from the factory.
My personal 12" gun uses a single .145" port and it has worked well for years.....and I never clean it. I rebuilt the gun recently and went with a mag well and SRT, and contemplated welding it up and going with a 4 port setup, but decided against it, since the gun has been working flawlessly since the day I built it with the large single port setup.
All Saiga shotguns are on the ragged edge of running, right out of the box. I wouldn't cut it down at all if you want it to run light loads guaranteed. Of course with SOME guns, you can get away with it, but who knows with yours. They are all different.
Jeez.....I don't know how many times I'm going to have to answer this question......The Saiga shotguns, of all gauges, are on the ragged edge of not running with standard off-the-shelf U.S. birdshot loads right out of the box. Some guns may work cut down, but most will not. Cutting it down ANY is not a good idea unless other changes are made to the gas system.
I don't like to go below 16", without moving the gas block rearward. The factory gas ports are about .073". I would re-drill them .101" and angle them WAY back, so you have a bit of "trough" rather then a straight-in hole. There is no magic with the gas ports, you can drill them as large as you want, but the trade off is increased wad fouling in the manifold, so you will have to clean it more often. On the Tromix 8" guns, the four gas ports remain at the factory .073" size and still cycle light loads without a problem. Moving the gas system rearward is a lot of work, and not really necessary in your case, unless you want to shoot birdshot type loads.
SBS and Top Cover
There's no silver bullet here. The shorter you go, the larger the parts need to be and that will increase your fouling. Or you can just heavy loads and leave the ports smaller. You can actually go down to 11" with the stock gas system, if you don't mind having large gas ports (higher fouling) and only fire heavy loads.
You need to weld an extension hood back out over the top cover or it will eventually pop out of its track in the front.
You can get away without it about 50% of the time, but the other 50% of the time the gun will be like a boomerang and come right back to you for rework. About 10% of the guns have bolt/carriers that will ride up so high when the carrier comes out of the gas tube that the bolt is pulled away from the ejector and misses it. So....on those guns, you need a shim under the front of the top cover to keep it down in the pathway of the ejector. There is no way to tell which guns will be affected until you shoot them. You can leave the shim out too....but you'll have about a 10% boomerang rate with that as well. Now you're at about a 60% return rate, calling me, and asking me what to do. Just print off this post and keep it handy.
SBS and piston rod length
On the 8" guns, the bolt carrier comes completely out of the gas tube and if the carrier fit in the rails is sloppy, it will fly up and strike the top cover. I weld an extension out over the top of the top cover to keep it from popping loose on the 8" guns.
On a standard gun, bending the rear of the top cover out to "lengthen" it a bit will usually fix the problem. I have seen some guns come from the factory with the top cover barely long enough to even engage the groove in the front.
SBS and handguard length
Just install the gas block in its new position, then install the gas piston (puck) and screw the regulator in all the way and back out to the first position 1 or 2. Then install your bolt carrier and slide it forward until is stops. Measure the remaining distance between the trunion and the carrier on the L/H side. That is how much you need to cut off the carrier's extension rod to get it to work.
Keep in mind; if you have moved your gas block back more than about 3", then you will also have to open up the gas block for the carrier to slide through it. Normally just the skinny extension shaft passes through it, but when you move the block way back, the front of the carrier itself has to slide through the opening as well.
You can go with an 8" or 10" barrel with the shorty handguards. The 12" uses a different gas block position, a new gas tube, new carrier extension, longer hand guard etc....It is much more work to make, and has been discontinued.
If you want a longer handguard on your 8-10" gun, I can do that, but you will end up with a big-ass ugly gap in front of your gas block, where the hand guard extends past it. Additonally, you can't get to the detent to make adjustments to the gas regulator without pulling the hand guard off. I will tell you, almost every time someone deviates from a Tromix design and goes with what they "think" is better...the customer ends up getting a complete piece of shit (that they designed) and then complains to me about it. If you think you are a better gun designer then myself, that's fine, but don't bitch when I deliver you, your own custom POS that you designed.
Edited by BobAsh, 07 April 2009 - 01:16 PM.