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Posted: 7/10/2003 6:46:03 AM EDT
It has been explained that the main reason for fragmentation at lower velocities with the heavier .223 bullets is they are longer and therefore present a larger "side" area to the target medium when yawing. This larger area increases the drag force on the bullet, thus allowing it to fragment at a lower velocity than the lighter and shorter .223 bullets.

My question is this: Why doesn't this same effect occur with M855 bullets? We hear about their significantly increased length, not just from their additional mass as compared to M193, but also because the steel penetrator is less dense than lead and therefore takes up even more volume than an all-lead 62 grain bullet would. Shouldn't this exceptional bullet length ensure fragmentation at velocities much less than the 2700 fps normally applied as the threshold? Wouldn't this negate it's deficiencies when used in the M4, relative to M193?
Link Posted: 7/10/2003 7:41:36 AM EDT
[Last Edit: 7/10/2003 7:44:10 AM EDT by Forest]
Originally Posted By chuckhammer: My question is this: Why doesn't this same effect occur with M855 bullets?
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We do see this effect on M855. You have read the Oracle right and the briefs at FirearmsTactical.com, Right? When the M855 first was tested it was actually fragmenting better (10% more) than M193. This looked good. However as there is no specification for the thickness of the jacket - it seems there is some variation during manufacturing. When the round has a thicker jacket it may not fragment at all (particularly from the short barreled M4s). Bullet construction is the most important part of the 'fragmenting' equation, more so than length or velocity.
Link Posted: 7/10/2003 7:57:16 AM EDT
Yes, I've read the Oracle. I remember the standard of 2700 fps being applied to both M193 and M855 even though the 62gr projectile is so much longer. I guess this is due to the inconsistent bullet construction of M855, just to be on the "safe side"?
Link Posted: 7/10/2003 8:54:52 AM EDT
Remember the length isn't the important part - its the jacket thickness. From what I've been hearing some of the M855 rounds have had jackets so think they weren't fragmenting at all. Now there is a lot I'd dump in a hurry.
Link Posted: 7/10/2003 10:49:02 AM EDT
M855 is a lot more complex round to manufacture than M193 or the 77gr rounds. It consists of the lead, the steel penetrator and jacket. Variations in construction can give widely varying results among different lots of M855. For example [url=www.dtic.mil/ndia/2001smallarms/parks2.pdf]Page 15 of this PDF[/url] shows a lot of M855 that is getting good fragmentation as low as 2,570fps and minor (Wolf-like) fragmentation as low as 1,932fps. Then again, some lots of M855 don't fragment at all. On top of that, even the good lot mentioned above showed a "neck" of about 4-5". That means on a frontal shot or extremity the bullet could penetrate entirely before fragmentation ever started.
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