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Posted: 12/27/2020 11:24:20 PM EDT
[#1]
You can find 9mm and it's cheap?
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Posted: 12/27/2020 11:26:58 PM EDT
[#2]
The 9mm bullet does not really benefit much from high velocity. if shooting JHP, all you need is enough velocity to reliably expand. These days, you might even prefer using something like lehigh defense extreme defense which is even less sensitive to velocity. A 4-5" barrel is plenty.
On the other hand you will probably want to add 7" of suppressor to the end of it, so will want to keep your barrel short to keep the overall length down for maneuverability. Therefore my choice would be a 4-5" barrel |
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Posted: 12/27/2020 11:27:56 PM EDT
[#3]
I have an 8.5" which gets about all the velocity a 9mm will get. Some people run 4, 5 and 6 inch barrels but I like the little bit more handguard I get with 8 or 8.5" I really enjoy mine a lot.
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Posted: 12/27/2020 11:34:25 PM EDT
[#4]
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Posted: 12/27/2020 11:41:31 PM EDT
[#5]
Yes research lead me to 8.5 as well. It provided enough barrel for a decent handguard. Mine is an SBR with a Battle Arms Development Vert stock. If you are going to shoot 147gr bullets, or something with a flat nose profile, make sure your barrel will feed them. I went with a Foxtrot Mike barrel and now it will feed anything.
 If i was only building a pistol, i may have gone shorter, but this will have a can on it eventually, and the rifle has a 8.5 black out upper i use on it as well. |
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Posted: 12/27/2020 11:51:12 PM EDT
[#6]
I only went 4”. But I’m planning on having a full sized, full time can on it. So, that’s why I went that length.
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Posted: 12/27/2020 11:57:50 PM EDT
[#7]
8" on mine.
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Posted: 12/28/2020 12:01:53 AM EDT
[#8]
I went with a 4.5". There's very little benefit in going longer in 9mm.
There is a good argument to go longer if you want to use a standard handguard, though. I used a slightly longer handguard than needed and added a longer flash hider because I felt the short barrel+short handguard combination was a little more hazardous than I was comfortable with. At some point I may put a can on, but I'm not quite there yet. |
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Posted: 12/28/2020 12:03:05 AM EDT
[#9]
I did an SBR and went with a 10.5 to give me a decent handguard and grip length.
8.5 would have been plenty but I had a particular length in mind. |
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Posted: 12/28/2020 12:29:13 AM EDT
[#10]
Roughly 5 inches or so.
But your 7.5" .300blk is FAR more effective. Especially if you can hunt down some of the hotter Wilson Combat loaded 110gr Tac-tx. |
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Posted: 12/28/2020 12:43:43 AM EDT
[#11]
I am also of the camp who built around a desired handguard length. I wanted enough room for a light and my hand and 10" was the ticket. I went with the BA 8.3" barrel and KAK slimline flash can to get there. Most 9mm bullets are designed to "work" at velocities easily generated from 3" barrels or so, but a TC, SWC, or hardcast with a wide flat meplat will benefit from more velocity to create a larger wound cavity and deeper penetration.
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Posted: 12/28/2020 6:23:21 AM EDT
[#12]
Barrel length
- 9mm tends to increase velocity as barrel length increases. - The increase in velocity usually drops off significantly after 8" - 10" of barrel travel. - Longer barrel lengths may cause some subsonic loads to become supersonic, affecting suppressor performance. - Longer barrel lengths may cause poor terminal performance from hollow point ammunition designed for typical pistol barrel lengths. Velocity continues to increase after 8-10" of barrel, but the amount of increase per inch is much smaller, and can be inconsistent depending on load. |
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Posted: 12/28/2020 10:24:01 AM EDT
[#13]
I went with the 10.5”, thinking Colt put enough research and development into their smg.
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Posted: 12/28/2020 1:05:10 PM EDT
[#14]
Quote HistoryQuoted: Roughly 5 inches or so. But your 7.5" .300blk is FAR more effective. Especially if you can hunt down some of the hotter Wilson Combat loaded 110gr Tac-tx. I use a 300 blk pistol with 7.5" barrel as a HD gun. I like it a lot but i do think there are some areas where a 9mm PCC would be better. One is that good 300 blk performance really requires specialty ammo...either the 110 tac-tx super or 194 lehigh for subs. Both are extremely difficult to buy today and probably for the next couple years. In contrast you can use just about any brand of defensive 9mm and get decent results. so there is an advantage to someone thinking about getting into it. Second is if you plan to use it suppressed, the 300 blk requires a longer starting barrel length and will not be as maneuverable as a suppressed 9mm with a hand guard over the suppressor. In addition, there are multiple delayed blowback options for 9mm (mp5, mdp9, cmmg) but nothing i'm aware of for 300 blk. Third is you can have a lot more options for folding or compact stocks in 9mm -- eg, MDP9 or MP5 platform. This may be possible on the AR platform but they are expensive and not fully proven tech. The main advantages you get with 300 blk are longer range, and increased barrier penetration, and ability to use AR magazines. For a lot of people those benefits may not outweigh the negatives |
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Posted: 12/28/2020 1:25:56 PM EDT
[#15]
Quote HistoryHere's a graph of the Ballistics by the inch page. As someone pointed out, most of the improvement occurs by 7 or 8".  |
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Posted: 12/28/2020 2:10:42 PM EDT
[#16]
ability to use AR magazines And you can even do that with 9mm now thanks to the folks at Mean Arms. The AR-9 has a lot going for it. Another advantage over the 300 is noise level indoors, if you aren't using a suppressor. |
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Posted: 12/28/2020 2:40:20 PM EDT
[#17]
Quote HistoryQuoted: And you can even do that with 9mm now thanks to the folks at Mean Arms. The AR-9 has a lot going for it. Another advantage over the 300 is noise level indoors, if you aren't using a suppressor. That's pretty cool, although for folks living in certain states (MA, CT, VT) there's still a distinct advantage to being able to use preban GI mags at full capacity ;) |
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Posted: 12/28/2020 3:47:25 PM EDT
[#18]
Here is an easier to read version of the 9mm chart from Ballistics by the inch.
 5"-7"-9"...all those seem to be fine barrel lengths....BUT.....it is still 9mm. If it is an ammo price/ availability item, that makes plenty of sense. But that is where it stops. 9mm in the AR platform made more sense 15 years ago, then today. Remember, AAC took .300 Whisper and developed into into .300blk as a replacement for the 9mm MP5SD while using the AR platform. I'm in the market for a 7.5" .300blk barrel myself...as I have 8.3", 8.5" and 9" already (I use 110 Vmax for HD). Because when you start getting into the 7" and above barrel length, there is no comparison. Shooting 110's out of 7.5" .300blk....what are you getting? 2025fps 2050 fps? That is about 1000 ft-lbs of energy and cutting through IIIA armor like it isn't there. On the other side, things like the Flux brace kit or Recover Tactical brace kit have squeezed 9mm AR's from the bottom. Happy switch aside, there isn't much ballistic difference between a braced G17 and an AR9 with a 5" barrel, but there is a huge weight/bulkiness difference. If you want to shoot on the cheap, it is hard to be .22LR. |
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Posted: 12/28/2020 8:15:35 PM EDT
[#19]
Quote HistoryQuoted: Here is an easier to read version of the 9mm chart from Ballistics by the inch. 5"-7"-9"...all those seem to be fine barrel lengths....BUT.....it is still 9mm. Sure, but velocity does not really effect terminal performance of a 9mm bullet. As long as you exceed the expansion threshold and penetration threshold, additional velocity serves no benefit. These velocity by the inch charts are much more meaningful for rifle calibers, where velocity equates to range, penetration capability, fragmentation potential...but 9mm will never excel in those categories, and "energy" delivered does not really equate to wounding potential (at least not with traditional JHp, maybe with the new Xtreme defense stuff it might..) |
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Posted: 1/2/2021 2:45:11 AM EDT
[#20]
Quote HistoryQuoted: I use a 300 blk pistol with 7.5" barrel as a HD gun. I like it a lot but i do think there are some areas where a 9mm PCC would be better. One is that good 300 blk performance really requires specialty ammo...either the 110 tac-tx super or 194 lehigh for subs. Both are extremely difficult to buy today and probably for the next couple years. In contrast you can use just about any brand of defensive 9mm and get decent results. so there is an advantage to someone thinking about getting into it. Second is if you plan to use it suppressed, the 300 blk requires a longer starting barrel length and will not be as maneuverable as a suppressed 9mm with a hand guard over the suppressor. In addition, there are multiple delayed blowback options for 9mm (mp5, mdp9, cmmg) but nothing i'm aware of for 300 blk. Third is you can have a lot more options for folding or compact stocks in 9mm -- eg, MDP9 or MP5 platform. This may be possible on the AR platform but they are expensive and not fully proven tech. The main advantages you get with 300 blk are longer range, and increased barrier penetration, and ability to use AR magazines. For a lot of people those benefits may not outweigh the negatives I like my 300 BLK the problem I have is that I don't have much ammo stocked up for it and I'm looking to cast and reload rounds for it. Why I'm looking at 9mm carbine is ammo is easier to find and cheaper not buy much but it is also during a situation where I might have to scrounge for ammo I can find 9mm easier then 300blk. Also like carbine or pistol size AR because of how small they are and I have a home with two females under 5'3 and they both like the pistol 300 BLK and 223 I have. Also like how mags if you get Glock lower are cheap and you can get hi-cap drums for them also cheap. |
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Posted: 1/4/2021 7:12:43 PM EDT
[#21]
Quote HistoryQuoted: Here's a graph of the Ballistics by the inch page. As someone pointed out, most of the improvement occurs by 7 or 8". https://imgur.com/gallery/Grv2nTX Back to the OP's question, I think what this is telling us is that for most loads, including the more common 115 gr type, by about 7" or 8" the burning propellant has achieved peak pressure from the powder burn and isn't adding significant additional velocity if a longer barrel is used. Perhaps there are 9mm loads / powder combinations that are intended for carbines that would give better performance.  |
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Posted: 1/4/2021 7:26:18 PM EDT
[#22]
I have found the performance for me on accuracy and effective range to be about the same between a 4-5” and an 8” barrel. I have found the comfort really comes from handsize / user friendliness. My wife (small 5-2 tiny hands) loves running the smaller barrel 5” AR9 or Stribog with a brace versus a longer option while I prefer something that is no smaller than the Stribog for comfort.
Best of luck! |
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Posted: 1/5/2021 9:36:28 PM EDT
[#23]
I went with a 5.5" Ballistic Advantage barrel with a flash can and 7" handguard. In retrospect, I probably should have gone with a 7.5-8" barrel so I could use a 9" handguard.
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Posted: 1/7/2021 9:41:16 PM EDT
[#24]
I have a 16" that I use at the action range, ( no .223 / 5.56 allowed so the 9MM mimics a 5.56 size.
I also have a 10.5" ( just so I can have some rail to mount stuff to, Lol ) and I still get decent velocity advantages... or for me, extended effective range for the various handgun bullet designs. The 8" barrel would have been preferred... but ... that darned short handguard. FWIW... and this might help show which rounds could give a decent velocity increase... here is 129 different factory rounds through my 16" Not to mention the various problem child rounds... bullet setback, HP just to darned wide, just plain dirty running.. pics might not all be there. https://www.ar15.com/forums/ar-15/-/16-712312/?page=1&anc=7429025#i7429025 |
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Posted: 1/10/2021 5:35:56 PM EDT
[#25]
I went with 5.5 inch on my 9mm build just because.
Historically speaking (going from memory) most 9mm sub guns ran an average 7.7 - 8 inch barrel |
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