Has anyone seen ammunition testing done with very short barrel 5.56?

The current PDW thread has me wondering...

A few years ago I built a 7.5” AR pistol as a range toy. However, somewhat to my surprise I’ve found it is actually very handy and reliable over the course of 800 or so rounds, and with current events it has been pressed into trunk service. I figure it’s better than throwing rocks, and I can easily make accurate hits under stress out to the limited distance that I could reasonably and legally be expected to defend myself as a civilian. It has a 1/7 barrel.

By way of background (and as an attempt to head off the “7.5” 5.56 is crap and will get you killed” comments) I’m using it strictly as a “oh shit” weapon - when I feel the need a more capable carbine rides on the floor behind the front seat. The 7.5” currently stays in the car all of the time stashed and tether locked under the parcel deck just like my fire extinguisher, trauma kit and jack. I realize it’s not optimal, but neither is the small fire extinguisher I carry.

My question - has anyone seen testing on what type of quality load is likely to stabilize best in such a short barrel? Heavy or light? I’m not concerned about terminal effects beyond the ability to stabilize at this point - there is a bit of talk in the PDW thread where commonly used defensive rounds tumble. I’ve shot mostly crap range ammunition through it (probably 90% WWB .223) and have never seen evidence of tumbling.

This is likely to get rebarreled as a .300 BLK at some point but it’s what I have right now.

What is the barrel twist?

With such a short barrel in 5.56mm, you are likely best off using an expanding projectile like a 50-55 gr TSX or GMX, 55 gr Gold Dot/Fusion, or 55 gr TBBC.

Under 10-12" barrels or so, .300 BLK is superior to 5.56 mm.

It’s a 1/7 - that was buried above.

There’s a series Of 7.5 gel tests in the YouTube channel poboyspecial
Also great for figuring out what 5.56 does at long range.
Spoiler it’s not like getting smacked with a .22

Do we already have a thread or resource on this? Perhaps 8" is the wrong threshold, maybe it should be <10"?

I'm curious as to where we hit the "floor" with specific loads as well as perhaps recommendations for loads given that the decision to fire them from (for example) a 7.5" barrel has already been made.

I started this one about 5.56, but it didn’t attract a lot of attention.

https://pistol-forum.com/showthread....rt-barrel-5-56

Shit, the blast alone from 5.56 at that barrel length is enough for me to go .300BO, not to mention that if you want to suppress it, your choices are somewhat limited.

Quote:

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Originally Posted by HeavyDuty

I started this one about 5.56, but it didn’t attract a lot of attention.

https://pistol-forum.com/showthread....rt-barrel-5-56

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maybe we could get @LittleLebowski to merge them to talk about both calibers

Quote:

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Originally Posted by LittleLebowski

Shit, the blast alone from 5.56 at that barrel length is enough for me to go .300BO, not to mention that if you want to suppress it, your choices are somewhat limited.

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I know there are a ton of other issues, but I was hoping to strip this down strictly to the ballistics at various lengths.

I was going to start a similar thread but since its already here.... Id be interested if 7.62X39 could be added to the discussion? The data im looking for is what is the barrel length threshold for effectiveness to distance X. This would be helpful for individuals to evaluate which solution fits their circumstances.