I've been building my 20" Bushmaster in a 'Designated Marksman' type of rifle.  To that end I decided I wanted a 'range adjustable' BUIS so I could shoot the rifle at longer distances with irons, than I could with my ARMS#40.

I checked on AR15.com's Equipment Exchange and found Grant at G&R Tactical had a good deal on brand new KAC 600M sights.  I ordered one ($176 with shipping) on Tuesday and it was in my hands Thursday night (typical G&R efficiency).  The sight came in a brown box (not unlike the ARMS sight) and sealed in a plastic bag.  Upon ripping open the bag I began to examine the sight, and try out it's mechanisms.

Remember that feeling when there was a 'special toy' that you saw advertised that you had to have, but when you got it it was a letdown?  That is how I felt.

Obviously the KAC 600M has seen and survived 'real world use', but upon examination I think that is 'in spite of' KAC's engineering rather than due to it.

The entire sight is steel.  Not bad in itself, and the body had a nice phosphate finish much like a barrel.  The sight clamps onto the rail with a short (very short) bit of metal and a steels screw.  This is where the problem started.  The clamping piece of metal is roughly 1/4" long (compared to just over an inch on the anchoring side), it's even shorter than the similar piece on the ARMS#40).  The metal is a dull 'gunmetal grey'.  I think there is a finish on it, or there was one and it had been worn off.  The lip of this clamping piece is very small - it barely has any grab on the rail.  I've seen Leapers mounts with better clamping ability.  The screw is also a gunmetal grey - it's round (instead of having a square profile to properly lock it in).  Looking at the head of the screw you can see the finish vary (more in the middle - not as much near the edges, again like it's worn off).  I'm not confident in the anti-corrosion capabilites of the 'grey' metal so I plan on keeping it doused in CLP.  Why couldn't they finish these parts like the sight body?  For those thinking the parts must be stainless, I doubt it, they stick very well to magnets and most stainless steels are not magnetic.

The sight itself is a marvelous idea.  It uses a micrometer type adjustment to raise and lower the hooded small aperture.  It also folds VERY flat, about half the height of an ARMS#40.  The sight does not 'lock' into position but there are detents to keep it in place (up or down).  Seems like a flimsy arrangement after comparing to the locking Troy and GG&G sight or the spring loaded ARMS sights.  Again the sight is a nice idea - poor execution.  The range numbers (and pointing arror) are raised (meaning you can't fill in the numbers with a china marker to make them easier to see - especially in low light).  I counted clicks from '2' to '3', then from '3' to 'z' (zero).  From 2 to 3 I consistently get 5 clicks (normally I should get 4 for a detachable carry handle).  The first two are really close together, the next one is really long, then I need two more to get *exactly* on the 3.  Kinda funky but range time will determine if it works or not.  I got 3 clicks from the '3' to the 'z' mark - which is funny becaus there should be 2, if one is following the military standard.  Maybe they are calibrating the sight differently, but the clicks don't seem to have consistant rotation and I would have preffered them to duplicate the detachable carry handle.

The unit is adjusted in windage by the use of an A2 type knob on the ejection port side (like the A2 carry handles).  It's stiff to turn (I like that), but it's not marked as to which direction you turn to change point of impact to the right. Also the amount of windage travel for the sight appears to be much less than any other rear sight I've used on an AR-15.

I'm going to keep this unit as there are few units that will adjust for range, and this is considered "the best" (to me that isn't saying much).

To recap, the KAC 600M is a flip up BUIS with range elevation adjustments from 200 to 600M.  It's intended for precision shooting, not CQB type engagements.  Issues I've found with this version:
1) Missing/minimal finish on rail clamp and screw.
2) IMHO an undersized rail clamp (especially considering this is supposed to be a precision sight).
3) Screw is round instead of square (this is a cheap way out and not as precise as a square screw - poor form considering the price paid and the intended use)
4) 'Clicks' are not consistant, nor do they duplicate the detachable carry handle (which this sight is meant to replace).
5) Lacking the ability for the sight to lock in the up position.

Submitted for your consideration,
Forest

Since a picture is worth a thousand words...............


 

Thanks F4YR - my digital sucks so I didn't bother.  

But I should note - my screw is not an allen head - it's a standard machine screw (for use with a regular bladed screwdriver).  Also the clamp portion is a bit different (a bit wider but not nearly as tall).

If you could bring your camera next week we could post pics of my KAC 600M.

Quoted: To recap, the KAC 600M is a flip up BUIS with range elevation adjustments from 200 to 600M.  It's intended for precision shooting, not CQB type engagements.  Issues I've found with this version: 1) Missing/minimal finish on rail clamp and screw.

The finish should be the same or better than the rest of the steel parts on your rifle. After machining, the parts are manganese phosphated (hot bath parkerized) followed by application of a dry-lube film.

2) IMHO an undersized rail clamp (especially considering this is supposed to be a precision sight).

I've never heard of one of these sights (or any similar sight, even from other brands) being ripped right off the rail. Until that occurs, I'm sure it is just your humble "opinion".

3) Screw is round instead of square (this is a cheap way out and not as precise as a square screw - poor form considering the price paid and the intended use)

You must not have had that toy when you were a kid... Square pegs don't go through round holes.

Given the mass of the sight, the recoil of the gun will not accelerate it so much that it will shift the sight/screw fore and aft in the recoil groove, inspite of the screw being round or the clamp being "undersized". Just make sure to properly and occasionally tighten the screw.

There is a difference in why a scope ring will have a larger or in some cases use multiple clamps and has a square lug - it has to hold a heavier object (scope) in place (cross slot) while the rifle tries to recoil rearwards out from under it.

4) 'Clicks' are not consistant, nor do they duplicate the detachable carry handle (which this sight is meant to replace).

Thie 600m BUIS is NOT meant to replace the carry handle. It is designed to act as a BACK UP iron sight in case the user is forced to take a shot without the use of his primary optic (originally, the Leupold Mk4 M3).

5) Lacking the ability for the sight to lock in the up position.

This was not a requirement specified when the sight was originally designed several years ago. I have seen and played with prototypes that lock in the up position, however I have no idea if KAC plans to release them for public consumption.

Quite informative, thanks.  Seems as though there is room for competition in the long-range BUIS market.

Quoted: The finish should be the same or better than the rest of the steel parts on your rifle. After machining, the parts are manganese phosphated (hot bath parkerized) followed by application of a dry-lube film.

If there is a gray dry-film lube over the parkerizing that would explain the color and look of the parts.

I take it they only use it on the screw & clamp?  (as the sight base definately doesn't have any dry film lube)

Thanks for the info - makes me feel much better about the parts.

I've never heard of one of these sights (or any similar sight, even from other brands) being ripped right off the rail. Until that occurs, I'm sure it is just your humble "opinion".

Agreed I haven't either - but that is no excuse for poor engineering.   The managers at NASA said the same thing about the foam on the fuel tanks - just prior to the Columbia...

You must not have had that toy when you were a kid... Square pegs don't go through round holes.

You must not be an engineer - we know how to make square pegs fit into round holes.  The slots in the raill ARE square and the screw should mate with them for optimal security and return to zero.  There are a number of ways you can accomplish the 'square peg into the round hole' through the use of sleeves or fixed screws with a nut on the end.  Other (lesser) companies have done this.

Just make sure to properly and occasionally tighten the screw.

I plan on it - but if were built right from the get-go a screw loosening would have less impact.

it has to hold a heavier object (scope) in place (cross slot) while the rifle tries to recoil rearwards out from under it.

You are right - but what is wrong with doing it for a lighter item?  The only reason not to is to cut corners and 'do it on the cheap'.  Not something I had associated with KAC products.

Besides if the sight gets a heavy impact (say from dropping it as I go for a twinkie ) would not the square peg do a better job of preventing any movement?

Thie 600m BUIS is NOT meant to replace the carry handle. It is designed to act as a BACK UP iron sight in case the user is forced to take a shot without the use of his primary optic (originally, the Leupold Mk4 M3).

Isn't the detachable carry handle used as a back up for some soldiers?  I seem them attached to handguards all the time (while the M68 is on the receiver).

In effect the KAC 600M is a replacement for the detachable carry handle.  Instead of having to carry the handle and reattach it when needed - all the warrior has to do is flip up the KAC.  Makes his life much easier.

In any case the point is minimal - the primary focus was the micrometer 'clicks' 5 irregular movements instead of 4 consistent movements.

This was not a requirement specified when the sight was originally designed several years ago. I have seen and played with prototypes that lock in the up position, however I have no idea if KAC plans to release them for public consumption.

To be fair the detents are pretty solid (now) I don't know if they will soften over time & use.

Harv, you seem to have lots of knowledge on this sight, do you know if the detents stay as firm after they have been used awhile?

IMHO this sight is a diamond in the rough.  Like they built it quick to meet an immediate need, then never went back to refine/improve the design.   My points my be minor - as you point out these have been working for a while, but it's the differnce between paying alot for a mediocre sight and paying alot for a great sight.

Ok tonight I installed the KAC 600M.  Installation was straightforward.  loosen the screw pop the sight on - tighten the screw.  There is already thread locker in the threads of the base.  Not as secure as the ARMS but it'll work.  I measured the clamps - .51" for the KAC, .65" for the ARMS and the arms has a fixed continuation - which requires the sight to be slid onto the rail (talk about secure).  

I zeroed the irons to the 'spare' red-dot which I use then the TA50 isn't installed.

Now I'm looking forward to trying it out 'at range' .

I bought one as well, and while the finish didn't bother me at all, I must say I was a bit disappointed at the "feel" up and down, as well as the clicks and raised numbers.  It's completely understandable that it wasn't a requirement to lock in the "up" position at the time.  Many manufacturers (GG&G, Troy) have added that feature after feedback from the end user, so it's a fairly new thing.  Like some other KAC offerings though, I wish they were more open to sharing with us lowly civilians (can you say H&K?)

I disagree to some extent that this is just a "backup sight" in the same sense that the ARMS or the others are...  This is a secondary sight in case the optic fails, but it's supposed to be a precise, long range capable sight to be used on precision rifles, not just a hole to look through in the back to see the front in a CQB environment, so I'd expect the clicks to be consistent.

To my untrained eyes, and although I believe the KAC to be a sturdier sight, I like the features of the MATECH BUIS better.  It flips up under spring pressure, and like the ARMS #40, it bounces back up if knocked down.  It also ranges, using a big fat dial on the right side that has white numbers and tic marks.  It has more mounting rail if that matters to you, AND it's also about $50 cheaper too.

I'll be keeping the KAC sight, and put it on whatever I end up building for long range fun at the range, because I always get bored with scopes and switch over to irons anyway.

I have a KAC 600m BUIS also.I dont have some of the problems that you mention.It is 4 clicks from 200 to 300.Also it is 2 clicks from 300 to Z.The windadge knob does have a R and an arrow showing the direction.I have used it out to 400 yards and the elevation marks are acurrate.SJR556.

Isn't the difference in clicks is a BDC thing?

Quoted: I have a KAC 600m BUIS also.I dont have some of the problems that you mention.It is 4 clicks from 200 to 300.Also it is 2 clicks from 300 to Z.The windadge knob does have a R and an arrow showing the direction.I have used it out to 400 yards and the elevation marks are acurrate.SJR556.

My 600M rear is tha same as SJR 556. Well finished has the "R" and arrow on the windage knob and mine seems to have a larger clamp an the left side than those shown in the pictures. Mine has never "folded on me" at an inoportune time so the need for it to lock in the up position has as yet to show itself.

Where did you get your rear sight? it could be a very old one or God Forbid an airsoft conterfit. I was at a gunshow and a fellow was selling both 300m and 600m rears in KAC boxes for $75.00 a piece. Upon close inspection they turned out to my eye not to be real.

IPSC_GUY

Quoted: "...The sight came in a brown box (not unlike the ARMS sight) and sealed in a plastic bag.  Upon ripping open the bag I began to examine the sight, and try out it's mechanisms. The entire sight is steel.  Forest"

The boxes we use are more "white" colored-no way are they "brown", and should also have a standard white lable as well.  The base of our (KAC) sight (which is the largest component of the sight) is aluminum not "steel"), but all the other parts are steel.  Sorry you don't like the screw, but if you ever need to turn it and all you have is a coin, you will perhaps appreciate it a little more.

In the picture that follow your original input, the sight in the top photo has the original clamp that was required to have a threaded hole for securing a wiring harness per Army directive.  This was later dropped as the other two pictures show.  The clamps hole is not in the center (i.e., not symetrical),  its shorter half should be rearwards.
All the internal parts are also dry-film lubed and baked on for increase corrosion resistance.  As the sight is used, the detents will become more distinct as the dry-film burishes.

Quoted: Where did you get your rear sight?

As I indicated I bought it from G&R Tactical and Grant doesn't deal with Airsoft...

Coldblue - I appreciate you checking in.

I went back to look at everything after your post.  I was mistaken on the box it has a white exterior with a brown INTERIOR.  Yes the label is there (I'm surprised I didn't mention that in the initial writeup).

The base is a flat black and my magnet WILL stick to it.  Possibly it could be the attraction to the parts inside - but at this time I'm not willing to take the unit apart to test the base w/o the internal parts.

My 'clamp' area is similar to the 2nd photo (clockwise) in Fight4YourRights post.

There is definately no arrow (or engravings for one), and I keep recounting and get 5 clicks from 2 to 3, and 3 from 3 to 'Z'.   I'll play with it while watching TV and try to speed up those detents becoming distinct.

Forest, great post. Thanks