Although manufacturers may promote that you can fire their product (PMC3 for example) at a temperature as low as 600° C (1110° F).Keep in mind that this requires the ability to hold that temperature for at least 30 mins.. So can you torch fire metal clay?
The simple answer: Yes (with limitation)
Consider You are limited to fine silver (at the time of writing), Sterling Silver, Copper, Bronze or Gold either require to be fired in a bed of carbon or at a temperature beyond your torches capacity and /or requires different firing in stages.
You will need a very high quality torch that will produce a consistent level of heat for the amount of time you need which can be 30 mins. or more. Running out of gas during firing can be bad to really bad! Also, expect the lifespan of your torch to be severely reduced if you use it on a regular basis.
You have no precise measure of the temperature that you are using. This means you will need to develop the ability to judge your firing by the color of your piece. This will implicate an investment in wasted silver during the learning curve which can be quite expensive.
There is a high level of risk of serious injury and damage to property. Working with these levels of heat of around 1110° F is more than double your kitchen oven and unforgiving of ANY mishandling. You will need to purchase heat protection for your work surfaces and your hands.
You will need to be prepared to hold (& move) your torch for quite some time! while maintaining the distance from the piece consistent while you are firing.
But maybe a more realistic question is "should I torch fire metal clay?" Most people looking to "try" or experiment with metal clay are looking for an inexpensive alternative to purchasing a kiln. This makes a great deal of sense to any budget conscience artist / artisan like myself. However, to answer the question, we need to determine what your objective is with working with metal clay.
If you are;
A hobbyist looking to make small pieces for yourself or gifts on occasion. "Sure" as long as you have the right setting (not the kitchen table or home office desk) and adhere to ALL the safety requirements. As long as you have the tolerance for the cost (and possible disappointment) related to the learning curve. Alternatives such as firing pots can be inexpensive and fun and provide an simpler way to fire PMC3. PMC Firing pot
A jewelry maker or artisan using other mediums (wire wrapping, glass bead maker, polymer clay etc.) looking to make small pieces such as findings, bales or decorative elements to be added to your projects. "Sure", as long as you have a tolerance for the limitation of working with fine silver and limited capacity for expansion. Also, you should seriously consider the "time" factor if you are planning to use this medium to create and sell pieces. There are a number of alternative firing products that you might want to consider for a budget of 100$ - 200$ US. However, I strongly recommend that you find consistent favorable reviews before purchasing. Again, even with these products you will encounter the same limitations.
Looking for ROI (return on your investment) in purchasing the equipment and products by selling your creations. Then your answer to torch firing would be "Not Really". Unlike starting photography where investing in a high level camera can actually hinder the learning process, the purchase on a small kiln (budget 400$ - 700$US) that can run on you home electricity circuit will not only help in your learning growth, but will also encourage you to constantly push your limits. In my mind, providing the expansion of possibilities is a key element that metal clay offers, your kiln will allow you to explore all the variations of techniques.