CMMG 9mm lower - what LPK?

AssMan · Oct 24, 2014

I'm buying 2 of the MK9 stripped lowers. Is a standard AR15 parts kit (pick your brand) what I need to buy for a 9mm, or are there differences I need to be aware of? Is it better to run a dedicated 9mm FCG or buy the CMMG "ramped" BCG? Thanks! :party29:

ericoak · Oct 24, 2014

I am no expert, but I believe they are the same, you just need to make sure you have the correct hammer. Someone more knowledgeable will correct me if I am wrong though.

Biggfoot44 · Oct 24, 2014

Also no expert, but I do recall that some 9mm bolts use standard hammers, some use specific hammers. So you need to decide on your bolt configuration, and work backwards.

rfawcs · Oct 24, 2014

http://www.ar15.com/forums/t_3_15/108261_9mm_AR_FAQ.html

dontpanic · Oct 24, 2014

Any milspec ar lpk is gtg. Do not need the bolt catch as it is already on your lower. No special hammer needed with ramped bolt. (CMMG and Colt)

Also need a 9mm buffer

AssMan · Oct 24, 2014

Great! Confirms my thinking. This is a dedicated 9mm lower, so I may just go with the 9mm hammer as I can't convert to 5.56. Will just come down to pricing I guess. Those ramped BCG's aren't cheap!

Biggfoot44 · Oct 24, 2014

Que up the debate of ramped vs non-ramped bolts.

HT4 · Oct 24, 2014

Just make sure you don't get a notched hammer... it will not work. The gun will lock up every time you try to charge it.

BAD:

dontpanic · Oct 24, 2014

snallygaster said:
Great! Confirms my thinking. This is a dedicated 9mm lower, so I may just go with the 9mm hammer as I can't convert to 5.56. Will just come down to pricing I guess. Those ramped BCG's aren't cheap!

Spend the extra money on a ramped bolt. Only $20-40 more. Down the road you will want to upgrade your trigger, without a ramped bolt your choices will be much more limited.

sailskidrive · Oct 24, 2014

I just went with the CMMG bolt and lower parts kit for mine...

MKR03 · Oct 25, 2014

sailskidrive said:
I just went with the CMMG bolt and lower parts kit for mine...

Same. I went with the standard CMMG LPK (any mil spec LPK will work), CMMG ramped bolt, and a Spike's ST9X buffer. If you have a spare carbine buffer, you can also buy a 9mm spacer in lieu of a dedicated 9mm buffer.

AssMan · Oct 25, 2014

dontpanic said:
Spend the extra money on a ramped bolt. Only $20-40 more. Down the road you will want to upgrade your trigger, without a ramped bolt your choices will be much more limited.

Yeah, good point.

dontpanic · Oct 25, 2014

MKR03 said:
Same. I went with the standard CMMG LPK (any mil spec LPK will work), CMMG ramped bolt, and a Spike's ST9X buffer. If you have a spare carbine buffer, you can also buy a 9mm spacer in lieu of a dedicated 9mm buffer.

The spacer is so you can use a carbine spring and 9mm buffer in a rifle length buffer tube. Not to replace a 9mm buffer.

Without a 9mm buffer you will break your bolt catch.

MKR03 · Oct 25, 2014

dontpanic said:
The spacer is so you can use a carbine spring and 9mm buffer in a rifle length buffer tube. Not to replace a 9mm buffer.

Without a 9mm buffer you will break your bolt catch.

I agree with part of this...if you run a regular buffer (especially a lighter one) by itself, you risk breaking the bolt catch. Some 9mm buffers (Spikes, Slash) are longer than standard buffers, and some (RRA, Colt) are the same length as standard 5.56 buffers. The spacers can be used in carbine length tubes in conjunction with the RRA/Colt 9mm buffers, or heavy carbine buffers to limit bolt travel. The extended length 9mm buffers eliminate the need for spacers in carbine length tubes. From Spike's website...the 9mm buffer spacer "will go perfect with the ST-T2 tungsten buffer." I've heard of people running standard carbine buffers and never having an issue with breaking the bolt catch. I've also heard of people using standard length 9mm buffers and breaking the bolt catch. With a carbine length tube, you can go with the extended 9mm buffer (Spikes ST9X or Slash) or the standard length (RRA/Colt 9mm, heavy carbine) with a spacer. Just not the extended 9mm buffer with the spacer (this may work in a rifle length tube...I don't know).

dontpanic · Oct 25, 2014

MKR03 said:
I agree with part of this...if you run a regular buffer (especially a lighter one) by itself, you risk breaking the bolt catch. Some 9mm buffers (Spikes, Slash) are longer than standard buffers, and some (RRA, Colt) are the same length as standard 5.56 buffers. The spacers can be used in carbine length tubes in conjunction with the RRA/Colt 9mm buffers, or heavy carbine buffers to limit bolt travel. The extended length 9mm buffers eliminate the need for spacers in carbine length tubes. From Spike's website...the 9mm buffer spacer "will go perfect with the ST-T2 tungsten buffer." I've heard of people running standard carbine buffers and never having an issue with breaking the bolt catch. I've also heard of people using standard length 9mm buffers and breaking the bolt catch. With a carbine length tube, you can go with the extended 9mm buffer (Spikes ST9X or Slash) or the standard length (RRA/Colt 9mm, heavy carbine) with a spacer. Just not the extended 9mm buffer with the spacer (this may work in a rifle length tube...I don't know).

Thanks. This is actually the best explanation of this I have read.

MKR03 · Oct 25, 2014

No problem...I'm no expert, just finished building a 9mm AR myself recently so I've done a lot of research lately. I've read a lot of conflicting information on buffers. Different rifle/ammo combinations act differently. Some people run H/H2 buffers by themselves without issue. Some people run the RRA or Colt style 9mm buffers and break bolt catches. Some people say adding a spacer and/or Wolff XP spring helped their rifle to run smoother. IMO, the best option is to go with the extended length 9mm buffer or buffer-spacer combo in the first place (Spikes ST9X and ST-T2/spacer combo are both around $50). I'd rather drop the extra $20 or $30 from the start, and not have to replace broken bolt catches while I try to experiment to find the right combination.

dontpanic · Oct 25, 2014

I'm building a 9mm right now. I've spent 2 mos gathering parts and still need to buy my buffer. That and my trigger are all that is left. Think I might be going with a Heavy Buffers Q buffer and a Wolf spring.
If not then the Spikes ST-9X

MKR03 · Oct 25, 2014

I don't think you could go wrong with either choice. The Spikes runs great in my gun....no experience with the Q buffer, but I've heard good things.

CMMG 9mm lower - what LPK?

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