Disclosure: I don’t mean this as a proper review as this was broken and missing parts when I received it.
The ARMS 40 Std A2 rear sight is an older designed BUIS that is spring loaded to flip up and does not lock. Windage adjustments are .75 MOA.
A few years ago now, I received a disassembled ARMS 40 rear sight. It was missing the aperture and was reassembled incorrectly. I had tried contacting them about purchasing the missing parts or sending it in to be rebuild. If I recalled correctly they never responded to me.
I thought that it would be easy to get an A2 aperture to drop in it and get it operational. Oh boy was I wrong.
Each time I ordered some part or accessory I needed, I tried to order an A2 aperture to go along with it. Every time until now the A2 apertures were out of stock. EVERY TIME!
I even tried to get one from White Oak Armament, they discontinued carrying the standard A2 rear sight aperture. WTF? I guess A2 sights are truly dead.
Finally I made an order from MidwayUSA and they had only had a couple DPMS A2 apertures left. So I got one.
That aperture installed just like how you would install one into a carry handle. Now I am able to use the sight.
To install one of the ARMS 40 series sights, you unscrew a nut. This nut has a wide slot on it so that you can use a screw to remove it. It is suppose to be secured with a wire tether to the sight, but this old abused sight lacks that. The base of the sight is slid onto the rail, the cross bolt inserted and then locked in place with the nut.
On the right rear of the sight is the latch that securely holds the sight down. It is quick and easy to release the sight and the sight springs up. You can also easily secure the sight down one handed.
The sight springs up. It is suppose to lean slightly backwards so that if the weapon is dropped the sight folds. It does not lock with the intent to hold to prevent damage. Mine seems to lean a little forward. Letting it spring up on its own makes noise, but I wouldn’t call it loud.
The sight is notched so that if it is pushed down it has clearance for the latch so that nothing is damaged.
With the A2 aperture this sight provides the same sight picture of any other A2 sight. The first ARMS 40 models had a cut down peep to make the sight shorter. They also offer the ARMS 40 STD A2 that has a standard A2 aperture like this one.
I had initially intended to fix this sight and then sell it. But I think I found a home for it.
I remember a short time back in the day when flat top uppers were first getting popular that the ARMS 40 was considered the best BUIS out there. But that quickly changed. MSRP is $136, so there are cheaper excellent options. The tall height of this sight prevented many optics from fitting over it. I found I couldn’t put an ACOG or several of my standard scopes over this BUIS when it was mounted to an AR15. ARMS later made the ARMS40L a low profile version of this sight.
I’d still love to have one of the low profile ARMS 40L-P models, but I’m not going to spend the cash for one.
This was a good rear sight, but when options like the Troy flip up sights came out, these seemed to be quickly forgotten. Locking sights were perceived as being more durable. Not to mention many of the good alternatives were cheaper.
Now, the ARMS 40 series is an expensive obsolete relic.