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Okay - I dug out some votive holders and tea candles from our stash of wedding stuff, and went to town to soot up some bullets.
Prior to doing this, I did try again with some bullets that I marked up with a blue marker, and I failed to get any marks on the surface in this Mossberg barrel, or in my Spikes carbine. Perhaps the mark I saw and measured yesterday was handling induced? I don't know.
So, fast forward to the candle sooted bullets. I decided to use Winchester Ranger 5.56 ammo with 64gr Nosler bullets. They have less taper than the 62gr OTM, or the 62gr PPU, so I thought I would have a better chance of getting visible marks with this setup.
The candle soot method is very good for easily getting a visual on any marks that will be introduced by the throat leade. It is also very good for getting a visual on all and any handling marks that may occur by hand dropping the round (if it rotates as it drops), and letting it fall out and whatever it may hit on the way.
With that said, I had to repeat this exercise with care many times to try and get results that were worth anything.
After many repetitions, I was able to decipher the 'noise' marks from the ones that meant something. These marks, as measured with my calipers collectively ranged from 1.96" to 2.00"
Here are two of the more clear ones:
These measured at 1.98" and 1.99" respectively.
For comparison sake, I did the same thing with my Spike's carbine upper. Measurements I took here fell in the 1.98" - 2.00" range.
So - what does it all mean? My impression so far, would be that given successful measurements of GO/NO-GO Headspace with the barrel and new BCG assembly, a successful test fire using 5.56 ammo and no signs of overpressure, and this somewhat subjective and margin of error analysis of throat leade showing closer to the correct 5.56 dimension - that maybe all is good after all, and the original issue may really have just been an overpressure round from Prvi Partizan.
Thoughts??
Do you know the lot number of the suspect ammunition?
The 5.56 drawing shows the throat should be straight out to 2.0026, with the end of the leade angle at 2.059.
Bullet ogives are all different, but with your alternates you're still showing a leade ending below 2.0".
I think you're closer to a SAAMI .223 than a .mil 5.56.
Here's how a weapon must be proof-inspected to be imported in Europe:
a weapon, once it passes customs, must be taken to a proof house. It will be proofed with a CIP import proof round (at 25% over accepted CIP pressure). If it passes it gets a stamp and can be sold within the country or exported to another European Union country.
If your Mossberg barreled carbine was to be proofed Euro/CIP style, would you feel comfortable shooting a single SAAMI +25% pressure round? How about a MIL 5.56 +25% pressure in your chamber?
Feeling lucky?
Call Brian at AIM -- I'm sure he'll help you out.
Would you recommend the Ned C. gage as a good final say for this?
I will re barrel this if I have to, I want the rifle to be safe. But before I go down that path, I would feel good about something to gage or measure that's a bit less subjective than what I have done so far...
I do have to say again - thank you - for all of the time and involvement for this thread. I can honestly say I have learned a great deal of knowledge through this issue, and that's invaluable to my future shooting endeavors.
Normally I'd probably use one of Ned's 5.56 reamers (if he was lending one), but with the Melonite I wouldn't want to ruin it if the barrel's harder than the reamer.
SAAMI .223 chamber pressure is 55,000 psi piezo pressure. CIP 125% would be 68,750. M197 proof is 70,000.
Dr. Phil Dater did some testing showing between 52,000 and 57,000 for nine M855 rounds (measured 3 inches in front of the chamber), so the military's stated 55,000 psi is probably close.
Mark 262 77-grainers can go up to 58,700, while the new M855A1 can go to 63,000.
The GI proof cartridge often blows out the primer and jacks up the nickel-plated case in a 5.56 chamber -- without damaging the rifle.
Your carbine blew out the case and bent the extractor. You still need to confirm what type of chamber you have and what pressures the Prvi 5.56 generates.
SAAMI formally states not to use 5.56 Military in a firearm chambered for .223 Remington:
http://www.saami.org/specifications_...mbinations.pdf
Read this from Armalite:
http://www.armalite.com/images/Tech%...%20Rev%200.pdf
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