300BK conversion help

[XLF30]

Gonna change a low-mileage DPMS AR-15 to 300BK. Barrel and block on its way...I have the wrench.

A friend told me I have to change the buffer spring. But I can't find confirmation anywhere. Opinions or experience?

Any good subsonic load recipes?

Thanks

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Carbine length.

[gwp]

The standard carbine spring and buffer should get you started. I used a H2 buffer in my first attempt, but changed the buffer to a standard buffer after the rifle was not 100% reliable. It operates well with the standard buffer and spring. I have several 16" barreled .300 BLK carbines, with pistol length gas systems, that work with the standard springs and buffers.