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Building out a .308 or 7.62 NATO lower means gathering a pile of tiny springs, detents, and pins, and it only takes one missing bolt catch spring to stall your whole project. This CMMG Mk3 Gunbuilder's kit hands you that entire pile of small parts in one shot, with the fire control group and pistol grip deliberately left out because those are the pieces most builders want to pick themselves. Everything is finished in matte black and built to mil-spec, so it plays nice with quality components across your build.
Inside you'll find the bolt catch with its screw-in pin, bolt catch plunger and spring, the safety selector with its detent and spring, and the trigger and hammer retaining pins. It also covers the magazine catch, magazine spring, and magazine release button, both pivot and takedown pins with their detents and springs, and the buffer retainer and spring. In short, this is the small-parts backbone of the lower group, minus the trigger, hammer, disconnector, and grip you'll add on your own terms. Pair it with a buttstock or brace kit and you've got a complete lower.
This kit is designed around the CMMG Mk3 and works with most LR-308 type lowers, but the .308 world is not as standardized as the AR-15 world. Not every 308 lower is cut the same, so it pays to confirm your receiver is set up for these parts before you start driving pins. Worth noting: the bolt catch pin here is threaded, so your lower needs to be tapped for that style rather than a standard roll pin. Builders who've run this on DPMS-pattern and 80 percent lowers report clean fitment when the receiver matches.
A smart move that comes up again and again is oiling every pin and spring as you install it, which keeps things moving and makes seating detents far less of a headache. Take your time with the safety selector and let it break in. Do it right and this kit gives you a solid, reliable foundation that should serve for the long haul, all covered by CMMG's Lifetime Quality Guarantee.
It's built for the CMMG Mk3 and is compatible with most LR-308 type lowers. The catch is that .308 lowers aren't as standardized as AR-15 lowers, so it's smart to confirm your receiver matches this pattern before you start. If you're running a CMMG Mk3 receiver, it's a straight fit.
The fire control group and pistol grip are left out on purpose, since those are the parts most builders like to upgrade or spec themselves. That means no trigger, hammer, disconnector, their springs, or a grip. You'll want to source those and a buttstock or brace kit separately to finish the lower.
This kit uses a threaded, screw-in bolt catch pin rather than a standard roll pin. Make sure your lower receiver is tapped for that style before you order, otherwise the bolt catch won't install correctly. It's a quick thing to check and saves a headache mid-build.
Oiling every pin and spring as you seat it makes a real difference and keeps detents from fighting you. Give the safety selector a little break-in time if it feels stiff at first. Take it slow, work from a good bench, and the whole install goes cleanly.
| UPC | 815835015415 |
|---|---|
| Manufacturer | |
| Manufacturer Part Number | 38CA61A |
| Caliber/Gauge | .308 / 7.62 NATO |
| Color | LOWER PARTS KIT |
| Length | 7.5000 |
| Model | |
| Product Type | Parts Kit |
| Shipping Weight | 0.225 |
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