View Full Version : PDW 8.5" 5.56 vs. .300Blkout
PatrioticDisorder
01-09-16, 18:00
So I've been flirting with the idea of building a PDW 8.5" with MVB ARC stock, I'll be using a Noveske 8.5" barrel, either .300Blkout or 5.56.
Obviously .300Blkout will be expensive to feed, defensive ammo would be Barnes Tac-TX 110gr. If I went 5.56 I have a bunch of fusion MSR I'd have to chrono but I'd consider running, if not I'd buy Barnes 50gr TSX. I also already have a Saker K I'd run on a 5.56 with trifecta flash hider, I'd need to buy another can for the .300Blkout (likely a Rugged Razorback with short flash hider).
So the purpose of this rifle would be occasional concealed carry in 5.11 select carry bag, mainly a truck gun and I would also be able to bring it to my girlfriend's house in the carry bag & set it up with the can and I'd have it as a to go HD rifle.
My questions are as followed:
1. With supersonic ammo (mainly the ammo selections listed above with the flash hiders), would there be any difference in blast/concussion between the 2 calibers?
2. Would .300Blkout have a significant advantage over 5.56 in terminal ballistics based on the ammo choices listed above?
I'd really hate to get into another caliber, along with buying another can for this project, but if the .300Blkout has legitimate significant real world advantages on this size carbine, I guess I'll be going in that direction.
I'm planning pretty much the same thing but with the Rainier Medcon 8.5. I am going with 300BLK as I don't trust any 5.56 rifles with bbls under 10.5 and very few under 11.5.
firefighter37
01-09-16, 18:58
I have the Noveske 8.5" 300 barrel and it is phenomenal. The concussion to me is similar between the two, with the 5.56 probably being more harsh, but I don't have an 8.5" 5.56 to compare, only a 10.5".
Ballistics I don't know... That Barnes 110 is a bad mofo though.
firefighter37
01-09-16, 19:02
I'm planning pretty much the same thing but with the Rainier Medcon 8.5. I am going with 300BLK as I don't trust any 5.56 rifles with bbls under 10.5 and very few under 11.5.
I agree with the nothing below 10.5" in 5.56
PatrioticDisorder
01-09-16, 19:38
I kinda new the general consensus would be .300Blkout, but I think there is something to be said for keeping everything 5.56. Too bad 5.11 didn't make that damn select carry bag just a little bit bigger, if it would fit a 10.5 with PDW stock this question would be a non-issue.
Rayrevolver
01-09-16, 19:58
What about the Law Tactical folding stock kit? Not trying to steer you away from 300BLK, which I have and really enjoy shooting suppressed, but to keep with 5.56 and you already have a suppressor.
Hell, it might be cheaper to get the new folding stock Sig in a 10.5" (can't remember what its called).
PatrioticDisorder
01-09-16, 20:05
What about the Law Tactical folding stock kit? Not trying to steer you away from 300BLK, which I have and really enjoy shooting suppressed, but to keep with 5.56 and you already have a suppressor.
Hell, it might be cheaper to get the new folding stock Sig in a 10.5" (can't remember what its called).
Good thoughts, i have a SCAR 16s SBR, if I really wanted to use that I could (proally have to change the charging handle to the right side however).
The 50gr TSX seems to be the exception to the bbl length problem in 5.56. It seems to do quite well (reports of Barnes/black hills stating this bullet giving you reliable expansion in this length barrel out to 75 yards).
With those numbers, already having the can, and staying out of another caliber, I would say that might be the way to go.
The 50gr TSX seems to be the exception to the bbl length problem in 5.56. It seems to do quite well (reports of Barnes/black hills stating this bullet giving you reliable expansion in this length barrel out to 75 yards).
With those numbers, already having the can, and staying out of another caliber, I would say that might be the way to go.
For me it's more than a ballistic issue when going super short. I have concerns with reliability under 11.5". Only a couple makers I'd trust with a 10.5/10.3. I haven't seen a 5.56 rifle with a bbl less than 10.5" I'd trust my life to yet.
PatrioticDisorder
01-09-16, 20:55
For me it's more than a ballistic issue when going super short. I have concerns with reliability under 11.5". Only a couple makers I'd trust with a 10.5/10.3. I haven't seen a 5.56 rifle with a bbl less than 10.5" I'd trust my life to yet.
I think I'd trust the Noveske 8.5" barrel...
domestique
01-09-16, 22:24
300 blackout is the way to go in SBR sub 11.5" IMHO.
Here is a reply from another thread.
www.m4carbine.net/showthread.php?176100-5-56-vs-5-45-vs-300-blk-in-a-8-inch-sbr
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300BLK with the right load is effective out to 320-360 yards (9 inch barrel).... also less flash and concussion than a 8" 5.56. I personally wouldn't go less than 11.5" for a 5.56 SBR.
An example of the 70gr. TSX: 2,400 FPS out of a 8" 5.56 would yield effective expansion to 200-230 yards. A 11.5" barrel would yield 2,600 fps and reliable expansion to 300 yards...... this is even assuming you can get the 70gr. bullet moving that fast. I was optimistic in my numbers for the 5.56 load as the graphs represent the 62 gr. M855 round.
ETA:
From another thread:
-1800fps for the 70gr TSX
-1900fps for the 55,62 gr TSX
-The "non 5.56" 50gr bullet (handloading component) is also 1900fps
-The 5.56 loading by Black Hills using the 50gr Barnes has an expansion threshold of 2300fps, as it is a tougher design meant for use at close ranges against windshields, etc.
-300 BLK 110gr Blacktip has an expansion threshold of 1300fps. The blue-tip 110gr .308" dia TSX bullet has an expansion velocity of nearly 500fps higher, as it is meant for other cartridges, if you will.
Hope this helps. If anything it proves that you need to know the EXACT bullet beign discussed, and "transposing" expansion velocities doesn't work with the Barnes. It's very very VERY caliber/loading specific.
5.56 barrel lengths with 62gr. M855 "green tip"
www.sadefensejournal.com/wp/?p=1093
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domestique
01-09-16, 22:28
The 50gr TSX seems to be the exception to the bbl length problem in 5.56. It seems to do quite well (reports of Barnes/black hills stating this bullet giving you reliable expansion in this length barrel out to 75 yards).
With those numbers, already having the can, and staying out of another caliber, I would say that might be the way to go.
The black hills 50gr TSX is actually worse in expansion vs. the regular 50 gr. TSX available as a reloading component. The black hills version has stronger petals and is designed to not break apart when fired through auto glass. However it only expands down to 2,300 fps.
The commercial 50gr. TSX breaks apart easier, but reliably expands down to 1,900 fps. If auto glass isn't a concern, buy the regular 50gr. TSX.
In contrast the 110gr. TSX "black tip" yields expansion down to 1,300 fps.
For me it's more than a ballistic issue when going super short. I have concerns with reliability under 11.5". Only a couple makers I'd trust with a 10.5/10.3. I haven't seen a 5.56 rifle with a bbl less than 10.5" I'd trust my life to yet.
I have been running a 7.5" Noveske Diplomat but mine is not 5.56, it is chambered in 6.8 SPC. It is about three years now and have had absolutely ZERO problems. No FTE's, FTF's, or hiccups of any kind. I have shot a little over 6,000 rounds through it. Loves all factory ammo I can get my hands on as well as the three or four hand loadings I make up for it to same money.
Just sayin.
I built this recently. 8" Aero Precision 300BO. Even sans suppressor it doesn't have nearly the blast as my 11.5" 5.56 does....
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***started new thread so not to derail***
PatrioticDisorder
01-12-16, 13:54
I have been running a 7.5" Noveske Diplomat but mine is not 5.56, it is chambered in 6.8 SPC. It is about three years now and have had absolutely ZERO problems. No FTE's, FTF's, or hiccups of any kind. I have shot a little over 6,000 rounds through it. Loves all factory ammo I can get my hands on as well as the three or four hand loadings I make up for it to same money.
Just sayin.
What mags are you running? Barret? And how reliable have they been?
For me it's more than a ballistic issue when going super short. I have concerns with reliability under 11.5". Only a couple makers I'd trust with a 10.5/10.3. I haven't seen a 5.56 rifle with a bbl less than 10.5" I'd trust my life to yet.
From a reliability standpoint, does it have to do with the gas system? Is it the lack of dwell time that makes it unreliable? What if you had the 7.5" 5.56 suppressed 100% of the time to increase pressure and dwell time?
Reason I ask this is because I've been considering building up a 7.5" with dedicated suppressor (reflex design - Ops Inc M4S) as a PDW. I have the M4S currently on an 11.5" but will be getting a SiCo Omega and really wont have a use for the Ops Inc M4S unless I dedicate it to something like the PDW I've been thinking about. Everything I own is 5.56 and I'd really rather not get into a different caliber. It's gotta be at least better in terminal ballistics than 9mm and with a dedicated suppressor, might run reliably (?)
domestique
01-12-16, 14:17
Kind of OT, but this chart always bothered me. What's with the dip showing lower velocity with a 12.5" barrel.
Lots of love for the 12.5" reading through threads, but the chart makes it seem pointless vs an 11.5" and doesn't really make sense.
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I've always been more interested in what's happening at 21". There is an even bigger droppff in velocity, and then an increase.
From a reliability standpoint, does it have to do with the gas system? Is it the lack of dwell time that makes it unreliable? What if you had the 7.5" 5.56 suppressed 100% of the time to increase pressure and dwell time?
Reason I ask this is because I've been considering building up a 7.5" with dedicated suppressor (reflex design - Ops Inc M4S) as a PDW. I have the M4S currently on an 11.5" but will be getting a SiCo Omega and really wont have a use for the Ops Inc M4S unless I dedicate it to something like the PDW I've been thinking about. Everything I own is 5.56 and I'd really rather not get into a different caliber. It's gotta be at least better in terminal ballistics than 9mm and with a dedicated suppressor, might run reliably (?)
100% dedicated is a little different than unsup/supp systems, but don't just think about it in terms of time that the pressure is high (dwell time), also consider bolt velocity.
Too high a velocity and you can have FTE and bolt over run problems were the magazine spring isn't pushing the next round up fast enough, bolt too slow and with a fixed mass as it has you can have short stroke or failure to feed, etc. Both change in terms of each gun's tolerances and amount of dirt in the system, etc. I've never once seen a truly legit running 7.5" 556, I've see TONS of safe queens and image thread models though. Do you have the time and tools it takes to really work this stuff out - or should you just buy a quality 11.5" and be done with it?
Short story, 556 at 11.5"-20" are easy to make run well. Compromises are made at 10.5". Under 10" is just dumb considering the prevalence of 300blk that works pretty well from 8" and on.
Kind of OT, but this chart always bothered me. What's with the dip showing lower velocity with a 12.5" barrel.
Lots of love for the 12.5" reading through threads, but the chart makes it seem pointless vs an 11.5" and doesn't really make sense.
Careful. That chart is from one gun on one day, one example. It's an anecdote, not a rule.
Careful. That chart is from one gun on one day, one example. It's an anecdote, not a rule.
Yeah, but it is the only numerical data i've seen comparing 11.5-12.5. Anyway forget I said anything...started a new thread so as not to derail this one.
What mags are you running? Barret? And how reliable have they been?
I have been using both Barret and PRI mags. Both have been flawless but I like the PRI's more mainly because they seem a little easier to load. I think there is a hint more room for rounds with a slightly longer OAL.
Seriously guys, when the barrels get this short, some things come up.
While you can make it 5.56, 6.8, 300 BLK, or whatever. What tends to work preferably of those in these short lengths? What dedicated parts do you need to run that? Are you willing to spend for the extra expense?
If you are caliber limited, then something in the range of a 11.5" 5.56 can fit many. It's not great, but not too bad.
The range of barrel lengths could shorter with 6.8 by some, but the balance has many sacrifices in many ways.
You can run a 6" 300 BLK platform pretty well, but that is also a balance.
There is a lot in play here. Basic operation in terms of the AR platform is forgiving.
Would you prefer to be on one side of either end of the spectrum, or closer to the middle for operation?
KalashniKEV
01-19-16, 02:20
300 blackout is the way to go in SBR sub 11.5" IMHO.
This, period. Done.
5.56s PDWs suffer from poor performance, spotty reliability, and are 100% neck-beard-status.
.300 BLK is made for going short and quiet.
Most of you guys complaining about $ and stocking a new caliber would be much better served by a 10/22 takedown.
Isn't the purpose of a "truck gun" to get stolen anyway? Plus it fits better into all sorts of odd bags and compartments for psycho operations...
I had the same question, and the same reasons for the questions. I asked an owner of the 8.5 556 and he said the blast was similar with supers but less with 300 subs for what that is worth. I would Imagine that having a more complete powder burn in 300 would reduce the concussion somewhat, but by how much I couldn't say. I would say that the flash seems to be universally agreed to be less. Im not sure it is enough to pay more then x2 for the ammo though.
Springfield
02-18-16, 06:10
I don't have any experience with 5.56 in barrels less then 11.5'' but I do have a 8.2'' Noveske upper that runs like a top. I feel the muzzle blast is similar to a 14.5'' 5.56 and those 110 gr Barnes rounds pack a punch. Swap in some subsonic loads and a suppressor and they are about the most fun you can have with your clothes on.
Many of you probably already know this but I haven't seen it mentioned on this thread yet and I think it is relevant. 300 blk is loaded with magnum pistol powder vs the rifle powder used for 5.56. Faster burning powders do not suffer as significant of velocity drops when the barrels get shorter which is why the blackout still has respectable numbers in less then 10'' barrels.
If you want a very short barrel for anything besides range use, I would favor the .300 blackout.
I would say that the flash seems to be universally agreed to be less. Im not sure it is enough to pay more then x2 for the ammo though.
If the requirements call for under 10.5 I would say the ballistics are.
From a reliability standpoint, does it have to do with the gas system? Is it the lack of dwell time that makes it unreliable? What if you had the 7.5" 5.56 suppressed 100% of the time to increase pressure and dwell time?
Everything is relative.
The fundamental issue is 7.5" is very short for the pressure curve of 5.56.
Gas port pressures at the pistol length start very high but drop very quickly.
7.5" is good match for 300 blk pressure curve.
eljimbo142
02-19-16, 00:39
my 8.5" noveske w h3 buffer has ran perfectly 4 well over 1000 rounds. 193, 855, and the cbc 77 grainers. no problems what so ever. it is my primary hd weapon. i am in a wheelchair and it fits through doorways nicely in my lap. VERY loud. i also considered 300 blk but i like to shoot. i still do not have all of the necessary loading equipment. when i do, i will get a 300 blk upper. for now i have no doubts that my 8.5 noveske in 5.56 will protect me and family inside of 50yd. i think i will try some of those 50g tsx though.
hope that helps
james
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