Home Forums Hunting & Shooting AR and Tactical Rifles KP-15 Monolithic Polymer Lower

I typed out a big response that disappeared, but long story short, it reminds me of a Troy Battle Ax, which to me always seems " just big enough." Slimmer than a BCM or MFT, but not so small and thin as to feel uncomfortable. That's my first impression anyway.

It does not have the deep stippling of the Troy, just seems similar to me in size.

KNS makes a set of non rotational pins for the M&P 15-22 that is also wider than mil spec receiver.

I noticed my hammer pin was rotating and didn’t like the idea in a plastic lower so I ordered them and solved that issue. Might take a look and see if it’s about the same size, a little added insurance if it is.

I built a AR-45 on a Cav Arms, the mag well is wider in the middle to accommodate a M3 magazine, and it has had a lot of rounds run through it and is still going strong.

Got my KP-15 specific lower parts in, that I ordered from KE Arms. The special extra wide (or long? whatever) hammer pin is 1.1 inches, in case anyone gets one of these and wants to look for an anti-rotation option (I might in the future).

The special safety selector appear to be just an ordinary milspec safety, with a 45 degree bevel milled or ground into it as shown below. I think the purpose is to allow the safety to be pushed out if the selector is turned to 45 degrees, according to the instructions.

I may try to put mine together next weekend if I get the time.

Around 5.7 pounds. I feel I could have got down to 5.5 pretty easy with lighter guts and one of those Faxon or Ballistic Advantage 16" barrels. I think this one is a little heavier than those are. Carbon fiber handguard would have of course saved a bunch of weight too. This is a cheap build, wasn't trying to go as light as possible.

It looks a lot better in person - this pic is from a weird angle. That's a 16" barrel and I think 12.5 or 13 handguard, if I remember right.

Auk, what trigger did you install? Trying to figure out if a LaRue MBT will work with a non KE ambi safety. Maybe it’s easy to grind a 45 deg ramp in a milspec safety since ive got multiple spares?

I did the LaRue MBT with the KE safety, works fine. You can see my pic up there, that's all there is to the KE safety. I think a person could probably do it themselves pretty easy. But I definitely suggest getting the KE hammer pin. I may eventually look into TWR's suggestion of the long S&W anti-rotation pin, if I could figure out the length of it.

Edit, I have the cheap KE safety, not the KE ambi safety. But I assume the KE ambi works on the same principle of an angle ground into the detent pathway.

Looks good! Thanks for the update.

Which upper is on it? I kind of like it without the forward assist.

A little better pic. That is a billet upper and Spear handguard combo from AT3 Tactical.

That’s great it works with the non-ambi safety. I’m going to go that route. From what I can tell below it doesn’t work with the ambi due to clearance but I’m not exactly clear on the issue since I haven’t seen it myself.

I did get the KP15 hammer pin when I placed the order from brownells, thanks to your previous post, thanks BTW




https://www.reddit.com/r/ar15/comments/kvgpdn/kp15_larue_mbt2s_and_ke_arms_ambi_safety/

The cheap KE non-ambi appears to just be a generic milspec safety with the extra angle ground into the detent path. I just put mine together, but it does seem to function perfectly fine with the MBT trigger. Good luck with yours.

PS, the hole for the safety spring and detent is drilled EXACTLY the diameter of the detent. If your safety detent is oversized any (mine was), you may have to turn it down a little to fit the lower.