They keep talking about pressures and barrel life, yet 120mm M256 barrels are rated for 1,000 EFC (effective full charge: SABOT), and operate at working pressures/peak chamber pressure of 96,000 psi (661.9 MPa) at 120 °F (49 °C) and 82,650 psi (569.85 MPa) at 70 °F (21 °C).
I don’t have specs for the 155mm, but the Germans are getting nearly 70 km out of their guns. No word of early erosion. Interesting.
Usage of the PzH2000 in Ukraine has shown that the expected barrel life of 4500 rounds was a gross underestimation, the Ukrainians got up to 20000 rounds through the barrels without issues with the barrels. Proper cleaning to remove propellant residues is obviously mandatory but that is nothing new.
Electronics was overheating but that is not a barrel issue, just needs proper cooling.
I can’t compare the barrel designs of the PzH 2000 and the Crusader. I lack certain data. But propellant residues don’t cause erosion and pitting by themselves. The high pressures and temperatures (PV=nRT) inside the bore, not the chamber, were the concerns of the US team.
They suspected they might have problems when they developed two goals for the reject
1- go long: this was always the primary goal of the project
2- figure out autoloading
The excessive wear of the L/58 barrels was a serious concern, and the ballooning budget drove termination. I suspect the Ordnance and Artillery people are looking at the PzH 2000 barrels (L/52, thus 930mm longer and burning hotter), but right now it’s a bit of apples versus oranges. They are both fruit (cannon barrels), but not the same.
I got the specs on the German ERCA 155mm ammunition for the PzH.
The data shows 395 MPa, which is significantly lower than the XM1299 gun barrel was seeing. In at least one case, the L/52 saw a max pressure of 494 MPa, still well below that seen on the XM1299/XM282E1 system.
Those pressure differences mean significant increases in thermodynamic loads.
Source:
Thanks, I’m not too far from it.
Like me and the Armor & Cavalry Collection on Fort Moore. I’ve a docent/volunteer there. We now have hundreds of AFVs inside, and even more in dedicated refurbish/preservation bays. We have several AT guns from various countries, and some experiments like the Crusader.
Made the trip to the Armor & Cavalry Collection’s open weekend in April this year. As you say, fantastic collection. Having been fortunate to visit the collections at Bovington, Saumur, Latrun, Munster, Cairns, Puckapunyal, & Hudson (AHM), I’d say the US Army collection is the best I’ve visited.
That’s high praise. I’ll pass this on to the Director, Curator and Volunteers this weekend.
We wish that it were more readily accessible by the public. At the same time, the notion that the Collection is a font of knowledge for the current and future generations of AFV crews drives us to make it so.
Next time you attend an Open House, check back by the T-26/IS-3/Hellcat spaces. I’m usually there as I have connections to several of those vehicles and their place in time.
My T28 for this weekend’s show:
PS- I lived at Saumur as an infant. My Dad was the US LNO to ‘’l’ecole de cavalerie” 1951-1953. I was able to visit his office in 2000, and see the preps for that summer’s displays.
The T28 is a beast, iirc it’s displayed next to a M22 Locust?
(upload://bo2g5bHASTqj6RleVOXjnQfF7TF.jpeg)
It’s a fair hike to visit from Australia, but I’m trying to make it work next year.
Nice work your T28, btw.
OZ! Now THAT is amazing. Should yo be able to pick and choose, perhaps you can visit during one of the few two-day events we schedule. Would love to get acquainted and share a beverage of your choice.
Yes the T28 is on the front row to the right of the entrance. The M22 has a faux main gun, sadly.
Kind words on my T28. First model I’ve built since the lat 1990s. I’ve been a volunteer at the Collection for several years, and am thrilled at the reception. It’s an interesting project with limited funding and thousands of volunteer hours per year. They’re a great bunch.
As we learned from Hollywood: G’day!
Are the 155mm tubes smoothbore like the 120mm?
KL
Negative-
All the US barrels are rifled. L/52 (155mm) makes for a VERY long smoothbore over 8m. That’s a long as an MBT hull.
There are some limitations to smoothbore guns, and I’m not certain if the metallurgy and manufacturing can keep it straight. Look what MBTs do to keep the gun shooting well: the thermal sleeve and the MRS (muzzle reference system). An L/52 has a lot of droop on a very hot day!
I think artillerists like the rifled gun, and the resultant dispersion of dumb rounds is pretty normal.
That’s my point: Rifled weapons are more sensitive to erosion than smoothbores, everything else being equal, so the comparison of the XM907 and M256 operating conditions is missing a lot of context.
KL
And the exterior ballistics of finned projectiles at ranges exceeding 70km, (and flight paths approaching 100 km up and down) are not well-studied IME.
In high angle fire, the max ordinate (iirc) of a 155mm ER projo approaches 14km. That’s antiaircraft height, and one reason the JSOC is such an important member of the team: clearing fires. Imagine dodging artillery rounds as you concentrate on a strike mission.
I don’t have any research on the type and size of non-penetrating projectile that addresses high altitude flight of fin-stabilized artillery rounds. Air density affects fin-stabilized (hence gimbaled rockets) in adverse ways.
At 14km, the density of air is calculated by eight variables and one constant. The result (from one of my tables) is less than 20% that on the surface of the earth. Fins are much less effective. Think of the controls required on the X-series of experimental aircraft, and descriptions of how typical aircraft controls were ineffective. Also, air density varies as a function of temperature and humidity, both being immeasurable at the artillery plotter’s table (or today, tablet) in the FDC. I imagine the FS projo would depart from predictable/controlled flight.
I opine (I might be thinking, but at best I’m using an eSWAG: educated silly wild @$$ guess) this is the biggest reason for using spin-stabilized projectiles for long range indirect fires. Their external ballistics are well calculated over decades of use by all the major calibers. The science is limited to the metallurgy of the barrel, and the chemistry of the propellants used to achieve ER (extended range) ballistics.
IF artillery is fired at low angles, the air density sensed by the projectile is nearer to that of the ground level values, and the round encounters more drag. Drag is directly proportional to air density, so a round flying a few hundred meters above the elevation of the gun tubes is encountering ~5x the drag a similar round experiences flying between 10,000 and 14,000 meters. That amount of drag reduces range significantly.
My head hurts ——-
That’s probably because you are jumping all over the place. You started off talking about erosion and tube life (internal ballistics) of the XM907, then pondering why smoothbores like the M256 can tolerate demanding operating conditions, then going into some discussion of exterior ballistics. All those twists and turns are giving your brain a workout!
KL
Well, I could write a paper about the relationships. Oh wait, I already did in 1975!
But the problem for the artillerist is complex: higher velocities of thin-walled HE projectiles require extraordinary muzzle velocity and less acceleration, and that requires a combination of new propellant chemistry and barrel length (caliber). This require new metallurgies. The relatively higher velocities of smoothbore tank rounds is achieved in a barrel length required to meet the terminal velocity (Vt) requirements of the long rod penetrator. For an equal amount of penetration, the Vt of DU (aka Staballoy) is ~15-20% lower than that of WHA (aka tungsten) penetrators. Hence the L/44 M256 versus the L/55 Rh120.
The interesting part of artillery design involved the HARP guns, and the Iraqi super guns, developed by Gerald Bull. But that is another model!
