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Thread: 357AR (Max-Rimless) AR15

  1. #1
    Boolit Master Moleman-'s Avatar
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    357AR (Max-Rimless) AR15

    Here's the 357AR (Max rimless) I built for my son last year. It's a decent little round that's on par with 35rem (at standard pressures) with similar barrel lengths. Built the first upper in it in 2012 and worked out the bugs. I carried a pistol chambered in it for the 2013 deer season and of course saw no deer. State land, saw lots of other guys though. 2014 MI allowed pistol caliber rifles so I was all set and got a 6pt in the same spot (had 13 guys wander by the stand first). 2015 we got a peaceful private land spot and my son was finally able to gun hunt. Figured it was time we made him one. I had previously made a few chamber reamers and set of headspace gauges. While the cartridge is basically the same as a 357Max, you need to have a headspace gauge that sets the headspace off of the case mouth. We ordered a .358"/.350" Green Mountain 1:14" barrel blank http://www.gmriflebarrel.com/rx358-3...-barrel-blank/ . I already had several barrel extensions, an upper, extra bolt carrier group, and an unfinished 80% lower. The barrel was set up with a pin gauge and beveled so the barrel section could be turned between centers down to 1". Once that was done the chamber end was cut for the barrel extension threads 13/16"-16tpi .620"(ish) long. The bolt was put in the barrel extension in the locked position and the distance from the front of the bolt to the front of the barrel extension. Subtract .010" for clearance and Around .004" for crush. Also measure the bolt face depth and add at least .020"-.050" or more to get your rough Go-gauge protrusion for headspacing and write that number down. After verifying the barrel extension screws on smoothly the barrel was reamed with the reamer held in a floating reamer holder. I mark the reamer with a sharpie for depth and once you're close to that, clean the chamber, threads, extension and bolt. Insert the "go-gauge" and with the bolt locked into the extension, lightly screw on the barrel extension until you feel resistance. Use a feeler gauge to measure the gap between the barrel shoulder and extension. I generally loose .003" to .005" clearance once the extension is torqued down. In the pic the (ar10 best pic I had of it) barrel extension is .003" from closing on the "go-gauge". I cut the chamber .006" deeper knowing that I'd most likely have to touch it up a thousand or two once the extension was torqued down. Turns out it was spot on. You can feel a slight bit of resistance with the "go-gauge" and the "no-go" won't even begin to turn.
    Attached Thumbnails Attached Thumbnails 357AR-floating-7.jpg   more357goodness.jpg  

  2. #2
    Boolit Master Moleman-'s Avatar
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    The barrel was turned to 16.5" for a standard carbine gas port profile barrel. The only difference being the muzzle threads were 5/8"-24TPI with an 11 degree target crown. Once that was all turned the barrel extension was torqued down (you can do it before profiling if you want) and headspace verified. The barrel was set up in a dividing head and the gas port was drilled. Before it was removed it was turned 180 degrees and a small dimple was made with a 3/16" ball end mill opposite of the gas port. The passageway in the gas block for the gas port is drilled through the rear setscrew hole in the low profile gas block that was used. So the dimple automatically locates the gas block in the correct position and gives it a much better bite. The barrel was then abrasive blasted and parkerized. At this point we had a barrel, scope, BCG, charging handle upper, and 80% lower
    Attached Thumbnails Attached Thumbnails IMG_0596.jpg   N-15-1.jpg  
    Last edited by Moleman-; 07-28-2016 at 02:33 AM.

  3. #3
    Boolit Master Moleman-'s Avatar
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    My son picked out a Michigan logo with a deer skull superimposed on it. So we sent the unfinished 80% lower to Roy at Shockbottle (shockbottle.com) and had him engrave the MI/deer logo and other info on the lower. Once back it was machined to complete it. The upper and lower were abrasive blasted and coated with Gunkote flat dark earth and baked. The logo was painted with black gunkote and baked again to highlight it. He picked a cheap railed free floating handguard and scope mount off of ebay and a lower parts kit and Magpul stock was ordered from Palmetto Armory. Once those were added we had his deer rifle ready to take to the range.
    Attached Thumbnails Attached Thumbnails IMG_0648.jpg   IMG_0650.jpg   357AR.JPG  
    Last edited by Moleman-; 07-28-2016 at 01:40 AM.

  4. #4
    Boolit Master Moleman-'s Avatar
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    Barrel extension mods. A standard unmodified barrel extension will not feed these wide nosed cartridges. I've modified them two ways. The first few I simply opened up the smaller feed ramps with a 3/8" carbide end mill. The second way was to make them look like a big bore barrel extension and just continue the feed ramp so they both join into one. The second pic is one I pulled off of the net until I can find a pic of one I did hiding somewhere on my computer.... or just go take another one. Both styles worked.
    Last edited by Moleman-; 07-28-2016 at 01:55 AM.

  5. #5
    Boolit Master Moleman-'s Avatar
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    Magazine mods. A standard USGI magazine will not work due to the bullet feed guides pressed into the front sides. Pmags are probably the easiest to modify. Just take a dremmel with a sanding drum and remove the two ribs inside the mag towards the front. I have modified thermomags (they suck), Bulgarian ar15 mags -they work well, but you can't fully remove the bullet guide. Basically you'll need a plastic mag with the feed guides molded in so they can be removed. The cast 208gr (weighted in at 215 with gas check and lube) were wide enough at the front that they didn't like Pmags unless you set them in deeper to avoid the front guide nub (you can remove it) and the narrower front, but fed out of the Bulgarian mag and the thermomags. There are other plastic mags out there that will work, but the Pmags work the best so far.
    Attached Thumbnails Attached Thumbnails pmag10-1.jpg   pmag10-2.JPG   pmag10-3 357AR.jpg  
    Last edited by Moleman-; 07-28-2016 at 02:12 AM.

  6. #6
    Boolit Master Moleman-'s Avatar
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    I had him shoot quite a few 158gr xtp's out of it getting ready for deer season. He was able to repeatedly shoot about 1.5"-2" at 100 yds with the 180ssp bullets at 2150FPS. It's his rifle but ole dad had to see if it shot any better and it does. I wasn't able to keep them all touching but most were so I was happy it shoots well and I felt confident he was fine out to a little past 100yds. Good thing as the doe he got was about 110 yards out when he took a shot. Broke a shoulder and took out a lung and the heart. It took about 3 bounds before dropping with each bound a little lower to the ground.
    Attached Thumbnails Attached Thumbnails 357AR-2015.JPG  

  7. #7
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    Excellent, looks like way too much fun.

  8. #8
    Boolit Master
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    Excellent report and awesome pics. I studied my sons upper many a time dreaming of the same as you did but I don't have the metal work skills to pull it off!
    Look twice, shoot once.

  9. #9
    Boolit Master

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    Mole man,

    First, congrats to the boy! It's a rare thing a Dad being able to build a rifle to that degree for his son, well done.

    Im very pleased to see you post about this cartridge, I've had it rolling around in th back of my mind for quite some time, and have found a few others that have wondered about doing it also. So glad to see it come to fruition!

    Very nice write up by the way!
    Last edited by Hamish; 07-28-2016 at 08:53 AM.
    More "This is what happened when I,,,,," and less "What would happen if I,,,,"

    Last of the original Group Buy Honcho's.

    "Dueling should have never been made illegal in this country. It settled lots of issues between folks."- Char-Gar

  10. #10
    Boolit Grand Master popper's Avatar
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    I've modified a couple BO extensions but not to that extreme (post 4 ) with a dremel. Do you see signs of wear or stress on the extension or bolt? DPMS GenII bolt & extension (AR10) have rounded corners and a smaller lug on the extension at the feed ramp. Don't know if they do it on 223. Always wanted a Marlin 357 but for the price I went to the BO. Inquiring mind.
    Whatever!

  11. #11
    Boolit Master Moleman-'s Avatar
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    popper, No issues. The two styles of barrel extensions are similar to extensions made for big bore cartridges that have more bolt thrust than this cartridge produces. The bolt is a standard ar15 an should be stronger than one opened up for a 450 bushmaster or 450 socom. The ar10 extension shown in the first picture (pic with feeler gauge) is one I'm working on right now for a 44BGM (44x1.8"). I have another barrel blank and an ar15 450 bushmaster BCG that I've been thinking about a similar 44x1.7" (so a higher pressure 1.8" won't fit it) upper to launch some heavy cast bullets out of. Looking at the ar15 450 bushmaster bolt I am surprised there aren't more failures with those.

  12. #12
    Boolit Buddy FrankG's Avatar
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    I probably missed it , but are you using straight 223 casings ?

  13. #13
    Boolit Master Moleman-'s Avatar
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    Quote Originally Posted by FrankG View Post
    I probably missed it , but are you using straight 223 casings ?
    Yes, I put up a thread in the case forming area. http://castboolits.gunloads.com/show...223-5-56-cases I know a few guys who are using 357Max cases and just turning off the rims, but I like using much cheaper 223/5.56 cases.

  14. #14
    Boolit Master Moleman-'s Avatar
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    These are the cast bullets I've shot out of this rifle. They came from KLR a member here for me to test out. The wide flat tip gets a little rounded from striking the feed ramp so I've debated getting a slightly different mold, but haven't found one that's exactly what I want yet. Other than that I've tried 140gr flextips (don't feed well), 158gr SJHP (wide soft hp occasionally hung up), 158 & 180gr xtp (feed well), 180gr ssp (feeds well), 200gr sierra (feeds well), and a few others. I was a little concerned about a piece of the gas check pealing off into the gas port, but it doesn't seem to be an issue. I have a couple gas operated 9mm luger uppers that I shoot Lee 124gr TLrn bullets out of. Leading doesn't seem to be an issue and although they get very dirty from the tumble lube, it just seems to build up to a point and the rest gets blown out the carrier vent hole. The most I've shot of those at a time is around 500.
    Attached Thumbnails Attached Thumbnails 357AR-lead3.jpg  
    Last edited by Moleman-; 07-28-2016 at 11:59 AM.

  15. #15
    Boolit Master

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    Thanks .....Thanks a LOT LOL

    Now I have a new AR upper to build or have built for me
    IMO it will be perfict for deer hunting here in Ohio

    Not that I need another deer rifle , as any of the 45/70's work
    But I just like the looks of that round

    John
    Yea, thou I walk through the valley of the shadow of death, I will fear no evil; for thou art with me; Thy rod and thy staff, they comfort me.
    And I carry a LOADED Hell Cat

  16. #16
    Boolit Buddy


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    I have been toying with the idea of a 35 Herrett Rimless (6.8 SPC parent brass). This looks easier and cheaper. Were you able to order just the 2 blanks from GM or did you have to go thru a distributor or order 10 barrels...?

  17. #17
    Boolit Master Moleman-'s Avatar
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    cowboybart, I've always just ordered straight through them. If you call you'll likely speak with Michael or Heather who have always been pleasant and helpful. They offer a discount to members of Weaponsguild (perhaps others as well) and can't hurt to ask. It usually pays for a good chunk of the shipping. I have been happy with all of the blanks I've got from them over the years.

  18. #18
    Boolit Master

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    I smell a Group Buy for barrels if there's a way to pull it off while keeping the completed barrel cost down.
    Last edited by Hamish; 08-02-2016 at 06:37 AM.
    More "This is what happened when I,,,,," and less "What would happen if I,,,,"

    Last of the original Group Buy Honcho's.

    "Dueling should have never been made illegal in this country. It settled lots of issues between folks."- Char-Gar

  19. #19
    Boolit Buddy


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    I have ordered from Green Mountain before, but when I looked into the Herrett rimless they recommended I go thru Trident if I was only getting 1 barrel. Because I am a little ignorant on the AR and barrel extension set up, Trident was going to do all that and just send me an unchambered AR barrel. Can barrel extensions be purchased for different case sizes?? Are they threaded on with non metric threads?? Is drilling the gas port rocket science?? Does it need to be in a groove or on a land??
    Last edited by cowboybart; 08-03-2016 at 09:20 PM.

  20. #20
    Boolit Master

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    More "This is what happened when I,,,,," and less "What would happen if I,,,,"

    Last of the original Group Buy Honcho's.

    "Dueling should have never been made illegal in this country. It settled lots of issues between folks."- Char-Gar

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check