View Full Version : Is a 7.5" Barrel Viable?
So as the title asks, is a 7.5" barrel viable? I was involved in a discussion on a small forum I frequent, and one of the posters seemed to think so. I know what I've read here that a 10.5" barrel is really the minimum viable length, and tried to explain that terminal ballistics suffer dramatically below that length. I explained that rifle wounding is based on hydrostatic shock, and that once you lose that much velocity, you may as well be using a PCC.
His response was that he was getting 2300 fps with Barnes 60 grain TSX bullets, and that they expand down to 1800 fps, and that hits at 100 yards were easy. Doesn't this just bolster my comparison to a PCC?
Would any of you kindly educate me a bit further, please?
I did a bunch of reading up on this too. What I came up with is that it is viable as a very short range tool. With modern ammo that does its work at lower velocities, it should work. It won't be ideal though. I stayed with a 11.3 because of the muzzle blast and reliability over a broad range of ammo types.
PracticalRifleman
08-10-20, 09:37
The shorter the barrel, the less range it is effective and the more important ammo selection is. If going under 11.5”, I would choose .300 Blackout.
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Well, if by viable you mean would I want to get hit by a bullet coming out of a 7.5" barrel, then yes, sure they are viable. But you are absolutely giving up a lot of velocity, and with it potential terminal performance and, IMHO getting almost nothing back in return. I owned a 7.5" upper for a while, but rarely shot it and eventually sold it. At that length you are getting a huge fireball out the end of the barrel. Also, you end up having to put your support hand almost against the receiver. I'm not someone who does that whole "C clamp" thing with my support hand, but having to put your support hand that far back is just not ideal.
To me, if you are going the SBR route, a barrel between 10.5" and 12" is the ideal. Still very short, maneuverable and light, yet you maintain decent velocity. Or you could just switch to 300 BO and get even better ballistics.
Viable for a small niche. Discrete carry, break contact type weapon system. That’s what they’re for.
Viable for a small niche. Discrete carry, break contact type weapon system. That’s what they’re for.
I think this is really it's niche, right here. But the question I have is why would this be any better than a PCC?
There is a youtube channel that I subscribe to, the guy is former LEO and worked in the industry blah blah. But he swears by the 7.5 for vehicle stuff due to the over all size, but I really can't behind the whole thing especially when he says 55grn is as heavy as he can use to be effective or accurate.
There is a youtube channel that I subscribe to, the guy is former LEO and worked in the industry blah blah. But he swears by the 7.5 for vehicle stuff due to the over all size, but I really can't behind the whole thing especially when he says 55grn is as heavy as he can use to be effective or accurate.
And?? Who is it?
The cahnnel is under Abner Miranda. I hope I spelled that right, I like his info as another perspective.
So as the title asks, is a 7.5" barrel viable? I was involved in a discussion on a small forum I frequent, and one of the posters seemed to think so. I know what I've read here that a 10.5" barrel is really the minimum viable length, and tried to explain that terminal ballistics suffer dramatically below that length. I explained that rifle wounding is based on hydrostatic shock, and that once you lose that much velocity, you may as well be using a PCC.
His response was that he was getting 2300 fps with Barnes 60 grain TSX bullets, and that they expand down to 1800 fps, and that hits at 100 yards were easy. Doesn't this just bolster my comparison to a PCC?
Would any of you kindly educate me a bit further, please?
That condensed generic answer is no, 7.5" is not a viable barrel length for shooting people who are intent on killing you (assuming we are talking 5.56 / .223). Don't listen to people who comment that they can get hits at 100 yards as that means nothing. EFFECTIVE rounds on target is what counts.
I know some people will say that it is only for short range engagements, but the problem is that you don't get to pick and choose your distances. I don't care if you think you will only shoot in your house, a 7.5" barrel still sucks.
I also know that some people like to say. "Would you want to get shot by it"? My answer is yes, I would much rather be shot by a 7.5" barrel than an effective barrel length like 10.5"+ barrel lengths. Once again, ignore the ignorant people who are making comments like that.
There is a youtube channel that I subscribe to, the guy is former LEO and worked in the industry blah blah. But he swears by the 7.5 for vehicle stuff due to the over all size
No. Just no.
That condensed generic answer is no, 7.5" is not a viable barrel length for shooting people who are intent on killing you (assuming we are talking 5.56 / .223). Don't listen to people who comment that they can get hits at 100 yards as that means nothing. EFFECTIVE rounds on target is what counts.
I know some people will say that it is only for short range engagements, but the problem is that you don't get to pick and choose your distances. I don't care if you think you will only shoot in your house, a 7.5" barrel still sucks.
I also know that some people like to say. "Would you want to get shot by it"? My answer is yes, I would much rather be shot by a 7.5" barrel than an effective barrel length like 10.5"+ barrel lengths. Once again, ignore the ignorant people who are making comments like that.
Agreed. My response to him was that I'd seen people make hits at 300 with a .22LR, does that mean that's all we need? Ultimately my opinion on the matter is that what makes a rifle a rifle is hydrostatic shock producing velocity. Once you lose that, you're reduced to having to use "tricks" such as expanding bullets, and you may as well just use a PCC.
turnburglar
08-10-20, 15:40
I would rather Rock my Cz Scorpion in 9mm, than a AR that short. Too much blast for me. And a 10.5 isn't THAT much longer in the total over all length. My go to is a 10.5 AR so I am not biased against short AR's.
I would rather Rock my Cz Scorpion in 9mm, than a AR that short. Too much blast for me. And a 10.5 isn't THAT much longer in the total over all length. My go to is a 10.5 AR so I am not biased against short AR's.
^^Agreed^^
No. Just no.
Oh I know if it isn’t 300 bulk I’m going 11.5 like I did with my current house gun. But the new BRN 180s uppers in 300 blk is calling me.
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The shorter the barrel, the less range it is effective and the more important ammo selection is. If going under 11.5”, I would choose .300 Blackout.
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This ^^^^^^^
ODgreenpizza
08-10-20, 21:31
Viable for recreational purposes
OutofBatt3ry
08-10-20, 22:00
300blk out of a 9 inch barrel makes roughly 1100ftlbs of energy.
5.56 out of a 7.5" Barrel makes roughly 700ftlbs of energy.
Pretty huge difference.
With that being said, a .357 mag makes about the same energy in common barrel lengths. (between 600 and 700ftlbs)
For comparison, 9mm makes around 400ft/lbs on the high end.
Are there better options for a 7.5" barrel? Absolutely.
Is a 7.5" 5.56 effective for self defense, especially inside of 50 yards. Yes.
If you don't want the hassle of chasing a hard(er) to find and more expensive caliber, and still want significantly more power than a 9mm/.45 PCC, and want a super compact and an incredibly accurate AR pistol, a 7.5" is fine.
Would I rather get shot with a 11.5" or a 7.5" 5.56?
The correct answer is neither. In both scenarios, you'll probably die equally as fast.
I’ve been close to building/buying a 7.5 barrel rifle several times. But posts like Stickman‘s and others easily found on the net have held me back. Also many prebuilt complete 7.5 rifles from different companies use a 2-3 inch long flash hider device of some sort, which begs the question why not just go with a 10.5 to start with? They look cool and I like the idea of a short 7.5 barrel in close quarters... but my shortest barrels currently are 10.5 and 11.5. Physics and all that. Just not sure I want to spend the time and money to find out in person.
There is a youtube channel that I subscribe to, the guy is former LEO and worked in the industry blah blah. But he swears by the 7.5 for vehicle stuff due to the over all size, but I really can't behind the whole thing especially when he says 55grn is as heavy as he can use to be effective or accurate.
Has he ever shot a 7.5” gun from inside a vehicle? I’ve shot 10.5” 5.56 guns from inside a vehicle and it sucks.
Has he ever shot a 7.5” gun from inside a vehicle? I’ve shot 10.5” 5.56 guns from inside a vehicle and it sucks.
This is why all the complete 7.5 guns from companies have those big chunky 3-4 inch flash hiders muzzle breaks on them. My 10.5 isn’t that bad... but I haven’t shot it from inside a car. And I hope if I ever have to, it’s not from inside of my car.
:lol:
Has he ever shot a 7.5” gun from inside a vehicle? I’ve shot 10.5” 5.56 guns from inside a vehicle and it sucks.
He has and does quite often. He uses that or and SBR’d Glock 17 which makes more sense than the AR.
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7.5" is absolutely viable. Just not in a 5.56/.223 chambering...
Don't argue with idiots, use your time and energy more productively.
Defaultmp3
08-11-20, 01:11
His response was that he was getting 2300 fps with Barnes 60 grain TSX bullets, and that they expand down to 1800 fps, and that hits at 100 yards were easy. Doesn't this just bolster my comparison to a PCC?I mean, 1800 FPS is still a fair bit faster than what you can drive most pistol calibers, and is still very much supersonic. Combine that with higher BCs on rifle bullets compared to pistol bullets, and I do think that a 7.5" barreled firearm shooting rifle rounds is generally going to be a better bet than a PCC. There is also the question of, what is meant by "viable"? As others noted, there certainly is a role for these kind of guns in NPEs; generally, they're not competing with the MK18 or HK416 10.4", but the MP5, APC9, or MPX, which they certainly have the edge over ballistically; yes, terminal ballistics will suffer due to such a short barrel, but with proper ammo, you still have acceptable expansion, and I've not yet heard of the limit for velocity for the round he is using where there is minimal effects for temporary cavitation. As Gary Roberts noted:
Substantial temp cavity effects can be seen with a shotgun slug at 1500 fps, while minimal tissue damage can occur with a .224" rifle projectile at 7000 fps--all depending on bullet upset. Likewise, as noted, the type of tissue subjected to stretch is also a critical component in assessing injury potential.
Obviously, there are problems with blast and possibly reliability, along with the fact that the vast majority of us do not have any practical need for a weapon that small; a MK18 with a LAW folder or a SCAR-16S with a chopped barrel can fit a normal sized day pack, and would be far more versatile.
vicious_cb
08-11-20, 03:24
His response was that he was getting 2300 fps with Barnes 60 grain TSX bullets, and that they expand down to 1800 fps, and that hits at 100 yards were easy. Doesn't this just bolster my comparison to a PCC?
Would any of you kindly educate me a bit further, please?
Doesn't he mean 62gr TSX? Sorry but 2300 fps doesnt pass the smell test. Most 5.56 55gr loads are coming out of a 7.5" barrel at ~2000 fps. I dont see how hes getting those velocities safely.
The Ballistics By The Inch website gives results with a 7” of 2190 and 2199 for 55gr 223 loads, and 2321 for a 50gr load. Their results for a 10 inch are very close to my 10.5 chrono numbers with 223 loads. I typically see 100 o5 200 fps more with 5.56 loads using the same bullets.
That should give you the 1900 fps expansion velocity to 125 yards with 55s and around 175 with the 50s.
So yes, a 7.5” could be an effective tool if it fit your needs and was sufficient for the ranges you would realistically encounter. But dang, it would be brutal to light off, especially in an enclosed space.
With the interest lately in uber-short 556 rifles I imagine there will be some better loads in the future. A fast-burning, low flash powder behind the 45 or 50 gr tsx might do well.
Stick's first reply basically says it all.
If I needed a more compact rifle (or "pistol") than a 10.5" AR, I would be looking for a smaller package, probably something with a collapsible stock/brace and no buffer tube, and not in 5.56.
I enjoy my 11.3" 5.56 but don't recall ever wishing the barrel was 4 inches shorter.
Andy
Doesn't he mean 62gr TSX? Sorry but 2300 fps doesnt pass the smell test. Most 5.56 55gr loads are coming out of a 7.5" barrel at ~2000 fps. I dont see how hes getting those velocities safely.
He’s probably guesstimating with 50TSX.
A 7.5” 556 gun is <probably> superior to 9mm terminally, up close. However, comma, guns of such short length are often plagued by reliability and ergonomic issues. As well as absolutely stupendous blast and flash. And the ballistics are needlessly sub-par. If one must have such a short gun, an 8.5” 9mm is roughly the same OAL +1/2”. Put a KX3 or one of those stupid ass flash cans on the 5.56, and suddenly even 10.5-11.5” 9mm barrels become similar. Or a 10.3” 556 with an A2.
~8” barrels set up for full time suppressed with long and quiet cans and full time subs make sense. Kinda. In a niche way. Particularly if you don’t use a flashlight or IR laser.
The real problem here is not having the knowledge or skill to manage and manipulate your rifle. Suppressed 10.3-11.5” barrels work just fine in a structure or car. Unsuppressed 12.3”-14.5” guns also work fine. I’ve got an A1 stocked 18” gun that I routinely use to prove that point. If you need the gun to fit in a laptop bag, or you clear narcosubs for a living, then just ignore me. But, I clear meth trailers, professionally, and pretty much anything works. Including a suppressed 16”. The 11.5” buys you ~4” of laziness with driving the gun.
Leaveammoforme
08-11-20, 13:17
Doesn't he mean 62gr TSX? Sorry but 2300 fps doesnt pass the smell test. Most 5.56 55gr loads are coming out of a 7.5" barrel at ~2000 fps. I dont see how hes getting those velocities safely.
I've chrono'd M855 at just under 2400fps. I have a very light 223 load with a 55 grain VMAX using 21.2 grains of R10X that still runs 2100 fps. I start having cycling issues when loading down to around 1950 fps with a 55 grain projectile. Maybe I have a fast barrel, dunno.
I recently acquired some I4198 that seems like it will be a great powder for the 7.5". Excited to load up some light projectiles with it. Still chasing my 3000 fps from a 7.5" unicorn. :)
~8” barrels set up for full time suppressed with long and quiet cans and full time subs make sense. Kinda. In a niche way. Particularly if you don’t use a flashlight or IR laser.
The last sentence of this went over mind head. Do you mind explaining?
PracticalRifleman
08-11-20, 19:20
The last sentence of this went over mind head. Do you mind explaining?
He’s meaning being discreet with passive aiming under NODs.
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I would never buy a <10.5” 556. Thats what 300blk is for. The blast and reliability are the two biggest reasons.
Also, if I need something tiny, Ill probably just use a pistol.
Lastly, Im beginning to think what you lose in terminal ballistics can be “made up with” in many situations with speed and maneuverability. Something offensive would be different, but for surprise defense use, getting a holstered pistol out and on target is going to be faster than digging out a rifle.
Under 10.5 with a 556 you are buying a range toy in my opinion. You are money ahead to get some type of PCC if you need a working gun.
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.223 Speer Gold Dot 55g from a 7.5 AR Pistol. Video includes gel penetration, velocity, and expansion results.
https://youtu.be/6R2_h27yIWQ
This is why all the complete 7.5 guns from companies have those big chunky 3-4 inch flash hiders muzzle breaks on them. My 10.5 isn’t that bad... but I haven’t shot it from inside a car. And I hope if I ever have to, it’s not from inside of my car.
:lol:
That blast hurts, you better be running dual ear pro.
The last sentence of this went over mind head. Do you mind explaining?
Lack of rail restate
He’s meaning being discreet with passive aiming under NODs.
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Lack of rail restate
Yup. Both of these are what I was getting at.
I guess ultimately, a 7.5" 5.56 is a limited role niche weapon with serious drawbacks, but in 300 BO is probably just fine. Which was my perspective from the get go. Some folks just need to justify their purchases.
Glock9mm1990
08-19-20, 08:23
I honestly don’t like anything less then a 14.5” barrel.
Revolution37
08-19-20, 20:29
Depends what you're going to use it for.
A 7.5" barrel may be fine for playing with on the range, but if you're ever going to have to maybe use it to defend yourself (even if it's "just a truck gun") you'd be better served with .300BLK, or probably better yet, a similar size PCC like a CZ Scoprion. 147gr bonded hollow point ammo from the 7.7" barrel on the Scorpion is probably a better bet than 60gr ammo from a 7.5" AR, and the 9mm will suppress better if you're into that sorta thing.
Just my two cents. FWIW, my agency does not allow AR barrels below 10". I think 11.5" is probably the sweet spot in size and ballistics. Ballistic Advantage makes a 12.3" barrel that I think would be nice on an SBR, too.
Ballistic Advantage makes a 12.3" barrel that I think would be nice on an SBR, too.
It is.
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