Sub 2K Critical Parts Upgrade

I have a Sub 2K, Gen 1 with about 500 rounds in use. I am considering using for home defense purposes and would appreciate insight as to suggested MCARBO critical reliability parts upgrades. Thus far I have upgraded to the stainless steel feed ramp, recoilless charging handle, and the integrated tool-less locking pin for the charging handle upgrade.

I’ve had good reliability with the limited shooting I’ve done so far. Would appreciate any further recommended upgrades for critical parts reliability. I plan to send the Sub 2K to the MCARBO site to do any/ all upgrades at the same time.



The Mcarbo sight mount is a useful accessory when accompanied by a decent RDS.

The Red Lion fore grip is also outstanding. High quality manufacturing. The MCarbo sight mount mentioned above assumes the factory Handguard. The Red Lion fore grip (Handguard) allows for the rifle to be folded with an RDS or other optics or lights, it just works differently from the MCarbo sight mount.

Both excellent choices. Pick the one that works for you. Maybe add a light since you mentioned home defense.

Im surprised that you did the feed ramp without any of the other internals? I have the Mseries and so happy with the full MCarbo setup , the springs and trigger, i cant imagine opening it up without doing everything available.


If you got a gen 1 sub2k i would first think about swaping it in to keltec for a gen 2. I beleave @Dung just traded in a gen 1 for a shiny new gen 2. Either way i would deffently swap out all the internals with mcarbo parts. The trigger bundle is a must have for sure.


Agreed, I should have held off on the feed ramp change until all other upgrades were identified. Trying not to make that mistake again and identify any/ every critical part upgrade. I can live with some stock parts, like the shoulder stock for example (it isn’t the most comfortable stock, but does not impact the carbine functionality/ reliability or my shooting accuracy).

You are recommending all internal springs and trigger, correct?


Thanks much for the recommendation!


The swap is a great deal. What other gun maker gives you a new firearm in trade for the old one?

The fee is $150. Plus shipping.

My gen one was getting tired. I put a lot of rounds thru it over several years.

The trade-in…. you have to be willing to spend $150 bucks. A brand new S2K gen 2 is around $450.

There’s additional savings in buying the internal parts kit from Mcarbo vs. each upgrade one at a time. But since you have already begun upgrades, you should weigh the benefit of the kit.

150 trade In + 250 for upgrade parts and you get a vastly improved S2K.

But if you don’t want to plunk down almost 500 bucks, you can continue to improve your gen 1 a step at a time. It will run well and serve its purpose for home defense.

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Thanks much for the advice and analysis Dung. I don’t put a lot of rounds through the Gen 1, 500 so far. I am comfortable with operation and accuracy at the distances I would likely use the carbine for, just trying to identify what critical parts seem to fail most frequently at my rate of use. I’ll take a look at the trigger and spring upgrades and definitely check out the trade deal you mention.

Thanks again!

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NP! And welcome to the group.

I estimate my Gen 1 had somewhere between 20-30k rounds thru it. I didn’t baby it at all.

Some find the trigger upgrade complicated but if you watch the vids and be patient you’ll be fine. Mcarbo can also do it for you.

Good luck and be sure to check out Red Lion.

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