Otto -
I have no idea why a company would resort to using a copper-based alloy to make a fine weapon like the one you're trying to build, but here's the skinny on your delima...
First off you need to know exactly what the alloys are and their content. For you, this means a phone call to whomever you bought it from or the company itself that manufactured it to that stage. My guess is they're one in the same, but...for know I'm going to give you info which will be very broad but you'll be able to understand it more after you follow-up with the mfg. and get the alloy specifics from them.
"Among copper alloys are the copper/aluminum alloys, of which the aluminum bronzes rank very high in aircraft usage".(My dept.) "They would find greater usfulness in structures if it were not for their strength-to-wieght ratio as compared to alloy steels. Wrought aluminum bronzes are almost as strong and ductile as medium-carbon steel, and they posses a high degree of resistance to corrosion to air, salt water, and chemicals. They are readily forged, hot- or cold-rolled, and many react to heat treatment."
"These copper-based alloys contain up to 16 percent of aluminum(usually 5 to 11 percent), to which other metals such as *iron, *nickle, or manganese may be added. Aluminum bronzes have good tearing qualities, great strength, hardness, and resistance to both shock and fatigue. Because of these properties, they are more commonly used for diaphrams, gears and pumps." In other words Otto, high wear parts that see alot of friction. Also note the asterisks near the words Iron and Nickle, above. This means HEAVY, and harder than most aluminum.
This info was taken out of my Airframe and Powerplant/ Mechanics General Handbook Publication EA-AC 65-9A, as it was the only place I could find any information on aluminum bronze configurations. As you can plainly tell, it leaves alot to be desired, as you, nor I have ANY idea as to what exactly are the "ingredients" to the matrix/metal make-up of your reciever. The only thing I can tell you is what you already know...
1. It's heavier than hell because of the amount of copper-tin and who knows what else is in there...(Note asterisks above)
2. It's harder than hell, more so than aluminum, due to the tempering of specific alloys contained inside.
So there you go for now. In short, your not a whimp nor do your files need replacing. The shit is heavy and hard. Call them and then let us know why they use bronze in normally light weight weapons recievers!
Semper Fi -
Cpl West