It is documented that HK sold exactly 125 SR9 rifles in the "TC" configuration (PSG1 stock and trigger group). The "TC" was hand stamped after the "SR9" on these rifles after arriving in the US by an HK USA employee in Virginia. Many of these stampings are crooked and were obviously done by hand.
The majority of these seem to fall into some of the later serial number SR9s (2500 and above) and have a KD date code. There is not an exact serial number range for them as HK seemed to just grab random SR9s and convert them.
However, based on my research the consensus seems to be that it is possible that the first 25 of SR9 rifles sold in the "TC" configuration were not marked "TC" because they were just special orders from customers and were not actually available in the catalog. These rifles would most likely be a KA date code.
After this first batch of 25, HK decided to officially offer the SR9 in this ("TC") configuration and started stamping them as such. This stamped batch consisted of 100 rifles.
Unless you have documentation (such as the original manual with the warning sticker for the PSG1 trigger) it is impossible to prove if the SR9 you are looking at was shipped from HK in the "TC" configuration or the PSG1 parts were added later on by an owner.
I just bought and SR9TC on Thursday so I have been researching them extensively.
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