Ultra short barrel review NEW UPDATE: Third article page 5

[withoutremorse42]

V7 and R2B are both in, Mc6-sd and Veritas are both still coming, just a bit behind. I'm thinking I'll make this two range days instead of one big one, then splice the videos together

[10Driver]

I’ve gathered together virtually all the lower and upper parts I’ll need for my build. The only outstanding items are barrel, gas block/tube and the associated hand guard. Still deciding between 5”, 6”, 7” or 7.5” barrel.

I want the ballistics of the 7.5” in the compact size of the 5” barrel


Talked to SLR and a Veritas Armorer about their micro 300BLK 5” barrel assembly. They both said their non-adjustable gas block with carbine spring and H or H1 buffer is a no issues “four way” build. Not requiring an adjustable gas block.

[dellet]

I’ve gathered together virtually all the lower and upper parts I’ll need for my build. The only outstanding items are barrel, gas block/tube and the associated hand guard. Still deciding between 5”, 6”, 7” or 7.5” barrel.

I want the ballistics of the 7.5” in the compact size of the 5” barrel


Talked to SLR and a Veritas Armorer about their micro 300BLK 5” barrel assembly. They both said their non-adjustable gas block with carbine spring and H or H1 buffer is a no issues “four way” build. Not requiring an adjustable gas block.

I'll go in the skeptical camp on a lower with 5" barrel surviving a normal lifespan with suppressed supers, not to mention how many cans will hold together with 30,000+ pounds of muzzle pressure.

For a compact, suppressed rifle the way to go would be a 8-9" integral. basically the same overall length with better suppression and higher velocity for supers.

[10Driver]

Not to hijack this thread, but I probably should clarify my four ways comment.

Here’s the original post on the parts for my build:

viewtopic.php?f=128&t=102171


For now, I don’t have a suppressor. If I ever get a suppressor, I would most likely just assemble a dedicated upper that was purpose built for suppressing.

So, I’m looking to assemble a short barreled upper to fire unsuppressed supers (Barnes Blacktip, various 125-130 varmit bullets and 150 Gold Dots) and hoping I can also shoot some of those heavy Acme “Dolomite Special” cast bullets.

I would like the build to reliably function with the above loads.

[withoutremorse42]

...not to mention how many cans will hold together with 30,000+ pounds of muzzle pressure.
.

A few years ago I would have totally agreed, but with the prevalence of 300 WM rated cans (64K psi) I think they'll be fine

But it is true, anything that increases the abuse inside of the can will reduce the functional lifespan, even if only incrementally

While 8-9" may be a more optimal setup, here we're measuring out the extremes. If most civilian shooters are like me in this regard, they won't be near the functional end of a barrels lifespan before getting bored and rebuilding the upper

[dellet]

...not to mention how many cans will hold together with 30,000+ pounds of muzzle pressure.
.

A few years ago I would have totally agreed, but with the prevalence of 300 WM rated cans (64K psi) I think they'll be fine

But it is true, anything that increases the abuse inside of the can will reduce the functional lifespan, even if only incrementally

While 8-9" may be a more optimal setup, here we're measuring out the extremes. If most civilian shooters are like me in this regard, they won't be near the functional end of a barrels lifespan before getting bored and rebuilding the upper

Peak pressure and muzzle pressure are not the same. I know of no suppressor on the market that is rated for 64000 pounds at the muzzle.

The average muzzle pressure of a 300 win mag will be in the low 20k range in a 16" barrel. A sample model load of 69 grains of Varget with a 155 AMax would have 65,000 peak and less than 22k at the muzzle. In a 18" barrel that drops to 19k.

A mild load in a Blackout 125 sst 19 grains h110 is 55,000 peak and 21k at the muzzle. Run that load a bit hot at 62,000 and you have better than 22k.

So basically a 300 Blackout shooting supers in a 6" barrel will have more muzzle pressure than a 300 WM in a 16" barrel. That's why you will have a hard time finding a can rated for supers in a Blackout with less than a 7" barrel.

So the question becomes not if you get bored before you wear out the barrel, its whether you blow out $1000 can before you get tired of a $100 barrel.

I'm all for testing and innovation, but looks like you might want to look at real numbers on this project. Factory subs won't be a problem. Factory supers in a 5" barrel will have more pressure than most cans are rated for.

[withoutremorse42]

...not to mention how many cans will hold together with 30,000+ pounds of muzzle pressure.
.

A few years ago I would have totally agreed, but with the prevalence of 300 WM rated cans (64K psi) I think they'll be fine

But it is true, anything that increases the abuse inside of the can will reduce the functional lifespan, even if only incrementally

While 8-9" may be a more optimal setup, here we're measuring out the extremes. If most civilian shooters are like me in this regard, they won't be near the functional end of a barrels lifespan before getting bored and rebuilding the upper

Peak pressure and muzzle pressure are not the same. I know of no suppressor on the market that is rated for 64000 pounds at the muzzle.

The average muzzle pressure of a 300 win mag will be in the low 20k range in a 16" barrel. A sample model load of 69 grains of Varget with a 155 AMax would have 65,000 peak and less than 22k at the muzzle. In a 18" barrel that drops to 19k.

A mild load in a Blackout 125 sst 19 grains h110 is 55,000 peak and 21k at the muzzle. Run that load a bit hot at 62,000 and you have better than 22k.

So basically a 300 Blackout shooting supers in a 6" barrel will have more muzzle pressure than a 300 WM in a 16" barrel. That's why you will have a hard time finding a can rated for supers in a Blackout with less than a 7" barrel.

So the question becomes not if you get bored before you wear out the barrel, its whether you blow out $1000 can before you get tired of a $100 barrel.

I'm all for testing and innovation, but looks like you might want to look at real numbers on this project. Factory subs won't be a problem. Factory supers in a 5" barrel will have more pressure than most cans are rated for.

I'm not gonna pretend I knew the difference, and appreciate the education. I'll send an email off to SAS and see what they say

[dellet]

Here's a random sample pressure curve. Peak pressure is the highest point in the explosion that happens in the barrel, generally about an inch after the bullet leaves the case. Muzzle pressure is when the bullet leaves the muzzle and the pressure of the gasses that will need to be absorbed in the blast chamber of a suppressor.

This is a 30-06 load.


Peak pressure is 60,000, muzzle pressure at say 22" is around 10,000. At 5" there would be around 38,000psi and 20,000psi would be around 12". So a 30-06 at 12" would have the same muzzle pressure as a 5" 300 Blackout.

Most subs peak less than 25,000 psi unless you use real fast powders, in a very short barrel. The faster the burn rate, the higher the peak will be, but the faster it will drop and the lower the muzzle pressure will be..

When you look at minimum barrel lengths for cartridges in suppressors, this is most of what they are looking at.

For example this is the ratings for a Thunderbeast Ultra 7

APPLICATION NOTES
Minimum barrel lengths2:
6" 300 Blackout (subsonic)
8" 300 Blackout (full power)
10" 6.8 SPC, 7.62x39
11.5" 223 Rem, 5.56, 6.5 Grendel
14.5" .308 Win
16" .260 REM, 6.5 Creedmoor
18" 7mm RM, 300 WIN MAG
20" 7mm RUM, 300 RUM, 6.5 SAUM
22" 300 Norma Magnum, 28 Nosler, 7 STW
23" 26 Nosler

Note the minimum lengths highlighted and the comparisons I made in the previous post. It looks like Thunderbeast is rated to around 20,000 pounds.

Hope that clears things up a bit

I will add that some of the hottest loads will be in excess of 25,000 psi at 5"

[withoutremorse42]

I'm waiting back on an email from SAS, 7 more days until my first scheduled range day.

If I don't get a go-ahead from them regarding supers, I'll run the blast can on supers and suppress the subs

Dellet, I appreciate you helping me to learn about this and not blow my can up. This article may be for work, but work isn't buying me a new can!

[withoutremorse42]

The response from Tim at SAS was to stay under 20K and/or 6" and above.

Again, I appreciate the education! That would have been an expensive mistake