G/M are a compression formed hull like STS hulls or one piece hull. That is they are formed from a single tube and the base wad is part of that one piece of tubing.
The Promo Fed shells have a paper base wad as do the Rem Promo shells.
I use G/M because I get more reloads from a hull than with STS. No real preference just started with G/M and liked them. It cost less to load one hull as you do not have to have a bunch of components that are required for different hulls.
I am a lazy loader I guess in the fact that I don't want to spend the time to inspect the inside of each hull before I load it. With G/M or STS you can tell if you want to reload it by the case condition before it hits the loader.
Of course they are really a two piece hull if you take the metal head as a part of the hull.
Just curious, as I shoot new ammo for handicap and reload it for singles and doubles. When my supply of old one piece AA,s is used up I`ll need to know what new one piece hull to replace them with. Thanks for the responces, Phil.
Fed Gold Medal hulls are formed as one piece according to Federal. It can be deceiving because when you look down the hull there seems to be a seam where the base wad meets the straight wall hull. Cutting one in half and removing the brass (real brass), it seems like the hull tube was melted to the plastic base wad.
I am in the same situation as you, but started a stash of STS/Nitro hulls when they first came out and Win AA quality control when south. I guesstimate I'll have to switch next year some time. I prefer Rem STS/Nitro to Fed GM because it takes less powder to get the same velocity with Rem STS/Nitro. Also, GM work better with wads designed for straight walled hulls.
Sorry to disappoint some of you, but Federal GM hulls are billed as one piece, because the separate base wad is "bonded" to the straight walled hull. When you cut them apart you can plainly see the seam. Some of them are not so well "bonded" and fall out when cut apart. If you put them in the freezer for a while after you have sectioned them, you can knock most of the base wads off with just a tap.
I have had instances (2 or 3) where the base wads separated from the hull after firing. They were still in the hull proper, but closer to the front as throw some kind of suction pulled them forward. I will say that those hulls had been reloaded 3 times. I've also had my ejectors rip the whole back section of the hull off, but leave the tube section stuck in the chamber. I'm going to opine this is gun dependent. Although it happens to others, I have a friend who says they last forever, especially the old ribbed ones. Go figure.
Phil, IMO the best hulls for reloading are Remington STS hulls (green and gold). Gun clubs reload well also, but do not last as long. STS hulls are truly one piece, as you can easily demonstrate by cutting some apart. They have an smaller interior volume than other hulls, and the cuvrature of the base is substantial. For that reason, Remington wads work the best. The pattern superbly also, so no worries there. The DRM replacements fit well also, but I have not patterned them yet. Wads designed for straight walled hulls, or even the Federal wads will cause some fit problems in an STS hull.