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Reviews & Ratings for Stern Defense SD Mod4 M-Lok 9mm Complete Upper Receiver — 5 reviews

(5 reviews)
Stern Defense SD Mod4 M-Lok 9mm Complete Upper Receiver
Stern Defense SD Mod4 M-Lok 9mm Complete Upper Receiver
$429.27 $419.27 Save $10.00
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Most Helpful Positive Review It's cool for an all-in-one 9 mm upper
I assumed that it was a dedicated 9 mm upper that it would not have a forward assist it seems as though they used some surplus uppers 4 rifle cartridge and just built pistol caliber uppers still cool just not dedicated more like a Frankenstein
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Stern AR9 Upper Receiver

by Jimbob408, Verified Owner from MI, United States Written on February 5, 2026
Was pleasantly surprised to find the quality of the upper to be better than expected. Fit/finish was excellent and dropped perfectly on to both my Daniel Defense and Anderson carbine length pistol lowers without issue. Paired up with their Glock magazine adapter in the lowers I have run over 300 rounds through reliably with last round bolt lock for every mag. Ran 115, 124 and 147 grain rounds and all have cycled perfectly with or without a can. Have not tried with a super safety but 100% works with cassette style FRT’s. Paired with red springco spring and stiffer hydraulic 9mm buffer it’s a blast and still very controllable. Just don’t expect recoil to be like an MP5…
Would recommend: Yes
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Feed Me More

by Joey C, Verified Owner from WI, United States Written on December 3, 2025
Second trip out today with this upper. Has eaten everything 115gr I have fed it; on-line remans, reloads, new brass, steel & aluminum. Not as loud as I expected. I assume the blast forward device helps. Only downside so far is accuracy. My groups started opening up at 15 yds & by 25 yds were beyond 6 inches. I realize 9mm PCC’s are not tack drivers; but D@mn. ALOT OF FUN HOWEVER!
Pros:
  • FUN FACTOR A+++
  • Eats everything
Cons:
  • Accuracy is questionable
Best Used for:
  • Fun . Speed practice
Would recommend: Yes
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9mm Complete Upper

by Sp33dy, Verified Owner from NH, United States Written on April 2, 2025
Great upper receiver couldn’t pass on a deal when it went on sale. Watched videos and reviews how well Stern Defense 9mm holds up and I was very impressed how sustainable the barrel is. After receiving my upper, I test it at the range and I was at awe. The quality, the smoothness, and precision was worth it.
Would recommend: Yes
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great to shoot

by jimbo, from TX, United States Written on February 12, 2021
Great to have and fun to shoot. Small light weight and versatile. Using if for multiple applications either hunting coyotes or training. I’m in love shooting it but since ammo is rare and hard to come by I haven’t had much play time lately.
Pros:
  • light but solid
Cons:
  • None
Would recommend: Yes
2 of 2 found the following review helpful.
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