I have a Sig SRD556-QD supressor, mounted on a Sig 516 Patrol AR-15 rifle. The supressor manual says the max bullet bullet weight I can shoot w/ the barrel twist I have (1-7) is 77 grains. This round is very quiet, but doesn't cycle the action. Muzzle energy is 188 ft-lbs.
I also have a round that is advertised to cycle the action, but the bullet is 112 grains, energy 275 ft-lbs. So, if the only limitation the manual shows is bullet weight, I can apparently shoot a 69 grain bullet, which generates 1379 ft-lbs, with no problem.
Seems to me that if the can will take 1379 ft-lbs, it should survive 275, but the Sig customer service guy says for "legal & liability" reasons, if the manual says max 77 grains, he can't tell me anything that differs from that.
This is my first rifle suppressor, so I don't have any prior experience to fall back on..
I would like to give these 'cycling' rounds a try,.. any thoughts?

Welcome to the forum.

Can you provide a link to the ammunition you are referring to? I believe I understand what you’re asking about, but more details might be helpful.

There are usually two primary issues to be concerned about when using a suppressor: the effects of the muzzle blast gasses and the stability of the bullet.

The muzzle blast becomes a problem when it is so great that it damages the suppressor in some way. That’s why some suppressors are rated for how short the barrel can be. That should not be a problem with the load you’re referring to, based on my understanding.

The more common problem with firing very heavy bullets is because they may be too long to be stabilized by the rifling of the barrel. As I recall without doing any research, 1/7" will stabilize conventional lead core bullets up to about 80+ grains in weight. I don’t know what the twist rate would have to be to stabilize a 112 grain 0.224" bullet, but it would have to be faster than 1/7". That means if you fire such a bullet from your rifle, it will start to yaw greatly and begin to tumble in flight very quickly after leaving the muzzle. How fast that happens I don’t know, but if it occurs before it can leave the suppressor, it will damage or destroy the device.

The muzzle energy of the projectile per se isn’t something that affects whether a load can be used with a suppressor.

Added:

If this is the ammunition you are referring to, the description clearly states, “These bullets will not tumble and result in baffle strikes in properly aligned and sized suppressors.” If that is true, then there should be no problem with using that ammunition. “If,” however, is the operative word; I assume (that word) that such a company wouldn’t make such a claim if it weren’t, but what would be your recourse if your suppressor were damaged? And keep in mind that confirming that the bullet is stable as it leaves the muzzle may be difficult. Bullets often yaw more at the beginning of their flight than later, so it’s necessary to check for excessive yawing at very close range with a target material that will withstand the muzzle blast.

There are some subsonic rounds that may somewhat reliably cycle a 5.56 but they are prone to failure, guns need tweaking and are pretty anemic. I wouid rather go with a suppressed .22 as the. 223 rounds have a hideous trajectory and you are still getting bolt clack.
I've bought commercial subs including ones that claim to cycle actions ... and they will in a clean and lubed gun. Suppressor choice is important also as a baffle stack may help with more back pressure to help the cycling than a monocore or and OSS type.
I've handloaded some of the 100 grain plus projectiles and can get particular guns to cycle with buffer and buffer spring adjustments, suppressed bolt carriers and adjustable gas blocks. Seemed like too much fine tuning and did not work across all the platforms and barrel length options I have.

Thank you for your comments, gentlemen. Very helpful indeed! The ammo I'm referring to is made by Atomic,.. (www.atomicammo.com) and is sold as ".223 tatcical cycling subsonic" rounds. 112 grains, 275 ft-lbs muzzle energy.
I don't so much care how much stability the bullet has after it leaves the suppressor,.. just don't want a baffle strike before it gets through it!

That bullet won't be well stabilized by that barrel. This is a function of bullet length, but weight is a decent proxy for length. I don't know if it will wobble upon leaving the barrel or how long it will take, but it won't be stable.

Why do you not care how stable the bullet is after it gets out of the suppressor? A wobbling bullet will not be accurate. Obviously a tumbling bullet will be almost useless.

Thank you for posting,.. your comments are much appreciated! I guess my thinking is that anything I would be shooting at with those rounds would be closer than 30 or 40 yards, so pin-point accuracy might not be essential. And with a muzzle velocity of only 1050 fps, I don't know how much beyond that they would be useful, even if they were stable.
These rounds are unbelievably quiet, when suppressed, and I don't mind cycling the action manually for the lighter bullet. I just have the box of 'cycling' rounds and was curious about trying them. After hearing from you and the others, who have much more experience that I do, I think I'll not take a chance on damaging the suppressor. I will, however, try some 'supersonic' (69 gr., 3000 fps) rounds, to see what kind of difference the suppressor makes with them, regarding both noise and accuracy.

I wouldn't shoot the 112 grain bullets in a 1/7 twist carbine with a 5.56 bore suppressor. Maybe with the .308 bore suppressor that I use on AR-15s, however. You are taking a risk that bullet wobble will begin immediately upon exiting the bore. Maybe it will, maybe it won't, but I won't do it in my gun. Baffle strikes are expensive to repair, and Surefire can take a few months to get the can back in your hands.

A subsonic 223 round will be quiet with a can. If you feel you need to go this way, I suggest the subsonic 77 grain Atomic load. Note that I have no experience with subsonic 223 loads in any of my ARs. I have shot many rounds of subsonic 300blk ammo, but that's a different animal.

You won't achieve muzzle velocity of 3,000 fps with your 16" barrel and factory 69 grain loads. Expect a MV range of 2600 to 2700 fps. Your MV should be very close to 3,000 fps with 55 grain ammo.

Supersonic loads with a AR-15 will be a lot louder than suppressed subsonic loads -- maybe even louder than unsuppressed subsonic loads.

Since I haven't shot subsonic 223 loads, I don't know what their accuracy might be. I do know a lot about 22lr loads in 22lr, which can be very accurate -- even out to 100 yards. But the wind really tosses these subsonic loads around. Expect to see a lot of lateral drift in winds, and maybe even some vertical drift if you shoot in terrain that isn't level.

Supersonic 223 ammo can be quite accurate -- when the specific ammo plays well with the gun's chamber & barrel, when the barrel is made well, and when the shooter has well-developed skills behind an AR15. The 69 grain Sierra Match King bullet is among the most consistently accurate bullets across a variety of barrels. So are the 55 Sierra Blitzking and the 55 Hornady VMax. For heavier bullets, many barrels do really well with 77 grain Sierra Match King and 75 Hornady HPBT.

Thanks very much for your thoughts, fritz. The 77 grain subsonic round by Atomic is what I'm using now, and per your advice and others' I am not going to try the 112 grain loads through the can.
The .308 bore suppressor is an interesting idea, and I'll have to decide if I'm willing to spring for another one, (and wait another year for the stamp), just to try the 'cycling' rounds.
Also appreciate your recommendations on some supersonic rounds.

What level of accuracy are you seeing from the 77 grain subsonic load? At what distances? And with which type of optics/sights?

I wouldn’t risk it either. Hate to say it ($$), but a .30cal suppressor and .300 Black upper are probably in your future.

You could be right on that, Matt.. :-)
Fritz, regarding accuracy, I really haven't a chance to get a feel for that, yet. First session w/ the ammo was mostly spent trying to adjust gas port to get the action to cycle, and getting the scope zeroed. Scope is a ATN Thor HD Thermal 2-8X. I'll post here again, after I've had a chance to put a few more rounds through, at various distances.

I would be curious to learn of your accuracy results. Most of the subsonic loads I have fired have exhibited mediocre to horrible precision. One 308 load I tried had a vertical spread of 18(!) inches at 100 yards.

See, I’m thinking similar things, for use on pigs, but I think a 45 or 10mm out of a Kriss vector is more effective than a 300 blackout.

What about a 223 bolt action? What about using a 22 mag can with those 112gr subsonic loads?