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Discussion Starter · #1 ·
I have a S&W M&P 15 and am thinking about getting a different upper to put on it. It would be in a different caliber. Maybe 300 Blackout, .243 or something else. What kind of prices should be expected?

Will any of these other calibers fit on my lower?
 

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Most of the calibers below .308 will with minor adjustments. And as far as prices, depends if you have connections lol. I've been looking for a 5.56 to complete my build and cant seem to find much from retailees, espically bcgs. Froom looking on armslist and gunbroker its all overpriced for the most part. But if you do decide to get a different upper, I'd be happy to take the one youve got off your hands. Happy hunting
 

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Discussion Starter · #4 ·
I would want a complete upper. I won't be interested in getting rid of my 5.56 upper. I'll have to check at my LGS. He had 6-7 in stock last week.
 

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I have a S&W M&P 15 and am thinking about getting a different upper to put on it. It would be in a different caliber. Maybe 300 Blackout, .243 or something else. What kind of prices should be expected?

Will any of these other calibers fit on my lower?
.243, .260, etc will not fit the AR15 lower, these are based upon the same case length as the 308 (7.62 x 51) or AR10. AR15 was designed around a 45 mm long cartridge, e.g. 5.56 x 45, the mag well will not accommodate the longer cartridges.

Some alternatives are: 6.8 spc, 300 blk, 458 Socom, 450 bushmaster, 500 beowolf, 6.5 Grendel, 5.45 x 39. There may be more.
 

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brettc said:
PSA has their 16" 300 blkout upper in stock right now, I believe it's $519 w/o bcg and ch.
Oh my goodness! Been coveting one of those, AAC wants $1200 for theirs.
 

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Discussion Starter · #7 ·
.243, .260, etc will not fit the AR15 lower, these are based upon the same case length as the 308 (7.62 x 51) or AR10. AR15 was designed around a 45 mm long cartridge, e.g. 5.56 x 45, the mag well will not accommodate the longer cartridges.

Some alternatives are: 6.8 spc, 300 blk, 458 Socom, 450 bushmaster, 500 beowolf, 6.5 Grendel, 5.45 x 39. There may be more.
Thanks for narrowing that down. Of those that would fit the 300 or 6.8 are the most interesting. Now that I'm reloading I'm not as scared of the higher priced cartridges. Within reason of course.
 
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