The difference is the weight of the buffer. The weights are as follows:
Carbine: 3 ounces
H: 4 ounces
H2: 4.65 ounces
H3: 5.6 ounces
The manufacturer doesn't state if the Aero Precision Enhanced Carbine Buffer Kit buffer tube is anodized or phosphate coated. I recommend contacting the manufacturer in regards to that information.
The Aero Precision Enhanced Carbine Buffer Kit is offered with 4 different buffer weights. Most 300 Blackout rifles can benefit from a heavier buffer. The H, H2, and H3 buffer would all work with your rifle, however, I would recommend using the H2 model (MPN:APRH101242).
The Aero Precision Enhanced Carbine Buffer Kit that I would recommend for your build is the model that includes a carbine buffer (MPN:APRH101240). Because of your caliber and barrel length, a heavier buffer is not required and may actually cause reliability issues.
I recommend using the carbine or H model of the Aero Precision Enhanced Carbine Buffer Kit.
The Aero Precision Enhanced Carbine Buffer Kit I would recommend for your 450 Bushmaster upper is either the H2, or H3 buffer kit. You can email us at Techsales@opticsplanet.com and let us know what barrel length and gas system length you currently have, that way we can recommend one over the other.
This Aero Precision Enhanced Carbine Buffer Kit fits Mil-spec, carbine length buffer tubes. Your Hogue stock fits commercial spec buffer tubes. I'd recommend the Luth-AR .223 Carbine Buffer Tube Assembly for commercial stocks, found by using the link below:
https://www.opticsplanet.com/luth-ar-223-carbine-buffer-tube-assembly.html?_iv_additional-features=commercial
The total weight of the H2 Buffer Kit is 11.45oz and the total weight of the H3 Buffer Kit is 12.4oz. The individual weight of the H2 buffer is 4.7oz and the H3 buffer is 5.6oz.
Yes, the Aero Precision Enhanced Carbine Buffer Kit that I'd recommend is the H2 kit (MPN:APRH101242) to allow for proper functionality while shooting suppressed.
For that set up I recommend using the H2 or H3 model of the Aero Precision Enhanced Carbine Buffer Kit.