I've studied this IOF 30-06, and there seems to be no definitive description of its operation or even an in-depth parts breakdown. The only description I could find was this:
The IOF 30-06 sporting rifle is a bolt-action rifle made by the Ishapore Rifle Factory. The rifle shares many design features with the Sauer 202 rifle, manufactured by Sauer & Sohn in Germany.
Which tells me very little, except that the IOF is "almost exactly the same but completely different" than the Sauer 202. (The sarcasm here is completely intended!)
So, looking at the available information about the Sauer 202, I find that it's not made any longer, but has been replaced in Sauer's product lineup by other rifles. This leads me to believe that IOF was able to negotiate the rights to use the Sauer 202, since as an older model, it wouldn't compete with Sauer's currently offered models.
The Sauer 202 was available as a "regular" rifle and as a takedown model. The takedown model used a cone and ball mechanism in the fore end with a quick release, which allowed removal of the barrel. The barrel was held in a close tolerance fit in the receiver.
The regular model had the barrel tenon held in the receiver in a similar manner as the old Colt Sauer bolt action, where the receiver ring was slotted and clamping allen bolts pinched the slot to tighten around the barrel tenon.
Colt Sauer rifle
Threading the barrel tenon to the receiver and making the receiver strong enough to hold this was avoided in this design, as the locking lugs at teh head of the bolt engage matching recesses in the barrel tenon. The receiver thus functions to hold and guide the bolt, attach a trigger firing group in relation to the bolt, and support the butt stock and fore end.
American Hunter, a publication of the American National Rifle Association (NRA) reviewed this Sauer system and said this:
The three bolt lugs lock into the barrel, so when the bolt is closed, barrel and bolt become a solid unit.
Frankly, this statement is rubbish. The system is strong, but there have to be clearances between the bolt and the locking surfaces in the barrel tenon, or one couldn't operate the bolt. Furthermore, as anyone familiar with two-piece billiard cue sticks or multi-piece fly fishing rods knows, these items simply don't and can't work and feel like a one piece cue stick or rod. Vibrations simply don't work that way in multi-piece structures!
Still, it is a good system and it works well in a number of firearms made in the past and present. The AR 15/M16/M4 is a rifle that uses this system, but the one that quickly comes to mind for me is the Sportco/Omark 44, an Australian target rifle that I'd very much like to own:
My point here is that the system of locking the bolt directly into the barrel is sound, and regarding the "pinch" system of holding the barrel tenon into the receiver with a direct bolt-barrel lock, this has also proven to be a sound system.
I found this picture of the Sauer 202 parts diagram, obviously a Sauer diagram:
The Sauer 202 was available with a steel receiver, and a light weight rifle was available with an aluminum receiver.
Kittu, regarding your experience of trying to repair the crack and the seemingly low melting point of the receiver, and also your reference to it being made of aluminum and zinc, I wonder whether IOF used zamak to make the receiver.
https://en.wikipedia.org/wiki/Zamak
The Henry Rifle Company of the USA uses zamak in the manufacture of some of its guns. Hi-Point, maker of low cost pistols, also makes extensive use of zamak to make its products. The (in)famous Raven/Jennings/Jimenez/Lorcin/Phoenix/etc ad nauseam 25 Auto pistol also was made largely of zamak. Recently, Ruger has come out with a cheap version of its Single Six 22 LR revolver that uses zamak for the grip frame. The Heritage 22 LR revolver is largely made of zamak.
As you look through the Wiki on zamak, you'll note that the melting points of the various zamak alloys are less than 400* C -- close to that of lead. This allows easy and quick casting methods.
Zamak can be a suitable material, especially for low cost guns, but it does not retain all of its strength over extended periods of time. In low-stress situations, this may not be an issue.
I can't say for sure whether the receiver of your IOF 30-06 is made of zamak, but from the description of your attempted repair, it does sound like it may be so. If I'm right, you will probably not be able to repair it.
As for making a steel receiver to replace it, consider the Sauer 202 parts diagram above: the receiver isn't a simple piece, like some bolt action receivers are. You would have a challenge in making that on a CNC machine, I think.
Single versus double column magazines: Some bolt action rifles, like the Colt Sauer and the Sauer 202, use a single column magazine. This allows for thicker stock walls around the action and reduces the openings needed in the bottom of the receiver, which can increase the receiver strength and the ability to bed the action firmly in the stock. Bedding may not be an issue in the Sauer 202's two piece stock.
Double column magazines, where the cartridges are held in two staggered columns, can increase magazine capacity, but at the cost of additional width. Another issue here is that it is easier to get cartridges to feed more reliably from a single column magazine that a double column, because the cartridges are only fed through the action at one angle in a single column design, rather than from two angles. This isn't to say that double column magazines aren't as good or can't be made to work reliably, because they are good and have been successfully made to work well for well over 100 years.