I would recommend getting a MDT send it level and the Brandt ACI. This will put the level right in your eyepiece and you will subconsciously always be level. As distance increases, any cant gets magnified, especially if you hold wind. Its a game changer.
200% agree. For long range, I shoot more accurately, faster and with more enjoyment with a send it level. I have multi-focal glasses so have trouble focusing on a bubble with both eyes open while staying on the target. With the a Send-it, as DBD says the lights make leveling almost subconscious because you can sense the colors without breaking focus and attention from the in-scope sight picture and target. However the Send-it takes up considerable space, is an appendage that can get in the way and has batteries, which are the downsides for some applications.
The next best level in my experience that is not as good as the Send-it but considerably better than other bubbles is one of the Badger C1 mounts with the ACD (anti-cant device). For some reason that level (which is a bead not a bubble) is easier to see in my peripheral vision without focusing off of the sight picture and the target. However, the metal housing shades the bead and tube quite a bit so if the light is low (or it's dark) the bubble can be hard to see. I have some tritium rods I purchased to install under the bead tube to see if that will help but haven't done that yet. The other bubble level that is not as good as the send it but better than most bubbles for seeing in your peripheral vision is the Hawkins bubble that is built into the top portion of the front ring and points away from the scope tube on the non-dominant eye side. This one is much easier for me to see in poor light and is almost as easy to pick up in peripheral vision as the Badger ACD. I have standardized on Badger C1 for both canted and non-canted and Hawkins heavy tactical and ultra light rings because (A) they are excellent quality and (B) they have good bubble levels that are easy-ish to see without focusing on them and do not take up much space or weight. I use both the Send-it and a bubble when I use the Send-it so there is a backup to the electronics/battery and I can check to see if the send it is out of calibration. There are many, many other great mounts/rings you can look into, I have standardized because these four cover all the applications I have so my approach is why keep others around that require more spare parts.
One of the other replies says not to skimp on mount/rings and that is very important IMO. You are spending a ton on your rifle and your scope, and the mount/rings make a big difference so I don't recommend skimping here. In addition to the above bubble issues, minute movements in the ring-to-rail or ring-to-scope interface with cheap mount/rings will change your zero (e.g. "slips" caused by imperfections in the inner-ring surfaces, stresses due to low quality materials and/or poor machining that vary with temperature causing POA shifts, and/or or insufficient screws/holding force). High quality rings have tight tolerances on rigidity, dimensions and straightness, have a good number of properly sized screws, don't put stress on the scope tube and generally don't mar the scope finish even if you mount and dismount the scope a bunch. With a high quality mount some swap the scope by just backing off the rail screws and not loosening/removing the rings, but I always loosen rings, mount the rail and then re-tighten the rings just to make sure there are no residual stresses that change zero with temperature shifts.
If you are shooting a red dot for CQB out to a hundred yards or so, then a quick disconnect mount might be fine as long as it is high quality. For long range you want a minimum of 2 and preferably 3 or 4 heavy rail mounting screws/bolts. For a mid-range (say 600 yard) application some use quick disconnect mounts, but I don't recommend it because it introduces potential zero/POA shifts and it's super easy to carry a portable torque tool kit like fix it sticks and use it properly.
If you do mount and dismount a scope more than once or twice, or if you see any signs of wear on the ring screws, change the ring screws. Also, I recommend you use blue vibratight or locktight on the rings and even the rail screws/bolts and of course spend the time to look up the correct torque specs for both the mount/rings and scope, and use a high quality torque tool to establish the right torque - don't over or under torque (most people over-torque).
There are tons of posts on how to true your vertical reticle cross hair to gravity and your level (bubble, Send-it or both). For long range shooting this is very important because even the best level in the world is worthless if your cross hair is not trued to it within a few tenths of a degree. There are lots of good ways to do this, including an old fashioned plumb bob with string on a calm day. Some just level the scope body (either top of turret or bottom of turret housing) with the rail and then true the bubble to the rail, but I have never trusted this so I always true the vertical cross hair to gravity simultaneous with truing the level to the rifle rail and the scope tube angle at which the vertical cross hair is trued to gravity. Many years ago I purchased a high end laser level that projects a near-perfect vertical line for this so I don't have to find a tree and use a plumb bob and string on a windless day.
