// Upper Receiver Groups
Complete uppers, built like our rifles.
Assembled, gauged and checked to the same standard as our complete firearms — ready to drop on your lower.
ARROW-INDEXED CAM PIN
Always installed the same direction, for consistent wear and longer cam pin life.
INDEX-MARKED GAS KEY
So you can see at a glance whether anything has moved.
LASER-ENGRAVED CALIBER
Inside and outside the ejection port cover, so the caliber can be confirmed visually in an instant.
// Two series
Choose your upper
// Series 01
SOTM4 Complete Upper Receivers
Small-frame complete uppers on the SOTM4 receiver — the forged SOTM4 MOD-0 thermal fitted to the barrel, or SOTM4 Billet with a bedded barrel extension — in 5.56 NATO and our 6mm SPIRE calibers.
- 5.56 NATO
- 6mm ARC
- 6mm MAX
- MOD-0 forged
- Billet
Why choose it
- HM Defense Monobloc® barrel with the gas block machined in and a threaded barrel extension
- SOT Enhanced HMB™ bolt carrier group — nitride standard, hard chrome optional
- Forged SOTM4 MOD-0 receiver thermal fitted to the barrel, or SOTM4 Billet with a bedded barrel extension
- 5.56 NATO in 12.5″, 13.9″, 14.5″ and 16″; 6mm ARC in 14.5″ to 22″; 6mm MAX in 16″, 18″ and 20″
- Arrow-indexed cam pin, index-marked gas key and laser-engraved caliber markings
// Series 02
SOTM5 Complete Upper Receivers
Large-frame complete uppers on the SOTM5 Billet receiver, for full-power cartridges — .308, 6.5 Creedmoor and 8.6 Blackout.
- .308
- 6.5 Creedmoor
- 8.6 Blackout
- Billet
Why choose it
- Large-frame SOTM5 Billet receiver
- .308 and 6.5 Creedmoor in 16″, 18″ and 20″
- 8.6 Blackout in 8″, 12″ and 16″
- Arrow-indexed cam pin, index-marked gas key and laser-engraved caliber markings
The Monobloc difference
On the HM Defense Monobloc® barrel the gas block is machined into the barrel, and the barrel extension is threaded. Paired with the SOT Enhanced HMB™ bolt carrier group — nitride standard, hard chrome optional — in line with Bombproof by Design™.
// SOTM4 MOD-0 Forged Monobloc® Complete Uppers
11 configurations · 5.56 NATO
Every upper is built on an HM Defense Monobloc® barrel (4150 CrMo, 1:8 twist, mid-length gas, 1/2×28 thread), thermal fitted to the SOTM4 MOD-0 forged 7075-T6 upper, and ships with the SOT Enhanced HMB™ Black Nitride bolt carrier group and a Breek Arms WARHAMMER Mod2 ambidextrous charging handle. Complete uppers ship direct; they are not firearms.
SOTM4 12.5″ Monobloc®, 11.7″ M-LOK
UPR-MB-B125-H117M-F
$735.00
- 12.5″ barrel
- Standard bore
- Black Cerakote®
- 11.7″ SOT Wedge-Lock M-LOK
- 1:8 · mid-length
SOTM4 13.9″ Monobloc® Chrome-Lined, 11.7″ M-LOK
UPR-MB-B139CL-H117M-F
$900.00
- 13.9″ barrel
- Chrome-lined
- Black Phosphate
- 11.7″ SOT Wedge-Lock M-LOK
- 1:8 · mid-length
SOTM4 13.9″ Monobloc® Chrome-Lined, 13″ M-LOK
UPR-MB-B139CL-H130M-F
$900.00
- 13.9″ barrel
- Chrome-lined
- Black Phosphate
- 13″ SOT Wedge-Lock M-LOK
- 1:8 · mid-length
SOTM4 14.5″ Monobloc®, 13″ M-LOK
UPR-MB-B145-H130M-F
$835.00
- 14.5″ barrel
- Standard bore
- Black Cerakote®
- 13″ SOT Wedge-Lock M-LOK
- 1:8 · mid-length
SOTM4 14.5″ Monobloc® Chrome-Lined, 13″ M-LOK
UPR-MB-B145CL-H130M-F
$925.00
- 14.5″ barrel
- Chrome-lined
- Black Cerakote®
- 13″ SOT Wedge-Lock M-LOK
- 1:8 · mid-length
SOTM4 14.5″ Monobloc® Chrome-Lined, 13″ FDE Anodized M-LOK
UPR-MB-B145CL-H130M-BP-FDEA-F
$955.00
- 14.5″ barrel
- Chrome-lined
- Black Phosphate
- 13″ FDE anodized M-LOK
- 1:8 · mid-length
SOTM4 16″ Monobloc®, 13″ M-LOK
UPR-MB-B160-H130M-F
$835.00
- 16″ barrel
- Standard bore
- Black Cerakote®
- 13″ SOT Wedge-Lock M-LOK
- 1:8 · mid-length
SOTM4 16″ Monobloc® Chrome-Lined, 13″ M-LOK
UPR-MB-B160CL-H130M-F
$925.00
- 16″ barrel
- Chrome-lined
- Black Cerakote®
- 13″ SOT Wedge-Lock M-LOK
- 1:8 · mid-length
SOTM4 16″ Monobloc®, 13″ FDE Anodized M-LOK
UPR-MB-B160-H130M-FDEA-F
$865.00
- 16″ barrel
- Standard bore
- Black Cerakote®
- 13″ FDE anodized M-LOK
- 1:8 · mid-length
SOTM4 16″ Monobloc®, 15″ FDE Anodized M-LOK
UPR-MB-B160-H150M-FDEA-F
$865.00
- 16″ barrel
- Standard bore
- Black Cerakote®
- 15″ FDE anodized M-LOK
- 1:8 · mid-length
SOTM4 16″ Monobloc®, 13″ Quad Rail
UPR-MB-B160-H130Q-F
$865.00
- 16″ barrel
- Standard bore
- Black Cerakote®
- 13″ SOT Wedge-Lock quad rail
- 1:8 · mid-length
// SOTM4 Standard Monobloc® — No Forward Assist
2 configurations · 5.56 NATO
The same Monobloc® barrel, BCG and charging handle on the SOT Standard forged 7075-T6 upper, without a forward assist.
SOTM4 16″ Monobloc®, No Forward Assist, 13″ M-LOK
UPR-MB-B160-H130M-NOFA-STD
$835.00
- 16″ barrel
- Standard bore
- Black Cerakote®
- 13″ SOT Wedge-Lock M-LOK
- No forward assist
SOTM4 16″ Monobloc® Slim Line, No Forward Assist, 14″ M-LOK
UPR-MB-B160-H140M-NOFA-STD
$835.00
- 16″ barrel
- Standard bore
- Black Cerakote®
- 14″ Midwest Industries Slim Line M-LOK
- No forward assist
- 4 lb 0.5 oz
WARNING: These products can expose you to chemicals including lead, which is known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov.
// Calibers and lengths
What each series is offered in
Monobloc (SOTM4)
5.56 NATO — 12.5″, 13.9″, 14.5″ and 16″
6mm SPIRE
6mm ARC — 14.5″, 16″, 18″, 20″, 22″
6mm MAX — 16″, 18″, 20″
SOTM5
.308 — 16″, 18″, 20″
6.5 Creedmoor — 16″, 18″, 20″
8.6 Blackout — 8″, 12″, 16″
Shipping restrictions. We do not ship AR-15 upper receivers, conversion kits or barrel assemblies to CA, CT, DE, DC, HI, IL, MD, MA, NJ, NY, RI or WA, or to certain localities including Denver, CO and Cook County, IL. Exception: Monobloc uppers are marked and marketed as HBAR and can ship to Maryland. Questions? Consult your local FFL.
Monobloc® and HMB™ are marks of HM Defense, LLC, used under license.
Bombproof by Design™
Precision // Purpose // Performance