IPB

Welcome Guest ( Log In | Register )

 
Reply to this topicStart new topic
> Full Auto/Burst Tangent (LONG), Ballistics is bloody complicated
mckay421
post Aug 20 2003, 10:48 PM
Post #1


Target
*

Group: Members
Posts: 41
Joined: 1-August 03
From: West Jordan, UT
Member No.: 5,192



Austere Emancipator raised valid points in the Full Auto/Burst thread that the weight and bullet design (spire point, boat tail, wad cutters, etc.) are extremely vital in the raw ballistics of any cartridges performance. That performance being measured as the energy that the bullet possesses, not only at the muzzle BUT ALSO throughout its trajectory. Performance should also include HOW that bullet reacts upon striking the target and the transfer of energy in creating a wound channel.

The importance of different powders, primers, and bullets when combined together can allow a hunter/target shooter to achieve a more accurate round for a SINGLE weapon. Let me give an example…

My father some years ago purchased six pre World War II Mauser 98K bolt action rifles. Having a professional gunsmith rechambered two of these rifles for the 7mm Remington Magnum. The modifications included free-floating heavy barrels (crowned) sometimes referred to as sniper barrels (with all of the NEGATIVE connotations that conjures up these days), adjustable fiberglass stocks, I forget which scopes he originally had mounted but after his death I had Leupold Mk4 Ultra x16 power scopes mounted. These two target rifles are EXACTLY identical and are rated at MOA (which is FAR more accurate than I could EVER hope to utilize). So one would imagine that you could shoot the SAME hand loads out of each rifle with the same results. Such is NOT the case. After much testing I found that a 150 grain Spire Point Boat Tail performed better in one rifle than in the other, which prefers a 175 grain Spire Point Boat Tail. And without boring you anymore then I already have, the powder and primers are different in each cartridge.

So have I found ballistic bliss with these two rifles?
No. For once I used up my lots of powders, primers, and bullets the process has to start ALL over again.
Why?
Because there are variances in each and every lot of powder, primers, and bullets. Those variances may not make not be noticeable when shooting at paper targets at 100 yards but stretch that distance out to 800 yards and suddenly they make a HUGE difference (the two aforementioned bullets can drop in excess of 40 inches at 500 yards!).

Can I point to any single factor as to the cause for the different tastes that these identical rifles have in cartridge preference?
Not definitively. There are probably minor variances in the barrels…although they have the same rate of rifling and were mounted by the same gunsmith.

Here is another point. In spite of my rabid love of the 7mm Remington Magnum cartridge it (or the two afore mentioned rifles) this cartridge is not suitable to all types of shooting. Those two rifles are great for long range target shooting (iron silhouette shooting in particular) but the thought of lugging one of those 19.7 pound rifles through the back country of Utah hunting elk makes my back ache at the thought! Different firearms and cartridges for different applications. Which may be why non-shooting enthusiasts here about so and so have a dozen rifles and think that they are some sort of survival nut. My best analogy is that most golfers don’t use one type of golf club for every shot that they take.

The importance of powder, primers, and bullets in terms of ballistics is that you want to stabilize the bullet as it leaves the barrel. Bullets that aren’t stabilized tend to tumble/keyhole. Imagine throwing a football without putting spin on it…and that is something of an exaggerated example of tumbling. Achieving a stabilized bullet is NOT always achieved with stock ammunition…although some firearms will do just fine.

Tumbling is also often used to describe the effect of what happens when a round like a 5.56mm military ball ammo does when it hits a target. Although I have one friend in the army that was describing how he was happy with his M16 because the range instructor showed him the paper target where the bullet had made a keyhole (hitting the paper other than point first). I didn’t have the heart to tell him that was NOT a good thing…since he needs to believe in his weapon. And I think more than likely he was using one of the older M16’s and not the newer M16A2’s which I believe addressed this with a different type of ball ammo.

In fairness to Austere Emancipator he is correct in his points concerning bullets and ballistics. My points would be FAR more relevant to precision shooting and NOT full auto/burst fire shooting. So thinking back it was NOT fair of me to include those points in regards to full auto/burst fire.

There are just SO many factors when it comes to making a ‘realistic’ ranged combat system. And even then…my idea of realistic may not be the same as yours.

In terms of Shadowrun, and even sniping, within the context of the game’s mechanics there are variances that need not be addressed. Any such rules would make the decking rules read like Amber!!! :D
Go to the top of the page
 
+Quote Post
Austere Emancipa...
post Aug 20 2003, 11:35 PM
Post #2


Great Dragon
*********

Group: Members
Posts: 5,889
Joined: 3-August 03
From: A CPI rank 1 country
Member No.: 5,222



I'm just going to say that, never having owned firearms, never having hand loaded them, never having fired anything but standard army issue rounds with them, I wish to minimize the impact things like primers have on ranged combat in my games.

That is to say, I do make my players re-zero their weapons when they change ammunition, if they wish to be accurate with them at extreme ranges (not just Extreme range, but long range in general). I do not, however, wish to include rules as to exactly how accurate the different weapons are with different kinds of rounds, even if that could easily amount to a +/- 1 TN at Extreme ranges, which can be quite important when sniping. I think I'm speaking for the majority of gun nuts here in this issue.

I think the unstabile 5.56x45mm problem occurs when firing the new SS109/M855 bullets out of an old NATO standard rifle, like the M16A1. The new NATO standard ball round is longer than the old, so it requires tighter rifling (1 turn in 7"), while the old only needed 1 turn in 12" rifling. Apparently, some manufacturers even produce 5.56x45mm weapons with 1 turn in 9" rifling, which doesn't work very well for either the old or the new standard. I'm not exactly sure, though, it might be that the older NATO standard also had stability problems.

These kinds of problems with bullet stabilization, if they are common, I could take into account. In fact, if they really are common, I certainly will. However, because it is so rarely mentioned, I have always assumed that it only happens in special, rare instances, like with the 5.56 NATO standard. Is it possible that you could pick up generic .308 Winchester ammunition from a gun store and find out that the rifling in your hunting rifle isn't tight enough to stabilize the bullet properly?

QUOTE
In fairness to Austere Emancipator he is correct in his points concerning bullets and ballistics. My points would be FAR more relevant to precision shooting and NOT full auto/burst fire shooting. So thinking back it was NOT fair of me to include those points in regards to full auto/burst fire.

All's fair in love, war and internet discussions, as long as it doesn't break the ToS. ;)

Because my only real shooting experience comes from the military, where I've fired weapons on full auto many, many times but only ever fired, I think, 20 rounds with a sniping rifle, I am certainly biased when discussing ranged combat rules.
Go to the top of the page
 
+Quote Post
mckay421
post Aug 21 2003, 12:51 AM
Post #3


Target
*

Group: Members
Posts: 41
Joined: 1-August 03
From: West Jordan, UT
Member No.: 5,192



QUOTE
Is it possible that you could pick up generic .308 Winchester ammunition from a gun store and find out that the rifling in your hunting rifle isn't tight enough to stabilize the bullet properly?


Yes...it is possible. Is it common? Yes and no. Yes...many rifles will fire off rounds that have a tiny (perhaps the word infintesimal is better) bit of yaw at their tip. No...it doesn't mean that generic ammunition is going to start tumbling at range X. Think of it as degrees of stability. I think that Raygun might have a link from his site to another website where they actually have animations that demonstrate this. I will have to search and see if I can find that site. Back to your question though...

The animation that I saw shows the bullets yaw (which may not be the correct term) starting out as relatively minor. The tip of the bullet, is making a small circle, while the base of the bullet remains relatively paralell to the initial force. As the distance increases this movement becomes MORE pronounced.

Is this a critical point? That depends on the type of shooting that you are doing. Hunting elk below the treeline...I have found that I prefer to take my shots at no more than 100 yards...most often at 50-70 yards. At those ranges, even generic ammunition fired from a maintained rifle with 1 MOA accuracy those rounds are going to perform very well. Hunting antelope on the Wyoming high plains...where shots are going to be MUCH longer...then no I wouldn't use generic ammunition.

But here is the rub... Shooting at an animal that I want to harvest to eat and shooting at another person. Well that is comparing apples and oranges. When I hunt (and not all hunters are like me) I will only take head shots for two reasons. First, to ensure a quick kill (I don't like the thought of an animal suffering because of poor shot placement). Second, because I hunt for the meat and that ensures that no meat is wasted. It also means that I will fore go questionable shots and sometimes fail to fill my permit. Shooting at somebody who is shooting or may start shooting back...center mass shots are the rule. So as far as Shadowrun rules are concerned...you are really are correct. Although somebody who is into HYPER realism would say that I am full BS.

Pistols actually have a lot more problem with stabilization because of their short barrels, the design of the bullets, and the very short bearing surface that they have when traveling down a barrel.

QUOTE
These kinds of problems with bullet stabilization, if they are common, I could take into account.


I think that TNs for the various range categories take this into account.

QUOTE
Because my only real shooting experience comes from the military, where I've fired weapons on full auto many, many times but only ever fired, I think, 20 rounds with a sniping rifle, I am certainly biased when discussing ranged combat rules.


I have only shot a handful of fully automatic weapons over the years...BTW the MP5 rules and the mini-uzis are just freaken scary. So I will defer to your experience. :D But I am far from being an expert on the subject of rifles, shotguns, or pistols...Raygun is far more educated than I. Even as a hunter I have LOTS of room for improvement!

Go to the top of the page
 
+Quote Post
Raygun
post Aug 21 2003, 10:33 PM
Post #4


Mostly Harmless
**

Group: Dumpshocked
Posts: 937
Joined: 26-February 02
From: 44.662,-63.469
Member No.: 176



QUOTE (Austere Emancipator)
Is it possible that you could pick up generic .308 Winchester ammunition from a gun store and find out that the rifling in your hunting rifle isn't tight enough to stabilize the bullet properly?


Well, like mckay said, yes it's possible. No, it's not common. The vast majority of .308 rifles marketed for hunting are sold with a rifling twist of 1/12", which is in popular opinion believed to be enough spin to stabilize bullets up to 168 grains. However, bullets heavier than that are commonly found for use in other cartridges of the same caliber, usually in 175, 190, 200, 220, and 240 grain bullets. All of these bullets need a twist of at least 1/10" to be properly stabilized.

Here's the link to Ruprecht Nennstiel's How Do Bullets Fly? website. No animations, but plenty of pictures and explanations.

And here's an equasion that you guys might be interested in. It's the Greenhill Formula for Rifling Twist. It's an approximation, but it will work fine for our purposes here. (This came from the book Understanding Firearm Ballistics, BTW.)

Twist = (150 * bullet diameter)/bullet length to diameter ratio. Use inches.

Okay, I have a .308" 168 grain Sierra Matchking right here. Its length is 1.137".
1.137/.308=3.69
150/3.69=40.65, or one turn in 40.65 calibers.
40.65*.308=12.52, or one turn in 12.52 inches.
Most .308 rifles will properly stabilize this bullet.

Now, here's a .308" 180 grain Swift Scirrocco. Length is 1.370".
1.37/.308=4.45
150/4.45=33.70, or one turn in 33.7 calibers.
33.70*.308=10.38, or one turn in 10.38 inches.
Most .308 rifles will not properly stabilize this bullet, but most .30-06/.300 Win Mag rifles, with a 1/10" twist, will. (This bullet is for the .30-06 or .300 Win Mag anyway.)

Here's a .308" 240 grain Sierra Machking . Length is 1.601".
1.6/.308=5.19
150/5.19=28.90, or one turn in 28.9 calibers.
28.9*.308=8.90, or one turn in 8.9 inches.
Neither .308, 30-06 or .300 Win Mag rifles will properly stabilize this bullet, and neither will most custom barrels! A very fast twist-for-caliber is required. Obviously, this is a very specialized bullet for special applications.

Using this formula, I also calculated the twist rate for the 5.56x45mm M193. The bullet length-to-diameter ratio is 3.4. The twist rate in that case comes out to 9.88, which suggests that the M16A1, with a 1/12" twist never properly stabilized the M193 bullet. Newer rifles with the 1/9" twist will.

And to get into the argument you guys were having about primers, powders and accuracy: Many other factors are far more important here. What kind of powders and primers you use, especially primers, make relatively little difference when considering other factors such as the uniformity of the chamber, throating, headspacing (all important in seating the bullet), rifling twist, barrel crown... One powder may be better than another at a particular barrel length because of its rate of burn. Generally, the shorter the barrel, the faster you want the powder to burn so that velocity is maximized and muzzle blast has the least effect on the bullet's stability as it exits the muzzle. But considering how modern powders are marketed for specific uses (and that ammo manufacturers know what the hell they're doing), tailoring loads to this degree only becomes important after you've addressed or corrected any other, more serious mechanical issues.

At any rate, that kind of stuff is sooooooooo not worth dealing with during a game. Micromanaging a game down to the most minute detail of modern ballistics is just fucking silly, IMHO. Not that this kind of thing isn't fun to argue about, it just doesn't do much for the whole gaming side of things. :spin:
Go to the top of the page
 
+Quote Post
Austere Emancipa...
post Aug 21 2003, 10:57 PM
Post #5


Great Dragon
*********

Group: Members
Posts: 5,889
Joined: 3-August 03
From: A CPI rank 1 country
Member No.: 5,222



QUOTE (Raygun)
And to get into the argument you guys were having about primers, powders and accuracy [...]

Well, it wasn't really an argument. :) I just though they wouldn't matter at all, and was corrected.

I've read the How do bullets fly? article once, a long time ago, but I didn't really understand most of it and didn't even try very hard. Having taken another look there, I was only discussing static/gyroscopic stability. And I'm now thinking that I'm better off not using that in game except in very special situations for a +1 TN & -1 Power / range category.

And I think I've now come to the point in my own ranged combat house rules where it's better to try to simplify the old rules and balance them better than it is to make up new ones. This discussion was the equivalent of a new smoker looking at a slide show of lungs of people who have died of lung cancer as a result of smoking.
Go to the top of the page
 
+Quote Post
mckay421
post Aug 22 2003, 01:05 AM
Post #6


Target
*

Group: Members
Posts: 41
Joined: 1-August 03
From: West Jordan, UT
Member No.: 5,192



Raygun, as usual :D , is correct. There are SO many things that go into ballistics (hence the descriptor...Ballistics is bloody complicated) that the thought of micromanaging (in game terms) at this level would probably make most physicist's brains melt.

Raygun...a question though...

Has anyone come out with a better bullet design then the Matchking for big game hunting...i.e. elk or moose?

I latched onto the Matchking and really haven't used any other type of bullet for big game since.


For the record...
I use SR standard rules for 99.999999% of all issues. I was never advocating for people to actually TRY and figure out all of the variables. For me it just isn't worth the time and hassle to rework the mechanics when I really need to be working on adventures.

I understand that everybody has their own personal interests and that no given set of rules is going to please everyone. For example...a friend of mine as a hobby enjoys cryptography...he shakes his head when it comes to SR's rules covering decryption. And he is right. However...for the sake of telling a story and making the games more interesting I believe that the SR decryption rules work very well.

Go to the top of the page
 
+Quote Post
Kagetenshi
post Aug 22 2003, 05:44 AM
Post #7


Manus Celer Dei
**********

Group: Dumpshocked
Posts: 17,006
Joined: 30-December 02
From: Boston
Member No.: 3,802



So on a tangent, what are the downsides of a fast twist? What reason is there to not just make the twist as tight as it can be on any given gun?

~J (A gun newbie, as is most likely obvious from the question)
Go to the top of the page
 
+Quote Post
Raygun
post Aug 22 2003, 08:09 PM
Post #8


Mostly Harmless
**

Group: Dumpshocked
Posts: 937
Joined: 26-February 02
From: 44.662,-63.469
Member No.: 176



QUOTE (mckay421)
Raygun...a question though...

Has anyone come out with a better bullet design then the Matchking for big game hunting...i.e. elk or moose?

I latched onto the Matchking and really haven't used any other type of bullet for big game since.


Well, the Matchking is for target shooting. There's been a lot of back-and-forth about how good a match bullet is for hunting (they apparently don't tend to expand much), but I've never used them for hunting, so I have no first hand experience. If you're just doing headshots, a Matchking is probably going to work just as good as anything else. I see no reason to go with another bullet if they're working for you.

Personally, I use a .243 for pronghorn and deer, and .30-06 for elk. I don't handload either cartridge. For the .243, I just use Federal's 100 grain Gameking load, which is just a softpoint with a pretty high BC. Last year I had a 250-300 yard shot on an average pronghorn buck. The bullet entered the chest on the right side, took about a two-inch chunk out of the heart and broke the shoulder on the other side without exiting (it must have gone through the lungs too, but I didn't see where). Dropped him in his tracks. That, by my standards, is perfect performance, and it's why I plan on sticking to that load.

For the .30-06, I plan on using Remington's Premier 180 grain Swift Scirrocco load. It's a high BC, polymer-tipped expanding bullet like Nosler's Ballistic Tip, but the jacket it wayyyy thicker, so expansion is more controlled. I didn't get an elk permit last year, so I haven't had the chance to try it out yet. My girlfriend's mother used it last year and bagged a cow with a neck shot, but I wasn't there to see it so I can't tell you how it worked. All I know is that I have a freezer half full of elk. :)

QUOTE (Kagetenshi)
So on a tangent, what are the downsides of a fast twist? What reason is there to not just make the twist as tight as it can be on any given gun?


Well, internally, it tends to increase friction and pressure slightly, wearing down the barrel faster and causing more recoil, both by a very small degree. Externally, it causes bullet overstabilization. To quote the following link: "The bullet's longitudional axis becomes incapable of following the bending path of the trajectory." (How Do Bullets Fly?) This will also cause that "keyholing" effect to a lesser degree, depending on the angle of trajectory. Generally, overstabilization is considered a more acceptable evil than understabilization because its negative effects are less dramatic.
Go to the top of the page
 
+Quote Post

Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 23rd April 2024 - 07:15 AM

Topps, Inc has sole ownership of the names, logo, artwork, marks, photographs, sounds, audio, video and/or any proprietary material used in connection with the game Shadowrun. Topps, Inc has granted permission to the Dumpshock Forums to use such names, logos, artwork, marks and/or any proprietary materials for promotional and informational purposes on its website but does not endorse, and is not affiliated with the Dumpshock Forums in any official capacity whatsoever.