Sig AR15 compatible?

Discussion in 'Black Rifle Forum' started by mj9mm, Oct 23, 2020.

  1. mj9mm

    mj9mm

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    so i warmed up to the AR15 platform. as expected, availability was slim, and even though i had tried to research before and during my hunt for the best possible rifle the few rifles i could afford were not what i had seen online. well i bought a Sig M400 thread, 5.56, seems to be everything i need. the 5.56 is what i wanted, but i am curious about some larger calibers, 300blk, 6.5 Grendel, maybe a 45type option. what i am wondering about is whether anything but Sig uppers will fit? i am guessing i could buy something off PSA or most any other builder offers, but i have guessed wrong occasionally in the past. is Sig a true AR compatible platform or is it proprietary in any respect. I had looked at an entry level Ruger, forget the model, but i was disappointed in the finish so i kept looking. then i found the Sig at a LGS that i like. i am pretty happy with the fit and finish of it, seems to be Sig Sauer grade quality... anyone else own a Sig M400? make any modifications ?
     
  2. bubbatime

    bubbatime

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    Its an AR15. It is compatible with all other AR15 rifles. Yes you can buy a 300BLK upper from somewhere else if you want to try new calibers.
     

  3. mj9mm

    mj9mm

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    ok, i am thinking thats true, just that i have heard Sig has played around with things like pin diameter.
     
  4. bubbatime

    bubbatime

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    Every AR15 made today uses the exact same pin diameter.
     
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  5. quantico

    quantico 1911 lover Millennium Member

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    Be aware a while back colt made ar lowers with large or small diameter pins.
     
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  6. mj9mm

    mj9mm

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    thanks, so i am new to the AR scene... owned guns all my life, just not this kind. seems like they have a learning curve. i got to admit i was a bit intimidated, i don't have too many people around to bounce this stuff off of. way more interesting than my bolt actions. sounds like this Sig is true ar... thanks.
     
  7. quantico

    quantico 1911 lover Millennium Member

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    Yes the sig and the ruger and the s&w AR are all good. I assume you are aware of piston designs vs DI designs. DI direct gas systems are the orig design.. they put some crud back into the chamber area. And they can run hotter but they are fine for 99 percent of applications.. durable and reliable..

    The piston designs are more similar to the Ak design where a short stroke piston located at the front quarter of the rifle moves the action thru the power of the moving piston. Many high end expensive rifles use this design. The adjustable gas block combined with this design can make tuning a supressed rifle easier to get reliable without excessive wear.

    In both designs heat and crud end up somewhere..

    Years ago people seemed to migrate towards the piston design.. and its a great design. But over time people seem to be headed back to the lower cost DI designed ar design. I own both and find the 600 dollar budget designed rifles are just a great reliable value.. if your going to be on a battlefield moving around armored vehicles unable to clean your rifle.. and no parts available it might be worth the huge price increase from a more value rifle.


    I like my s&w ar rifles in 5.56 and in 308.. and I like my sig 516 and 716 more costly piston ar's. In 5.56 and in 308..
    My 1994 vintage colt HBAR heavy barrel ar's are still running great after 26 years as well..

    You can spend a lot of money building your own ar... or spend a little on a factory built one. Its up to you. Swapping out a ton of parts for upgrades...is quite costly.. its far better to buy what you want day 1.

    Unless you are competing with your ar and sending thousands of rounds I would advise a much cheaper base rifle over some FN or other high end machine. I just never see people wearing out rifles... especially with ammo expensive and scarce..
     
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  8. quantico

    quantico 1911 lover Millennium Member

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    AR pistols are the current trend.. but the ATF starting to mess with the legal aspect of a pistol brace makes that a bit more tricky.
    Also super short barrels do limit bullet speed.. and range. And in my opinion the better barrel lengths are from 10 inches to 14. So not a huge difference from an actual 16 inch rifle.