Is a 7.5" Barrel Viable?

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08-10-20, 23:30
9X19mm

Quote:

Originally Posted by CRAMBONE

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:
08-10-20, 23:34
Nowski87

Quote:

Originally Posted by CRAMBONE

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.

Sent from my iPhone using Tapatalk
08-10-20, 23:40
Sry0fcr

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.
08-11-20, 01:11
Defaultmp3

Quote:

Originally Posted by georgeib

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:

Quote:

Originally Posted by DocGKR

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.
08-11-20, 03:24
vicious_cb

Quote:

Originally Posted by georgeib

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.
08-11-20, 06:07
SBRSarge

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.
08-11-20, 07:53
AndyLate

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
08-11-20, 08:47
1168

Quote:

Originally Posted by vicious_cb

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.
08-11-20, 13:17
Leaveammoforme

Quote:

Originally Posted by vicious_cb

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. :)
08-11-20, 19:17
Disciple

Quote:

Originally Posted by 1168

~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?

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