Been working on this AR-15 build and loads for about 6 months now. It is basically a 358 Winchester in a little light weight AR-15 Carbine. The first version with a polymer lower and 16.5 inch barrel weighed in at 6.4 pounds even with its bull barrel. I soon found it necessary to add a recoil pad, steel tactical rings, a RRA Operator forend and a heavy tactical scope to bring its fighting weight up to 11 pounds so I could stand to shoot 50 rounds at a time.

It works with a full loaded PRI 6.8 mag with most of the front rib removed, 10 for 10 and 15 for 15.

The case is the 358 MGP, a rimless 357 Harrett based on the 6.8 SPC cartridge necked up to 35 caliber with the shoulder moved forward to about 50% of the neck. The case itself was developed by Mike Plinkington of www.MGPCustoms.com whom has barrels and dies for sale on the net. It has a ferocious muzzle blast, sounds like a cannon. The 16.5 inch stainless barrel has a 1-22 twist rate that is surprisingly accurate (.5 to .75 inches at 100) for the 200 to 115s, the groove diameter is 357 for pistol bullet use and the bore diameter is 350 so you can shoot 9mm, 357 and 358 bullets in it. It shoots cast bullets real well, I use powder coated 200gr hard cast to fireform the brass at 2,400 without any leading.

It is my truck gun, I figure it will stop a truck pretty easy, with a 200gr at 2,400 fps or a 180gr at 2,500fps. Plenty of folks are now using the cartridge on hogs and bear I build my 358 AR for a daylight hog gun at my farm.

These are some stats no group at any load level over 1.2 inches. The cartridge works with Lil Gun, 4227, 1680, H-110 and 296 The use of the AR action allows the cartridge to exceed the 357 Harrett stats by almost 50% with less powder and equals mid 358 Win loads found on the Hodgdon site with less powder an 8 inches less barrel.
200 RCBS Hard Cast powder coated 2,400
200 Horn FTX 2,370
200 Rem RN 2,350
180 Horn SSP 2,500
140 Hprn FTX 2,720
125 Rem JHP 2,780

This is a cartridge lineup and a picture of the new AR. Just got in some 180 Hornady JHP Power Shock bullets to try.
Ed

That's cool! It's got the wheels in my head turning and that's not good for my bank account...

I just got rid of my 458 Socom and I've still got my 6.8 laying around, so I really don't need a 358 MGP...

What about the 450 Bushmaster?:smokin: the OLD THUMPER by Cooper?

Customer Reviews for BUSHMASTER Bushmaster® .450 Upper Complete Kit


Bushmaster® .450 Upper Complete Kit


This product is no longer available. Continue shopping at Cabela's.

Bushmaster® .450 Upper Complete Kit

It’s called "Thumper" and it’s capable of taking any game animal in North America. Engineered to mount on your mil-spec AR-15 lower, this 20" model hurls the 250-grain Hornady SST/FT .450 Bushmaster bullet downrange at 2,200 fps. Though not designed as a long-range caliber, there’s nothing on this continent capable of standing up to the firepower of Thumper and inside 200 yards its accuracy is outstanding. Recoil has been compared to that of a 20-gauge shotgun. A tubular-aluminum forend allows the barrel to free-float from the nut forward to enhance accuracy. Chrome lining in both the bore and chamber makes the .450 Bushmaster easy to clean and extends barrel life. A five-round magazine is included.

Bob,
If you go to the 6.8 forum and look under the sub-forum heading of alternate calibers you will find the 450 VS 358 MGP discussion, with printed out ballistics runs for comparisons already made. The 450 can not make up for the difference in sectional densidy at velocity. The 358 simply runs up its backside at 75 yards, then runs away with the retained velocity.

Now about that 458, 250 gr bullet, I happen to own three 458 guns, all bolt guns, and all a lot good bit more powerful than the 450. The coffe cup saucer of a bullet is not really a 200 yard bullet at 2,200 fps or any other velocity, now a 300 or even better, a 350 for light bullets might work out to 200 OK with a lot bigger gun, like my 458 Lott at 2,800 fps which is a real true thumper, at both ends.

There is one thing about the 358 MGP it only takes a 6.8 rifle with a 6.8 bolt and a new barrel and gas block to shoot it. I also like an adjustable gas block myself in order to reach up on the ladder to get top shelf velocity. The PRI mag you cut the fron rib out down to the top of the mag release cut with a motor tool or mill. Mike will cut them and refinish them for $20 each. He does a nice job.

I am not getting paid nor do I own any stock in the Co, so do as you like. Oh, yes when you get tired of buying gold for bullets think on this, I can buy 200 gr RCBS plain base for $6.00 per 100 and powder coat them for next to nothing and they do 2,400 and shoot.5 inch groups at 100 with no leading. I am part Scott so cheap is my middle name. By the way, just how much modification does your AR require to shoot the very first bullit, without the magazine?

Oh, I have a 1-12 twist barrel ordered for a heavy bullet sub gun with a can. It will be a big brother to my 6.5 Grendel Sub Gun carbine that shoots 160s at full function, it is my night gun with its can.
Ed

Guessing this would be about the same for the S & W 460 out of the TCA 20 " barrel?

I am not much on ballistics, how does this round compare to the .35 rem ? It has to be souped up some.

Im not here for the gun discussion....



but I see "raper" everytime I see your forum name

Sorry, I tend to be a little dialectic myself. My radio call sign was Rapier. In the Airborne you do a lot of things, I was an Artillery Chief Surveyor, when we finished surveying we became an AFO, artillery forward observer. I did a bit of that and served as the commander's radio man and his FO, I could read a map and keep him out of trouble, like not dropping a round on the wrong guys. When all that got done, I was the Battalion sniper for the 2/319th, 101st Abn. But all of that was a long time ago, in a galaxy far, far away.

Since the 6.8 is based on the 30 Remington, expanding the case to 35 caliber, shortening it a tad to 1.635 trim to length, then blowing the case out with the shoulder moved forward results in pretty much a 35 Remington exterior. However for some reason this case is very efficient and pushes the 358-357 bullets up into the 358 Winchester performance with the 358 Win being a bolt action with a barrel almost 8 inches longer. It is fun to shoot and it would make a dandy road block or check point gun. When shooting 1/4 inch plate it actually carries steel with the 200, making 50 cal holes rather than 35 cal holes with a bullet now wrapped in steel. It also penetrates an engine head so I am told. The 140 FTX will cut a coyote in half.

By the way, American Reloaders has pull down brass, powder and bullets for sale. They have some 180gr Power Shock bullets for $64 at 500 and primed 6.8 brass at decent prices, just got in 1,000 of each. The Administration is playing games again, buying millions of rounds then DXing the lot. There is no way that the 6.8 could be outdated or salvage.
Ed

Figured I would drop back in to do an update on the Hornady 180gr JHP Power Shocks and the 225 BT Plastic Tip with the tip pulled to make mag length.

Loaded up some 1680 in the 358 MGP with the 357 PS bullets at a 2.165 OAL, it is a short bullet for a 180gr and I figured I could get a bit more powder under it, which I did. It was 64 degrees at the farm.
1680 35gr 2,472 fps @ .502 group
36gr 2,518 fps @ .867 group slight crater
36.5 2,522 fps @ 1.03 group slight crater
37gr 2,781 fps @ blown primer

Obviously the 1680 went over pressure, vertical in its curve, by a bunch, at .5 grains as is indicated by the jump in velocity. I might be able to get to 2,500 with 35.5 grains that will be the max load. I am working to velocities, to try to find out just how much the 358 MGP in the AR is capable of. Mike is working accuracy.

I happened to carry along five rounds loaded with the 225gr Nosler Acu Bond, tip pulled, to make length for the magazine. The OAL being 2.257 the load I used was my fire form load for the 200gr bullets of 32 grains of 1680. it is a .5 inch load and does a dandy job of fireforming with one shot.
1680 32 grains 2,137 fps @ .235 group no pressure signs

Did not think to much about it except for the accuracy and the potential to get perhaps to 2,200 fps until I read the Hogdon reloading site data on the 358 Win with 220 bullets. This velocity is equal to the 358 Win top loads shown, with 25% less powder, a different powder for sure, but still pretty impressive for accuracy and performance. These are pictures of some of my dummy cases with the bullets being used.
Ed

Damn
That's Impressive

Mike has put together a pretty impressive package for the AR-15 in this cartridge. It seems like every time I try a different bullet I am suprised somewhere in the process.
Ed

I have been patiently waiting for my new 1-12 twist McGowan barrel with a threaded muzzle. This barrel is for the heavy sub sonic bullets (200, 225 and 250). She finally came in yesterday afternoon. Now we start the upper build. This like most of my uppers will be based on an RRA upper receiver, free-float tube, low profile gas block and miscellaneous stuff, like a light and sight attachment. I think I will try a Photon XT 4.6 x42 day and night scope with the add on of a high power CR IR laser. I will use my other 6.8 bolt to fireform the brass to be ready for the return of the F 1 form suppressor approval. Nothing to see yet, just a barrel. Come to think of it, I will recut the ramps for the flat nose bullets while the barrel is out. Easier to wash out and clean before it is set in the receiver.
Ed

Check out the .416 Hushpuppy...

http://am-tac.com/site/mobile?url=http://am-tac.com/416_HP_Hushpuppy.php#2762

Here is the new 358 MGP Sub Gun ready for brass forming. I will use the original lower and the old cheapo scope to do the forming. I think I will try a Day/Night Sightmark Photon XT 4.6x42 on it with a 20-IR illuminator. Problem is that no one has the Photon in stock right now. But I have heard good things about them with the 20-IR added to them.

The barrel is a 16.5 inch McGowen 1-12 twist 357 grooved with 350 bore. This gas block is a 875 full open, no adjustments, for 1,100 fps loads. I will start with the same powders used by the Whisper, 2015 BR, H-110, etc. The altitude at my farm is 245 feet and the speed of sound is about 1,108 fps.

The flash suppressor is on as a thread protector until I get my F1 form back from the ATF. This barrel is threaded 5/8x24 just like my 300 BO barrel. So I can get double duty from the can. I have all of the parts to build an 8 inch long titanium tube suppressor, without the internals being drilled or set as a can build, got to wait for the papers.
Ed

Shot 50 rounds fireforming brass on Saturday 2-14-15. 15 of the rounds were the take-down 6.8 SPC with a primer and primer crimp. The RCBS swage removed the crimp without effort and new primers went right in with no problems. The old primers were squeezed down so that after the swage was applied they could be just stuck into the case by finger pressure.
The load I used was my starting load with the adjustable gas block, 34gr of 1680 and the 180gr Hornady Power Shot pistol bullet. The OAL was reduced to 2.070 to facilitate feeding without jamming which worked very well and resulted in no problems at all. One thing that I did see while prepping, trimming, etc., the brass was that every case had at least a small amount of gas scraping. There never was gas scraping with the adjustable block at this level. In the 1-22 gun this load velocity was 2,371 fps at .5 inches.
I did a standard break-in with Sweet Shooter with a wet bore at each shot. At the end I shot a group ending the day at my range with .454 for 3 shots.
Ed

Got the Form 1 suppressor finished and the tube back from being engraved by the nice folks at Infinite Laser. Had to go up to the farm yesterday to talk to the contractor that is building the shop so I took the 1-12 twist gun with me and about 25 cartridges. All but 5 were loaded with the 200gr RCBS Cast the other five were loaded with the 250gr Hornady JSP. The first cast round did not function the action but the can was still in one piece, so I tried a 250gr, the can still held together, but the bullet's crack obscured the impact, super sonic. So I picked out a tree at 100 and shot it about 10 ft above the ground off hand, with the first load in the 200gr scale (12.5 grains of AA-2015 BR), the bullet impact could be clearly heard and the bolt locked back...... subsonic with full action function using a 3 oz buffer and a full carbine spring. The test got me to a good starting point.

How I arrived at the 2015 BR load is simple, it is the same load I developed and use with 160 gr .267 bullets in my 6.5 Grendel 16.5 inch subsonic gun.

Returned home and took the can down to check for baffle strikes, there were none. Cleaned the can in the parts washer and put it back together then cleaned the 1-12 twist gun. We are now ready for some real testing with the chrono and several bullet weights. I found a 300 grain cast 358 bullet that I am considering.

I will also run the 300BO with the 225 cast, powder coated bullets at the same time I start testing the 358 in ernest. Probably will have to wait until I return from the show in Tulsa.
Ed

Does all your brass have to be fire formed...? Also on the lead PC bullets...do you have to add a gas check.? Good info here....looks like a lot of work IMHO to run this rifle. Thanks for the good write ups so far.

Yes, all of the brass die forms with a long neck. When it is fire formed the neck is shortened about 50% into a blown out body / shoulder. The chamber is set up to headspace on the untrimmed mouth of the case. When it is fireformed you trim the case to 1.63 inches then it headspaces on the shoulder. NOE makes a plain base 200gr RCBS flat nose 358 bullet. When powder coated the bullet does not lead, even at 2,400 fps. It also shoots to .5 inches while doing 2,400 fps. You use a 357 case mouth flaring die before you seat the bullets so the mouth will not scrape off the coating. The seating fie straightens the neck.

Here is the lovely part, you can powder coat the bullets using air soft pellets, powder coat from Harbor freight, an old empty butter bowl and a toaster oven set at 400 degrees for 20 minutes. I use a square of 1/4 inch hardware cloth opened up with a punch then set the bullets in nose first. The bullets you see, I powder coated myself with black ran them through a 358 sizer and walah I am shooting for pennies not dollars.
Ed

Here is a DYI Tie Dyed anodized titanium suppressor tube, shown above. Used a tea pitcher, three 9v batteries hooked together in series, 6 tablespoons of baking soda, distilled water, an aluminum foil strip that reaches top to bottom, titanium wire (Amazon) with a hook to hold the tube suspended and a versicle belt sander with 320 grit belt, tube on a wood dowel that allows a wobble. Hook the negative to the aluminum large button and the positive to the titanium wire, small button. Took maybe 10 minutes at most. Note how the light changes the photo colors on the same tube. When holding the tube, it looks like the top picture.
Ed