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Posted: 1/27/2003 7:00:03 AM EDT
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I UNDERSTAND THE IMPORTANCE OF THE AR15/M16 HEADSPACE TOLERANCES AND WHAT AND HOW THE (HEADSPACE)WORKS. MY QUESTION IS,HOW IS HEADSPACE ADJUSTED IF AT ALL ADJUSTABLE,I KNOW ITS IMPORTANT FOR CORRECT HEADSPACE FOR SAFETY REASONS. I HAVE SEVERAL UPPERS, AND WHEN PURCHASED FORM J&T AND OR MODEL 1,WAS ADVISED THAT HEADSPACES TOLERANCES WERE ADJUSTED. DO YOU GUYS THINK THAT TOO MUCH HEADSPACE EFFECTS ACCURACY? |
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Eddiesar15, Lets start off by looking at a few things. First, headspace is the distance from the face of the bolt, to the shoulder of the chamber. If the headspace is too long, then when the round is fired, the case expands and fills the void. If the expanding case distance is too great, the case metal (brass) will become thin and crack/separate. This is why you need to have the chamber with the spec'd headspace. Throat lead is the distance from the last chamber cut (end of case) to the beginning of the rifling lands. This area dictates the amount of free movement that the bullet can move from the case, before it engages the lands. The less distances that the bullet moves forward (with out spinning) and engages the rifling, the more accurate the barrel/bullet will be, due to less bullet deformities at the rifle engagement into the bullet and the less likely that the bullet will engage off-index with the bore line. But, there must be a slight free run, or the bullet will engage the rifling on loading, and the pre-engagement will cause the round to be over pressurized, due to the initial pressure required to overcome the bound (stuck on the rifling) bullet. What it boils down to is that you need the correct headspace to keep the case from bursting, and the correct throat lead for the round that you will be firing. But, to throw a wrench into the works, since most auto loaders may shoot a variable of different types of ammo (bullet octave designs) and must be able to self-load, the chambers and throats are cut to the maximum of spec to allow this to happen. Such would be a barrel that is reamed to 5.56 Nato. To answer your question," DO YOU GUYS THINK THAT TOO MUCH HEADSPACE EFFECTS ACCURACY? " Yes, the round will lose too much pressure (not a constant) on case blow-by (before the case seals the chamber when expanding) and the case set back will increase the distance of bullet free run until it engages the rifling; deviations in bullet speeds and deformities to the bullet on rifling engagement. Then if you throw barrel harmonics into the mix, with the deviation of bullet speeds, the barrel end is not is the same place (barrel harmonics/whip) from shot to shot. Sorry to give you a crash course on chambers/barrels, but if you see the big picture, it answers a lot of questions. Dano |
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Dano523 (YOU THE MAN) I understand what can happen if headspace is too much or too little, but you answered an important queation for me about the length of space between bullet and land and groove in the rifle,Ive purchased a Stoney Point oal gauge which measures the total amount of free space,so I measured my AR uppers and came up with a large amount of free space in all of my uppers,the gauge works great,and it gave me important info on bullet seating depth,youre one of the first,who has agreed with Me, and Stoney Point on measuring oal(over all lenght)to gain accuracy because of less bullet deformities,Im for darn shure going to load my reloads for my 24 " S.S 1/8 twist and only for this upper will I do this because im going for distance,you also gave me an idea on how to measure my headspace using the oal gauge and a new .223 cartridge with the bolt installed,less the extracter.I will be extra carefull to set my bullet depths at the correct settings and not have a rd thats too long. ______________________________________________ Live long,shoot well |
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