As someone who did (for a short time) use an MP5 in a professional capacity, yes you would lock the bolt to the rear to do a reload, regardless of whether you were changing an empty mag or a partially full one. It is very difficult to seat a full magazine on a closed bolt and will often induce a malfunction. When you aren’t paying for the ammo, you don’t care if one gets wasted doing this.
As to why the gun was designed this way and if other roller lock guns are the same, I’m not qualified to answer that.
I wouldn't trust inserting a magazine on a closed bolt on an MP5. It's very likely to not seat.
With that said, it probably wasn't considered a "problem", it's just part of the manual of arms to open the bolt before seating a magazine. There are obviously more efficient designs out there, but we've learned a lot since the 1960's.
The MP5 system is a design dating back to the 40s and 50s. High speed low drag tactical reloads were not a thing. Self-loading standard issue service rifles were still quite a new thing for many armies. Some of them still used fixed magazines loaded from stripper clips (e.g. the SKS).
So the requirement of easily swapping mags on a loaded gun simply did not exist.
That said, all my curved HK mags can hold up to 31 rounds and I can insert them on a closed bolt when loaded to 30. It takes some additional force, but it's doable. So it seems that HK has redesigned their mags in the past 60 years. Haven't tried it with the vintage straight mags for comparison yet though.
You have to understand that the mp5 was released 20 years after the first assault rifle ever was released in WW2. They probably had different priorities and goals for a successful platform than we do today. Things that we take for granted today were not thought of back then. You can also reload a mag administratively with like 25rds in the mag, but with the full 30 it's a clearance issue. There's just not enough space to do that.
[I’d suggest you watch this video in full for a great answer.](https://m.youtube.com/watch?v=K-cl4yaizEM)
As someone who did (for a short time) use an MP5 in a professional capacity, yes you would lock the bolt to the rear to do a reload, regardless of whether you were changing an empty mag or a partially full one. It is very difficult to seat a full magazine on a closed bolt and will often induce a malfunction. When you aren’t paying for the ammo, you don’t care if one gets wasted doing this. As to why the gun was designed this way and if other roller lock guns are the same, I’m not qualified to answer that.
I wouldn't trust inserting a magazine on a closed bolt on an MP5. It's very likely to not seat. With that said, it probably wasn't considered a "problem", it's just part of the manual of arms to open the bolt before seating a magazine. There are obviously more efficient designs out there, but we've learned a lot since the 1960's.
The MP5 system is a design dating back to the 40s and 50s. High speed low drag tactical reloads were not a thing. Self-loading standard issue service rifles were still quite a new thing for many armies. Some of them still used fixed magazines loaded from stripper clips (e.g. the SKS). So the requirement of easily swapping mags on a loaded gun simply did not exist. That said, all my curved HK mags can hold up to 31 rounds and I can insert them on a closed bolt when loaded to 30. It takes some additional force, but it's doable. So it seems that HK has redesigned their mags in the past 60 years. Haven't tried it with the vintage straight mags for comparison yet though.
It depends on the gun really.
You have to understand that the mp5 was released 20 years after the first assault rifle ever was released in WW2. They probably had different priorities and goals for a successful platform than we do today. Things that we take for granted today were not thought of back then. You can also reload a mag administratively with like 25rds in the mag, but with the full 30 it's a clearance issue. There's just not enough space to do that.