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Author Topic: Building an AR-15 in 450 Bushmaster  (Read 7506 times)

Offline MichiganLouie

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Re: Building an AR-15 in 450 Bushmaster
« Reply #30 on: March 10, 2017, 07:22:13 AM »
Haven't read much about the cerakote, but how long do you have to bake the stuff?  I know for powder coating cast bullets, you have to maintain 400 deg for 15-20 minutes, or at least till you see the powder coating turn shiny. 
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Offline MI_Bowhunter

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Re: Building an AR-15 in 450 Bushmaster
« Reply #31 on: March 10, 2017, 07:32:17 AM »
Haven't read much about the cerakote, but how long do you have to bake the stuff?  I know for powder coating cast bullets, you have to maintain 400 deg for 15-20 minutes, or at least till you see the powder coating turn shiny.
Normal time is 2 hours at 250deg or if you must hurry the process you can do a fast cure at 300deg for 45 minutes.
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Offline MI_Bowhunter

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Re: Building an AR-15 in 450 Bushmaster
« Reply #32 on: March 11, 2017, 05:57:44 PM »


Started working on my 80% lower today









These are the side pates for the jig. The upper screws go thropugh the take down pin holes.



This is the jig used to drill holes down through the main and rear pocket.



These are the templates for the main pocket, rear pocket and trigger hole.  They also have the depth gauge for the holes as well as the mill bit.



Holes drilled into lower using jig.  These holes help facilitate the milling process.  I had a heck of a time drilling these holes.  I am  not used to working with aluminum but I went through 2 drill bits and it took a long time to drill these holes.



Jig set up for milling the main pocket.



The large top plate gives some surface for the router to sit stable.



Router set up and ready to start.

I am a little disappointed.  I only milled down about 1/4 of an inch before the bit stopped cutting.   I'm not sure If I was trying to take to much each pass or if I was just going to fast but I got to a point where it just bounced around and would not cut anything.

Between the problems I had drilling the holes and the issues with the mill I can say that this process is not as easy as they make it look in the video.



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Offline MI_Bowhunter

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Re: Building an AR-15 in 450 Bushmaster
« Reply #33 on: March 12, 2017, 12:59:21 AM »
I was letting the bit get to hot and it got clogged up with aluminum.  I cleaned it out and was able to continue on.I found I was trying to take too much off in each pass.     My router has a dial gauge that allows pretty precise adjustment to the bit depth. I ended up dropping the bit 1/32 each pass after I got the bit cleaned out and it worked really good.   It took a while but it cut clean and it greatly reduced the jumps and stutters.   I think the most difficult pass was the last as it was cutting the entire floor of the pocket as I was at the bottom of the pilot holes.

I think the problem I had drilling those holes was due to going to fast and getting the aluminum to hot.

https://www.youtube.com/watch?v=c4A-km5CqD4&feature=youtu.be

Here is a small portion of the milling process.  Darn I hate my voice on recordings, not at all how I hear myself.





Got the main pocket milled out.





Got the rear pocket milled out.  I did have to remove the rear screw from the jig for this, I had already reinstalled it by the time I took the picture.



Drilling out the hole that will be used to start milling out the trigger opening.



Ready to mill out the trigger port.



Trigger port opened up.









After drilling the hold for the trigger/hammer pins and the safety lever it's all done.

Needs just a little sanding to smooth out some of the edges but as far as milling and drilling it's complete.

This was an interesting endeavor.
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Offline Madgomer

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Re: Building an AR-15 in 450 Bushmaster
« Reply #34 on: March 12, 2017, 06:51:38 PM »
Thanks for the continued reports - aluminum can certainly be finicky to machine, gotta be patient to keep from getting it hot & smeary.
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Offline MI_Bowhunter

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Re: Building an AR-15 in 450 Bushmaster
« Reply #35 on: March 12, 2017, 07:18:41 PM »
Thanks for the continued reports - aluminum can certainly be finicky to machine, gotta be patient to keep from getting it hot & smeary.
Now you tell me. LOL
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Offline MI_Bowhunter

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Re: Building an AR-15 in 450 Bushmaster
« Reply #36 on: March 13, 2017, 09:29:30 AM »
I tried to do a bit of a function check on the lower and I am glad I did.   When the trigger is installed there is no movement whatsoever.  I will have to put it back into the jig and remove a little bit more from the floor of the main pocket.


Edit:   Measured it.   My depth should be 1.250" and I am right at 1.1945.   Just need to lock it back into the jig and fine tune it.
« Last Edit: March 13, 2017, 11:35:36 AM by MI_Bowhunter »
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Offline MI_Bowhunter

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Re: Building an AR-15 in 450 Bushmaster
« Reply #37 on: March 13, 2017, 04:04:49 PM »
Adjusted the depth so the trigger works now.  I overshot a bit this time but it still seems to function good.



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Offline Madgomer

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Re: Building an AR-15 in 450 Bushmaster
« Reply #38 on: March 13, 2017, 04:08:49 PM »
Looks pretty good with that milled external finish on it - maybe just round off the corners & clear coat it?
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Offline MI_Bowhunter

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Re: Building an AR-15 in 450 Bushmaster
« Reply #39 on: March 13, 2017, 10:21:09 PM »
Looks pretty good with that milled external finish on it - maybe just round off the corners & clear coat it?
This one will be painted but I also really like the machined look and will be making one at some point that leaves it in that state.
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Offline Madgomer

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Re: Building an AR-15 in 450 Bushmaster
« Reply #40 on: March 14, 2017, 06:55:50 PM »
I ran into some minor issues on my second build with a 100% factory lower, so have started doing basic checks on everything before I drive in the roll pins (they're too much of a pain to remove).  I use small drill bits as temporary pins to make sure everything is fitting up right, then drive in the pins.  I think you'll want to check things out carefully before you paint it in order to avoid having to come back & touch it up.
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Offline MI_Bowhunter

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Re: Building an AR-15 in 450 Bushmaster
« Reply #41 on: March 14, 2017, 09:07:28 PM »
One of my concerns if that the paint will close up the tolerances a bit.  Anything that fits quite snug now will not fit at all after a cote of Cerakote.

I have not fit test everything but the front pivot pin already fits very tight.  I will probably ream it out a tad as the paint will tighten it back up.
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Offline MI_Bowhunter

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Re: Building an AR-15 in 450 Bushmaster
« Reply #42 on: March 15, 2017, 08:02:32 AM »
Looks pretty good with that milled external finish on it - maybe just round off the corners & clear coat it?

Thinking it would go good with this upper:

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Offline Madgomer

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Re: Building an AR-15 in 450 Bushmaster
« Reply #43 on: March 15, 2017, 07:45:01 PM »
Yeah, I did a rattle can camo job on one of my builds.  It looks nice enough (didn't spring for Cerakote) but in hindsight there are a few things I would mask off more carefully.  The oblong hole for the mag release and the inside surfaces of the slot for the bolt release would be a couple of those.  When I did it I just closed the dust cover, put foam in the magwell and charging handle openings (left the CH black), and in the trigger opening.  I had the receiver pins installed.  Also masked off the rail to make sure I had a good metal to metal fit when I mounted sights or optics.  Given that you need to bake the Cerakote you probably won't want to have everything installed but you could mask those surfaces to avoid the paint issues (although I guess that would leave raw aluminum showing which you may not want).
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Offline MI_Bowhunter

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Re: Building an AR-15 in 450 Bushmaster
« Reply #44 on: March 15, 2017, 08:07:54 PM »
I would like to coat the entire lower with the Cerakote.

I was watching a video where a guy got too much paint buildup around the top of the receiver when trying to get paint in the magwell and trigger pockets. His two receivers would not mate up just due to tight tolerances and excess paint layers between.

 I'm thinking of masking arount the openings then remove the tape to continue painting the outside.

This is my 2nd go around with Cerakote. I painted a shotgun a few years ago. This time I plan on using an airbrush as opposed to the HVLP spray gun I used with the previous project. I am hoping to get a little less overspray and even better control with this approach.
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