I replaced the PRI gas block/front sight with an ARMS 41B-L.  This one has a bayonet lug, in my case is rendered useless by the use of the Daniel Defense 12.0 FSP, but I like all the evil features I can get

Sight in the up position.  It does mimic the shape of a standard FSB pretty well, from a distance one would be hard pressed to notice it's different.




To fold the sight, press down the top of what normally would be the support beam on a standard FSB


As it nears the bottom, its downward motion induces the upper half of the front sight post to pivot


In its fully folded position


The 45 degree, two parts support "beam" is spring loaded.  As it's nearly folded, the spring tension snaps the sight down.  To unfold the sight, just grasp the top of the sight and pull up, it's also spring assisted.

Couple of gripes.  This must be the only ARMS product I've owned and seen that's not in the color of Colt gray.  The black finish seems to come off and gets on my fingers.  Already you can see some finish has been worn off in the second picture.

It can be hard to press down on the element that folds the sight, I think with some breaking in, the problem may solve itself.

I've always just used the tip of a bullet to adjust the front sight, the 41B is finely machined, unhappily there isn't much room for a bullet to rotate the post once the detent is pressed.  I used two small drift punches, still failed to rotate the post because there simply isn't enough purchase to motivate the post.  I gave away from front sight tool years ago, now I have buy another one



It is very well made and looks great folded or unfolded.  Aesthetics mean little to folks that use rifles for a living, but for a firearms enthusiast, it still matters a little.  This could be the only gas block/front sight that looks good both in the up and down position

Excellent review. By any chance, did you happen to weigh the sight before installing it?  What did you think of the cross-bolt set-up that secures the sight to the barrel?

Unfortunately I don't have a scale, but when I received it, my first thought was "dang it's heavy!"  It felt heavier than the PRI gas block/front sight it replaced.

Re: the cross bolt, in my case, I can't use the bayonet lug and the sight will be in the folded position for the most part, it should hold up just fine.  Should the rifle fall clanking on the ground while the sight is up, I'm fairly confident it will not unduly rotate on the barrel.  Vltor did a test with its gas block/flip up sight combo, it too uses the cross bolt mounting method, Vltor's test shown on MM's site has me convinced

Very good review.  Any thougths on the best/cheapest place to purchase it.

Can we get a shot like the last pic with the sight down?

Ok here's a quick and crappy pic

Thanks!

I have the earlier version without the bayo lug.  I was relatively pleased with it.  Mine is pretty easy to fold down, as long as you push straight down on the support bar.  I think it would stay up if hit from the front.

I have a 41-B with bayonet lug, and I really like it. Mine came with a spacer for use if a front handguard cap is not used. Flips up very easily, and folds easy with one hand. I did use loctite on the mounting screws just to ensure it didn't come loose from firing. Surprisingly, the bayonet lug although split to accomodate the mounting method, works just as well as a standard FSB lug.

I am happy with mine, and would encourage anyone else interested in this style of front sight to go ahead. I compare it to the YHM flip up with bayonet lug, and in my opinion, this sight is a much more solid unit than the YHM. Cost can be considered high, until you realize that it is both a gas block and folding front sight, which puts things back into perspective.

Thanks for the review, I am still not sure whether I want another Vltor or an Arms for my current build with a DD 9.5FSP. I like the spring assist and the fact it takes AR front sight posts.

I like the Vltor, the 41B is less expensive, the Vltor folds down lower so the rails are in line with the handguard....

True, but mine has a huge post, i wish i could find a thiner ak post, i might try and remove some material on mine.

The post is big or the protective ears?

Post, Vltor has an AK front sight post, and it is FAT, i will have to take out the calipers, but off hand i would guess it is about 1/3 or more wider than the AR post.

btw, i revived this thread because i am planning on buying a 41B for my SPR build and was hoping for more feedback/pics

SPR?  Mod0 uses PRI, I have one if you're looking

Not going with a Mk12 Mod 0 (or 1) clone, I am going to go with my on version, i have personal preferences on certain parts and it will be closer to a mix of Mod0 and 1. I decided that i didnt want a PRI for optic mount reasons, preferred the DD Lite rail, and that since i cannot get cans in my state don't need to do the Ops collar. Its going to be on par with my RECCE. I am too young to get stuck on details and "perfect clones", but thanks for the offer.