556 NAS3 77gr SMK
- Thread starter jeff
- Start date
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bpaich1225
Member
I look forward to your results
Milo'sSyndicate
Well-known member
Which Chrono did you get?
I’m interested to see the results on this.
jeff
Well-known member
It’s the Garmin Xero.
jeff
Well-known member
I’ll let you know. Can is a Hux Flow6K.
jeff
Well-known member
I have a 10.3 and a 13.7” for testing. Not apples to apples, but I have Bonefrog 77gr SMK’s for “comparison”.
Spencer
Member
Been looking for a good (not overly expensive) 5.56/.223 77gr to shoot suppressed. Keep us posted.
jeff
Well-known member
Finally had a chance to get out to the range ro capture some data. I had the 10.3 up first. After 4 rounds of the NAS3’s I stopped testing it and you can see from the pictures why. Velocity > 2500 fps from a 10.3.
Here is why I stopped testing any further:
I have no ideas on what to attribute this to but where the cases are seperating, are where I believe the 2 case materials join. I’m going to share this with the manufacturer to see if they have seen this before in an SBR.
I may try another run to see if I have same/similar results in my 13.7”. Maybe a bad Lot?
Disappointed but this isn’t ammo I would use normally.
Here is why I stopped testing any further:
I have no ideas on what to attribute this to but where the cases are seperating, are where I believe the 2 case materials join. I’m going to share this with the manufacturer to see if they have seen this before in an SBR.
I may try another run to see if I have same/similar results in my 13.7”. Maybe a bad Lot?
Disappointed but this isn’t ammo I would use normally.
jeff
Well-known member
Just spoke with the manufacturer. I submitted a contact form on their website and they reached out within 10 minutes.
We had a good phone conversation and there is the potential that this is a case of premature extraction due to the larger volume of gas produced by these rounds. It’s not so much an increase in pressure, but volume. These rounds are dwell sensitive and this gun is a carbine length gas system.
They are sending me another box for testing and I’ll report back. In the meantime, I’m going to test the current batch in my 13.7, with the mid-length gas system, and record the reaults.
Steve Johnson
Active member
Gross oversimplification...the gun is trying to extract a case that has not yet finished the firing process. Based on my experience with the Stoner platform...most shortys use a pistol length gas system... the folks loading the ammo are increasing gas pressure and gas volume to increase velocity....maybe even testing in an actual Piezo transducer barrel...??maybe?? (grinning) One of the Engineering 101 rules is: "There is no such thing as a free lunch." This means that the additional propellant burns and creates additional gas and pressure as they pass through the port and head into the BCG. This renders the system under higher pressure with a larger volume of gas behind supporting said pressure increase. (it's ejecting hardAF) The further the muzzle is from the gas port, the longer that pressure "dwell time" on the operating system will be, and the more energy will be transmitted to the BCG, which is, meanwhile, actively trying to rip the case from the chamber....while the cartridge case is still under pressure. I suspect the separation exhibited in the images is a mechanical separation caused by the firearm, not the cartridge case separating because of pressure alone. I suspect the ammunition would not do the same thing if fired in a fixed breech firearm. Also, please keep in mind bolt and extension metallurgy is engineered to deliver safe and reliable performance at around 60,000 psi... Running pressure up 30%-ish will also disproportionately increase the interface pressure between the bolt and extension lugs as the same thing described above is also happening to those parts. Not all bolt and extensions are created equal from a metallurgical perspective and if they let go all the way...the buffer and spring might not be enough to get the BCG stopped prior to it encountering "other things" on it's path rearward...
jeff
Well-known member
“while the cartridge case is still under pressure. I suspect the separation exhibited in the images is a mechanical separation caused by the firearm, not the cartridge case separating because of pressure alone.”
Yes. This tracks with my conversation with them. Which I probably failed to accurately post.
The reason he is sending me a new box is NOT due to suspect ammo per se. But, they did have some minor quality issues with some of the case heads and the lot I have here falls into that . They are sending me a box from the newer lots for comparison. This issue is not something they are seeing from anyone else. As you mention, it’s something mechanical.
They also suggested marking up the case rims with dry ease marker to look for extractor “swiping”.
Yes. This tracks with my conversation with them. Which I probably failed to accurately post.
The reason he is sending me a new box is NOT due to suspect ammo per se. But, they did have some minor quality issues with some of the case heads and the lot I have here falls into that . They are sending me a box from the newer lots for comparison. This issue is not something they are seeing from anyone else. As you mention, it’s something mechanical.
They also suggested marking up the case rims with dry ease marker to look for extractor “swiping”.
Steve Johnson
Active member
I will definitely be curious to see how it works out...I try and be very judicious with unsolicited advice, and I know you didn't ask, but man, I'd really make sure you're running a squared away bolt and extension. I suspect that is the most likely next "point of failure" in the system when you start stacking double digit percentage pressure increases.
jeff
Well-known member
You see the build here ->
Thread 'Winter Build Part 2'
https://society.fieldethos.com/threads/winter-build-part-2.668/
Steve Johnson
Active member
Very cool build. I do like the carbine length system on the 10.3 with the small port for what you're doing here, that's a good call.
jeff
Well-known member
Thank you. With regards to advice… Thats generally why I post here. There is a vast pool of experience here in the Society. Being that I’m a hobbyist at best, sage advice and commentary are welcomed
If you want to argue large scale video distribution over multicast or IP, I may have some strong opinions to share. Or even *nix enterprise virtualization systems
Steve Johnson
Active member
Happy to help with what I am able... I don't believe you could have built a short 5.56 any better than you did, objectively speaking.
I'm going to have to google what you said in the second two sentences, but if you know digital stuff and how to get it in front of a lot of people... I would LOVE to work out some kind of a knowledge swap... haha
I'm going to have to google what you said in the second two sentences, but if you know digital stuff and how to get it in front of a lot of people... I would LOVE to work out some kind of a knowledge swap... haha
