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Thread: Finally finished my 450 BM Dissy retro build

  1. #1
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    Finally finished my 450 BM Dissy retro build

    Just ended up a long Sunday in the shop finishing up an idea I had a long time ago. I am not a machinist, so I had to overcome some hurdles to get there, but I got there. I had been planning a 450 Bushmaster build for a while and when CDNN had their 20" original Bushmaster barrels on sale for $99 I jumped on it. When I got the barrel and put the mic on it my mind went into high gear. I have always loved the look of a Dissy and when the caliper read .745" at the muzzle my mind went into overdrive. Found an ad from someone selling some A2 FSB's and the ball was rolling. The big holdup was an upper, as we all know all receivers are slim pickins. I posted a WTB ad and damned if a fellow didn't have an Aero assembled upper he didn't need, was hoping for an XL butyou take what you can get. I got a set of Bushmaster rifle length A2 handguards from CDNN as well as the gas tube. The AGB I had on hand and the triangle handguard cap I got from BA for $3 shipped (not sure how they could make out on that). I grabbed a new Aero carry handle, and an A2 flash hider from Hilltop Gun Shop (another hard to find part) and now all there was left was to find the time.

    The biggest hurdle was cutting and threading the barrel for the A2 flash hider that was threaded 11/16"x24 TPI. Cutting and squaring the crown would be the easy part. If the FH would have been 3/4"x24 TPI it would have been a breeze, but alas my life story. I went ebay'ing and for a total of $27 I had a 3/4"x24 TPI and an 11/16"x24 TPI die headed my way. My plan was to thread the barrel with the 3/4"x24 die first and then file down the major diameter thread til there was just a trace of minor diameter left and then run the 11/16"x24 die behind it. After filing down the 3/4" threading I was still about .012" over major diameter for the 11/16"x24 die but once I got a hook I was able to crawl along to the shoulder that I had filed with the help of a piece of conduit serving as a stop.

    The FSB had been pinned prevoiusly, so I threaded the existing holes for #8x32 set screws, but before I threaded the holes I used them as drill guides to drill flats partially into the barrel to give the set screws a better purchase. This also makes the FSB windage adjustable as I can loosen one side and tighten the other in case I missed the eyeball on the FSB. I threaded the hole under the sling swivel as well to serve as a tensioner. I attached the handguard cap to the GB via #10x32 screw.

    I was holding out for an XL upper so I wouldn't have to open up the one I had but none showed so I went to work on it with the (ahem) "rotary tool" and it came out really nice.

    Anyway, here she is. Far and a way my most prideful build given all that went into her. I took a pile of pictures of the process so would be happy to share the story if there is a proper place for it. It was a long day, the G hit the spot.



    Under the hood:



    Oops, almost forgot the sling swivel:



    I have the Aero stripped lower that will sport an A2 stock and pistol grip to keep in the moment.
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    Last edited by s4s4u; 05-18-21 at 13:52. Reason: grammar

  2. #2
    Join Date
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    Wow. Persistence and dedication.

    Looks great. Have you shot it??
    A true "Gun Guy" (or gal) should have familiarity and a modicum of proficiency with most all firearms platforms.

  3. #3
    Join Date
    Aug 2017
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    Lowcountry, SC.
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    Awesome rifle. I, too, have a thing for mock dissy’s.

  4. #4
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    Quote Originally Posted by gaijin View Post
    Wow. Persistence and dedication.

    Looks great. Have you shot it??

    Thanks. Haven't had the chance to shoot yet. Just finished it up late Sunday. Hopefully soon.

  5. #5
    Join Date
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    Definitely a two thumbs up ! ! !

  6. #6
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    Mar 2021
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    Finally got the lower parts for it and finished up. Still haven't had time to shoot yet. Hope soon. I have loaded up a ladder starting @ 38 grains of lil gun and a 250 to send.
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    Last edited by s4s4u; 09-08-21 at 22:42.

  7. #7
    Join Date
    Jun 2015
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    Indiana
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    Man, that's a BEAST! Looks better than I could do...great job!
    Good night Chesty...wherever you are.

  8. #8
    Join Date
    Aug 2021
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    South Louisiana
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    Nice! That’s a pretty clean looking rifle. I’ve never shot a 450 BM, but would really like to try one out.

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