AR15 .223 to 350 Legend: different upper or different barrel ?
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Thread: AR15 .223 to 350 Legend: different upper or different barrel ?



  1. #1
    Sidewinder
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    AR15 .223 to 350 Legend: different upper or different barrel ?

    I recently purchased a Smith and Wesson M&P 15 Sport II rifle. I would like to convert it to fire the new Winchester 350 Legend round so that I could deer hunt with it this coming winter. I live and hunt in Iowa, which recently legalized straight walled, center-fire rifle cartridges for deer hunting.

    So I have a few questions regarding my rifle and the .223 to 350 Legend conversion.

    A) Would it be wiser to acquire a new barrel or an entire new upper ? How difficult would it be to swap out barrels ? How much, roughly, would it cost to have a gunsmith swap out the barrel for me ?

    B) I am aware that new magazines will be needed to feed the 350 Legend rounds. Are there any other issues to deal with when making this caliber change ?

    C) Could someone recommend a sling for my rifle that would be functional (for a hunting rifle) and that would look good as well ?

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    Fairly easy to change out a barrel
    Only a barrel change needed
    Favorite sling for an AR is a Vickers 221
    Savage303 likes this.
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    Wrangler
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    I am building one right now. Ammo should be here tomorrow and barrel Monday so yea I’ve been figuring this stuff out.
    First, keep your upper and build another. This way you have essentially 2 guns.
    Second. All parts except the barrel and supposedly the mags will interchange. CMMG will have dedicated mags that you can get one before deer season. In the meantime you can get a 10 round PMag for $13 and shave down the 2 inside ribs. Same mod as done for 450 Bushmaster. I’ve seen reports this is an easy task and works just fine. I’m doing mine this weekend.
    Third, you only need a few tools to build an upper. A vise, an upper block or something like the Magpul Bev Bloc to hold the upper in place while you tighten the barrel, and depending on your forearm rail a big crescent wrench. Buy a buddy a case of beer to use his tools or buy them for yourself. For what you’d pay someone to do this once you would have what you need for future projects.
    If you watch a couple you tube videos you will see just how easy building an upper really is.
    The upper receivers, bolt carrier and bolt, buffer system and all other stuff are the same.
    Plus if you go this way you could have a complete second upper for about $250-300 depending on how many sales you can catch.
    Im excited about this caliber and look forward to using it this fall.

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    Gunfighter
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    I recently built a 300Hamr with is about the same thing only the last part of the case is necked down to 30cal. The only problem I have had is the magazines. I have had no problems with specific 300bo mags.
    bassetman1974 likes this.

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    I agree with Buckeye33 about finding parts on sale and building your own upper. I'm fairly new to the AR thing but I am confident in my garage gunsmithing skills to assemble a quality AR upper. However, I just don't have the time. I need to be at work all the time and they do pay me extra for that time, so it was cheaper for me just to order a complete custom upper for my needs while being at work all the time.

    Below is my 6x45 with Shilen match barrel. It will shoot 5 shots under an inch at 100 yards with any fire forming load I've tried. Just makes me wonder what it can really do with some judicious handloading. Anyway, $800 shipped to my door and assembled on my LMT lower in 20 seconds ready to shoot. I could have shaved $150 off by supplying my own bolt and carrier group, but I really didn't want to be swapping bolts back in forth in my LMT upper.

    I too have looked at the 350 Legend, 300 Ham'r, and the 450 Bushmaster for a deer thumper. By the time I decide there will be another wiz bang AR cartridge on the market.

    Good luck in your AR quest.
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    Last edited by bassetman1974; 04-24-2019 at 07:07 PM.
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    Distinguished Master
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    Go to Brownells and get a Viper barrel vise.You can get one for $75 delivered.Works without a bench vise.You can bolt it to a 2x 6 and clamp it,like I did.Makes easy work of even the tightest barrels.
    I originally got it to remove my Ruger precision 308 barrel,which the AR shop could not loosen.Viper did it with ease.Excellent tool for a low price.Just have the right dia gas block and tube length and you’ll be done within a 1/2 hr.
    Hardest part is if your hand guard rail screws are stripped.Had a couple of my buddies’ that each had one stripped screw.You’lol have to drill them out.Other than that,it’s easy.don’t forget to put black grease on the barrel nut.
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    Quote Originally Posted by Savage303 View Post
    I recently purchased a Smith and Wesson M&P 15 Sport II rifle. I would like to convert it to fire the new Winchester 350 Legend round so that I could deer hunt with it this coming winter. I live and hunt in Iowa, which recently legalized straight walled, center-fire rifle cartridges for deer hunting.

    So I have a few questions regarding my rifle and the .223 to 350 Legend conversion.

    A) Would it be wiser to acquire a new barrel or an entire new upper ? How difficult would it be to swap out barrels ? How much, roughly, would it cost to have a gunsmith swap out the barrel for me ?

    B) I am aware that new magazines will be needed to feed the 350 Legend rounds. Are there any other issues to deal with when making this caliber change ?

    C) Could someone recommend a sling for my rifle that would be functional (for a hunting rifle) and that would look good as well ?
    Yes---I own several big bore AR's all of them made by yours truly. I have 1 Std A2 lower that works with all the big bore uppers.

    1) It would be wiser to build a new upper in the 350 Legend caliber because a big bore upper ( A3\A4 receiver) must have an enlarged ejection port to allow the bigger shell to eject. These enlarged port upper receivers are what is used on the 450 Bushmaster, 458 Socom,and 50 Beowulf AR conversions.
    2) The bolt must be changed to match the new cartridge head----Barrels are usually sold with a matching bolt that is head spaced ----you can use your old bolt carrier and firing pin.
    3) Some of these big bore barrels are made with a Mid-length gas system---this equates to a 10 inch free float hand guard and matching gas tube. When building your big bore upper equip it with an adjustable gas block so you can tune the gas to your load as you will most likely need to hand load your own ammo.

    4) Magazines may only require you to change the follower to accommodate the new 350 cartridge---no matter what caliber you are always limited to an overall length of 2.260 inch as the mag is the limiting factor for cartridge length.

    5) Change out your lower receiver pins to the easy pull type so it makes it a breeze to swap uppers----just pull 2 pins and swap uppers (Provided you also buy new bolt carriers for each upper).
    rob42049 likes this.

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    Wrangler
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    Actually Cowboy the 350 doesn’t need anything special. It is a 223 case essentially so bolt head is good and no need to enlarge the port door.
    The mags are different because there is no rib in the front that aligns the shoulder on the 223 cases. This is what will foul up with the straight case.

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    Quote Originally Posted by Buckeye33 View Post
    Actually Cowboy the 350 doesn’t need anything special. It is a 223 case essentially so bolt head is good and no need to enlarge the port door.
    The mags are different because there is no rib in the front that aligns the shoulder on the 223 cases. This is what will foul up with the straight case.
    Thanks---have not investigated the new 350 Legend but then it seems it is along the lines of the 300 Blk except larger diameter bullet. Good as Std A3 stripped uppers are 42 bucks. Versus about 100 bucks for the enlarged ejection port uppers. May as well go straight to 450 Bushmaster-----it will drop game in their tracks.................

  11. #10
    Sidewinder
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    Please list a complete list of parts (and tools) need to build a complete upper (AR15 ignorant here, but a fast learner ).

    Thanks for the replies and for the information, by the way !


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