I’ve been using the Steiner MPS for a few years now. I originally picked mine up just a few weeks after release back in 2022, curious to see how it compared to my beloved Aimpoint ACRO P1. Initially living on a pistol, it eventually found a home on my Beretta A300 Ultima Patrol. In short, I like it a lot more on a long gun than on a handgun. It’s not perfect, but it’ll do for a training and teaching gun.
One of my biggest complaints about the MPS is the battery cap. For starters, you need a proprietary tool to loosen or tighten the cap itself. That’s a huge red flag, and an outlier among optics today. On top of this, the cap strips fairly easily, even with their special tool. This is partly due to how tight the cap is, using an o-ring to help seal things up properly. With battery life equaling the P1, you’re getting about 3 weeks on max brightness, which means you’ll be fiddling with the battery cap often if the gun sees much use. Now we’re starting to see the problem.
OP Engineering Battery Cap for Steiner MPS
Enter the OP Engineering battery cap for Steiner MPS. I first saw this piece in an Instagram story from Steve Fisher of Sentinel Concepts in mid-2024. What stuck out to me was the mention of tool-less installation. I certainly had some reservations about that, but I needed a new battery cap anyway, so I figured I’d give this a shot. As an added bonus, the OP Engineering cap also allows for storage of a spare battery inside the cap. I jumped onto their website, placed an order, and had a new cap in just a few days.
Installation is extremely simple. Plop your battery into the optic, and a second battery into the cap, then just screw the cap into the optic with your fingers. Considering the forces of recoil, I tightened mine as much as I could by hand. No thread locker, no tools, keep it simple. OP provides a set of o-rings which sit inside the cap to act as spaces to keep everything secure.
Range Time
First rounds with the OP Engineering battery cap were done in regular range time. I ran through a handful of drills prepping for class. Eventually this made its way to the inaugural Rangemaster Advanced Shotgun Instructor course, and to the 2024 Thunderstick Summit. As of this writing I’ve fired approximately 520 rounds with the OP cap installed, with about 3/4 of that being buckshot and slugs.
- 13x Remington Gun Club #8 2-3/4″
- 25x Federal Game Shok #7.5 2-34″
- 100x Federal Top Gun #7.5 2-3/4″
- 10x Federal Power Shok 00 buckshot 2-3/4″
- 10x Federal Flite Control 9 pellet 00 buckshot 2-3/4″
- 10x Hornady Critical Defense 9 pellet 00 buckshot 2-3/4″
- 16x Federal Premium Personal Defense Reduced Recoil 00 buckshot 2-3/4″
- 54x Federal Personal Defense NRA 00 9-pellet buckshot, 2-3/4″
- 84x Federal Tactical LE Hydra Shok 1oz slug 2-3/4″ low recoil
- 10x Fiocchi Defense Dynamics 1oz slug 2-3/4″
- 31x Remington Slugger Low Recoil 1oz slug 2-3/4″
- 51x Winchester Super X 1oz slug 2-3/4″
- 105x Federal Power Shok 1oz slug 2-3/4″
Initially I experienced some flickering under recoil with full power slugs and buckshot. I reached out to OP Engineering on Instagram to help troubleshoot this issue. They sent me a spacer kit, and offered some advice regarding battery inconsistencies. After a few dozen reps this flickering went away for several weeks, despite not having added any spacers. I decided to keep going with making changes, hoping that things had settled into place. Unfortunately I was wrong.
About halfway through the first day of the Rangemaster Advanced Shotgun Instructor course the flickering returned. At this point I added some spacers to the battery compartment to try and remedy the issue. Since then I’ve had no further flickering. The cap has stayed firmly in place through recoil and a subsequent battery change.
All of the flickering took place in the first 1/4 of shooting, which leads me to believe things are right as rain now. Additionally, I’ve never encountered any loosening of the cap under recoil. Considering things are only hand-tight, I’m really impressed by that.
Customer Service
Customer service from OP Engineering was fantastic. OP replied extremely quickly, they were informative, and even answered messages at odd hours of the night.
They provided multiple options in a building-block format to try and remedy my issues in a very straightforward way, which also worked without issue. As someone who has seen customer service take a major hit over the past few years, this is refreshing.
Final Thoughts on OP Engineering Battery Cap for Steiner MPS
While my preference would be for Steiner to make a durable battery cap that can be removed without a proprietary tool, I doubt that will happen any time soon. Until then the OP Engineering battery cap has been a solid addition to my MPS after installing their spacers. If you’re like me, and find yourself in need of a replacement battery cap for your MPS, give OP Engineering some consideration. It’s been great for me, and I don’t see it leaving my gun any time soon.
MSRP on the OP Engineering battery cap for Steiner MPS is $45. You can get yours >>HERE<<
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