Path: cygnus.com!enews.sgi.com!logbridge.uoregon.edu!elk.ncren.net!news2.wam.umd.edu!gun-control From: FRANK Newsgroups: rec.guns Subject: Some interesting 5.56 and .223 facts Date: Fri, 29 Mar 2002 12:34:11 +0000 (UTC) Organization: Giganews.Com - Premium News Outsourcing Lines: 43 Approved: gun-control@cs.umd.edu Message-ID: This thread has gone on for a long time with many statements re comparative chamber pressures etc of these two calibers, such as a chamber pressure for the 5.56 of 60,000cup, so I decided to go to a reliable source, i.e. the military technical manual TM43-0001-27 and find out what the facts really are. Very interesting. Cartridge, ball M193 (M16 and M16A1) 56gr bullet, velocity 3250fps, chamber pressure 52,000 psi Cartridge, Ball M855 (green tip) (for use only in M16A2 and M249E1 machine gun) 62gr bullet, velocity 3025, chamber pressure 55,000 psi. Then, so I do not have to hear about the difference, if any between CUP and psi, I went to the Alliant reloading manual, which quotes chamber pressures in psi, and found that their recommended load for a ..223 with a 60 gr Hornady bullet has a chamber pressure of 53,000 psi- right in the ballpark with the M855. According to the manuals and my measurements, all of these cartridges are the same length (2.26" +or- .01), so the only difference I can see left is how the chambers are bored. Leade length has been mentioned by Clint of Fulton Armory as allowing military cartridges to have a higher chamber pressure. I consider him to be an expert, and I am not, but I have heard other experts argue this proposition. People wondered for years why the German army had a greater leade length in rifles chambered for the 7.92x57 (8mm Mauser) with 147 gr bullets, untill they found out that there were cartridges available for it with 198 and 236 gr bullets. My conclusion is: If you have a marginal rifle for the .223- junk it.. If you have a good strong rifle, M193 5.56 ball is probably ok unless the rifle manufacturer says not to use it. It is clearly ok with Ruger as I read their manual on the Mini 14. Get on the mfgr's website and ask before shooting. M855 green tip ball, do not use in a civilian weapon unless the rifle mfgr says ok, and this includes weapons marked 5.56. Remember the military says it is only for use in M1A2 rifles and machine guns. The foregoing is provided only for general information, and is not a guarantee of what will be safe in any particular weapon. Frank ------------------------------------------------------------------- Learn about rec.guns at http://doubletap.cs.umd.edu/rec.guns