A Question About a bullet's performance

[pmulcahy11b]

The .270 Winchester, by FF&S rules, has semi-decent penetration and poor range. I am thinking of rectifying this -- basically by treating it as a magnum round for game purposes. This would increase penetration by one band and increase range by about 1.2.

What's your opinion on this. I'm especially interested in the opinions of shooters of the .270 Winchester.

[swaghauler]

I have been playing with the Penetration ratings and have decided that Penetration is primarily a function of Velocity with both bullet diameter and a bullet's Sectional Density a distant second. I have tentatively arrived at the following Penetration Ratings for both pistols and rifles based on the maxim "Velocity Defeats Armor," which has been proven time and again by such Youtubers as The Military Arms Channel, ShootingtheBull410 and The Wound Channel (which has several good barrier and armor tests). Here are my Penetration Levels/Ratings by Velocity:

Pistol Velocity Thresholds:
1801ft/sec + = PEN 1/2
1501ft/sec to 1800ft/sec = PEN 1
1101ft/sec to 1500ft/sec = PEN 2
701ft/sec to 1100ft/sec = PEN 3
699ft/sec or less = PEN 4

Rifle Velocity Thresholds:
3001ft/sec + = PEN 1/2
2001ft/sec to 3000ft/sec = PEN 1
1501ft/sec to 2000ft/sec = PEN 2
1000ft/sec to 1500ft/sec = PEN 3
999ft/sec or less = PEN 4

The PEN can be increased by 1 step for any pistol caliber of less than .30 caliber that is within 10% of the Velocity Threshold. Any pistol caliber that is .25 caliber or less may be bumped up 1 PEN Level if it is within 20% of the Velocity Threshold of the next step and 2 PEN Levels if it is within 10% of the next PEN level's Velocity Threshold due to its bullet's generally higher cross-sectional density.
For Example: The 7.62 Tokarev cartridge has a velocity of 1420ft/sec in the standard Pact loading. This would normally result in a PEN of 2 at short thru long range, and a Pen of 3 at extreme and max range. However, it has a .30 caliber diameter and is within 10% of the 1501ft/sec Velocity Threshold. Therefore, when you compare its velocity by range band, its PEN Values become 1(short), 1(medium), 2(long), 2(extreme) and 3 (maximum)
The PEN of any rifle round which is LESS THAN .30 caliber may be increased by 1 PEN Level if it is within 10% of the next PEN Level's Velocity Threshold. Any rifle round that is LESS THAN .25 Caliber may increase its PEN Level by 1 if it is within 20% of the next Velocity Threshold or by 2 if it is within 10% of the next Velocity Threshold.

It should be noted that I have adjusted Armor Values in my game to reflect the NIJ Standards. The AV for my body armors are:

NIJ Level 1 = AV 1/2S
NIJ Level 2 & 2A = AV 1S
NIJ Level 3A = AV 2S
NIJ Level 3(rifle)/SAPI Plates = AV 4
NIJ Level 4 (rifle)/ESAPI Plates = AV 5
PASGT Helmet = AV 2S
Steel Helmet = AV 1

The "S" designator indicates a soft armor designed to defeat ONLY pistols and fragmentation. In game, you HALVE the AV of soft armor when determining the base AV for resisting Rifle rounds (before multiplying it by PEN). This is the reason pistols even have a PEN in my game (instead of nil). Armor values without the "S" designator are treated normally when opposing Rifle rounds.

Also note that I use 1D10 for Rifle Rounds and 1D6 for pistol rounds (designating pistol damage with a P to differentiate the damage). I have also increased the Damage Dice for my pistols. The damage for a 9mmP is 2d6/2d6/2d6/2d6/1d6 (by range band) while a .45 does 3d6/2d6/2d6/2d6/1d6 (by range band) and a .44 Magnum does 4d6/4d6/3d6/3d6/2d6 (by range band). By comparison, a 5.56N does 2d10/2d10/2d10/2d10/1d10 (by range band) while a 7.62X39mm does 3d10/3d10/2d10/2d10/1d10 (by range band) and a .308 does 4d10/4d10/3d10/3d10/2d10 (by range band) I figure my damage by using the round's energy at a given range. A round's energy can drop significantly by range band, hence the reducing damage.

[Draq]

Well its velocity and bullet weight that determines penetration, then factor in bullet type ei: hollow point or not. .22lr has decent velocity, but low weight, so its penetration is low.

[swaghauler]

Originally Posted by Draq

Well its velocity and bullet weight that determines penetration, then factor in bullet type ei: hollow point or not. .22lr has decent velocity, but low weight, so its penetration is low.

Except that if you actually research it, this doesn't hold up. The Wound Channel has clearly demonstrated with his armor tests that VELOCITY IS FAR MORE IMPORTANT THAN BULLET WEIGHT OR CONSTRUCTION in defeating armor. So has The Military Arms Channel.
The Wound Channel fires the 55gr 193 Ball round at a level 3 (rifle) plate and that round WILL PENETRATE the plate where a 62gr M855 (green tip) WILL NOT PENETRATE (irony?) the same plate. The difference? The M193 will push past 3200ft/sec while the M855 does around 2900ft/sec. The sweet spot for a level 3 plate seems to be 3000 ft/sec. Even hunting "soft points" that exceed 3000ft/sec will penetrate the plate. This has been tested by SEVERAL Youtubers with exactly the same results. This is confirmed by the fact that the new M855A1 ammo which is 16% faster than the old M855 will ALSO PENETRATE a SAPI plate. This round hits the same 3200ft/sec that M193 does. The 77gr MK282 and the Marine Corps new MK318 rounds (ranging from right at 2800 ft/sec to just below 2900ft/sec) WILL NOT PENETRATE A SAPI plate. MAC showed a 90gr 9mmP bullet going 1800ft/sec BLOW RIGHT THROUGH A LEVEL 2A SOFT VEST. This was a normal FMJ bullet, NOT an AP round. SPEED DEFEATS ARMOR. Bullet weight and sectional density CAN HELP, but they generally take a back seat to velocity in determining real world penetration.

[Legbreaker]

That makes a fair bit of sense, especially when you think about the dangers of high speed rubbish in orbit. A tiny fragment travelling at several kilometres per second will blow right through anything you put in it's way, while a larger, slower object is more likely to deflect (but still probably kill anyone aboard the target).

[swaghauler]

You can actually use the various armor tests to calculate armor values for Twilight. Armor is rated by Brinell Hardness Ratings. AR500 actually stands for Abrasion Resistance 500 (the Brinell Rating of the steel). AR650 is a Brinell Rating/Abrasion Resistance of 650. AR500 is the equivalent hardness of RHA Steel. Hardened Tool Steel starts at AR700 and goes up from there.
When you compare what these plates will stop to the Damages in Twilight, you can get a sense of what AV a given thickness of steel should stop. For instance;
An AR500 plate 1/2" (12.7mm) thick will routinely stop .308 rounds (DAM4)
An AR500 plate 1" (25.4mm) thick will easily stop a .50 Cal BMG round (DAM8)
so looking at these rounds you can determine that roughly 3mm of AR500/RHA will equal 1 point of AV. By extension, looking at the Brinell Hardness of other steels should give you the Armor Values of those steel types by thickness. For example, 1mm of high-grade Hardened Tool Steel should give you an AV of 1 (although nobody would use this in a vehicle...it's simply too hard to shape). 2mm of AR650 should equal 1AV and 5mm of M1/T2 Carbon Steel should equal 1AV while Mild Steel (the stuff Home Depot sells) would need 6mm to equal 1 AV. High-Tensile Aluminum (which generally cannot be welded, hence the pop rivets on planes and armored cars) would give 1AV per 5mm while the more ductile Structural Aluminum (which can be welded) used as armor on so many AFV's and ships would give 1 AV per 8mm. Basic Anodized Aluminum (like you buy at Home Depot) would require 12mm for a single AV. Weldable Titanium would yield 1AV per millimeter but is HUGELY EXPENSIVE TO BUY AND FORM as it generally requires TIG welding with Helium shielding gas instead of TIG/MIG/STICK welding with CO2, CO2/Argon (steel) or Straight Argon (Aluminum). Scandium would be as hard as Ti to weld.

If one looks at these numbers, you can see that certain armored vehicle's armor values are "off" on their level of protection. They can be easily fixed if you ask yourself a few questions:
1. Did they use RHA/AR500 (the standard steel for armor) or something else (mild steel, surface hardened/carbon steel, or aluminum)?
2. How much "angle" does the armor have (angled armor equals greater thickness in armor)?
3. What "threat" does the armor say it stops? A 7.62mmN AV is 4. The AV of .50 Cal is either 8 or 9 (if you believe the DAM for the M82...which I DON'T...because the Barrett's barrel is SHORTER than the M2's)?

These questions will help balance Armor Values in Twilight2000 V2.2.

[Blink_Dog]

I ran into a similar quandary when revising my 1st ed weapon damages and ranges. I solved it by calculating a new stat maximum range, to get maximum range take the damage multiply by 2 and add it to 8 (extreme range). This is the new maximum range for that particular round. so for example a 5.56N has a max range of 12x the rng stat and a 7.62N has 16x the rng.

Think of the listed range as how flat a round shoots when fired, the higher the velocity the flatter assuming the gravity is constant (it is on earth). The problem with this is that the way extreme range is determined a light high velocity bullet like the .17 Remington will have a further range than .50 BMG.

The reality however is that a lighter bullet will loose it's velocity sooner and with that accuracy. This is why all the long range sniper shots are accomplished with rounds like the .338 lapua and .50 BMG. Using the damage rating of the round accounts for the mass of the bullet.

[copeab]

Lighter bullets tend to be smaller diameter bullets, so you are focusing the energy over a smaller area. It's like a 1 kg icepick vs a 1 kg hammer. Both ht with the same force, but the icepick concentrates it over a much smaller area.

Also, remember that kinetic energy is velocity squared times mass, divided by two.

[swaghauler]

Originally Posted by copeab

Lighter bullets tend to be smaller diameter bullets, so you are focusing the energy over a smaller area. It's like a 1 kg icepick vs a 1 kg hammer. Both ht with the same force, but the icepick concentrates it over a much smaller area.

Also, remember that kinetic energy is velocity squared times mass, divided by two.

This is why I allow pistol rounds of .30 Cal or smaller and rifle rounds UNDER .30 cal that are within 10% of the Velocity Threshold to jump up the PEN (and smaller .25 cal rounds to jump 2 PEN). This is an easy way to factor in bullet diameter and cross-sectional density without forcing you to do the math. The original Damage and Penetration systems are not that precise anyway.
My goal is to give the casual GM a chart they can look at without having to do a lot of math to reach a realistic Penetration (and Damage). My system is still in its infancy, but if you check out modern armors and ballistics, you'll find my system takes into account a lot of the small details of weapons without changing the base gameplay that Twilight2000 established long ago. I even use FF&S's formulas so as not to upset the game too much. I just "tweaked" what the Devs' started based on my 40 years of shooting experience.

[pmulcahy11b]

I've never fired a .270 Winchester rifle. But the reason I ask is due to conflicting reports in the press about it's long-range accuracy and flat trajectory, and others in the press who decry it as a useful hunting round compared to others.

It's case is loooong -- as long as many magnum rounds. It's also narrow. It has a decent powder charge, but not much more than many other hunting rounds -- makes you wonder what they are loading in that case. The velocities of most loadings are comparable to other similar hunting rounds, but they are pretty fast velocities pushing a long boattailed bullet that is not that heavy.

It makes me a little confused. Sure none of you have experience with the .270?

[Legbreaker]

I assume you've done the google thing and found this?
http://gundata.org/blog/post/270-win-ballistics-chart

[Blink_Dog]

https://en.wikipedia.org/wiki/.270_Winchester

It could easily be considered a magnum since it is a necked down .30-06. The velocities are up there with .223 aka 5.56x45mm N. About 100m/s faster than the .30-06. I would simply take a .30-06 example and if the barrel length is the same just add about 10% to the .30-06 range.

[unkated]

Hmmm. I see no reason to give it any extra armor-piercing capability - the .270 is a hunting round. Its T2K numbers (based on 130gr/8.4 gram bullet at 3040 fps) are good as is:

3 Dmg, 2-4-6 pen

(actual damage value is 3.2, so its not on the border with a next value).

Besides, isn't there a .270 Winchester Short Magnum round to leave room for?

The simple truth is that T2K is not a very nuanced system. A lot of rounds fall into given damage or performance bucket. There is nothing special about the bullet design to warrant any change.

Uncle Ted

[pmulcahy11b]

Originally Posted by unkated

Hmmm. I see no reason to give it any extra armor-piercing capability - the .270 is a hunting round. Its T2K numbers (based on 130gr/8.4 gram bullet at 3040 fps) are good as is:

3 Dmg, 2-4-6 pen

Uncle Ted

The figures I get from FFS are almost always Dam 4 Pen 2-3-Nil. About like a 7.62mm NATO. But with about 75% of the range.

[Blink_Dog]

I would just ignore their range value and keep damage/Pen the same.

If this helps at all here is how I am equating for my rules set:
20" Barrel length, Both FMJ:
.30-06 Dam: 6, Pen:x1, Range: (20x2.7)= 54 m (point blank range), Max Range: (54x20)= 1080 m
.270 Win Dam: 6, Pen:x1, Range: (20x3.1)= 62 m, Max Range: (62x20)= 1240 m

I determine range using a rng x multiplier = Vel (m/s) / 300. so a slow round will have a point blank range less than the barrel length etc.

[CDAT]

As far as Penetration It has a lot to do with the bullet type. A FMJ will penetrate much better than an expanding hollow point. Which brings up a good point, just because it is a hollow point does not mean it is designed to expand on impact. Also a lot of armor piercing bullets will actually do less damage to a human target than many other types.