Question on the USMCs new open tip 5.56 SOST round

[LeeAdama]

I was reading about the new open tip 5.56 SOST ammo used by the marine corps and I read that the new round's load has been optimized for ballistic performance and reduced muzzle flash from short barrels. From a 14" barrel is achieves 2925 fps. And that is uses a temp stable flash reduced propellant.

So what is the powder load compared to the M855 is it the same? And does the new flash reduced propellant effect the noise at all or is there no noise difference?

Like M4 with 5.56 SOST vs M4 with M855
And M16 with 5.56 SOST vs M16 with M855

[LeeAdama]

If the MK318 has been optimized for ballistic performance in short barreled rifles, does that mean it has a high powder loading than the M855 and in turn a high chamber pressure?

[Palmetto-Pride]

Another question will it also go faster in longer length 16" and 20" barrels as compared to M885.......:confused:

[LeeAdama]

I think so which is why the USMC uses it for their M16A4s rifles.

But if it performs well in a short barrel 13 in SCAR-L or a 14.5 in M4 Carbine then it must have a higher powder charge than the current M855?:confused:

Thats why I'm asking.

[ranger dave]

no one will ever be happy with the 5.56x45 mm . i think its a huge waste of money . the jar heads allways have to have something different . first they wanted a round that would defeat body armor enter the m855. then we found that it sucks a cqb ranges . its just a loseing battle with the 5.56x45 mm . so what haptens when the jar heads wind up being suppored by a army group who all they have is m855 you have to re zero all your weapons ?? there is no one round that workes great all the time

[Crosshair]

Has anyone actually independently verified these velocity claims? This smells a lot like the early 6.8 SPC velocity figures that ended up being made of unicorns and rainbows.:confused:

[LeeAdama]

The velocity can be found here: http://www.dtic.mil/ndia/2009infantrysmallarms/tuesdaysessioniii8524.pdf

Look at page 23.

On a side note this is a stupid question but I read from this article that the new rounds load is design for short barrel rifles, does that mean it uses a faster burning propellant?

And does this mean an increase or decrease in the number of grains of gun powder? Any changes in chamber pressure?

And does flash suppressed powder effect the noise level at all?

If anyone can answer these question of mine I would be very thankful.;)

[TheManHimself]

If it is to be a NATO-spec round it has to fall within the same pressure limits as M855, M995, and the like, as 5.56 NATO weapons are designed to handle those pressures. Significantly higher chamber pressures would greatly decrease service life of the weapons, a significant factor when you're considering armies that have hundreds of thousands of these weapons in inventory. My guess would be newer propellant technology akin to Hornady's Superformance loads, advanced powders that produce higher velocities while staying within existing pressure specs.

[LeeAdama]

So these new loads will still have the same amount of powder but faster burning than the current M955/M995 NATO rounds?

[Jimro]

LeeAdama,

Ammunition is tracked by lot number, because ammo is made in batches or "lots" that meet certain specs.

As long as the ammunition performs within specifications the actual powder charge can vary quite a bit. An ammunition plant will have a ballistics lab to determine how much powder from a given lot is needed to make the ammunition perform within spec. When you buy your powder by the metric ton it is the only way to do business.

A couple years back the contractor running Lake City changed and a lot of ammunition recipes changed as well, but ammunition performance didn't.

Hope this explains things. Big ammo companies don't use a specific recipe for their product, they make each lot to perform to spec.

Jimro

[Crosshair]

LeeAdama

That's not independent verification.

[LeeAdama]

I found out that federal loads the new ammo.

[LeeAdama]

Could they use a larger amount of faster burning powder in order to keep the gas pressure up in the MK318 which is why it has a high muzzle velocity?

[jwfuhrman]

nothing wrong with 5.56x45, especially non-ball 5.56x45. Its just the fact that the military is limited to bull**** rules set by a Treaty we as a country never signed, is what makes 3 or 4rds needed to stop someone.

75gr Tap 5.56x45 T2 ammo is great. Its exspansion and heavy weight bullet it make it a very lethal round.

5.56x45 is here to stay, so get used to it.

[BlueTrain]

Not only might the marines have to be supplied by the army but sometimes maybe even another army. That's why there are NATO specifications. There are still differences but the ammuntion is completely interchangable.

[Jimro]

All the M855 I've dissassembled over the years has a ball powder in it, last I heard it was Winchester 844 which isn't available except as surplus pulled powder (if then). The closest you will get with a commonly available powder is Win748.

A larger amount of faster burning powder is a recipe for spontaneous rifle dissassembly.

More likely it is either the same amount or smaller amount of a faster burning powder.

Jimro

[johnwilliamson062]

Maybe the marines have realized the best way to get new rifles is to start shooting ammo that is too hot:) I doubt it, but it wouldn't surprise me either.

'Oops, that new round damaged all our rifles. We need new SCARs'

[Crosshair]

Could they use a larger amount of faster burning powder in order to keep the gas pressure up in the MK318 which is why it has a high muzzle velocity?
That helps somewhat, but still doesn't get them up to the velocity figures they claim. The problem is that you still have the MAP to contend with.

[LeeAdama]

What is the MAP?

Also it does not make sense to use less faster burning powder, makes more sense to me to use the same amount of a mixed powder IMO but I don't really know.

[Crosshair]

Sorry, MAP is 55,000 PSI

Duplex charges don't really work in small arms cartridges.

[LeeAdama]

Than maybe they are not using a faster burning powder.

Since they also use the MK318 in the M16 with a full 20 in barrel, in order to do that you need enough burn time in the powder to build up velocity until the end and with a small amount of fast burning powder you can't do that as well, but the MK318 is good for short barrel rifles as well....

Perhaps its the same amount but more efficient?

[5whiskey]

no one will ever be happy with the 5.56x45 mm . i think its a huge waste of money . the jar heads allways have to have something different . first they wanted a round that would defeat body armor enter the m855. then we found that it sucks a cqb ranges . its just a loseing battle with the 5.56x45 mm . so what haptens when the jar heads wind up being suppored by a army group who all they have is m855 you have to re zero all your weapons ?? there is no one round that workes great all the time

kind of like the army wanted that starship trooper looking "xm whatever it is" rifle that no one has spoken of in years? :barf:

Friendly inter-service ribbing goes both ways ;):D

[johnwilliamson062]

Hey I saw something to the effect of that XM starship trooper rifle might be brought back on the table not so long ago. Radio controlled exploding ammunition and all.

If there is less muzzle flash wouldn't that mean the powder is done burning at the end of the barrel? Or at least more done than M855?
Seems to me this has to be a faster burning powder.
Even if it isn't still burning when the bullet reaches 20 inches the pressure can still be higher behind the bullet than in front so it will continue to exert force. Right?

[callme_crazy]

what is the point of nato regs any ways? I strongly disagree with NATO rounds this means our enimies can use our ammo as well so what would be the point of that? correct me if im wrong please but why not keep all us forces to the best ammo and weaponry that accually works.

[BlueTrain]

In reply to the previous post, I suspect there is less advantage to having common ammunition with your allies than is generally claimed. However, in WWI and WWII both, there were as many common calibers, including artillery, as could be conveniently arranged. I say there is less advantage than is claimed because most armies sometimes wound up using multiple calibers without exeriencing total meltdown in their logistics even when fewer would have been better. As an example, the British actually used .303, .30-06, and 7.92mm machine guns in front line service, although the reason was because of adoption of certain guns, not because of adoption of certain calibers. More often allies and not just ours, use a common caliber because they are using the same weapons. In WWII the British could use some captured German ammuntion, provided they could actually manage to capture some, and it's not unknown to use captured enemy weapons.

Now regarding the powder used in small arms ammuntion. There is the idea that you have to have complete combustion or burning of the powder within the barrel to have maximum efficiency. That is not correct, although it isn't a simple thing. It rarely is, after all. One can sometimes achieve a higher velocity with a slower burning powder in a relatively short barrel in spite of the fact that it does not all burn inside the barrel. There might be negative side effects such as increased blast or flash and I have no hands on knowledge on dealing with flash. Those may be considered important to the users, especially flash. But the efficiency of a given load (the powder, that is) should be measured by the velocity achieved and not by the efficiency of the powder being burned, provided it all happens within permissable pressure limits. Most handloaders know that if they like to play around with more powerful loads, though I doubt many handloaders have any way to measure pressure beyond looking at the primer of the fired cartridge.

[LeeAdama]

I did some searching around and I got a reply quote:

"the propellant was designed to provide optimum performance from a 14 inch barrel carbine. We are getting right around 100 fps higher muzzle velocity from the M4A1 and MK 16 SCAR L than we get with M855. M855 was designed for the M249 SAW which has a 20 inch barrel. It was later adapted for use in M16 (1:7 twist only). You fire a rifle cartridge in a carbine, you loose velocity. You design a cartridge for a carbine, you can gain some velocity back. (some, not all). MK 318 Velocity from a 20 inch barrel is still higher - around 3,025 fps.

As far as charge weights, both M855 and MK 318 are very close (full case capacity). They do not use the same propellant. M855 propellant was designed in the late 70's. MK 318 propellant was designed for the MK 318, and actually the MK 319 (7.62mm SOST big brother)."

[Jimro]

LeeAdama,

Even M855 doesn't necessarily use the same propellent. The '96 small arms manual lists two powders used to manufacture M855. Like I said before, if the ammunition meets performance specs then the factory will load up a bunch with that lot recipe and ship it off.

Jimro