The Saiga 12 is a good shotgun and brings some serious fire power to bear. It has strengths and weaknesses and for each person they must be weighed out.
The fact that it is magazine fed is both good and bad. So long as you have loaded magazines to feed the machine it will be a beast. When and if you run those magazines dry you are going to begin having real problems. The magazines take up a good deal of space and they have a really low capacity for what they do. This will make it difficult to carry a significant amount of ammuntion. Then we come to the issue of possibly needing a slug in certain situations. Granted in CQB there may be little if any need of slugs, but there is the possiblity and it must be taken into account.
The solution to this problem is to have one or more magazines loaded with slugs. It is a trade off since you will now have lost at least one magazine that could have held more buck shot for the fight. Another problem arises as well from this necessary method and that is the loss of rounds when you transition back to shot.
Just for comparison sake. Two people are performing the same operation and encounter the same problems. The first is using a Saiga and the other an Mossberg 930 in tactical guise. The Saiga user has one mag with buck in his shotgun holding 6 rounds with one in the chamber. He has 2 magazines loaded with specialty rounds. One is loaded with slugs the other with breaching rounds and he has 4 more magazines loaded with buck shot. Now we have the magazines holding 7 rounds to make sure there are no issues with the bolt being forward and causing difficulties in an already difficult situation. So Saiga man has 35 shots of buck total, plus 7 slugs and 7 breaching rounds.
The Mossberg user has 6 rounds of buck in the tube and one in the chamber which allows room for a select slug drill. 7 slugs in a side saddle and 7 breaching rounds in a forearm worn cuff. He then has 28 rounds of buck stored in pouches on a chest rig. The details here really won't matter too much. It just serves to put both users on similar levels in regard to their available muntions. It is an attempt to make this apples to apples, although it is a red apple and granny apple comparison.
Both men are moving in and encounter a locked door leading into an gymnasium. There are active shooters inside and a great deal innocents running about in the chaos.
S-12 guy removes the magazine and retains it in his dump pouch. He then removes the breaching mag and inserts it into his shotgun and cycles up a round and ejects the buck in the chamber. He then shoots both hinges off the door. After this he must remove his breacher mag and place it back in it's pouch and then put the buck mag back in his shotgun and cycle up a round of buck shot. He loses a single breacher round and a round of buck in the process as he has no time to retrive them. He is now ready to enter.
930 guy simply takes two breaching rounds out of the cuff and inserts one in the tube and cycles the action, ejecting a round of buck, and then loads another breaching round in the tube. He shoots both hinges and the shotgun has automatically cycled up a round of buck shot and he now inserts a round of buck off his chest rig to top off and still leaves room for a slug if needed. There has been no loss of breaching rounds and a loss of one round of buck. He is now ready to enter.
As they enter they see the threat. There is no clear shot and they must resort to using slugs. S-12 removes his mag once again repeating the previous process and cycling out the round of buck and losing another to time constraints. He inserts his slug mag and engages 3 BGs with 1 shot each. He then changes out his mag back to buck shot. Cycles out the slug, which loaded automatically and loses it to this action. He replaces the buck shot mag that is down by two rounds as another was also lost in the course of action yet again.
930 guy sees the threat and loads a slug and cycles it up ejecting a round of buck. He needs three shots and loads another slug into the magazine. This puts the 930 mag at max capacity. He fires one round and loads another slug into his mag tube. Once he engages and neutralizes the 3 men. His shotgun has once again cycled up a round of buck. He has lost 1 round of buck and leaves it on the floor in favor of pulling one off his chest rig to bring his tube back to 6 rounds.
In this process. S-12 has lost 2 rounds of buck, a breaching round and a slug to his manual of arms. 930 guy has lost two rounds of buck only. Now this isn't a realistic encounter in that it will often take more rounds of a particular type to accomplish the task and you can't be sure how many you may need. The point here is that a typical semi-auto shotgun isn't at that much of a disadvantage as many might think and that a magazine fed shotgun doesn't have as much of an advantage as some might think.
In no way am I trying to say that a tube fed shotgun will match the Saiga's abilty to throw rounds down range in a short period of time. However, I am saying that the abilty to sustain that fire is limited at best and that because the Saiga is specialized as a matter of design, it does suffer from a lack of versatlity when compared to the typical tube fed shotgun.
Any advantage it does have is lost in uneeded bulk of the shotgun itself and the required mags as well. Once those mags are spent. It will be far more difficult to keep it in the fight, whereas the typical tube fed shotgun can be port loaded and/or topped off much more easily.
This is also assuming that the Saiga user will do tactical reloads as well. If he chooses to resort to speed reloads and just dumps his mags on the ground to load a different mag type it could get real ugly real quick for him, as he will realize in short order that he really should retain his mags. If you go through the same senario as above and do speed reloads. The 930 guy ends the same way. The S12 guy ends up losing 14 rounds of buck, all of his remaining slugs and breaching rounds to the operation. Now we all know that would be plain stupid to do, but how many guys do you know that like to just dump a mag on the ground and retrive it later? IMO it is a bad habit and tactical reloads are slow with anything other than a pistol. Everything has it's trade offs. think real hard about how such a firearm may be used and weigh them accordingly. Range shooting isn't field shooting nor combat shooting.
Just a few thoughts to chew on.
If you plan to switch single rounds quickly in a dynamic situation, the Saiga is going to be disadvantaged…training will mitigate this but it’s still a disadvantage. If a “multipurpose” breaching-slug round was developed, it would be more ideal to go from breaching to engaging.