by Rob Kay and RN Price
In the last column we began the actual build of the lower receivers. Let’s continue where we left off.
Placing the Front Pivot Pin
There are a number of ways to do this. I think the Cheaper than Dirt folks (see video) did a good job. They used an allen wrench to keep the detent at bay. The way we did it (using a hobby knife to hold down the detent) certainly worked, but if your knife slips, the detent goes flying across the room into oblivion. These tiny suckers can be hard to find. As the video depicts, just drop in the spring and force the detent into the orifice behind the spring with the pliers. It’s best to use needle nosed pliers to insert the detent. Don’t even bother to try with your fingers. Make sure, if only one end of the detent is tapered, to orient that end away from the spring.
If you’re really worried about parts flying into the great abyss, both Brownells and Wheeler Engineering offer special pivot pin installation tools. While you’re in the market for tools, you’ll also want to pick up a AR combo type wrench to tighten up the buffer tube nut and the barrel. Wheeler Engineering has a AR combo tool if you can find it in stock.
If you’re going to do this drill on a regular basis, you’ll want to pick these items for your home armorer’s kit.
https://www.youtube.com/watch?v=jp9lbQiUn4s
Next you’ll need to add the hammer assembly. I had difficulty doing this. The spring is quite strong but as always, there’s a technique. Just make sure you keep to receiver immobile as you lay down the two hammer springs and align the hole (once again with a punch) so that you can pop in the hammer pin from the right side of the receiver. Tap it and bingo, you’re there.
https://www.youtube.com/watch?v=OPomHJtqotU
Installation of the Safety Selector Lever
Dave, the head of sales at Franklin Armory, said that they had received some LPK parts that were out of spec and surmised the detent was the culprit. He suggested gently sanding the edge of the flat “bottom” of the detent around the edges to provide more space. I sanded and over the course of an hour tried again and again to get the part to fit properly. I must have tried half a dozen times. It always seemed to stick. After a certain point (and obviously too much sanding) the part was irredeemable. Dave at Franklin responded by sending three selector detents.
For good measure I also ordered one from Windham Weaponry in Windham, Maine–a company that has great service.
One of the parts was bound to work.
One out of the three did in fact work, but not without some coaxing. The safety did move at first so I took off the grip and turned the lever so that it was able to brush against the detent without the force of the spring. After a few back and forth movements between “safe” and “fire”I put the grip back on and it was able to move the selector.
Next, pop the retainer over the spring and drop it in the hole in the receiver. Now turn the retainer while simultaneously holding down the retainer, until it holds the detent in place. Note that you don’t want to touch the center part of the pin and impede its movement. Insert the take down pin detent and then the takedown detent spring. Then tighten the stock in place over the spring. If you cock the hammer back (set the safety selector to “on” so that you don’t inadvertently drop the hammer), it will be easier to do. You’re going to need a special wrench to tighten the castle nut. Wheeler Engineering makes a reasonably priced combo wrench that can be used for this task. Once you tighten the nut, you’re done.
https://www.youtube.com/watch?v=bpsQqZIKHPs
Postscript
Given that we had parts kits from different manufacturers, we tried a modest experiment. We wondered how the Stag LPK would fit on the CMMG and vice versa. We weren’t expecting any problems–after all these items are built to spec and presumably most of the manufacturers by parts from OEMs who supply everyone. Our hunch was correct, everything fit splendidly. The only issue we had with any of the parts was with the aforementioned Selector detent from Franklin. As mentioned above, that problem was rectified with a new part.
We needed buffer tubes for this build and ended up with units from several different manufacturers–Stag, Vltor and Palmetto State Armory . All fit correctly with no installation problems. The buffer tube from Palmetto State Armory was the only one I had to order separately. (It didn’t come with a lower or with the buttstock). It was one of the only companies that seemed to have buffer tubes in stock. I was very happy with both the product and their service. It was sent to me in about a week, which was pretty amazing considering the current environment.
Many thanks again to Windham Weaponry, which produces some well-reviewed rifles and, sells a comprehensive selection of AR parts. They are great to deal with. Thanks also to Franklin Armory, CMMG and Stag Arms for their cooperation in helping us put together this story.
All three companies make very fine rifles.
As an added reference to building an AR 15 we suggest you look at Brownells, which has an excellent series of videos an other learning resources. Here’s a good place to start: https://www.brownells.com/.aspx/lid=11011/learn/
We’re not finished yet. In our next article we’ll look at the completed lowers in detail and take them out to the range.
Stay tuned.
Questions? Comments? Contact us directly at ontargethawaii@gmail.com
Hello Rob!
These series are very interesting and I learn a lot. I will like to know what is your opinion of the LPK triggers. A few people in the IE state not to use it and buy a two stage trigger. What do you think?
Jesus Franco
San Juan, PR
Aloha Jesus,
Sorry about the late response. LPK triggers, from what we've seen, really vary in quality. They are by definition, "Milspec" which means the pull will be around 6 lbs. The ones we tested were about that. So far, the best we've found was the Stag trigger which had a nice crisp action. If you want to upgrade you can always drop in something like a Timney or another aftermarket product. There are differences between the two stage and the single stage trigger. It really depends on what your needs are. Your best best is to find someone who has one, so that you can see how it feels. It's all very subjective. FWIW the single stage on the Franklin Arms kit (which is a custom kit) was excellent at 4.5 lbs but it's not stock. We're going to do a round up on LPK triggers in an upcoming story. Stay tuned!
That looks like a strange weapon, but I admit I'm not a connoisseur.
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