The SR-5 is basically just a taller version of the BR-4. It's not uncommon for the Accutac's I've used to have a bit of play with the legs at 90. I believe the culprit is usually the leg attachment itself, if you want it to move freely you can't crank down the locknut too tight, so there's a very very narrow sweet spot where you can adjust it with no play but still loose enough to move with easy.
I'd say the one advantage to the Atlas Cal is it has more height range adjustment. The one downside IMO to the Accutac bipods is they have a very limited height range, so you really have to know your setup to make sure you get the right height. This is especially true of the "4" series legs, the "5" series is better as the leg extension is greater. I think the Accutac bipods lock up tighter for cant/pan than the Atlas does but I've never felt either of them didn't lock up enough.
For example the SR-5 goes from a min height of 6.5" (at 45 deg) to a max height of 11" at 90 deg. While the Atlas Cal in "short" form (they sell two lengths) goes from 4.8" to 9.2" and in the long version from 6.1" to 12.3" So the taller version of the Atlas Cal gives you the option to go 0.5" shorter and almost 1.5" taller than the SR-5.
You can also get aftermarket clamps for the Atlas that will mount to picatinny and Arca in the same clamp, Accutac does not offer that option. The Atlas is much lighter if you care, 12-14oz vs 23oz.
You really can't go wrong with either, as long as you end up with the right height.
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