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Discussion Starter · #1 ·
Hello all,

I haven't received my RDB but I am already considering what optic I will run on it. I will likely run an MRO on it to keep it light. I was wondering would a 1/2 co witness (perfect co-witness) give me a good cheek weld and line of sight? Trying to keep the height above the bore as low as possible given that its a bullpup. Id also like to consider an MRO mount with little to no height on it but that may be to low to be in line with my eyes. Opinions?

Thanks,
Mike
 

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850sub, 1/2 cowitness (aka absolute cowitness) puts the center of the red dot at the same height as the sights.

if you google "mro sight" you'll find that it's a Trijicon red dot.
 

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With mine, and my medium noggin, I like a 1.25"-1.5" line of sight height.
I believe 1.5" is going to be the standard ring height for AR15 ring sets.
All this "high, medium and low" nomenclature when shopping for optic mounts just drives me nuts.
I just ordered Aero precision 1" tube mount for my scope. They replied to my inquiry about the height because they don't publish it calling their profile "standard" which is 1.5".
I have no idea what the bore axis is in relation to the LOS, but it doesn't matter unless Im using a .223 BDC. And it matters even less within 100 meters.

And, if you needed to get extra height you can't find a mount for, you can remove the plastic cheek pad. It doesn't help much.
https://aeroprecisionusa.com/ultralight-1inch-scope-mount.html
 

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Discussion Starter · #5 ·
Thanks for the replies! On a seperate note, do younall recommend Loctiting the pic rail when I receive the rifle?
Ive heard of people saying that they back out and cause the rail to wobble.
 

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I currently am waiting for a new screw from Keltec as this happened to me. The pic rail screws loosened up, and I tightened them down. I stripped the head on one screw. I ran out of locktite so I did not have any to use, and it backed out again. I will locktite the new screw when it arrives. Do it immediately lol
 

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do younall recommend Loctiting the pic rail
Like anything else, I would see if you need to B4 going to all that trouble.
I would find a way to monitor screw head rotation, with a picture or make index marks on the rail. monitor the situation.
Im not really a fan of using Loctite when other methods are available.
On a side note, For any one interested, cranking down on any screw or bolt should only be done if the fastener and application is specifically spec'd for torqueing. Otherwise you will just do damage to a component. For most things a machine screw is used for, you are just "holding two part together". Once you are at finger tight, use a method to prevent screw movement, but tightening more is not the solution.
Staking, pinning, safety wire, anti-rotation washers, Loctite, and self locking fasteners are the norm.
Now that I think about it, I wonder if the rail screw head holes can be drilled out to accept cap-head screws and deep enough to use lock washers?
 

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I had the front two that hold the rail down on the barrel loosen, as well as the most rearward that has a washer under it and holds the rear rail down on the barrel. The front's didn't unscrew much, but the rear did and allowed about 1/16-1/8 inch of play in the rail. Happened twice. From factory, and after I cranked them back down.
 

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Dissimilar metals with different expansion rates. Your screws are walking out.
Not good, KT! Do we need to pin these screws?
 

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erica told me no loctite was necessary. a forum member posted that it was.
on the side of caution, i used blue loctite (not permanent) solution and at 800 rounds, no walking, very solid.

looks like the forums were right and erica (employee) was wrong.
 

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Hello all,

I haven't received my RDB but I am already considering what optic I will run on it....give me a good cheek weld and line of sight
I just mated my Leupy 2.5x to an Aero precision mount. Perfect height fir me at 1.5".
I roughly estimate LOS to bore axis about 3.25".
Product
 

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erica told me no loctite was necessary.
I don't disagree that LT works in many applications, is easy to apply and readily available. I use it quite a bit. My biggest complaint about the stuff is the Permatex red comes in a blue tube and the LT blue 242 is in a red tube. WTF?
I do have my doubts that on applications where high heat is involved, that it may not hold as intended. I would use blue LT if LT was my only option.
The hex holes in those forward rail screws are so tiny, they may strip out before LT red will release.
Red271 LT removes at 500d.f. and Blue242 at 482d.f. YMMV.
 

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(Think we are kind of thread jacking, sorry!) I did a write up on using loctite on the rail screw a while back as I believe we were originally told to do so by an official Kel-Tec contributor here on the forum.

The loctite was supposedly important because the rear most rail screw (the one with a spring washer) is not supposed to be tightened all the way down, allowing for some expansion as the barrel heats up, to prevent accuracy issues (potential vertical stringing from what I remember).

In short mine came loose early in it's life, so I used simple green to strip all oil/grease from the screw and screw hole. I recall seeing evidence of previous blue loctite as well. Applied a dab of fresh loctite (admittedly I don't recall which kind now, probably in my old post if I look for it). Screwed down to hand tight and then backed off 1/8th of a turn (as per the Kel-Tec contributors recommendation).

Screw has not come loose since (and this was early on, I'm at ~1,300rds now).

If Kel-Tec / Erica is saying otherwise, I'd like to know what their current official "fix" is.
 

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I have Four screws at the front of my rail.
Do earlier RDBs have fewer?
Looking at the parts diagram, i only see two.
 

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I'm a great believer in LT290. It's a green POST assembly wicking thread locker with medium holding power. Threads should be clean before assembly, then a drop can be placed at the perimeter of the head of the fastener. It will wick into the threads and set up. It's like the blue stuff, except you only apply it after everything is assembled and torqued to your liking.
 

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Discussion Starter · #17 · (Edited)
I'm a great believer in LT290. It's a green POST assembly wicking thread locker with medium holding power. Threads should be clean before assembly, then a drop can be placed at the perimeter of the head of the fastener. It will wick into the threads and set up. It's like the blue stuff, except you only apply it after everything is assembled and torqued to your liking.
. That sounds great! So it sounds like I wouldnt need to unscrew anything when I get the RDB I could just add the 290 green loctite to the pic rail screw heads as soon as I get it? Or would it be better to still unscrew the rail screws and clean them, screw them down to approx torque setting, and then apply the 290 green loctite? Also, is the green loctite more heavy duty than the blue loctite?
 

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The hex holes in those forward rail screws are so tiny, they may strip out before LT red will release.
Red271 LT removes at 500d.f. and Blue242 at 482d.f. YMMV.
That sounds great! So it sounds like I wouldnt need to unscrew anything when I get the RDB I could just add the 290 green loctite to the pic rail screw heads as soon as I get it? Or would it be better to still unscrew the rail screws and clean them, screw them down to approx torque setting, and then apply the 290 green loctite? Also, is the green loctite more heavy duty than the blue loctite?
There are 4 different versions of red and 2 different versions of blue so you can't just go by color.
Here's a nice PDF listing all of them and their retaining torque on a M10 nut:
http://www.henkeladhesivesna.com/aam/Threadlocker2_LT3770_AAM_Chart_Interactive.pdf
 

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I have Four screws at the front of my rail.
Do earlier RDBs have fewer?
Looking at the parts diagram, i only see two.
Yes, 2 from the top at the very front that hold the rail to the gas block and 2 from the bottom, in front and behind the "T22" marking. You only see the ends of those screws and they look like pins. The bottom 2 hold the "Recoil Lug" part #105 that is on the bottom of the rail.

Not sure if the earlier guns have the recoil lug or not. Check you parts diagram and look for #163 Gas Block Screw, #105 Recoil Lug and #162 Recoil Lug Screw.
 

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Yes, 2 from the top at the very front that hold the rail to the gas block and 2 from the bottom, in front and behind the "T22" marking. You only see the ends of those screws and they look like pins. The bottom 2 hold the "Recoil Lug" part #105 that is on the bottom of the rail.

Not sure if the earlier guns have the recoil lug or not. Check you parts diagram and look for #163 Gas Block Screw, #105 Recoil Lug and #162 Recoil Lug Screw.
MY #162 screws are on top next to the gas block screws. All four are in line, Identical and almost touching each other. I don't see any screws driven up from the bottom.
Font Text Metal Nut Still life photography
 
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