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Sig Sauer MCX Caliber Exchange Kit - 9" .300 Blackout


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Availability:Out of stock

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Sig Sauer MCX Caliber Exchange Kit - 9" .300 Blackout


Convert your 5.56mm or longer barrel .300 Blackout MCX to 9" .300 Blackout with this easy to install conversion kit!  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.

Note: ALL NFA RULES APPLY!  This is legal to install on an MCX Pistol, but not legal to install on an MCX rifle unless it is registered as an SBR on the NFA Registry.

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) 9.0 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

Is this a Gen 1 or 2 barrel?

Referenced product: WCALX-MCX-9B-300B

This would be a non TAP (tapered) barrel. Sig hasn't really designated the names Gen1 or Gen2 but it would be for the earlier released MCX pistols / rifles.

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Will you carry the tapered versions of these barrels, considering they are discontinued (at least as far as I know)

Referenced product: WCALX-MCX-9B-300B

Inquiry date: 7-13-2018

We do show that we have the following part numbers for the APP TAP CALX kits: 


The ones that aren't in stock or on the site are on order but we don't have firm delivery dates.

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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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