Doing my first build.

I have a Mega Gator stripped lower.

Installed everything (Stag LPK) with no problems except the buffer tube.

It's a brand new Magpul CTR (milspec) bought from Denny's.

Threads on the buffer tube look great.

Threads on the lower receiver look great.

Buffer tube starts threading into the lower smoothly and easily, by hand, until I get about 1/4 turn.

At 1/4 turn it takes a lot of effort to turn and at about 3/4 turn I would really have to force it to continue.

When I backed it out and inspected the threads they look fine except some of the black (anodizing?) has come off from both the tube and the lower. (much less from the lower).

My questions are:

1. Do I need to lube the threads on the tube ? (there is already a light coat of oil on the threads of the buffer tube. Came like that in the box)

2. Should I be able to thread the buffer tube all the way in by hand?

3. If I should be able to thread it all the way by hand should it be easy, tough, really tough (have to strain to turn it)?

4. Is there some type of tool that I should be using to turn the buffer tube?

Any help or insight would be helpful and appreciated.

I only have 1 build under my belt,  I used a DPMS lower and the 6-pos stock and tube from a Del-Ton kit.

My tube screwed in easily and smoothly, did not require any lube or special tools.  BUT when i got it in far enough so it captured the buffer plunger the tube was blocking the upper from fitting on.  Had to file a small amount of material off the tube


Perhaps a reayy small burr or a small spot where the threads are too wide on either the tube or reciever.

Maybe find a tap and die and run the threads?

Good Luck

Where did the actual tube come from?  I just built a lower with an LMT tube and it screwed in fine, no force required.  

Sounds like something is out of spec...I don't think I would want to ruin the lower.  

The tube came with the Magpul CTR stock, as a complete kit, in the box from Denny's guns.

Sometimes the anodized finish is real rough, is this the case on your threads?

The threads on both the lower and tube look really good and smooth.

The anodizing on the lower seems to be "thick" for lack of a better term.

I think that's what is making it tough to turn but I don't want to jack my brand new lower up forcing that tube.

Quoted: 1. Do I need to lube the threads on the tube ?

Try some grease on the threads. Any old bearing grease will do.

Pictures:

You can see where some of the anodizing is coming off the threads.

Before I tried threading the tube on both the tube and receiver threads were perfectly black.

The tube should screw in very easily, by hand.

I would lube it up good like Quib said and try it again. If it still won't go then I would hazard something, the receiver or the buffer tube, is out of spec.

Quoted: The tube should screw in very easily, by hand. I would lube it up good like Quib said and try it again. If it still won't go then I would hazard something, the receiver or the buffer tube, is out of spec.

Thanks,

I'm going to get some grease in the morning and try that.

I really think it is the black anodizing on the lower's threads. It's really smooth but seems "thick".

Quoted: I'm going to get some grease in the morning and try that. I really think it is the black anodizing on the lower's threads. It's really smooth but seems "thick".

Anodizing will add to the dimensional thickness of finished parts. I do not remember off hand approximately how much though.
If you try to screw two fairly dry, freshly anodized parts together you may encounter this problem of “dry locking” due to the roughness of the surfaces. I’ll call it “dry locking” but I think there is an actual industry term for this.
I’ve encountered this a lot with aluminum flashlights and their caps or lamp heads. I always apply a bit of industrial petrolatum to the threads.
I would try the grease and try working the tube in a few threads at a time.

Got some grease today and lubed it up good.

I worked it back and forth slowly and am about 1/2 way to where I need to be with about 20 minutes work.

I backed the tube all the way out several times, wiped the grease off the threads and everything looks just like it did when I started. No damage to the threads, no cross threading etc.

I'm thinking now it's extremely close tolerances on the Magpul tube and the Mega lower.

Calling it quits for tonight and figure with 20-30 minutes work tomorrow I should have it.

I'm waiting for my telestock wrench to come in anyway so until it does it's no big deal.

Thanks for the tips.

I will post again when I got it conquered.

Quoted: Quoted: Anodizing will add to the dimensional thickness of finished parts. I do not remember off hand approximately how much though. Regular type II anodizing is 0.0002" to 0.0004" "Hard" anodizing is around 0.0020 to 0.0030" buildup. You typically do NOT have to account for type II anodizing, but you do have to account for hard anodizing.

That's a BIG difference between two and four tenth's of a thou for Type two and two to three thousandths for hard anodizing--how do you tell which anodizing you have by visuals? Or can you tell?

Got it!!!

After greasing it up and working the tube in and out yesterday I got it nearly all the way in  but still needed 1/2 a turn.  

Today when my son got home from school I had him hold the lower while I turned the tube. (should have done this to begin with)

I don't think I ever have to worry about that tube backing out by itself.

After all is said and done I think it was a matter of the thickness of the anodizing in the lower threads.

Should have my upper in from Denny next week.

Thanks again for the tips.

I learned a lot on this first lower build.

Good deal!

Obligatory Pic:

Looks good!

Quoted: Looks good!

Thanks.

Can't wait to get the upper. Hopefully by next week!!!!!

I'm going to swap out the pistol grip eventually. Not sure which grip I'm going to go with so no hurry.

I really like those MagPul CTR's, and thanks to guys like you, I keep seeing pic's of them as subtle reminders that I need to buy one.  Thanks for your help in me firing up that plastic card again.  Since I've been hanging out here, that card is looking worse every day.

Oh, that looks sweet! Glad you got it on there.