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Ruffian wrote: RD- have to agree with you , that the throat's are different for sure, for sure. That's why one can fire the 223 in the 5.56 chamber but not the other way cause of the higher PSI.. YES or NO in my knowledge of the two ??? SOME H E L P here.
Correct, the throat differences cause the pressure problem, not the cartridges per-se.
The .223 Remington chamber is, according to my SAAMI pdf's:
The chamber ledge, is cut at a 45* angle, and exists from 1.7720" to 1.787" from the breechface.
At 1.787" from the breechface, the throat begins, un-rifled, groove diameter (.224").
The throat runs from 1.787" to 1.812", that is .025" un-rifled.
The rifling then begins at 3 degrees, 10 min, 36 seconds face angle, and is full depth by the time it is 1.8570" from the breechface.
That means, the entire throat area, from the case mouth to full rifling depth, is only .070" long, many places on the internet credit it with being "typically" .085" long.
The same area of the 5.56mm GI chamber, is over .200" long by the time you get to full rifling depth.
Not only is the un-rifled section far far longer (.055", that's over 2x as long), but the rifling entry angle is flatter.
I have some reamer drawings, that show the entry angle of the rifling to be only 1.2 degrees, that will take almost 3x the length to get to .005" of rifling depth that a 3.2 degree entry angle does. That flatter rifling entry angle AND the longer throat un-rifled section keep the heavier bullets from jamming in the barrel rifling.
So .223R has a throat that is only .070-.080" long and the 5.56 has a throat .200" long.
The really good borescope photos I have the address of, moved, can't find them. :(
As you can see from this one with dimensions, the 5.56 throat has an un-rifled section that is almost as long as the entire throat of a .223R.
The different shaped ogives of the 62 and 70-some grain bullets in .223's at magazine length can still jam into the rifling of a .223R chamber leaving zero bullet 'jump' or 'freebore'.
Hee is a photo of 3 milled-open barrels/chambers, the throat length difference is huge (sorry, Trump is president, "YUGE!!!!") ;)
I found the other good pictures I like:
The yellow line is the end of the chamber (the ledge)
The ORANGE line is the point of full rifling depth in a .223 Remington chamber.
The PURPLE line is the point of full rifling depth in a 5.56x45mm chamber.
The length between the orange and purple lines is over 1/8th of an inch.
Last edited on Tue Feb 28th, 2017 10:33 PM by Damannoyed