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Sig Sauer MCX Caliber Exchange Kit - 16" .300 Blackout


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Sig Sauer MCX Caliber Exchange Kit - 16" .300 Blackout


Convert your MCX from 5.56mm NATO or change barrel length with this new OEM Sig Sauer MCX conversion kit! Compatible with standard AR15 magazines. This kit will ONLY work with the pre-Virtus series or an MCX that does NOT have "-TAP" in the part number UNLESS you purchase and install the older non-tapered lug bolt on your MCX. Bolts are not included. APP MCX Conversion kits have chrome-lined barrels which differentiate themselves from the commercial variants.

Additional Information

UPC Code No
Caliber .300 Blackout
Manufacturer Sig Sauer
Trigger Pull SA No
Trigger Pull (DA) No
Overall Length No
Overall Height No
Overall Width No
Sights (detailed) No
Sight Radius No
Weight Empty No
Grips No
Frame Finish No
Frame Material No
Slide Finish No
Stock Material No
Barrel Length (in) 16.0 in
Rifling No
Number of Grooves No
Mag Capacity / Rounds No
Number of Mags No
Sound Reduction No
Accessory Rail Not Applicable
Features No
Safety (detailed) No
Competition Approval No
Magazine Well No
Additional Info No
Bullet Type No
FFL Requirements No
Warranty Warranty provided by Sig Sauer. Warranty information is available for Sig Sauer products at

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Product Questions

If this barrel comes back in stock what do I need in order to make my Gen 1 MCX work with this barrel? I currently have a 5.56 barrel that came with it. This is the non-tapered version.

Referenced product: WCALX-MCX-9B-300B

We checked with Sig on this and the barrels (CALX) are compatible across older / newer MCX rifles. The TAP barrels work on the early MCX and the older non-TAP barrels work on Virtus (TAP) rifles. The TAP barrels have different placement for the gas blocks depending on the barrel length and caliber. This means the the gas block adjustment selector on a TAP barrel may be covered by the older style handguard if the handguard is not swapped. If that happens, the handguard could be easily removed if you need to change from suppressed to unsuppressed and vise versa.

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