Need help selecting 9mm barrel length and buffer combo to go with

**bigguy1305** · 04-02-17, 22:25

Hello gang,

I was able to grab a Spikes 9mm lower this week and a Circle 10 MUR upper. Now I'm at a crossroad. I don't know what barrel length I should go with if 5.5" or 8.5". It will not be suppressed. Also if I go with one size barrel, what buffer and spring combo should I go with? I already have on hand a Springco white, blue and red. I see two styles of buffer which are the 9mm ext and the 9mm with spacer. Any pro-cons from one or another? All help is much appreciated. Thanks

**nate89** · 04-03-17, 01:11

Just my opinion. Unless you were tucking a can under the forend, I don't really see any benefit to a 5.5" barrel over something a bit longer. I have a 6.5" 300 blk barrel and I'm selling it to get something a bit longer. Unless you have a serious OAL requirement that drives you towards a short barrel, having something that allows you to get your arm a little further out in a more natural stance is a much bigger benefit than a gun that is a little shorter. Once again, just my opinion.

As far as the buffer, I would go with either a 9mm extended, or an A5 buffer (I use an H4) with a standard RE. It essentially does the same thing, reduces the travel distance back to prevent unnecessary battering to the bolt catch (assuming the spikes lower has a BHO, I'm not sure).

**bigguy1305** · 04-03-17, 05:53

The difference from what I've gathered is this. On a 6" and under 147+gr will travel subsonic but over 6" it heads towards supersonic. I don't know how true this is but I've been told by more than one person and 2 companies that work with 9mm ARs.

I don't mind going longer if need be. The handguard that I'll be using or would like to use is 7". So a 5.5" barrel with a linear comp or something of the sort should stick out about 1" (give or take 1/2").

You said I could use an A5 buffer which is the first I've heard. What I don't know is either go for a heavy 9mm buffer with regular weight spring or extra power spring with a regular 9mm buffer or both heavy. I've heard and read so many combos I'm really lost on what works with what.

**Clint** · 04-03-17, 09:15

Some relevant discussion of 9mm buffer weights here.

https://www.m4carbine.net/showthread...pressed-9mm-ar

...and 9mm PDW stocks.

https://www.m4carbine.net/showthread...ks-9mm-and-you

**locknload223** · 04-12-17, 08:16

Where did you find the upper?

**Clint** · 04-12-17, 12:32

Originally Posted by bigguy1305

The difference from what I've gathered is this. On a 6" and under 147+gr will travel subsonic but over 6" it heads towards supersonic. I don't know how true this is but I've been told by more than one person and 2 companies that work with 9mm ARs.

I don't mind going longer if need be. The handguard that I'll be using or would like to use is 7". So a 5.5" barrel with a linear comp or something of the sort should stick out about 1" (give or take 1/2").

You said I could use an A5 buffer which is the first I've heard. What I don't know is either go for a heavy 9mm buffer with regular weight spring or extra power spring with a regular 9mm buffer or both heavy. I've heard and read so many combos I'm really lost on what works with what.

Good discussion on barrel lengths and specifically subsonic performance.

https://www.m4carbine.net/showthread...-barrel-length

**bigguy1305** · 04-12-17, 12:45

Originally Posted by locknload223

Where did you find the upper?

I bought it at Joebobsoufitters.com

**locknload223** · 04-12-17, 12:59

Originally Posted by bigguy1305

I bought it at Joebobsoufitters.com

Okay thanks, didn't see it there and have been waiting for QC10 to get them back in stock.

**utahjeepr** · 04-13-17, 19:53

Not going to run suppressed, I would say 8.5. Because - handguards. Just wondering why you care about it being subsonic with 147g if it isn't going to wear a can. With your buffer options, I'd run the extended buffer so that the spring runs full length.