Gunsmithing First AR-15 Build Questions

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Grumulkin

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Feb 5, 2008
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Baltimore, OH
www.orchardphoto.com
#1
I've just assembled my first AR-15 lower and have some questions:

1. On the bottom of the receiver are 2 screw holes. One accepts the long screw for the pistol grip. There is another hole right next to it with a large Allen head screw in it. It doesn't appear to serve any particular purpose in my case but maybe I'm missing something. What is it for?

2. Every thing in the lower appears to work as it should but I have one spring left which is a coil spring. I'm thinking my DPMS lower parts kit contained two springs for the bolt release lever. One of the springs fit its recess well while the other was slightly larger on one end than the other and didn't work. Information on this would be appreciated.

I watched Larry Crow's entire video on AR-15 assembly and disassembly twice and some parts more than that and couldn't find anything in it that described installing that lever though everything else was well explained.

3. I installed a JP trigger in my stripped lower which is working fine but the instructions recommend setting the screws with Locktite 271 which is meant for permanent placement of screws. Is this a good idea or should I go with a medium or low strength product like Locktite 222 or 242? I kind of like to be able to take things apart in the future if I need to.

Now, I have only a few months to wait until I receive the Rock River uppers I ordered in March and I'll be like a pig in mud.
 
#4
Re: First AR-15 Build Questions

If by selector you mean some part meant to be used with a full auto version that could be.

I think the extra spring may be for the front sight which my new upper won't have.

I do have a schematic very similar to the one the link is posted to and it doesn't show the hole/screw I'm referring to.
 
#6
Re: First AR-15 Build Questions

If you are not useing the trigger that came with the kit your extra one is the disconnector spring. As for the allen screw its for adjusting pre travel on your trigger. I'm not sure if it will work on a JP trigger, I've never tried one.
 
#7
Re: First AR-15 Build Questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Grumulkin</div><div class="ubbcode-body">I've just assembled my first AR-15 lower and have some questions:

1. On the bottom of the receiver are 2 screw holes. One accepts the long screw for the pistol grip. There is another hole right next to it with a large Allen head screw in it. It doesn't appear to serve any particular purpose in my case but maybe I'm missing something. What is it for?

2. Every thing in the lower appears to work as it should but I have one spring left which is a coil spring. I'm thinking my DPMS lower parts kit contained two springs for the bolt release lever. One of the springs fit its recess well while the other was slightly larger on one end than the other and didn't work. Information on this would be appreciated.

I watched Larry Crow's entire video on AR-15 assembly and disassembly twice and some parts more than that and couldn't find anything in it that described installing that lever though everything else was well explained.

3. I installed a JP trigger in my stripped lower which is working fine but the instructions recommend setting the screws with Locktite 271 which is meant for permanent placement of screws. Is this a good idea or should I go with a medium or low strength product like Locktite 222 or 242? I kind of like to be able to take things apart in the future if I need to.

Now, I have only a few months to wait until I receive the Rock River uppers I ordered in March and I'll be like a pig in mud. </div></div>

You should take a few pictures, then circle the two hole in a image editing program using two colors and provide a key for us to check what you are seeing.

You will not have extra parts after you finish putting together with a DPMS parts kit, and the description of the two holes does not sound familiar so pictures please.
 
#8
Re: First AR-15 Build Questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Grumulkin</div><div class="ubbcode-body">If by selector you mean some part meant to be used with a full auto version that could be.

I think the extra spring may be for the front sight which my new upper won't have.

I do have a schematic very similar to the one the link is posted to and it doesn't show the hole/screw I'm referring to.</div></div>

"Selector" is what you think of as the safety, even on your semi AR.

Think about it, you can select two modes; safe and semi.
 
#9
Re: First AR-15 Build Questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: will67</div><div class="ubbcode-body">If you are not useing the trigger that came with the kit your extra one is the disconnector spring. As for the allen screw its for adjusting pre travel on your trigger. I'm not sure if it will work on a JP trigger, I've never tried one. </div></div>

That would make sense since I'm using a JP trigger that came with springs and its own adjustment screws; thanks.

Now what about the Locktite? Is there a good reason to use the stuff that holds forever or would it be better to use the low or medium strength stuff?
 
#10
Re: First AR-15 Build Questions

What kind of lower did you get. I know there is a brand, and I can't think of which one, that has a allen head screw there that acts as a "accuwedge" sort of. It takes the "play" out of the upper and lower.
 
#11
Re: First AR-15 Build Questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JonLSU</div><div class="ubbcode-body">What kind of lower did you get. I know there is a brand, and I can't think of which one, that has a allen head screw there that acts as a "accuwedge" sort of. It takes the "play" out of the upper and lower. </div></div>

I was going to say the same thing. I have heard of some lowers having that feature.

As for your extra screw, if it looks like the one used on your trigger than it may also be a spring used for the bolt catch. Are you sure you put in your bolt catch spring?
 
#12
Re: First AR-15 Build Questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Grumulkin</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: will67</div><div class="ubbcode-body">If you are not useing the trigger that came with the kit your extra one is the disconnector spring. As for the allen screw its for adjusting pre travel on your trigger. I'm not sure if it will work on a JP trigger, I've never tried one. </div></div>

That would make sense since I'm using a JP trigger that came with springs and its own adjustment screws; thanks.

Now what about the Locktite? Is there a good reason to use the stuff that holds forever or would it be better to use the low or medium strength stuff? </div></div>

When using a JP trigger--FOLLOW JP'S DIRECTIONS! Once a trigger is set up for a particular lower--THAT IS IT. You will not be using that trigger on another lower. Once it is set locktite it in place. If you ever need to take it apart, it just takes a little heat. But there is no reason to take it apart.
 
#15
Re: First AR-15 Build Questions

I just assembled two Superior Arms and they both have an allen set screw about 1/4" to the rear of the pistol grip screw. With the standard trigger they are used for sear engagement. If turned in to far you will not be able to put the safety on.

Jim C
 
#16
Re: First AR-15 Build Questions

There are also lowers that use an allen set screw behind the pistol grip screw to adjust the amount of take-up on the trigger. The mfr's name escapes me at the moment.
Pic would show if its the "receiver play eliminator" or "trigger takeup adjuster",
 
#17
Re: First AR-15 Build Questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Grumulkin</div><div class="ubbcode-body">I've just assembled my first AR-15 lower and have some questions:

1. On the bottom of the receiver are 2 screw holes. One accepts the long screw for the pistol grip. There is another hole right next to it with a large Allen head screw in it. It doesn't appear to serve any particular purpose in my case but maybe I'm missing something. What is it for? <span style="color: #FF0000"> It is for removing the initial takeup from the trigger. As mentioned in another post, if it is adjusted too tight, you won't be able to set the safety.</span>

2. Every thing in the lower appears to work as it should but I have one spring left which is a coil spring. I'm thinking my DPMS lower parts kit contained two springs for the bolt release lever. One of the springs fit its recess well while the other was slightly larger on one end than the other and didn't work. Information on this would be appreciated. <span style="color: #FF0000"> The short spring that is larger on one end is for the disconnector and fits in the trigger. If you place the larger end in the trigger, then it won't fall out. There is only one spring for the bolt release. It is about the same size as the disconnector spring. That's how I tell them apart. The straight one = bolt release, the tapered one, disconnector.</span>

I watched Larry Crow's entire video on AR-15 assembly and disassembly twice and some parts more than that and couldn't find anything in it that described installing that lever though everything else was well explained. <span style="color: #FF0000"> Just remember, straight spring in first, the odd-shaped pin that partially fits inside the spring, then the bolt release and roll pin to hold everything in place. BTW, when tapping in that roll pin, put a piece of thick tape on the side of the receiver to stop any scratches.</span>

3. I installed a JP trigger in my stripped lower which is working fine but the instructions recommend setting the screws with Locktite 271 which is meant for permanent placement of screws. Is this a good idea or should I go with a medium or low strength product like Locktite 222 or 242? I kind of like to be able to take things apart in the future if I need to. <span style="color: #FF0000"> I usually use blue loctite for things that I might want to take apart later and red for permanent applications.</span>

</div></div>
 
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