The D.G.R.M could be for any item on the drilling from improvements in the locks, selector, pop up rear sight, or anything. With out the number, it is difficult to know. Krupp Stahl is often misunderstood as the "maker" by Americans, it just means the barrels were made from Krupp steel. Such guns without a makers name, are often misnamed "Guild Guns"; they actually are guns made for "the trade". That means they were made for someone else to retail, the retailer could add what ever name they wanted. Larger companies generally added a name, but smaller ones often did not.
Mike
