US Military choice of .300 WinMag over .338 Lapua

[Joseph5]

It is my understanding, and this is only from reading, that the anticipated mission environment that mostly makes the choice for them. Urban missions with typically closer ranges and more targets favor a semi auto which would be a 308 while rural with longer ranges and possibly less targets favors the bolt gun so a 300. Now with the Nemo Arms semi auto 300 WM there may not be a reason to have to choose.

[stanc]

Does anyone know if the 308 will still be used by snipers or has it been relegated to Designated Marksmen.

See pp. 3-4 of http://www.dtic.mil/ndia/2013armament/Lucas.pdf
That shows a compact version of the M110 to be used by snipers through 2048.

[Tony Williams]

A comment on the 220 grain SMK: from memory, I understand that it has the same ogive as the 190 grain, the extra weight coming from a longer shank. In other words, the form factor is no better, the improved BC comes only from the extra mass.

The .300WM and (to a lesser extent, I think) the .338LM suffer from the usual problem that the COAL is too short to permit the use of the long-ogive bullets which give the best long-range performance. I suspect that the .338NM may turn out to be the optimum choice......interestingly enough, the Rem MSR is advertised as available in this calibre.

[LRRPF52]

http://atk.mediaroom.com/index.php?s=25280&item=136851

ATK Awarded a Five-Year, Indefinite Delivery/Indefinite Quantity Contract Worth Up to $20 Million

I wonder who is providing the barrels...

[Joseph5]

If you are referring to the M2010, I think they are overhauled M24's with the overhauling being done by Remington. They make there own barrels don't they?

[Tony Williams]

If you are referring to the M2010, I think they are overhauled M24's with the overhauling being done by Remington. They make there own barrels don't they?

As I understand it, it's a different gun. The MSR was designed to meet the Army's Precision Sniper Rifle contract, and is a multi-calibre modular weapon. It won the contract only last year.

[nincomp]

Yup, now think about barrel life in a WinMag at 68,000 PSI at 70 degrees being shot in 120+ temps!

According to the following presentation from St. Marks Powder, the .338 Lapua Mag would be loaded to 65,000 psi. Does the larger diameter bore have any effect on barrel life?

Page 14 in this:
http://www.dtic.mil/ndia/2010armament/We...intich.pdf

[bwaites]

According to the following presentation from St. Marks Powder, the .338 Lapua Mag would be loaded to 65,000 psi. Does the larger diameter bore have any effect on barrel life?

Page 14 in this:
http://www.dtic.mil/ndia/2010armament/We...intich.pdf

Generally speaking, all other things being equal, the larger the powder capacity vs the barrel bore diameter (called "overbore") the faster erosion takes place. A Grendel with 35 grains of powder capacity will last longer than a 6.5x47 which will last longer than a .260 Rem, which will last longer than a 6.5x284.

Here's an article for you:

http://www.accurateshooter.com/technical...y-formula/

[nincomp]

The .300WM and (to a lesser extent, I think) the .338LM suffer from the usual problem that the COAL is too short to permit the use of the long-ogive bullets which give the best long-range performance. I suspect that the .338NM may turn out to be the optimum choice......interestingly enough, the Rem MSR is advertised as available in this calibre.

The .338NM (Norma Magnum) is pertinent to this thread since it is essentially a "Grendelized" .338 Lapua Magnum. The case has reduced taper and increased shoulder angle to allow increased powder capacity in a shorter case. The shorter case allows a longer bullet to be used while maintaining the same cartridge OAL. The two cartridges have the same base diameter. See the comparison photo here:
http://en.wikipedia.org/wiki/.338_Norma_Magnum

The .338 Norma Magnum has increased flexability over the .338 Lapua Magnum:
- If desired, the .338 NM can match the performance of the .338 LM (when using the same bullets) while using a shorter rifle action (this is one reason for its creation).
- When matching the cartridge OAL of the .338 LM, the NM can use longer, higher BC bullets to increase its effective range.
- A longer bullet can have increased internal volume that can be used to make it more effective as a tracer, AP, incendiary, HE, etc round.
- According to General Dynamics, the differences between the 338 Norma Magnum and the .338 Lapua Magnum round make the Norma a better machinegun round:
http://www.dtic.mil/ndia/2012armaments/W...teimke.pdf

[nincomp]

Generally speaking, all other things being equal, the larger the powder capacity vs the barrel bore diameter (called "overbore") the faster erosion takes place. A Grendel with 35 grains of powder capacity will last longer than a 6.5x47 which will last longer than a .260 Rem, which will last longer than a 6.5x284.
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The reason that I asked is that General Dynamics reports improved machinegun barrel life with the .338 Norma (over the .338 Lapua) even though the difference in the volume of the two cases is small. If the loadings match those in the NDIA presentation above, the propellant difference is only 1%

Only one article that I have read suggests that other factors come into play. In this article (from the same site you referenced) one shooter expressed his thoughts that a long case neck could reduce barrel wear. He postulated possible reasons:

- Reduced blow-by since the front of the bullet shank could be fully engraved before the back exits the case.

- The longer case neck helps align the unburnt particulates leaving the case. This in turn reduces the amount of particulates laterally impacting the barrel throat.

I have never seen a confirmation of either of these effects, but the author claims that the relatively long-necked 6mmBR demonstrates them.

[Tony Williams]

Only one article that I have read suggests that other factors come into play. In this article (from the same site you referenced) one shooter expressed his thoughts that a long case neck could reduce barrel wear.

That was one of the reasons for selecting the Norma round given by the GD team at the 2012 presentation in Seattle, but it was subsequently dismissed by Lapua. In fact, if you compare the two rounds side-by-side, there is very little difference in the neck length.

[bwaites]

I like both cartridges, and I like the fact that the Norma will go into shorter actions. One of my concerns with that is that simply shoving it into an action designed for a smaller and lighter cartridge might not be really safe.

I suspect that even the actions typically used by the longer Lapua are borderline safe, simply because there isn't enough metal around the cartridge. I'm no metallurgist or engineer, but it seems to me that more steel is better when you start talking about the case diameters of these cartridges.

Maybe LRRPF can chime in on hoop stresses of a 1-1.25 inch diameter action stressed by these cartridges?

[nincomp]

Had General Dynamics actually performed barrel wear tests or just guessed?

[nincomp]

I like both cartridges, and I like the fact that the Norma will go into shorter actions. One of my concerns with that is that simply shoving it into an action designed for a smaller and lighter cartridge might not be really safe.

I suspect that even the actions typically used by the longer Lapua are borderline safe, simply because there isn't enough metal around the cartridge. I'm no metallurgist or engineer, but it seems to me that more steel is better when you start talking about the case diameters of these cartridges.

What is the COAL typically used for the .338 NM and for the .338 LM? I have seen two: 3.600 and 3.681".

I hope that LRRPF will let us know how much duct tape should be used to provide the necessary margin of safety.

I noticed that there is also general concern about lug strength. Now we will need JB Weld suggestions.

[cory]

I like both cartridges, and I like the fact that the Norma will go into shorter actions. One of my concerns with that is that simply shoving it into an action designed for a smaller and lighter cartridge might not be really safe.

I suspect that even the actions typically used by the longer Lapua are borderline safe, simply because there isn't enough metal around the cartridge. I'm no metallurgist or engineer, but it seems to me that more steel is better when you start talking about the case diameters of these cartridges.

Maybe LRRPF can chime in on hoop stresses of a 1-1.25 inch diameter action stressed by these cartridges?

It's a pretty simple calculation.



σ(hoop) = p d / 2 t

where

σ(hoop) = hoop stress (MPa, psi)

p = internal pressure in the tube or cylinder (MPa, psi)

d = internal diameter of tube or cylinder (mm, in)

t = tube or cylinder wall thickness (mm, in) (outer diameter minus inner diameter)

Ideally you want sigma to be less than half of the yield stress of the material used.

[nincomp]

Maybe LRRPF can chime in on hoop stresses of a 1-1.25 inch diameter action stressed by these cartridges?

It seems that 1.12" is not enough when a cleaning rod is left in the barrel.
http://bulletin.accurateshooter.com/2014...lm-kaboom/

[LRRPF52]

http://lassengunsmithing.com/html/CylinderStress.htm