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Discussion Starter · #1 ·
Has there ever been anything written on parts interchangeability between the different sized rifles? 9mm, 5.56, 7.62. I assume if the length is right on the fore ends they will interchange. What about the stocks, bolt carrier groups, trigger packs, cocking tubes and supports and so on. I know newbie question. A lot of you guys probably know this stuff already but it may also help others.

Thanks!
 

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Has there ever been anything written on parts interchangeability between the different sized rifles? 9mm, 5.56, 7.62. I assume if the length is right on the fore ends they will interchange. What about the stocks, bolt carrier groups, trigger packs, cocking tubes and supports and so on. I know newbie question. A lot of you guys probably know this stuff already but it may also help others.

Thanks!
Well, I'm by no means an expert, but generally, I've found that the for the MP5 and HK33/53/93 series, the stocks will interchange (with the caveat you match up the buffer on the stock with the buffer or lack thereof on the carrier for the 5.56 variant). HK91/G3 stocks have 2 pins, rather than the single pin of the HK93 and MP5 guns, so they are different. Plus, the guide rod for the HK91/G3 series is attached to the stock, where as in the HK93 and MP5 series, it is not captured and just sits within the bolt carrier.

The trigger packs are fully interchangeable across more or less then entire family and the MP5/HK93 trigger housings can be used across platform, though the HK91 specific housings will only fit the larger rifle caliber guns. The ejector levers will need to be changed depending on caliber (an easy swap once the pack it out) and the hammer springs are different (though a lot of people, myself included, just run the full 7.62x51 hammer spring in their pack regardless of which caliber they are firing).

As to carrier groups, I don't really see how they could be interchangeable, given the different calibers (thus different bolts) and lengths of carriers. Some of the parts from them might be interchangeable, but I'm not sure.

For the rest of the furniture, like forearms, I supposed they could be made to fit if the other caliber weapons had a similar stock length, though I'm sure some work would be needed (but people have done it, cutting down a wood HK91 stock to fit an MP5, for example).
 

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The 9mm/5.56/7.62 (including the oddball K's) designs all share one design in that they are all slightly different variations in length. That being said, there is very little that is really interchangeable between them aside from trigger packs and housings, and there are more than a few caveats there as well. Bear in mind that clones and custom builders have expanded well beyond factory configs and models so calling something by an HK model designation is not always a universal language.

Cocking tubes: No interchangeability
Stocks: There are two main groups: single and double hole. Doubles are the 7.62 platform, there is some interchangeability between the single (5.56 and 9mm). You can also try and pass off a single hole on a double 7.62 but it's awkward and an eyesore.
Buffers: No interchangeability
BCG: No interchangeability
Triple trees: Mostly interchangeable
Trigger housings: Mostly interchangeable
Trigger groups: Mostly interchangeable when swapping ejector levers
Grips: Interchangeable across metal housings
Rear sights: Interchangeable but all calibrated differently so not really useful
Mag release: Non-interchangeable catches, interchangeable spring, retaining pin, and button
Dust covers: Interchangeable
Cocking tube stock hangers: Interchangeable
Safeties: Mostly interchangeable across metal housings or plastic housing, with the caveat that newer Navy style straight handle plastic trigger housings use a completely different drum configuration
Forgrips: No Interchangeability


I think the key to understanding anything about interchangeability with HK rollers is that they have a lot in the specific calibers but not across calibers. Hope this helps!
 

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Discussion Starter · #4 ·
Thanks, for a newbie it helps a lot. Are the front sight assemblies the same height between different models or calibers?
 

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The front sight assemblies are all the same, granted a few PTR bull barrels use different larger versions for use with their bull barrels. All the HK stuff is the same. All the sight blades are the same across calibers. The rear drum sight is the same in it's dimensions but the peep holes are different sizes and calibrated for each caliber, so you could get away with using a G3 sight drum on a MP5 (because when are you going to shoot at 400 yards with a 9mm) but generally they don't work together and the clone world confuse these drums all the time.
 
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