This is intended for people interested in the subject of military guns and their ammunition, with emphasis on automatic weapons.
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My basic take away. Replace both the 5.56x45 and the 7.62x51 with a new 6.8mm cartridge. There has been talk of upgrading the M240 to .338NM (8.59x63) which would give it much of the advantage of the M2 .50 cal but with less weight and recoil.
As for the M4, it may not go away for the support troops. However there has been some exploration of a PDW based on an M4.
Here is an example from Sig https://www.sigsauer.com/store/sig-mcx-rattler-sbr.html
Sig also has, so it happens, an upgrade kit for the M4 https://www.sigsauer.com/store/mcx-rattler-upper-assembly-5-5-300blk.html
You can't rechamber the M240 to .338 NM, nor would it be a good idea to if you could.
Enough of the memes.
In addition to 240's not being rechamberable to 338 as quintus pointed out, i have an issue with the idea that 338 is anything resembling close to .50 bmg performance. You can flat do things with .50 like raufoss that isn't even close to worthwhile in 338.
The one place that they are like .50's is in ammunition weight and bulk only without the performance increase commensurate to that added weight and bulk.
I also have another serious question for you. Why do you hate buffer tubes so much? Would a shortened buffer tube carbine be acceptable in your eyes?
I see a lot of people that seem to have a strange hate for the AR buffer tube and it honestly baffles me.
I own and shoot a bufferless AR as well as various other bobbed tube and etc mutants. They're cool, and kinda convenient, but in the end for a combat rifle reliability and consistency often outweigh convenience.
There's about a hundred other upgrades updates and reworks you could do to m4/mk18's that seem to have astronomically better payoff and usefulness imo.
So hopefully you can help me understand why a folding stock and no buffer, and ONLY THAT, is your focus to the exclusion of other approaches.
1. referred to the .338NM (8.59X63) rather than the .338LM (8.59x70).
2. Don’t discount the value of the .338 Lapua Magnum, though. It may seem like an inferior cartridge when all of the specs are listed side-by-side with the .50 BMG, but it can deliver nearly equal performance in almost all of the same scenarios. Its accuracy at 1000 yards is easily equal to the .50 BMG, but farther shots will probably require more sight adjustment due to the slightly lower muzzle velocity and more dramatic trajectories.
3. Buffer tubes make it difficult to have a compact weapon.
There is interest in replacing the .50 cal
Sig has one in development
The MG 338, a .338 Norma Magnum machine gun made by Sig Sauer, recently completed safety testing, according to a Wednesday announcement by the weapon-maker.
Yeah, you're not stuffing a 338 Nm Into a 240.
And also, I knew you were referring to Norma mag the whole time and all of my points still stand. It's marginally less bad than LM but that's nowhere near the same as good.
There are frankly lots of things that Norma mag can't do that bmg can that being more accurate to and beyond 1 kilometer doesn't come near making up for.
Now, onto the subject of buffer tubes. Let's take your rattler pdw with a stock attachment interface rail at the back as a baseline. You're giving up easy an inch to the back face of the attachment rail, then another inch or even a bit more for a hinge and lockup plate that may or may not actually lock the stock up well (and just how long is the right repeatable lockup going to last before your stock starts getting wiggly? Hint: not long, many if not most folder mechanisms are some degree of crappy) so you're sitting at 2" minimum beyond the rear wall of the lower.
There exists on the market one $59 retrofit micro buffer setup that uses standard bcg's and everything and gives you the equivalent 2" or so protrusion beyond rear receiver wall.
There also exists any number of retrofit systems some of which have very tiny integral telescopic 6 position telescopic stocks that fully collapsed range from about 4 inches of protrusion TOTAL including spring loaded telescopic pdw stock that can spring deploy to your desired adjustment point with a single push button action to about the same as a normal m4 stock which is something like 8 inches and changed fully collapsed.
These options are cheaper simpler and many of them require nothing but the new buffer system shorty tube and etc while using standard carriers and everything else.
So my first question is, does a whole 2" shorter warrant $1500 instead of $200-$500?
My second question is, does the extra inch and a half difference between an 11" 300 blk and a 12.5" 5.56 barrel Actually DO something meaningful?
The reason these questions are important is because what you're advocating for is loaded with serious pitfalls like accidentally blowing up guns, hoping that this time Sig isn't having paying customers serve as product development testers (see the origination of Sig's bufferless system two product names and a mark 1 and Mark 2 version of the original version before they renamed tge product line and went to the current version)
Bottom line is that you're pushing for the most technically risky approach that also involves REDESIGNING 300 BLK so it can't blow up 5.56 guns and truly MASSIVE cash outlays between the conversion kits ammo tools new armorer training and beyond.
Even worse than that though, you're doing it based around a round that's going to be actively worse at and beyond 300 meters
ALL over saving between 2 and 5 inches in stowed weapon length.
It's just so far beyond not worth it, the mind boggles.
Embrace the concept of carrying a slung M4 with the stock in the 2nd position. That way, if you have to shoot quickly, just unsling (if you don't have it hanging down front on a single point sling)unsafe, put to shoulder, and fire! Saves time over the additional step of unfolding your stock.
There is no point to a new gun unless there is a new round (apart from the 6.8 which is a going to see limited use). This also applies to the .338 NM. the .50 BMG needs a 25 kg gun and a polymer case, not a .338 that can't do 90% of the jobs and 240 does. . With a projectile less than 50 years old in design they overmatch the .338 in every category.
Yes. We're very much on the same page.
We already know sub 25kg 50 bmg belt feds are possible too since there were guns built in the mid 40's by one guy that ranged between 31 and 48 pounds with cyclic rates up to over 1000 rpm and as low as 350 rpm.
Assuming that you're modernizing the ammunition anyway, there are several things you could do to help compensate for the idiosyncrasies of such soft recoil action designs.
Ultimately and for many other reasons beyond this, I think that this is the right course of action and should be pursued.