Suppressed 7.5 5.56

[Ten8DoWork]

I have a 7.5in 5.56mm duty rifle that I am wanting to run my AAC 556SD (believe M4-1000 remake) on. 5.56 is the only caliber approved for us so 300, 6.8, etc. are just not an option.

What kind of damage/wear am I realistically looking at if I qualify annually (50 rounds) on this setup and occasionally shoot it? It's mainly going to sit on the gun for patrol when I know I won't have hearing protection on. I will use a blast shield on the muzzle brake (currently have AAC brake installed) when doing high volume training to avoid unnecessary wear and tear.

I keep reading that it is "too high of pressure" or it will "destroy the blast baffles" and I fully agree and understand that wear will be accelerated but considering the above, what do you guys think? I just don't see it being as bad as it's made out to be. There is too much regurgitated information out there from people that haven't actually used a 7.5 suppressed long term.

I ran a 10.5 upper for awhile and I am in love with the 7.5 upper. It works much better for what I use it for.

I appreciate the help

[curtistactical]

viewtopic.php?f=5&t=136342

This is what comes to my mind.

[Ten8DoWork]

Thanks. I actually read that and that is something I'm concerned about. Of course there is little chance I will be firing that amount in such a short time. If I am, I really don't care what the can does at that point.

[Grounded]

a couple of factors would come into play with your choice.

Whats your typical rate of fire and how high could that go at times.

Would you need it to be dedicated or could you use a muzzle brake to absorb some of that energy

I would then consider materials of construction.

[Ten8DoWork]

a couple of factors would come into play with your choice.

Whats your typical rate of fire and how high could that go at times. ROF would be fairly low with highest being at qualification (quick string of ~10 rds at one station). I doubt it will see any auto. The only time it might see auto or any higher rate of fire; we have a big problem and I'm not concerned with the can wear.

Would you need it to be dedicated or could you use a muzzle brake to absorb some of that energy
it's an AAC 556SD and I have an AAC brake on the gun, and it won't be used for most training

I would then consider materials of construction. inconel baffles

[briansp82593]

I kind of laugh because my thread is getting posted around.

Let me break it down on the 7.5" 223/5.56 and suppressors.

Prior to me blowing up my surefire, it and other socom cans of mine get run pretty extensively on a 7.5" barrel with a muzzle brake. The key is with the brake. The brake is taking the brunt end of the unburnt powder and is redirecting the heat and gasses into an extremely heavy duty part of the suppressor.

The surefire handled 7.5" 5.56 just fine, Surefire sells the SB model for short barrel use (less than ten). The only difference between the SB and the RC is the size of the bore in the suppressor. The big scare of shooting a suppressed 7.5 is bullet instability. Think about it, If you actually have one of the few 1/7 Twist barrels, there isn't 7 inches of rifling there. Same story with the 1/9 twist barrel. And 62 grain green tip ammo did not stabilize out of my 7.5" barrel. FYI (its inconsistent s--t anyways)

The other thing is the bore pressure. On a ten inch barrel bore pressure is 12140 PSI, whereas on a seven inch barrel it jumps to 17040 PSI. That's quite an increase.


Short answer; If you have a 1/7 twist barrel and plan to run a muzzle brake, I am confident the 556-SD would handle it without any issue. As much as people trash talk AAC, they make a damn good and durable rifle suppressor. I wouldn't have any issue doing it if it were my can and lord knows I don't really feel like ruining another suppressor.


Brian

[Ten8DoWork]

Yes, that was a pretty entertaining thread about that SF can!

That's exactly the kind of information I'm looking for. I think I can rest easy with the can for limited use on the shorty.

I have a 1:7 twist 7.5" barrel and it uses an AAC brake. This is the 2 chamber one; not their flash/brake hybrid.

[db0]

I was under the impression that a 10.3 barrel in 5.56 is barely adequate for cqb. Have you researched performance of your 7.5 barrel? I'm curious how you made the decision to go that short for that caliber.

[Capt. Link.]

I'm not a fan of uber short 5.56 rifles unless the bullets tumble all the time.With that said a custom built suppressor would be a viable option.

[Smokecloud]

I was under the impression that a 10.3 barrel in 5.56 is barely adequate for cqb. Have you researched performance of your 7.5 barrel? I'm curious how you made the decision to go that short for that caliber.

This is my biggest concern. When choosing SBR's for work, I put a lot of research into the reliability of the shorty's, but even more important is that the .223/5.56 is very dependent on velocity to be an effective fight stopper. 11.5" of barrel lowers the velocity enough that you have reduced your effective range to about 75 yards according to several different studies and bullet manufacturers. Go down to a 10.3" barrel and your effective range is reduced to 60 yards. When you couple that with the need to run very hot ammo to cycle the gun reliably, the 11.5 was the better bet for the increased range and increased reliability due to the longer dwell time. I know the 7.5" runs a pistol length gas system and changes your reliability curve, but 7.5" is not going to provide enough velocity to be an effective fight stopper. We all like how handy the super shorty's are, but handy only goes so far.

Another side decision point would be the minimum barrel specs from a specific suppressor manufacturer, if you go under their specs for bbl length, expect issues with them regarding warranty repair.

[thecameraman79]

Not to get into the ballistics of a 5.56 out of a 7.5" barrel but I don't believe AAC warrantees any of there cans shorter than 10". I'm not sure it's possible but I would look into getting another can that is designed/warrantied for something that short like the Silencerco Saker which warrantees there sakers down to a 7" barrel for 5.56. I don't own a Saker but have heard nothing but good things so I'm not trying to convince you to buy something I own but something designed for your intended purpose rather then use something in such a way it wasn't designed...

https://s3.amazonaws.com/com.silencerco ... /saker.pdf

I am not sure there are any other companies warrantying there suppressors on anything that short for 5.56 besides the saker. I personally wouldn't run my AAC mini 4 or SDN-6 on anything that short. Now if it's the departments suppressor and they will pick up the tab if anything happens to it then go ahead and find out what will happen and report back. I'm sure we'd all like to know how it turned out. My guess is it'll handle it for a bit but to what extent or how bad will it damage it I'm sure none of us will venture a guess.

[quiettime]

I am not sure there are any other companies warrantying there suppressors on anything that short for 5.56 besides the saker...

Rugged warranties the Surge and teh Razor down to 7" and Dear Air has no barrel length restictions

[uaspilot]

I personally would not run a suppressor on a 5.56 with anything shorter than a 10.5. With that short of a barrel you are barely getting one full rotation from the rifling before the bullet exits. You are almost asking for a baffle strike at that length.

[fishman]

I personally would not run a suppressor on a 5.56 with anything shorter than a 10.5. With that short of a barrel you are barely getting one full rotation from the rifling before the bullet exits. You are almost asking for a baffle strike at that length.

It doesn't matter how many times the bullet rotates in the barrel. What matters is angular velocity, which is a function of linear velocity and twist rate. A particular bullet needs a different angular velocity to stabilize. A shorter barrel gives you less linear velocity, therefore less angular velocity, but the bullet not making a full turn in the barrel is completely irrelevant. My dads 6" .357 barrel rotates the bullet far less than one turn in the barrel and he gets 1.5 moa at 100 yards, completely stable.

[Hned]

Go with the Rugged Surge 762. It has a no-questions-asked unconditional lifetime guarantee. It can handle barrels as short as 7" for 5.56, 300BLK, 6.8SPC, and 7.62x39mm. The Surge has a great double-seal quick-connect/disconnect mounting system. Enjoy!

[SilencedSBR]

I kind of laugh because my thread is getting posted around.

Let me break it down on the 7.5" 223/5.56 and suppressors.

Prior to me blowing up my surefire, it and other socom cans of mine get run pretty extensively on a 7.5" barrel with a muzzle brake. The key is with the brake. The brake is taking the brunt end of the unburnt powder and is redirecting the heat and gasses into an extremely heavy duty part of the suppressor.

The surefire handled 7.5" 5.56 just fine, Surefire sells the SB model for short barrel use (less than ten). The only difference between the SB and the RC is the size of the bore in the suppressor. The big scare of shooting a suppressed 7.5 is bullet instability. Think about it, If you actually have one of the few 1/7 Twist barrels, there isn't 7 inches of rifling there. Same story with the 1/9 twist barrel. And 62 grain green tip ammo did not stabilize out of my 7.5" barrel. FYI (its inconsistent s--t anyways)

The other thing is the bore pressure. On a ten inch barrel bore pressure is 12140 PSI, whereas on a seven inch barrel it jumps to 17040 PSI. That's quite an increase.


Short answer; If you have a 1/7 twist barrel and plan to run a muzzle brake, I am confident the 556-SD would handle it without any issue. As much as people trash talk AAC, they make a damn good and durable rifle suppressor. I wouldn't have any issue doing it if it were my can and lord knows I don't really feel like ruining another suppressor.


Brian

What bullet grain would you suggest running for a 7.5" 1:7 twist suppressed .556 Brian?

[Fulliautomatix]

What bullet grain would you suggest running for a 7.5" 1:7 twist suppressed .556 Brian?

.556"? Dayum, that's a big ol' bullet.

Fast twist rates are suitable for longer bullets. Longer bullets usually translates to heavier bullets.

http://www.gunsandammo.com/ammo/pair-ba ... ates-ammo/

1-in-7 Inches
This is the twist chosen by the military since the switch was made to the M16A2—and the 62gr. M855 cartridge—in the 1980s. This twist is found on the M4 carbine, the M16A4, the Mk12 Special Purpose Rifle and even the HK416. Its ability to stabilize tracer rounds in-flight is one of the reasons that the military chose this twist rate.

This barrel will stabilize bullets of up to 90 grains, and can handle the 70- to 77-grain bullets at just about any velocity, which makes it well suited for carbines with very short barrels. If you want a Mil-Spec clone, the 1-in-7 twist is the way to go.

I currently own two AR-15s with 1-in-7 twist rates—a 10.3-inch Mk18 Mod. 1 and an 18-inch Mk12 Mod. 1—both made by Monty LeClair at Centurion Arms. To illustrate how velocity and twist rates can be the ying and the yang of bullet stability and accuracy, I fired a variety of loads side-by-side from the two rifles. The 10.3-inch SBR shoots anything from 55-grain FMJ to 77-grain OTM with excellent accuracy, while the 18-inch Mk12 is scary accurate with the 70-, 75- and 77-grain bullets—but won’t shoot 55-grain or 62-grain FMJs worth a damn.