Quoted: Some more thoughts... Can a monolithic upper receiver with standard barrels be made as narrow as the MRP? Perhaps that is a another benefit of the proprietary barrel. The VIS is noticeably wider than the MRP. I hope that the LaRue offering falls somewhere in between. I believe that an extrusion for the forend section is the way to go, from a cost standpoint. Would I take a machined Larue extrusion permanently attached to a billet receiver? Absolutely. Especially when the LaRue comes at a lower price than the MRP. and allows the use of any AR barrel. Frankly, I feel that a machined, one-piece extrusion for the entire monolithic upper would be the way to go. Imagine an SR-25 upper extended into a monolith. Perhaps we have become too dependent on CNC based design at the loss of less sexy, time-honored practices. A hybrid of both an extrusion and billet mey be the most simple to design/produce, and that's what we'll see. Waiting for S.H.O.T.

If it is made from two separate pieces, one extruded and one billet it is not a monolith now is it.

Joining two pieces via welding can cause them to warp also the metalurgy will change which will require heating and stress releiving to correct and add another possible place for it to warp.

LMT makes the MRP from a forging.  A true monolithic upper would have to be made for either a continuous forging or one piece of billet.  

JMHO
Denny

Quoted: If it is made from two separate pieces, one extruded and one billet it is not a monolith now is it. It's really semantics, Denny, and I hope that you can supply more grey matter to the discussion than that! The LaRue forend is considered one piece--but is not. A one piece monocoque chassis is composed of many pieces of composite fabric laminated together with epoxy resin. A piece of stone--the form most associated with the term "monolithic"--is actually composed of different minerals held together by a variety of nature's manufacturing techniques (including heat treating and adhesives). I'm referring to the end product, not the construction methods. I shoot a firearm--not parts. Upon review of Mark LaRue's previous statements on the matter from July, the new LaRue upper was to be machined from one piece of barstock. Will manufacturing ease and price dictate something else?

Please quote my entire reply.  I do go into some detail as to problems with joining two pieces to make a pseudo monolith.

If LaRue does ever make one rest assured it will be made from one piece of alloy.

Denny

As many of you know I have an extensive hands on knowlege of machine guns from WW I to present and I am familiar with many quick change barrel designs, so of which with mods, could be applied to the mono rail systems.

That said, none of them would be cheap and therein lies the rub.  

I can tell by the less than stellar sales of the best mono upper out there, the LMT, that there are not many guys will to pony up the money for one of these types of systems.

People can say what they will about "if it took standard barrels I would buy one", but I pretty well know this market and in fact not enough would buy to make such a venture pay off.  

Sure if you could make a mono upper for $150 that would take standard barrels it would sell but I am thinkking more like $400 to $500 for the upper to be the quality people demand.  

With the quality of the uppers and rail systems in the market at the present time, and who knows what the future holds, I just do not see any real advantages in spending the $$$ to develop and market a true mono upper.  We have rail systems that draw more heat of the barrel and chamber that a mono offers and the top designs just to not come loose or rotate if properly installed.  The monolithic rail that does draw off heat is the LMT as it surrounds the barrel extension and chamber area with aluminum, minumizing cook-offs.

If LaRue or someone does come up with a reasonably priced quality system it may sell but most likely not in numbers that would justify the R&D costs, testing and marketing, but with our current uppers and rail designs I don't see any major advanges out weighing the costs at this time.

Denny

Let's not forget that there's another unit in this mix.

MGI QCB upper


"Permanently attached" type upper/handguard(becomes "monolithic" after assembly, and no changes to heat treating during the process)

Not oversize in handguard diameter.

4-rail billet handguard that is configurable with extension modules to allow for 3 different handguard lengths to suit various needs.

Fastest quick-change-barrrel system in the world, and is fully the equal of the LMT MRP in accuracy, maybe better

Takes normal AR barrels

Already machined internally to accept magazines from other firearms such as AK47, etc, when used with the MGI Modular Lower receiver as a pair.

All 7075-T6 alloy.


Perhaps there may be some things in other systems that some may prefer over what we present with the MGI QCB, but it certainly deserves to be in this conversation, because it is every bit as good as anything under discussion here, if not better.

Any optic with a co-witness can be set by verifying the dot with the backup irons(one of which is attached to the barrel, in a correctly set up gun). Zero the barrel at the front sight at the range, and it will return to zero(sub-MOA) when you put it back in.

Any optic with a good mount(such as Larue) can be "pre-zeroed" with a barrel at the range, and returns to zero under 1MOA when replacing the barrel AND the optic/mount in the field.

Great improvement over carrying 2 uppers, in both weight and bulk, because there's no need to carry unnecessary redundant parts.

Quoted: This discussion is pretty damn interesting.  But I am wondering something.  How could you make a one-peice monolithic upper like the MRP that used conventional barrels and a standard barrel nut?  On both the LaRue and the VIS, they have a removable lower rail so that you have access to the barrel and nut.  But this necessitates a two-peice design.  It seems that LMT had to develop a proprietary barrel system in order to keep a monolithic design.  If people want more options when is comes to barrels, perhaps people should petition barrel makers to offer barrels which use the LMT system.

It's not necessary to have a proprietary barrel, nor to have a multi-piece handguard, in order to have switchable barrels.

The MGI QCB has a single-piece billet handguard and uses normal AR15 barrels with its patented quick-change-barrel system.

Quoted: What I'm disappointed in are the lack of other calibers...  We now have the 6.8 and 5.56 as standard barrels.  Why can't we get some barrels in those other AR envelope compatible calibers - .204?  .458 SOCOM?  9MM?  6.5 Grendel?  There's a long list of possible calibers out there but only 2 are available.   About the only way to solve these issues would be for LMT to license folks to build barrels using their extensions.  That way there would be a greater variety of barrels but at the same time keeping tabs on quality control...

You said 9mm
Oh sh$t, I could do that right now, no extension required, just machine the whole ass end of the barrel!

As for the extensions, LMT's reasoning for not selling them is that the extensions get OD ground AFTER assembly on to the barrel blank.
This is done to control concentricity and hopefully make it so that swapping barrels will not require nearly as much sight adjustment.

I challenge you to take 3 or 4 regular barrel (like everyone is crying to have used) and install them on a receiver without changing the zero of the optic which would have to be receiver mounted.
Now, go shoot a group with each barrel.
I would like some real-world data on what you find as for the repeatability of the BARRELS themselves, all other components of the upper being identical.

This factor alone COULD be a major stumbling block to using standard barrels.
Nobody ever stops to think that MAYBE, just maybe, LMT knows a little more about this than a bunch of bench-racing gun designers on the internet.

LMT uses Rock barrels, so the price of the MRP barrels is slightly justified.
They are good barrels for sure.

Quoted: Could you explain to me how you make an AR15 barrel - how the barrel and the extension come together either here or via IM?  I've never read about that...

You could just read about it on my How an AR-15 barrel is made page on my website.

9mm barrels are different in that they do NOT use a barrel extension.
The rear end of the barrel that mounts in the receiver is simply machined into the barrel blank.
The chamber sits 1/2" further back in the barrel/action.
This is one reason that 9mm AR's can be 1/2" shorter overall length than 5.56 AR's and still maintain 16" legal barrel length.

I have measurements/drawings on MRP extensions so that's why I COULD make a 9mm barrel.

Do you realize what you have done?
Now I have to buy myself another MRP to fool with.
And I had just gotten rid of the last one...

Quoted: Could you explain to me how you make an AR15 barrel - how the barrel and the extension come together either here or via IM?  I've never read about that...

I also have these drawings showing the relationship of the barrel blank, extension and bolt head.

Quoted: I challenge you to take 3 or 4 regular barrel (like everyone is crying to have used) and install them on a receiver without changing the zero of the optic which would have to be receiver mounted. Now, go shoot a group with each barrel. I would like some real-world data on what you find as for the repeatability of the BARRELS themselves, all other components of the upper being identical. This factor alone COULD be a major stumbling block to using standard barrels. Nobody ever stops to think that MAYBE, just maybe, LMT knows a little more about this than a bunch of bench-racing gun designers on the internet. LMT uses Rock barrels, so the price of the MRP barrels is slightly justified. They are good barrels for sure.

Randall,
We have gotten real world data back from users who are changing Off-The-Shelf AR15 barrels in our QCB upper.
There can definitely be a POI variation with different barrels in different lengths and calibers, and that is to be expected when doing changes like that, as you know. Changing ammo can also cause a change in POI.

When re-installing a previously zeroed barrel, it can return to zero extremely well, less than half-MOA in many cases(when using the same ammo).

The advantage to using regular AR15 barrels, is that the user can select his grade of barrel from many sources. If he wants to get an "absolute top grade" barrel that is machined to "perfect" standards, then he can do that. But if he just wants a handful of rack grade barrels for blasting, then he doesn't have to go broke doing it.

It's all about more options for the user.

I'm pretty sure that LMT and everybody else has realized that there is no "perfection" to be had, and that a "really good" system that provides added functions and benefits can be appreciated by alot of sophisticated users to very good advantage.

A "perfect" system that will somehow automatically compensate for any variations in ballistics and point of impact for various calibers and conditions is not going to be available for quite a while, in my opinion.
But, if the person is realistic in his expectations, these barrel changing systems will provide additional features and benefits that a skilled individual can use to tailor his weapon system into a more complete and useful system.

If the platform will perform within the performance envelope of the ammunition used and the shooter's skill level, then it will not be any impediment to his success with the weapon system.

In the cases of the LMT MRP and the MGI QCB, these systems will perform within the performance envelope that almost anybody would be happy with in terms of accuracy and repeatability.
As for the VIS, it isn't a switch-barrel system, so it should be as good or better than any normal upper.

Quoted: I came up with the following minimal list of calibers which met those goals: 1. 5.56mm 2. 6.8SPC 3. 7.63x39mm 4. Pistol calibers 9x19mm/.40S&W/10mm/.45ACP

Go ahead and rule out the 40/10/45 due to lack of good magazines and bolts.
9mm is the only proven blowback system.

Quoted: If LMT expanded its caliber range to 7.62x39 (I think that it will be next), and worked with C Products to develop good mags, that would expand the appeal of the MRP platform to many more. I believe that they would sell as many, if not more units of 7.62x39 as they would 6.8SPC. Think about it: a user modifiable, monolithic, three caliber upper receiver system.

I agree with this assessment.
It would be a good thing.

As I'm sure you are aware, the 7.62x39 in a mag that will fit into an AR15 magwell is a very "iffy" proposition, and has been attempted countless times by many manufacturers over about 30 years with varying degrees of success, none of which would be called "reliable" in an overall sense. The taper of the cartridge(requiring magazine curvature) and the straight shape of the AR magwell are generally incompatible when high capacity(over 15 rounds) is attempted, and that is why the hi-cap AR type mags for 7.62x39 haven't been terribly successful to date. I wish Larry luck with this project, but the deck is stacked against him, due to the factors I outlined above. I hope he has success, but I'm not very optimistic about  the likelihood of it.
IMO, the proper way to address this situation is to use the AK magazines and provide the necessary changes to the weapon platform to suit it, as KAC did with the SR47, Special Weapons does with the AR47, and MGI does with the MGI Modular Weapon System(Hydra).

Regarding the "monolithic" topology of the upper, I think that it remains to be seen if the "true monolithic"(1-piece) upper actually provides any meaningful benefit over a receiver that is built-up from 2 pieces, but finishes up as a single "monolithic" receiver after it is completed(can't be disassembled after  manufacturing is completed). I can certainly see that some people will assume that it is better, but I'd like to see some comparisons as to whether it really IS better in a meaningful way that affects performance. Truthfully, from a design viewpoint, if the same performance(or better) could be gotten from a construction method that yields lower cost, then that might be considered as a better overall design option. And it is concievable that might be possible, and even available.

Naturally, I totally agree that an upper that can be easily user modified into various calibers, and provides excellent performance parameters, would be a very nice thing, and that's why we make a system like that. It may be debatable among some people if our "built-up" upper that becomes "monolithic" upon completion, is as desirable/good as one that is machined out of a single piece of alloy. Each person can make their own decision about that issue.

If you look at the system overall, we have addressed the strength/rigidity issues well, have provided an excellent quick-change-barrel system that needs no tools, and offer a lower that can use the proper magazines(via interchangeable magwells) for these other calibers to provide the needed reliability for feeding them. It is our contention that this is the logical and best approach to the desired goal.

IMHO and YMMV, of course.

Quoted: good posts, twl. sometimes we get so caught up in the minutiae of technical discussions instead of the practical impacts of what we discuss here. the issue of repeatability between quick-change barrels is one, for example. for most practical purposes, if the same barrel repeats within an MOA, that's fine. the optic should be zeroed for the most accurate configuration/barrel, usually the longer one. switching it out from an 18" to a 10.5" is going to have a change in POI of a couple of MOA. but when you look at the reason for changing to a short barrel - maneuverability in close quarters (vehicle, house to house etc), the shortened engagement distances render those couple of MOA null, for most practical purposes. while it may be nice to have a long and short upper with optics zeroed to each one, one extra barrel in the case or backpack takes up much less space. i'm going to start using the word 'bi-lithic' to describe two-piece/joined uppers that form a monolithic.

"Bi-lithic". Cool!

Anyway, you've raised some good points here.

It's been shown that both the LMT and MGI uppers can provide sub-MOA return to zero when returning barrels into the upper, and using same ammo in same conditions. So that part is possible, and currently being done, as you note in your post. So, that part is done.

Dealing with different barrels and different calibers which will have different point of impact is another matter, and we are dealing with that issue too.
Our system is designed to use barrel-mounted front sights. It can be configured with rail-mounted front sight, but we designed it for barrel-mounted sights, and we have a reason for that.
If you "pre-zero" each barrel at the front sight when you first sight it in at the range, then it will be zeroed(for at least elevation) when you return it into the upper for use. That is for iron BUIS sights.
However, with the red-dot type optics, or any other co-witnessing optic, you can use this iron sight alignments to then set or check zero with the optic. This gives you a "hard" reference of the iron sights with which you can adjust or check your red-dot zero.
I realize that this only addresses elevation zero, but we are finishing up work on a front sight(flip-up) which will also have windage adjustment on the front sight, so that W&E can be set on the front sight, and the rear BUIS can remain set at the centered position.
This allows all barrels that you have "pre-zeroed" at the range to be already zeroed when you install them into the upper, no matter what their various points of impact may be, because they are already accounted for by the sight adjustments made at the front sight. It makes for very quick and reliable barrel changes with POI accounted for.

To deal with the different gas system lengths, and thus the different FSB locations on each barrel, we have engineered a railed handguard extension that matches the construction of the billet handguard exactly, and bolts on very tight and secure. It is fully load-bearing and very strong, and allows you to change your handguard from carbine to rifle or midlength in a modular fashion. The basic carbine-length handguard stays in place(since it is permanent "bi-lithic"), and you just add the extension piece you need. Again, no redundancy, so you carry or buy minimal extra parts to accomplish this, and it all works with the same basic upper receiver system.
And, it allows those who wish to use the RECCE type configurations to do that, albeit losing that ability to pre-zero the barrels at the front sight, which I'd consider a practical function that I personally wouldn't sacrifice for sake of rail space. But, we make it so that it can serve many needs, not just what we think is best. If you want RECCE, you can do it, no problem.

Just so that folks which aren't familiar with out overall concept can understand, we are making a platform(upper and lower), which can serve all small arms requirements. Entry gun, duty carbine, sniper rifle, SMG, and LMG, in whatever calibers(under 2.8"OAL cartridges) might be needed, all interchangeable and re-configurable using all the same parts that all the other guys in your squad have(assuming an MGI equipped squad), so that any gun can become any other gun, in a very short time with no tools, in the field, by the operator, with the least possible number of parts to be purchased or carried to achieve the requirements(and maximum amount of interchangeability).

Considering that we have been working for many years on this concept, we have already seen and addressed most(if not all) of the issues that might need to be dealt with. Some things have not been released yet, and it may not be fully apparent to some people as to just where this system is going. But, as all the products get released and we add the W&E front sight, and the belt-feed module, and the Open-Bolt/Closed-Bolt select fire control group, and some more of the convertible magwells, it will become clear.

Quoted: we are finishing up work on a front sight(flip-up) which will also have windage adjustment on the front sight, so that W&E can be set on the front sight, and the rear BUIS can remain set at the centered position.

Does this mean that the current version of the QCB upper has a tighter index pin fit than the old one that I have?
If not, I would not trust it to repeat in windage at the front sight post.

all interchangeable and re-configurable using all the same parts that all the other guys in your squad have(assuming an MGI equipped squad)

That's quite an assumption!

Quoted: Quoted: we are finishing up work on a front sight(flip-up) which will also have windage adjustment on the front sight, so that W&E can be set on the front sight, and the rear BUIS can remain set at the centered position. Does this mean that the current version of the QCB upper has a tighter index pin fit than the old one that I have? If not, I would not trust it to repeat in windage at the front sight post. all interchangeable and re-configurable using all the same parts that all the other guys in your squad have(assuming an MGI equipped squad) That's quite an assumption!

I'm not sure, but the one I have will allow taking the barrel out, and putting it back in, and still stay in the X at 600. That's good enough for me.

Yes, it is quite an assumption, but it was useful for the description that I was trying to get across.