Photo of blowback through ejection port?

[dbooksta]

Earlier this year I remember seeing a photo of a suppressed SCAR during the ejection phase that clearly showed propellant gases being blown back out the ejection port. I've been searching for it for hours now to no avail.

Does anyone happen to have a URL for that photo, or any other good photos of the phenomenon on a suppressed autoloading rifle?

[continuity]

Not sure why you need a picture, unless it's for the cool picture value. It's a physics thing. When a semi's bolt unlocks and opens, there is always some residual pressure venting from the chamber. When a suppressor is added to the equation, that residual pressure is magnified.

[Historian]

Not sure why you need a picture, unless it's for the cool picture value. It's a physics thing. When a semi's bolt unlocks and opens, there is always some residual pressure venting from the chamber. When a suppressor is added to the equation, that residual pressure is magnified.

+1!

Pithy. Perfect.

Unfortunately today 'physics' for most 'Low Information - You Know Whom They Vote For Folks'
comes in a box marked Ex-Lax or MiraLAX.

[dbooksta]

It's a "picture's worth a thousand words" thing. When you see this picture you'll appreciate it.

It was posted on a forum, but since I've been on over a hundred different gun forums this year I haven't had any luck remembering where!

[dbooksta]

Found it!

[este]

Of course it's a physics thing. But it's pretty good proof that piston guns aren't actually any cleaner than DI because the instant that action opens which happens at high pressure with the can, all the crap is coming down the barrel.

I swear if all the DI guns came with gas regulators like all the piston guns do, it never would have been even a question as to whether retro-fit piston kit were a good idea (they aren't).

I think back to all of those silly animations that on youtube showed how DI would cough up a black lung every shot....

[dbooksta]

But imagine if you were building a piston action for a permanently suppressed gun. If you could count on that backpressure being there I imagine the piston system could be tuned to unlock later when chamber pressure has fallen off, resulting in significantly reduced blowback.

[este]

But imagine if you were building a piston action for a permanently suppressed gun. If you could count on that backpressure being there I imagine the piston system could be tuned to unlock later when chamber pressure has fallen off, resulting in significantly reduced blowback.

Where is anything you have written specific to a piston system? Noveske and others sell very small gas port (.046 or so) AR barrels on request that are for and occasionally marked "SUPPRESSED USE ONLY". This isn't entirely uncommon.

If you buy a thread-on can which are the lightest, cheapest, shortest cans available, and semi-permanently lock in on to the barrel, there would no sense in having a normal sized .067+ sized gas port. You'd want the small port.

But this isn't related to piston vs DI at all. Only that DI makes more sense in ARs of course. But yes, if you had a suppressed SCAR you could run a small port... Although that's what the adjustable regulators of piston guns are supposed to do, I've just found almost every single one of them to still be slightly overgassed.

[dbooksta]

that's what the adjustable regulators of piston guns are supposed to do, I've just found almost every single one of them to still be slightly overgassed.

Yes, maybe it's not unique to piston guns. It has just been my experience that piston actions are more sensitive to timing, volume, and/or pressure than DI when running suppressors and/or reduced loads. I've modified valves on them to compensate but it always takes more gas to cycle them than on DIs.

[bkoski]

Not sure if I'm adding anything to the discussion here, but I'll go ahead anyway, even if only for the "cool picture value".

http://www.youtube.com/watch?v=Taf1Ij5Ct9c

Noveske 10.5" 5.56 upper on a Stag SBR lower.
Noveske Switchblock - Normal or "unsuppressed" mode
I believe it was 5.56 62gr Green Tip

I just wanted to show that even unsuppressed, there is significant blowback into the ejection port area. Judging by the flame pattern, this doesn't seem to be coming through the gas tube, but rather back down the barrel. Maybe someone can explain this further if I'm incorrect in my assumption, as in maybe just hot unburnt powder that finally found some oxygen? Either way it's cool looking

[dbooksta]

That is pretty cool. Here's two frames of the "ejection flash."




You bring up another question I haven't found a satisfying answer to, which is "what causes muzzle flash?" I've been told all smokeless powder is formulated to be "rich," meaning they contain insufficient oxidizers to fully burn, and that this helps to keep chamber temperatures down. Seems like that would obviously cause flash when they hit the atmosphere. But then why can the flash be suppressed at the muzzle by flash suppressors that only change the direction of some of the effluent?

[Historian]

That is pretty cool. Here's two frames of the "ejection flash."




You bring up another question I haven't found a satisfying answer to, which is "what causes muzzle flash?" I've been told all smokeless powder is formulated to be "rich," meaning they contain insufficient oxidizers to fully burn, and that this helps to keep chamber temperatures down. Seems like that would obviously cause flash when they hit the atmosphere. But then why can the flash be suppressed at the muzzle by flash suppressors that only change the direction of some of the effluent?

Now I finally understand Smokey the Bear when he says
"Only you can prevent forest fires!"

Is the flash a function of the ammunition fired or is it independent?
Some wacky foreign imports have different characteristics.

[Fireman1291]

Blowback on a pistol.

Note has escaping the magwell.


video of it here under the title "Silencer Boosters explained"
www.youtube.com/fireman1291

[bkoski]

Is the flash a function of the ammunition fired or is it independent?
Some wacky foreign imports have different characteristics.

I'm pretty sure I was shooting Federal XM855LC1 (62gr FMJ Green Tip) from a 420 count bulk pack. I have some other 223/556 ammo laying about but that's what I normally put through my AR rifles.