Range Report Howitzers, Field Guns, and Autocannons

[Forgetful Coyote]

With modern standard shoulder-fired rifles, as everyone knows, one can reliably/repeatedly hit targets that are within the supersonic range of the projectile. Some cartridges are specially made to start off subsonic and have the ability to be very quiet. Older rifle cartridges, such as the .45-70, started off subsonic/barely supersonic because the knowledge of chemistry/ballistics wasnt up to par and the bullet design and gunpowder didnt allow velocities much higher than mach 1.
With that bad generalization said, I have a few questions for some of the ballisticians in here who may know what I want to know. I also didnt know exactly what forum to put this in as it is quite a wide subject so it would be awesome if yall could go easy on me. Im not an expert by all means.

1) Why do bullets that, as mentioned above, start off barely supersonic ~1300 ft/s, fly stably through the transonic region yet modern high-power centerfire bullets dont?
2) Do the shells from artillery pieces like the M102 105mm and M777 155mm stay supersonic throughout the entire range, which can be up to 25 miles or more? If not, why do they transition just fine yet smaller bullets dont?
3)Same as above, but for smaller cannons. The 40mm Bofors, arguably one of the most popular and great performing AA guns, has a range of several thousand meters. The 25mm Bushmaster and M61A1 Vulcan 20mm both have ranges well past 2500m, and Im assuming theyre still supersonic at that distance seeing as how they are made for defeating armor. What makes these larger projo`s different from standard rifle bullets that allows them to stay supersonic longer? Is it any different from the regular ballistics of a rifle, basically relying on ballistic coefficient and velocity?

Ive always looked at things like the .338 Allen Mag and .375 Viersco Mag as ultimates for line-of-sight weapons, yet over in Afghan I hear theres troops using 105 howitzers as LOS weapons and with the 30mm on an Apache very long range kills are possible.

The muzzle velocities of autocannons, field guns, modern howitzers, and standard shoulder-fired centerfire cartridges arent much different. So the only conclusions I can come to is that larger bullets have much better ballistic coefficients or just go through the transonic region very stably or both.

Would anyone be able to chime in on this?

 

[GMZ]

Re: Howitzers, Field Guns, and Autocannons

Interesting question. I work with Naval artillery so let me jot some thoughts down. Well I had a nice little paragraph down and IE took a dump so Ill give you a condensed version. Im actually going through a naval gunfire trainer this week so its funny you ask this. External ballistics are [mostly] the same, at least in principal. Autocannon, field guns, and howitzers also fire using different trajectories and their projectiles are designed as such.

Most of the difference is mass, were talking about very heavy projectiles here that are propelled at the same speeds as bullets barely a fraction of their weights.

Take a 175 SMK and a 5" gun for example: both a 175 SMK and a 70 lb 5"/54 cal (127mm) projectile travel at roughly 2650 fps. But the effective range of said 5" projectile is around 22k yds, with the max about 26k yds so there is a degredation in performance that is significant enough at the extreme edge of its range.

 

[ddavis]

Re: Howitzers, Field Guns, and Autocannons

Bryan Litz's Applied Ballistics book hits on the transition from super to subsonic. Some bullets survive the transition just fine while others do not. For example, the 168 Sierra Matchking is notorious for losing stability as it reaches the transonic zone. It has something to do with the design of the bullet, specifically the angle of the boat-tail.

 

[Deleted member 10043]

Re: Howitzers, Field Guns, and Autocannons

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ddavis</div><div class="ubbcode-body">Bryan Litz's Applied Ballistics book hits on the transition from super to subsonic. Some bullets survive the transition just fine while others do not. For example, the 168 Sierra Matchking is notorious for losing stability as it reaches the transonic zone. It has something to do with the design of the bullet, specifically the angle of the boat-tail. </div></div>

Litz provides no evidence that the SMK 168 is unstable other than it supposedly occurs in the dynamic range, which has no value to measure. He is silent on anything solid how he comes to this conclusion. If Sierra agreed with Litz they would fix the problem. I've asked Litz to comment and he basically just reiterated what little information he put in his book. As for myself, I see an appearance of a conflict of interest with Litz's association with one of Sierra's competitors and I wish he would have provided more data to support his claim about one of the most popular bullets Sierra makes for the .308. So, now is a good time to point out the elephant in the room. Litz's book is good. He is a smart fellow as well as a darn good shooter. But his book is self published, which means the book was never properly vetted, and provides little in the way of sources or how he came up with the occasional "wtf?" in his book, like the SMK 168, which comes right out of left field. I just wish people wouldn't believe everything they read just "because".

To keep this on topic I will say that Litz's SMK 168 comments are not good examples to help the OP. Nevertheless, Litz's explanation on dynamic stability, excluding the SMK 168, partly points the OP in the right direction. I say, "partly", because Litz's book is not about artillery/gun ballistics.

 

[MitchAlsup]

Re: Howitzers, Field Guns, and Autocannons

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: GMZ</div><div class="ubbcode-body">Take a 175 SMK and a 5" gun for example: both a 175 SMK and a 70 lb 5"/54 cal (127mm) projectile travel at roughly 2650 fps. But the effective range of said 5" projectile is around 22k yds, with the max about 26k yds so there is a degredation in performance that is significant enough at the extreme edge of its range. </div></div>

A 70 pound 'bullet' is 500,000 grains (+/-)
A 5" 'bullet' is 16.23 times the diameter of a 0.308 bullet
and has 263 times as much frontal area

So the mass to frontal area ratio is 500,000/263 = 1897 times as much.

Do we know the length of the 70 pound 5" 'bullet'?

 

[GMZ]

Re: Howitzers, Field Guns, and Autocannons

26"

 

[ddavis]

Re: Howitzers, Field Guns, and Autocannons

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Culpeper</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ddavis</div><div class="ubbcode-body">Bryan Litz's Applied Ballistics book hits on the transition from super to subsonic. Some bullets survive the transition just fine while others do not. For example, the 168 Sierra Matchking is notorious for losing stability as it reaches the transonic zone. It has something to do with the design of the bullet, specifically the angle of the boat-tail. </div></div>

Litz provides no evidence that the SMK 168 is unstable other than it supposedly occurs in the dynamic range, which has no value to measure. He is silent on anything solid how he comes to this conclusion. If Sierra agreed with Litz they would fix the problem. I've asked Litz to comment and he basically just reiterated what little information he put in his book. As for myself, I see an appearance of a conflict of interest with Litz's association with one of Sierra's competitors and I wish he would have provided more data to support his claim about one of the most popular bullets Sierra makes for the .308. So, now is a good time to point out the elephant in the room. Litz's book is good. He is a smart fellow as well as a darn good shooter. But his book is self published, which means the book was never properly vetted, and provides little in the way of sources or how he came up with the occasional "wtf?" in his book, like the SMK 168, which comes right out of left field. I just wish people wouldn't believe everything they read just "because".

To keep this on topic I will say that Litz's SMK 168 comments are not good examples to help the OP. Nevertheless, Litz's explanation on dynamic stability, excluding the SMK 168, partly points the OP in the right direction. I say, "partly", because Litz's book is not about artillery/gun ballistics. </div></div>

I've seen several pictures of sideways holes at long range from 168 SMK's, and Litz says they are a great sub 600 yard bullet, but not good for further ranges. Maybe Sierra acknowledges that they are a great benchrest bullet for shorter range. Litz cites that mass balance and the dimensions of the boat-tail are what cause its dynamic instability, but looking at his diagrams in the back of the book, there are several bullet with a very similar profile and an boat tail angle of ~13*. He talks about the 168s on Pg. 145 of the 2nd Edition book.

Here is another article reiterating the same thing:

http://www.shootingnews.com.au/Features/General/Ammunition/FEATURE%20Dynamic%20stability-PG1.php

Culpeper, I'm not arguing with you, just trying to make sense of it all the same as you are.
-Dan

 

[Red Mule]

Re: Howitzers, Field Guns, and Autocannons

My last up close and personal experience with a M198 was almost 30 years ago so I am sure that things have changed somewhat.

In my notebook I found the following:

155mm M107 HE

Weight in firing condition is 96.75 lbs ( 677,100 grains)
Length is 31.5 inches
Diameter is 6.10 inches (not the driving band)
Charge 7 Whitebag MV 1850fps
Max range 22.4KM

I understand that the new RAP rounds have an extended range but I don't know what that would be or what effect the RA has on the trajectory.

In looking at some old pictures, it looks like the M107 rounds have a +/- 10* boattail which falls into the ideal range of values and the form factor is probably less than 1.

I would say the answer to the question is mass and a very high BC. Additionally since artillery is generally used in indirect fire at max range the final trajectory leg might be very close to vertical so any instability might result in circular error in a horizontal plane. I never wanted to stand down range to observe

 

[Bearwalk]

Re: Howitzers, Field Guns, and Autocannons

A projectile with a sharp leading edge and boatail rear is designed with such to deal more effectively with the shock waves associated with supersonic flow. The associated price, at least for small arms, is that these very features make said projectile less efficient during transonic and subsonic flow than its flat nosed, flat based counterpart.

That's the short version, the long version required some nasty course work that I would not wish upon anyone else.. But, if you like pain, you can get started here:

[url="http://www.mtc.edu.eg/ASAT13/pdf/FM05.pdf"]www.mtc.edu.eg/ASAT13/pdf/FM05.pdf[/url]


and here:

2

 

[kraigWY]

Re: Howitzers, Field Guns, and Autocannons

I don't know anything about artillery. I've called it in, saying where I wanted the sells to land, and trust the Arty guys to figure out how to get it there.

I'm no where in the class of Litz and Hatcher. I've read their books, find them interesting, even understanding a bit.

I don't know the "whys" but I do know that happens. I've shot a heck of a lot of 1000 yard matches with the service rifle. I know that 168SMKs don't work, they're not accurate at that range and often keyhole. I've seen that in my shooting and I've seen it pulling targets for others shooting 168s. Sierra knows this, thats why they came up with the 175s (180 SMKs when I started shooting). The AMU knew this too. I spent time in their reloading shop in '78. They showed me the ins and outs of Mexican Match, using 168s for 200-600 and (the old) 180s for 1000. I took that advice back to my marksmanship unit and it works. I can not believe Sierre didn't know this, but since the 168s worked so well up to 600, and thats where most high power shooters were shooting, they probably desided not to fool with it.

I find it odd no one discusses small arms shooting at "extreme" distance any more. They use to. Some of Hatches books give tables of Angle of Departure/Angle of Fall for Machine Guns and the 1903 Springfield up to 3100 yards. Hatcher even gives the drift (spin drift) for the 1903 using the M1 ball up to 3100 yards.

As to the 45-70, I shot a time or two with the BP Creedmor guys. I tried to go the max velocity route and found my 535 grns would tumble when I tried to push them past 1300 MV. Also the 45-70 requires soft lead, not the hard stuff we use in pistols. Go figure.

I've read a lot on the subject, but I can't get a grasp on the math to figure it out. But I can "see". Even with my old eyes I can tell the difference between a clean 30 cal hole and one that hit sideways on the target.

I do know the nose and boat tail have a lot to do with it, but I don't know why or how to figure it out. I'll leave that to Litz and Hatcher. Besides they give me something to read on cold winter days when I'm too lazy to go outsde and shoot.

If you're into "big bullets" as in artillery, you need to study Ingalls and Greenhill.

 

[sinister]

Re: Howitzers, Field Guns, and Autocannons

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Litz's book is good. He is a smart fellow as well as a darn good shooter. But his book is self published, which means the book was never properly vetted, and provides little in the way of sources or how he came up with the occasional "wtf?" in his book, like the SMK 168, which comes right out of left field. I just wish people wouldn't believe everything they read just "because".

To keep this on topic I will say that Litz's SMK 168 comments are not good examples to help the OP. Nevertheless, Litz's explanation on dynamic stability, excluding the SMK 168, partly points the OP in the right direction. I say, "partly", because Litz's book is not about artillery/gun ballistics.</div></div>

Ballistic science applies to all projos and bodies shot through a <span style="font-style: italic">rifled</span> barrel, whether a conventional rifle, artillery and guns, or rifled mortars. There are volumes on the art that no longer apply to hobbyists (you recall most WWI-era rifles have extended-range ladder sights on them, like the Mauser, Springfield, Enfield, BAR, BMG, and Tommy gun). The US Army gave up indirect machinegun fire (using the equivalent of mortar sights and aiming posts) long before my father was born.

If you really want to go full-geek you need to start with Hatcher and McCoy (many cited items in the public Defense Technical Information Center archives, including a few really deep-end geeky articles on 168 Match Kings), Pejsa, and Bryan's book (an excellent layman's reference text).

There's an awful lot of publicly-available stuff published by both Picatinny and the Navy.

Here's one from Aberdeen Proving Ground (Hatcher's old outfit): http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA205633

It explains the "WTF?" comparing the 168 to the older 173 Match/Special Ball and 190 Match King.

Here's another: http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA441359

 

[Deleted member 10043]

Re: Howitzers, Field Guns, and Autocannons

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Sierra did. They engineered and produced the 175 SMK.</div></div>

Actually, that is not correct. Write Sierra. I think you would be surprised at their response. Just sayin'.

 

[sinister]

Re: Howitzers, Field Guns, and Autocannons

That would be an interesting read. Kevin Thomas (fomerly of Sierra, now with Lapua-USA) wrote some very good articles on 175 Match King development.

Off the top of my head Sierra used the old 155 Match King ogive and lengthened the shank to replace the older 172/173 M118 Boat-tail (itself an adaptation of the even older 30-06 AP profile).

 

[Deleted member 10043]

Re: Howitzers, Field Guns, and Autocannons

Well for clarification, I'm not saying Sierra didn't develop the 175 in case my comment is perceived as such. I'm saying to date if they thought the 168 was broken they would fix it. The 175 was not developed solely to fix the 168. Otherwise, Sierra would have ceased production of the 168. Just makes sense is all.

What is interesting is all these keyhole SMK 168s still hitting paper targets at 1000 yards.

Anyway, I can't find the magic bullet in the McCoy study. It does state one should use 1:12 twist with the 168 SMK, predicted cycle yaws are consistent with similar shaped bullets, and long range flight dynamics need independent experiment verification. Am I missing something?

Now, the PPU 168 acts like Litz describes. That bullet acts squirrely at all speeds not to mention within dynamic stability range. And it doesn't have a 13 degree boat tail.

To keep this on topic I'm backing off at this point. I may be wrong. Or I may be right. But somebody brought it up in this thread and somebody else wrote it in a book as a statement. All I want to push is that Sierra has a side to this story as well. All one has to do is ask. They are easy to contact. It would be step away from contempt prior to investigation for those that take offense to critics of some of the things Litz wrote. I'm trying to be objective and fair. I do apologize if I am offending anyone.

 

[Forgetful Coyote]

Re: Howitzers, Field Guns, and Autocannons

Thanks for the replies yall.
So there really isnt a whole lot of difference between regular centerfire bullets and huge artillery shells?

I shouldve clarified in the beginning, what I meant was : Why do artillery shells not tumble/keyhole throughout their entire range and always stay stable even while(Im guessing that they DO) they go through the transonic region? From what I can tell, most use flat based projectiles without a boattail at all. Im not an expert though and have never been up close and personal to an arty shell.

Also, is there any advantage at all ballistically(except velocity of course) with a sub-caliber discarding sabot(ala M1A2 Abrams), or is it purely for shorter range armour penetration? For example, Steyr made a 14.5mm(?) AMR that used a sabot round(not sure of parent case/capacity used), would this carry its velocity & energy downrange as well as say, a .50BMG or 14.5mm Russian? Do sub-caliber rounds have better ballistic coefficients than modern spitzer-boattail projo`s?

 

[Red Mule]

Re: Howitzers, Field Guns, and Autocannons

I think the big advantage to the sub caliber discarding sabot rounds like those used in M1A2 Abrams and others is the high muzzle velocity that can be achieved. I think the muzzle velocity is over 4500 fps. The sub caliber penetrator is essentially a big dart and is fin stabilized. The fins will always keep the center of pressure behind the center of gravity, which will lead to the maintenance of stability. Reportedly the effective killing range is in excess of 2500 meters which is not exactly short range.

HE rounds like the M107 don't require a high degree of precision to be effective. If I remember correctly, and I may not, within 50 meters of detonation everything dies and within 100 meters everything is a casualty. I think there is some instability in artillery rounds but it is not enough to make them in effective. A 100 meter circle is pretty large but at 14+ miles I think it is close enough.