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

This looks kind of interesting.


The history of polymer lowers is really interesting. Maybe its time has arrived?
This guy has some interesting videos.

Why?

I've had a stripped lower on order since February. Going to use it for a 16" build if I ever get it.

If you watch the videos, the main advantages cited are cost, weight, and reduction in the number of parts.

I've never really considered weight a factor in an AR. Having a lighter buttstock may make the gun unbalanced if you put any kind of beefy barrel or stiffer long railed forearm on it.

Yeah, these lowers are pretty much intended for pencil barrels. I have a Green Mountain 16" pencil barrel waiting on mine if it ever comes.

I think the guys behind the concept are pushing 16" Faxon pencil barrels as a standard build.

I’m going to pick up a couple. I like the idea. I do care how much my ARs weigh. Bargain compared to building a standard stripped lower and adding the RE and stock.

On this Brownell's video on the molding process they claim they can pump one out every 60 seconds compared to 35 minutes for milling a receiver. A technology change like this could have a big impact.

That's huge.

Now factor not making a buffer tube, pistol grip, or the whole annodizing
process aluminum needs.

The time to remove flashing is probably around 2 minutes if CNC is used.
Less if robotics were used to feed the mill.

Finally got my stripped lower today. Been on order since February. Weighs 18.5 ounces, as delivered. Hope to start sticking lower parts in it next week.

I use Tennessee Arms lowers if I want a light weight. It's the same polymer but there is a standard M4 tube and a collapsible butt stock. I have never weighed one so I don't know if I can beat auk1124's 18.5 ounces. I guess I should find a scale and find out.

None the less this is a good idea that has been improved on with modern tools, techniques and materials. As I recall the former maker built it out of carbon fiber and they had a problem breaking at the buffer tube.

kwg

The two previous iterations were all polymer and did not break at the buffer tube. This is basically just an evolution of the original design.

STarting in the early 2000's there was a company that I think changed it's name several times that was building the complete lowers and they would many times break at the tube or just in front of it. As I recall Cavalry Arms was the first successful version because they made their lowers out of polymer. The name of the company escapes me so I can't google it.

Anyway, the idea has come full circle and now that Brownell's has become involved I'm sure the finished product will now be successful.
kwg

I picked this up from a November 2008 entry on ARFCOM

STAY AWAY....

Hesse change to Vulcan. Then started Blackthorne. Now they are Velocity Firearms.

They keep changing their name but the lack of Quality stays the same.

I have redone many barreled upper that people got from Black thorne they seem to be put toghther by a monkey in the back room. And the monkey must have been drunk..

Cav Arms from Mesa AZ made the original monolithic versions. When they went under the molds went to GWACS in Tulsa, basically the same as the last Cav version. This new KE version looks like it is somewhat evolved but then I can't see the internals. Seems like everyone that tried to make a regular lower out of polymer found out a regular buffer tube caused too much stress at the rear, which seems to be avoided with the monolithic design and some judicious thickening in that area. .

Well, Brownells has their reputation on the line. I'm sure they did their home work and have a good product.

kwg

Two minor issues (quirks?) with this lower that I wasn't entirely aware of. There are two semi-proprietary lower parts needed. I say "semi-proprietary" because you can in fact use milspec parts, but it doesn't sound like it would necessarily be ideal.

1. The body of the lower is thicker at the location of the hammer pin. A milspec hammer pin would apparently work, but not be flush with the lower on either side. KE Arms makes an extra-wide hammer pin, available on Brownells or KE Arms websites.

2. I haven't looked at it close enough to figure out exactly why, but according to the instructions that come with the lower, a standard milspec safety that is installed in the lower will be permanent. Once in there, you can't remove it. KE Arms sells a special safety selector on their website that apparently has a special groove milled in it, that allows it to be removed. Brownells doesn't appear to have this special removable safety on their website for some reason.

I don't like the thought of putting a safety in it that I can't remove later, so I have a removable safety and an extra wide hammer pin on order from the KE Arms website. So once again I am playing the waiting game. Hopefully it won't be months to get these.

If I run into any more issues like this, I will update in case anyone is interested. Anyone thinking about ordering one of these should probably decide if they want the wide hammer pin and removable safety, and go ahead and order them at the same time they order their lower.

Gotta wonder why those parts aren't just included,
with a price adjustment.

They come in a complete lower. Poster purchased a stripped.

True, I failed to make that clear. I note KE Arms also sells a KP-15 specific lower parts kit on their website for 70 bucks, which in hindsight would probably be the way to go with one of these stripped lowers.

What do you think of the grip? Is it comparable to another type of grip you're familiar with?

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.