M855A1 ammunition...

Steel, UMWPE and ceramic behave differently. They also behave differently when the projectiles are made of different materials.

When we talk about armour penetration, we need to talk about the armour itself. In this case, the current issue and the driving force behind US development is personal armour made of ceramic. NATO, which is based on cold war threats, measure the distance of penetration based on CRISAT titanium and Kevlar testing plate.

We have a generation of rounds like M855, 4.6, 5.7.... that is measured against penetration of CRISAT plate. And the designs to defeat CRISAT plates favor high velocity rounds

But just because something is optimized to defeat CRIST plate, doesn't mean it is good against ceramic - what people wear in the real world now. In other words, is CRISAT plate a good proxy of ceramic armour. Apparently it is not - that is why the US is investing in new 7.62 AP round. Ceramic doesn't behave the same way as titanium plates and Kevlar, or steel for that matter.

I don't have my own finite element analysis software or a Master degree thesis to spend couple months on inputing different shape, material properties..etc to write a paper on this. It is not just the amount of energy, but also the method, the effect and the rate of energy transfer. My observations of what it is going on points to that core hardness is a more "economic" and "practical" way to defeat ceramic than getting to the velocity needed, but even with a high density hardened core there is still a minimum threshold of mass needed to defeat L4, within an envelope that is useable as a general purpose individual small arms cartridge. Yes, we can have an ultra high velocity tungsten core "SLAP" round with a lighter bullet that penetrate L4, but is it practical? No, it has been proven not. Why don't we use 338LM or NM - well, they are not practical individual GP rounds. Is 6.5 a better platform to get a "better" balance between core hardness, velocity and mass to defeat L4? I don't know - that goes back to finite element analysis software and some R&D.
 
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Greentips you have a very thorough understanding of these issues, your posts are coherent and concise. I take it you're an officer. No offense intended!

https://www.thefirearmblog.com/blog...mys-new-7-62mm-xm1158-advap-round-costs-much/

A side benefit of tungsten core bullets is increased ballistic coefficient. So about twenty five years ago I was reading about a new bullet that was being developed by the Oak Ridge National Laboratory, in Tennessee. It was a 5.56 round designed to engage troops to 1000 meters with a tungsten core. Seems to me it was only slightly longer than a regular 62 grain bullet but had a G1 BC of about .480

It had been mentioned in a Precision Shooting article. So I phoned them up to inquire if I could buy some. Needless to say I didn't get very far. They seemed a bit put off that their hush hush project wasn't so hush hush.
 
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When did A1 start to need new mags? Back in 2014 they were running it in standard metal mags.

I could be mistaken but i think the cyclic rate with a1 was faster and on worn guns there were bolt over base malfunctions with the tired old mags. And the tan epm mags use a stronger spring to counter the cyclic rate.
 
I could be mistaken but i think the cyclic rate with a1 was faster and on worn guns there were bolt over base malfunctions with the tired old mags. And the tan epm mags use a stronger spring to counter the cyclic rate.

The metal tips of the a1 were/are chewing up feed ramps. New mags (and M3 Pmags) present the round at a slightly different angle to prevent or minimize the damage
 
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