Yes, the barrel length will have little to no affect on using this scope to its full potential.
Yes, you can find that version here: https://www.opticsplanet.com/vortex-opmod-strike-eagle-1-6x24-limited-edition-riflescope-w-ar-bdc-reticle.html and it is designed especially for .223/5.56 NATO.
If you choose the kit with the mount, it will put your scope at lower 1/3rd co-witness, meaning that the scope will be high enough that while the sights will be visible in the scope view, they will be below the reticle.
You can absolutely use this with a Ruger PC9. Please keep in mind you will need to do some testing with the reticle to verify what the lines and hold overs correspond to for your specific set up as the reticle is predominantly meant for 5.56/.223.
Yes, this would work on your Remington 721. Due to the variation in bases and rings available for your rifle please contact us at techsales@opticsplanet.com so we may more accurately find a solution for you.
Yes, it is available in black.
Yes, you could use this scope on a 30-30. Please keep in mind you will likely need to do some testing with the reticle to verify what the lines and hold overs correspond to for your specific set up as the reticle is predominantly meant for 5.56/.223.
You would be able to use a set of low rings. These Vortex rings sit at a height of 0.09in and are a popular option: https://www.opticsplanet.com/v/pr30-l-vortex-pro-series-30mm-riflescope.html
These Burris Xtreme Tactical rings would also fit your needs and sit 0.05in lower at 0.85in:
https://www.opticsplanet.com/v/420160-burris-xtreme-tactical-picatinny.html
Yes, this scope would work great on a 300 Blackout.
Yes, you can use this scope with your Ruger. Please note you will likely need to do some testing with the reticle to verify what the lines and hold overs correspond to for your specific set up as the reticle is predominantly meant for 5.56/.223.