By the 1600's, the natives in the Northeast were obtaining copper and brass from the Europeans. Mostly in the form of copper or brass cups and kettles. These objects were then cut up for the production of brass and metal projectile points. Triangles were the most common design, as stone triangle points were in use upon the arrival of the Europeans. Sometimes these points display perforations. Here is a page describing trade points from the Posey Site, a 17th century Maryland native village, showing how the perforations aided in hafting such points. It is also believed the perforations permitted the points to be strung for travel .
Brass/copper triangles from the Dann Site, a Senaca Iroquois village in Lima Co., NY, and occupied c. 1655-1680:

Brass/copper triangles from the Burrell Creek Site, also Seneca Iroquois, mid to late 1600's:

  At times, when a rectangular or square piece of copper/brass were cut diagonally, two lopsided triangles resulted. This could then be hafted by notching the shaft at an angle and mounting the projectile point upward:

Here are 4 more brass/copper points from the Dann Site(1655-1680) in NY. Notice 2nd from left is slightly lopsided:

The lopsided triangle above with a smaller example found on a sand bar in RI:

Mounted this way:

Very often, "guide lines", for want of a better name, can be seen. On this example, easy to see how the edges were hand cut. A RI field find