There are a few options out there depending on your needs. Below I will list them from most expensive to least expensive (as of the time of writing, ~December 2023), I will not specifically recommend one version over another, but hopefully these notes help you make your decision depending on your goals and budget.
All three of the below options will clamp onto the BL-SD adapter. They are all made of rubber molded over steel. The primary differences between them are cost, fit, and finish. Fit and finish is subjective, since they are not all built in the same location or with the exact same materials, they will of course be a little different from each other.
Disclaimer – the links below will take you away from hkbryce.com. Parts can instead be found elsewhere on the internet in new and used condition, but at the time of writing these links are where you can usually find them in stock.
The German Handguard
A genuine German Heckler and Koch rubber handguard is what the BL-SD adapter was designed around. They are no longer manufactured so new ones are pretty much unobtanium in 2025, but you may be able to find them used.
These can be identified by looking under the two tabs on the top-middle of the handguard. If they are of more a capsule shape than a circular shape, it is a German handguard. The steel on the inside is silver. HK MP5 SD Rubber Handguard – German (hkparts.net)
The USA Handguard
HKParts makes their own “USA” version of the SD handguard that is fairly close to the German ones with some differences. They can be identified by the more golden finish of the metal, and by the spring steel coming up all the way to the top of the opening (whereas the German/BRT shroud has this part covered by rubber).
Fitment note: Fitment may vary, although I haven’t had complaints for a while. The two USA shrouds I own both fit, but it seems like one has more play than the other. If you attach the USA shroud and it doesn’t fit your BL-SD adapter quite right, I might be able to help – please send me an email.
These are around $170 + shipping. HK MP5SD Rubber Handguard – USA (hkparts.net)
The Broad River Tactical Handguard
Broad River Tactical released their own version of the SD shroud. It was modeled after the German shroud and is a very close replica. I find the finish is a little shinier than the German one, but I can only really tell if I put them side by side. These can be found between $80 – $100 (the former being the Blem versions, if available). Broad River Tactical
In my opinion, I think the Broad River Tactical shroud is best if you can’t source a German shroud.
Video Comparison
Photo Comparison
Inspecting your Handguard
Your handguard should have an inner diameter of about 47-48mm. Examine it from different angles to ensure the lines are reasonably straight, and that the tube is circular (or a very slight oval). Bent steel may prevent ideal fit onto the BL-SD adapter.