[sab567]

Personnaly I have both (IR and R-hop) and I tried both in the same setup.

You can see a difference between the IR and R-hop at a cold winter condition (I mean less than -10 deg.)
With the R-hop (wich is tune perfecly and shoot straight with 0.30g at summer condition with 0 pressure apply on the M-nub) during cold winter I saw that the bbs have an hop-up effect.
For this reason I try the IR-hop and it look better (But I didn't have the time to try it under -5 deg.) but at this time, it's work like a charm.

Is you look at the HS5 website, the difference between the IR and R-hop is not to big, and if you think playing during winter don't take a chance and go with the IR-hop for some few more buck. And if you want to safe some time, go with the "pre tune" Z-kit, you'll have less job to do with sanding and better result in less time.

When you'll have to tune it, take your time, it's the key. Fit it (with sanding the extra material) in your barrel that you will be abble to push the bbs in the barrel without pressure. Go to a field you know or a private place that have a lot of place and shot, sand, shot, sand, shot, sand. You can fin a lot of "how to tune a R-hop" on the HS5 website or google. You'll be abble to do must part of the job without a shooting range, and just do the fine tuning at a field.

Edit: HK5 --> HS5 (My mistake sorry)