Finished, all ready for its first range trip to sight in and chronograph my first batches of reloads.

DPMS Lower
Std A2 Receiver Ext and Stock
Std magazine latch/release, bolt catch, take down pins, trigger guard, etc
Geissele G2S Trigger
Magpul MOE+ Grip

Bushmaster 20-inch Upper receiver kit

Vortex Viper HS 2.5-10x44 scope
Vortex Cantilever 30mm mount w/ 2-Inch Offset
Vortex Defender Flip Caps

Quake Contour Sling

Made a few more 450 BM magazines by using a 458 SOCOM follower from CA legal mags.  They cycle dumbie cartridges fairly well, we'll see for real soon.

The response to my thread is overwhelming.  I never realized 450BM was such a popular cartridge around here...   

That’s a good looking hunting rifle! It will put a smile on your face when you shoot it. The Hornady 450B factory ammo that I have shot in my 20inch BM barrel is accurate enough that I didn’t even bother with buying reloading dies.

Thanks!

A buddy knew I was starting to buy parts for a 450BM build and drop over 300 pcs of brass in my lap before I had finished the build.  I had to give reloading it a try.  I manage to get my Dillon 650XL setup to reload 450BM though I don't think I will need that volume capability for such a cartridge.  Another reason I wanted to reload was to try pushing some 300gr XTP/MAG bullet out of it.  Been using that bullet for deer hunting from my muzzle-loader (TC Big Bore 58cal) with good results figured I would try that same bullet in my 450BM.  I would also like to try the 275 gr TSX from Barnes.

It's a nice looking rifle.  I was thinking about building one for Ohio's new reg allowing straight walled cases for deer hunting. But since I've only used a crossbow for the last 7 years, probably won't.  You should think about giving it a camo paint job.

I was happy to see Ohio made 450 Bushmaster legal.  I am from Ohio and my dad still has a farm back there.  Might have to make a trip back to shoot a big Ohio buck.  The bucks down here in Alabama and Tennessee where I do all my hunting now are not nearly as impressive as the Ohio deer I hunted.

I have the 16" BM upper for mine, getting ready for Ohio deer as well. So far I'm impressed. Haven't had chance to stretch out pat 100 yes yet but under that it's the most accurate gun I've ever had for Ohio.

I put a 16" 450 Bushy factory upper on one of my lowers about 5 or so years ago.  It kills our north Arkansas Ozarks white tails just fine.  I found Hornady ammo on sale for half price and loaded up.  I have enough to last probably a lifetime so this is one of the few rounds I don't load.

UPDATE:  I finally shot it last weekend.  This was the range report I wrote up for the reloading section over at 450Bushmaster.net forum.  Figure I would copy it here too.

So I tested my first batch of reloads (first shots ever in my new 450 Bushmaster AR) this past weekend.  All in all the gun ran well.  The only functional issue I had were a few failures to feed from one magazine.  Otherwise all my loads cycled the gun with no jams or failures to eject.

Glad I brought the sissy pad for the butt stock.  I have waffle tread bruise on my should from A2 butt stock and the first fifteen rounds.  Then I wimped out and put the pad on.  My shoulder thanked me.  The recoil was not horrible and for hunting with hunting clothing on I think it would have been fine but shooting over a bench with only a T-shirt on and that A2 butt stock the recoil got to me eventually.
Weather was about 75F and humid, with overcast sky.  My chrono is an old Chrony Alpha Master set about 12 feet in front of the muzzle.  My target was set  just 45 yards down range.  Once I have a load or two I am happy with I will setup for some longer ranges.  I plan on zeroing it at 100 or 150 yards for hunting.
I had three bullets each with three incrementally higher powder charges.  I weight every charge on my scale after it dropped and trickled to meet the load.

First was 230gr FMJ (Armscor)
Pushed by Lil'gun and lit by WSR primers OAL 2.065
These are 5 shot averages except as noted
33gr Avg: 2120fps ES: 165.7 SD: 64.98
35gr Avg: 2186fps ES: 150.5 SD: 86.04 (3-shots)
37gr Avg: 2294fps ES: 102.8 SD: 41.96

That was about what I expected velocity wise maybe even a touch faster than expected from my QuickLoad workup but the extreme spread and standard deviation was pretty bad.  The 33gr group is missing from the picture as it was used to bring the new scope reasonably close to point of aim.

Second was 240gr XTP/MAG Hornady OAL 2.060
Pushed by Lil'gun and lit by WSR primers
These are 5 shot averages except as noted
32gr Avg: 2132fps ES: 30.99 SD: 12.36
34gr Avg: 2203fps ES: 30.12 SD: 13.11
36gr Avg: 2297fps ES: 147.7 SD: 63.77 (4-shots)

So the first two charges were what I would expect for extreme spread and standard deviation what happen on the last one?  You can even see the group size open up on that one.  The flier in the 34gr group was totally on me I flinched on the last shot of the group.

And finally was 300gr XTP/MAG Hornady
Pushed by H110 and lit by WSR primers OAL 2.065
These are 5 shot averages except as noted
30gr Avg: 1653fps ES: 87.73 SD: 34.59
32gr Avg: 1739fps ES: 106.2 SD: 44.08
34gr fat-fingered the chrono and lost the data but this charge shot one of the best groups.

Surprisingly this load was a bit more comfortable to shoot even with the last load that I expect  should have been right at or just above 1800fps with that big heavy 300gr bullet.  More push than the sharpness of the lighter bullets.

That was a lot of rambling and pictures.  My big question, assuming you got this far, is what can I do to tighten up my velocity spread?  I would like to see that extreme spread well under 50 fps if I can.  First thing that comes to my mind is I did not crimp enough.  I used a relatively light crimp on these first loads since 450BM headspaces of the mouth.  I may have overdone(underdone?) that.  My crimp was roughly .476 but I was afraid to crimp too heavily especially with the cannelure on the XTP.  What other things could be causing such large velocity spread?  Thanks!

Its popular enough for starline to supply brass. Uses small rifle primer.

It's good to see Starline getting on board.  There is a thread about Starline over at 450Bustmaster.net about this new brass.

I wish they has stayed with larger rifle primers when the made 450 Bushmaster a SAAMI cartridge.  The parent case 284 Winchester and the earlier version 45 Professional both used larger primers.  Lighting 30+ grain of H110/W296 works best with hot primers.  Large Magnum Primers would have worked well in this cartridge.

For anyone running the A2 stocks on these big bores, the Limbsaver pad #10401 will fit these stocks almost perfectly. There is just a tiny bit of overhang side to side, not enough to worry about. The holes line up and the look much better than the slip on kind. Really helps take the sting out. Email me and I can send a pic of mine if you like.