as it pertains to rifles.

why do they use that term?

Rifles or bullets?
Haven’t heard it in reference to rifles, but when used about bullets it refers to bullets that are a solid piece of copper or some similar alloy without separate core and jacket.

It could refer to a nonjacketed lead bullet, but that's not common.

I typically see it in reference to AR style rifles. Handguard & Upper are one piece.

Example : LMT MLR Upper

In the case of AR15's, monolithic refers to an upper receiver group where the front handguards or rail system and the actual upper receiver itself are manufactured as one complete piece. Typically featuring a long, uninterrupted top rail.

Also used in reference to precision rifle bedding blocks. Search on "monolithic bedding block" for examples.

Means monkeys jump around it?

It means the handguard and the upper receiver are one piece and the rail on top is uninterrupted.

The issue with traditional two-piece systems is that there can be some flex between the rail (which is usually bolted to the barrel nut) and the upper receiver.

True monolithic rails allowed the forward mounting of an optic and it really didn't matter where you put the optic because the rail would not flex or be interpreted by a gap between the handguard and the upper receiver.

Most modern rail systems use a barrel nut as the mounting point for the handguard. Using a barrel nut as your anchor point also can increases the weight of the overall package because the barrel nut as to be beefed up in order to mount the handguard (instead of being just being just a small skinny ring that keeps the barrel from walking out of the receiver).

Alternatively, rails can use something like early POF, ARMs, and VLTOR handguards like the CASV-EL which ran rails over the top of the upper receiver (basically putting a picatinny rail over the picatinny of the upper receiver). This dealt with the weight issue, but messed with optics and sight heights. This solved the barrel nut weight issue and the receiver flex point issue. But now your optics and sights were about a quarter inch taller, which mean cheek pieces for some folks. And cheek pieces generally don't play well with traditional AR charging handle layout. It wasn't ideal.

LMT owned the patent for the monolithic rail and went after at least MEGA for patent infringement. I don't know if LMT went after VLTOR for their VIS system, but shortly after Mega changed their design, so did VLTOR.

Mega (which was eventually bought by ZEV) dealt with it by interrupting the rail. They just machined out a slot and added a retractable bubble level. Mega called this their polylithic upper.

VLTOR started out by making a large part of the rail detachable (VLTOR VIS-KM). Ostensibly, this would allow the mounting of an underslung launcher like a master key or 37 or 40mm. It also made the handguard multiple pieces, so it was no longer strictly monolithic. Their later VIS-Fusion has a trap-door type arrangement where you can access the barrel nut from underneath the handguard via a hinged door--also making the handguard technically polylithic.

Colt continued to make something very similar to LMT, with their 901 and 6940 so maybe they worked something out legally with LMT to continue producing what looked to me like a monolithic upper. Or maybe they just made a deal with LMT that once they ran out of 6490 and 901 parts, Colt would not make more of those particular two models because I haven't seen a new production run of 6490s or 901s in years.

This message has been edited. Last edited by: LDD,

Outstanding, thanks for taking the time to teach.

Are some shooters much more likely to benifit from the monolithic version,
Than other shooters ?

I believe the most advantageous aspect of a monolithic upper is the ability to mount optics without having to bridge the upper/rail, as well as maintaining zero for lights/lasers. Having a separate rail/upper can stack tolerances, and optics/lights/lasers mounted on a rail can shift when non-monolithic rail becomes canted due to stresses/heat.

Most running clean setups, such as a red dot, light, and vert grip will never have this issue. People that use their ARs for more specialized tasks, such as hog hunting, door kicking, etc, might be marginally better served by a monolithic rail/upper.

However, due to the relative scarcity of true monolithic uppers, thanks to the above mentioned LMT patent, the shooting world has made due, and most have found it’s not a big deal.

my monolithic upper Colt 6940

quote:

Originally posted by bendable:
Outstanding, thanks for taking the time to teach.

You're welcome.

quote:

Originally posted by bendable:
Are some shooters much more likely to benifit from the monolithic version,
Than other shooters ?

Those most likely to see true benefit were the rare purchasers of the .308 class monolithic upper receivers. This is because, with the larger caliber, they're more likely to need more rail space on top of the receivers for precision/high mag optics.

Precision/DMR builds were also more likely to benefit from the stiffer handguard/receiver arrangement with these poly/monolithic upper receivers.

These days, the only benefit for 5.56 users is possibly weight. The issue is that the industry has kind of moved on in a couple ways.

First, with modular handguards, we're all standardizing on M-Lok. But I don't know of any manufacturer making a monolithic/polylithic upper with M-Lok slots other than LMT's fantastically expensive MLR.

Colt not withstanding, the two other companies that were doing mono/poly uppers aren't making M-Lok versions. Mega got bought out by Zev. No more poly uppers from Mega since then, though Zev continues to make barrel nut based-handguards using the M-Lok pattern. I suspect that the Megalithic uppers (their name for their poly uppers with bubble level) were prestige items--sexy for press, but not big sellers or high-margin.

Vltor is an interesting case. Vltor was one of the primary authors of keymod. Their products have always been top notch but making an M-Lok version of their VIS might be kind of like conceding defeat in some ways. To my knowledge, Vltor has never produced anything M-Lok. Which is understandable, but too bad, because I really liked their VIS Fusion system, but I'm not going to buy a keymod version knowing that keymod likely won't be supported in a few years.

But as for mono/poly uppers, and this is my second point, the move toward mini RDS has really taken the steam out of mono uppers. They are now an expensive answer to a question that one in the 5.56 hunt is asking--which is how to mount a bigger optic on my gun? Back when RDS took up 75% of your rail space, and you still needed room for a BUIS and maybe a PVS-14 mount, a mono/poly upper made sense. But now MRDS are tiny and you can fit everything you want on a standard upper receiver without bumping over onto your handguard.

A standard A3 upper (before the crazy) would have cost you $45 retail? Add a reputable handguard like the BCM MCMR for $200 and your total is $245? Or you could get an LMT MLR for $849.00. Is it worth 3x more on a 5.56?