First off, this is not for a civilian/post-ban application -- think official end-user.  Let's start with one very basic assumption:  the 5.56mm NATO round will not work in this role.  Therefore, what round would you use?  Many of us in the know are aware USSOCOM combatant elements are experimenting with various wildcats that will work with the current M-16A2/A4 action. For the purpose of this exercise an M16-type action will be required.  However,the weapon will fire only in semi-automatic. Do not assume ammo availability will be an issue. Beyond the chambering, how else would the weapon be conceptualized and why? Your specific and detailed responses are most appreciated.

First off, let me start by stating that I think "civilian/post-ban application" Is an official end-user. I don't need no stinkin' badges.

That being said, you are asking us to pick a cartridge using the only criteria that the 5.56 is not suitable. Then make vague claims that the high speed low drag crowd are experimenting with wildcat cartridges but give no details or clue as to what they are.

So we have no mission, no specs as to use, and no idea what you are asking us. Sounds like a government project to me.

This has got to be either for Mall Ninja or Army SEAL use.
Given the parameters allowed, I would advise the use of a 90mm reckless rifle.  Good expectations of OSS.  I would fab a mount that would fit the RAS and hook it to an M4 (M16 wouldn't do, too much weight).  That should cover the M16-type action requirement.  Single shot is even better than semi.

Yes, this is purely for a USG application -- hence "official end-user".  Sorry if that term offends you.  I am keenly interested in the technical observations of the members of this forum and respect your considered opinions.  This is why we visit this forum from time to time.  Thus, the question here.

The mission of the second-generation SPR should be self-evident, and requires no explanation. I do not want to contaminate the data being collected by opining on one caliber or another, or for that matter any subsystems.  We are especially interested in practical and proven subsystems/components which CRANE-NSWC and USSOCOM, et al, has overlooked in constructing the first iteration of SPRs.

Again, I want to hear your precise observations on such a system and your rationale behind your thoughts.  Thank you for your contribution.  It will be most helpful, believe me.    

6.5-08 since it will work in a modified SR25/AR10 and produce accuracy and effectiveness at 600+ meters.

Please stop, your question is ridiculous, in your world of fancy where do your spec op guys get their ammo from?  Don't give me this garbage about "we get what we want".  Real world ops are still drawn around the basics, and magic bullets aren't included.

Sorry, but this is the real world.  For example, AMU reloads 6mm BR (and a whole lot more!), 5SFG(A) does other things, NSWC-CRANE contracts for even other types of interesting Class V.  It goes on and on.  Once limited fielding gets to a certain level, Picatinny (PMSA, JSSAP and others), step in with a contract solicitation or sole source award for a given stockage level.  This is how it works.  This is what I do.  Having said that, there are definite limits on whatever esoteric items the SOF community can order in any density.  It is not like the very abused system existing up till the early 90s that you allude to. This is where today's system of flexible program management based on operator input is proving vital.  In a sense, that's why I'm here.  Is the fog lifting?  I'm here for your ideas -- nothing more. Otherwise, time to bid this forum adieu.  Thought I would get significantly more enlightened and articulate responses.  

Quoted: Sorry, but this is the real world.  For example, AMU reloads 6mm BR (and a whole lot more!), 5SFG(A) does other things, NSWC-CRANE contracts for even other types of interesting Class V.  It goes on and on.  Once limited fielding gets to a certain level, Picatinny (PMSA, JSSAP and others), step in with a contract solicitation or sole source award for a given stockage level.  This is how it works.  This is what I do.  Having said that, there are definite limits on whatever esoteric items the SOF community can order in any density.  It is not like the very abused system existing up till the early 90s that you allude to. This is where today's system of flexible program management based on operator input is proving vital.  In a sense, that's why I'm here.  Is the fog lifting?  I'm here for your ideas -- nothing more. Otherwise, time to bid this forum adieu.  Thought I would get significantly more enlightened and articulate responses.

Life in a vacuum boys a gurls,

Current engagements "in a certain place" are happening at ranges over 1000m. This because our opponent likes to set out that far and lob RPGs, Mortars and HMG fire.

I respectfully suggest that the solution to that problem is better RPGs, Mortars and HMGs. NOT some half-baked attempt to shove a big ass round into a tiny action.

Aint no way in hell you ever make the M-16 a reliable killer at 1000+ meters. Even lightweight .50 cal rifles are iffy in heavy winds at those ranges.

Have you began to get a clue yet??
Now go read P.O. Ackley and grow up troll

If you want a serious answer and if this is such an imprtant issue that you come to these boards to get info on it, how about a little more info?
1.  The 5.56 will not work.  Why not?  What do you mean as "work?"  What is the assumption based on?
2. Wildcats tested.  Which ones? If you clued us in to which ones are already considered/eliminated, you might not get repetitive feedback.
3.  M16 action required.  Why?
4.  Semi only.  Why?  And if so, why put it on an M16 action?
5.  Availability not an issue.  Really?  Logistics are always an issue.
6.  Conceptualization.  Well, sense you give absoulutely no info, how can anybody give you a conceptualization?  Since you claim that it has to be on an M16 action, there's your concept.  What are you asking for?
As for complaining about getting enlightened answers, how about asking an enlightened question.  There's a lot of knowledge here, but if you don't supply any parameters, you're not going to get a whole out of it.
                 

Mach6, if you are really who you say you are, you don't need to come to this board for any advise.  military is full of talented people and talented suppliers to assist in building some excellent weapon systems.  I just spoke to Dave at PRI, he mention to me about a secret project he is involved with the go fast boys.  He will not elaborate on it any further, but did he tell me all in due time.  This new evolution will produce some new and wonderful accessories and components for the AR series weapon with performance enhancement in mind.