375-408 CheyTac (Kirby Alert!!!!!!) question

[1doug]

Kirby

they make a 338 bullet with a bc higher than the mk's but require a faster twist. It is made buy Lutz Moeller in Germany. It is a 270 grain solid copper bullet with drive bands on the outside.

from his website

You will have no Fun with the LM-105 in 1:10 Twist. Thy soon would fly sideways. The Bullet tip is Haack Contour shaped and is 6,5 Calibres long. So You need a 9 Degrees Twist (~ 1 Turn : 7 Inch). For existing 1:10 Barrels the regular Lapua or Sierra will do nicely. If You want higher Bc, You must equip Your Rifle with shorter Twist. Then I can supply You the right Bullets.

http://home.snafu.de/l.moeller/

about 2/3rds down

d-a

 

[triggerfifty]

Hi guys,

Will write a detailed replay later, have a volley ball game to go to. Just a quick note though, a singular BC value means nothing. A computer calculated BC values means a little more, but still is singular.

I offer the following doppler radar plot from testing of the 388 270 gr. LRBT bullet as evidence of no such thing as singular BC values. The average isn't right either, unless you split an average and use either just the supersonic average, or the subsonic average.

When pushing velocities up on a computer program, and using a single BC value, you represent the BC as a flat line, as you can see, it is more like a curve, the low spot in the wave is the point of transition to sub-sonic flight.

Gotta go, check it out. PS. Kirby, the 338 270 gr. can do about 2400 yards supersonic because it has a true .868 average BC over supersonic flight. At it's normal speed of 2900 fps, it will do 2075 yards of supersonic range.

Also, the 270 WILL fly out of a 1:10 twist barrel, those thoughts of a tighter twist barrel are wrong. Have shot them from Dakota Longbows, PGW, AI's newer 338 Lapuas, and they shot fine.

Sniping Operations Executive

 

[davewilson]

i would like to see a bullet that starts out at a faster speed, goes a ways til it slows down to the same speed as another is leaving the muzzle, and end up with a shorter overall distance of super-sonic? BC being the same, because it's the same bullet,this is impossible!

 

[Fiftydriver]

Triggerfifty,

My question if this then.

Say you take a 300 gr SMK at a muzzle velocity of 3200 fps. From the muzzle to the end of its trajectory it will follow a certain ballistic trail. Over this path, as you correctly state, the BC will continually be changing as the velocity of the projectile decreases.

So from the muzzle the 300 gr SMK will produce a certain ballistic path.

Is it not correct to think that if I take my 338 Allen Mag, load it to 3450 fps that once the projectiles velocity drops to 3200 fps, it will have VERY nearly the same identical ballistic path as the bullet that started out at that velocity?

Now I know to keep things as perfectly similiar as possible, we would have to use a slower twist with the faster Allen Mag to produce identical RPMs but both bullets path from 3200 fps to the end of their flight path should be extremely similiar.

At 300 yards, my 338 Allen Mag bullet will have the same velocity as the 3200 fps muzzle velocity of the other 338 bullet.

From this point on should they not have nearly identical ballistic performance?

Good topic, and interesting debate. By the way, where can I get ahold of some of those 270 gr pills to try out!!! If you have a link to them or a supplier I would be interested to get that information.

Good Shooting!!

Kirby Allen(50)

 

[bailey1474]

[ QUOTE ]
i would like to see a bullet that starts out at a faster speed, goes a ways til it slows down to the same speed as another is leaving the muzzle, and end up with a shorter overall distance of super-sonic? BC being the same, because it's the same bullet,this is impossible!

[/ QUOTE ]

That's what I'm sayin'. Of course, I have been wrong before.

Once......or maybe twice. Just don't ask my wife /ubbthreads/images/graemlins/blush.gif.

 

[gliechty]

Guys, I know that it may not sound right, but i would listen to what he (triggerfifty) is saying. This is his specialty and he has the real world experience to back it up. Velocity is not everything. Bullet caracteristics are more important than starting velocity. His facts are based on very accurate calculations and proven with on the range testing.

Hes been there, done that and then some so listen up!

BTW, the 270gr. bullets are lost river ballistics.

www.lostriverballistic.com

 

[Mountainsheep]

Hi guys,

I don't wish to flame on anyone or agree/disagree with anyone's ballistic calculations; but I will pass on a bit of physics theory:
With ALL conditions being equal; a projectile traveling at a given velocity will exert/expend an equal amount of energy upon encountering resistance. Therefore a projectile traveling at 3450 fps encountering a stationary particle (i.e.: air molecule) will exert/expend more energy than an equivalent projectile moving at 3200 fps. and encountering a particle of equal mass. Over an equivalent span of distance the energy of the faster projectile will deteriorate more rapidly, by comparison as the rate of exertion and expulsion of energy is accumulative.
This theory does not directly apply to bullets being shot from rifles under normal atmospheric conditions, nor does it account for gravitational force, it is simply an explanation as to why a faster projectile will lose more energy (velocity) than a slower projectile over an equal distance, assuming the velocity of both projectiles is measured from a starting velocity of 0.00 fps.

[ QUOTE ]
Is it not correct to think that if I take my 338 Allen Mag, load it to 3450 fps that once the projectiles velocity drops to 3200 fps, it will have VERY nearly the same identical ballistic path as the bullet that started out at that velocity?

[/ QUOTE ]

Kirby, if the above theory applies; your bullet would continue to shed velocity at the same rate that it did from its initial encounter with resistance as that rate is accumulative, this would indicate your bullet would be losing speed more rapidly than a bullet of equal speed which is exerting less energy against its initial resistance. If that is the case then gravity will create a greater effect on the flight path of your bullet.
Hey guys, this is all theory which is developed in a highly controlled environment. I have no idea how this could determine the approximate distance at which one bullet would go sub-sonic as compared to another.
Once again, I don't wish to create controversy, but I really enjoy these discussions and sharing of thoughts and ideas. LRH has got to be one of the top forums on the web, with a lot of knowledgeable participants and I have learned a tremendous amount since I joined the site.
Dave

 

[Jon A]

You're right Dave, the faster you launch a bullet the faster it is going to lose velocity and energy. It's sort of a diminishing returns-type thing. I think that's what triggerfifty was trying to illustrate.

For example, if you launch a 1.0 BC bullet 200 fps faster, you're going to have a 200-300 yd head start depending upon altitude, etc. This won't translate into a 200-300 yd farther supersonic range, but far less of a gain. Maybe as short as ~50 yds advantage in some cases as the two velocities slowly converge as they go down range. I think that's what he was getting at.

What got people was saying the faster bullet would have a 50 yd disadvantage in the end. That's hard to imagine without some sort of spin differences altering actual BC's, etc. I can see the slower bullet pretty much catching up, or coming close too it for range vs velocity. I don't know how it would pass it though, with all else being equal. Maybe he misspoke. If not it'll be interesting to hear his explanation.

 

[lerch]

"I can see the slower bullet pretty much catching up, or coming close too it for range vs velocity. I don't know how it would pass it though, with all else being equal. Maybe he misspoke. If not it'll be interesting to hear his explanation"

That is what I am getting out of this. I can see two bullets of the same BC catching eachother at extreme range but I dont understand how the slower bullet would pass the faster one.

That vast majority of this conversation is WAY over my head so y'all have fun. I already have my 338AM on order. When me and Kirby thump a chuck at 2miles this spring I will ask the little sucker if supersonic or not. /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif

Apparently none of you guys were criminal justice majors in collage cause ya lost me /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif

 

[dakor]

Kirby I don't want to get into a ****ing match about how you figure your bullets bc with clicks but I will give you a little insight on what happen to me. I now know why many members on here say that is not a true bc of a bullet. I shoot the 105 Berger in my 6-284. One day I wanted to test it out at 1000 yards but I ran out of scope adjustment. I bought Burris rings with the shim kit and re zeroed my rifle at 300 yards. Now I have a gong at 875 yards that always takes me 110 clicks to start hitting around the center on it. I went out to shoot at it I dialed up my 110 clicks and fired and heard no report. I fired again and this time just happen to see dust fly at the top of my dirt back stop. I was shooting about 8ft over my gong and the only change in anything was the shim kit. I was using the exact same ammo and the gong and shooting location never changes. So it now takes me 92 clicks to smack the gong. So after this my thinking is if you want to know what the bc is shoot it through a graph or radar it.

 

[Fiftydriver]

Jon A,

I agree with that. A 200 fps advantage at the muzzle will not be much of anything at all when the range gets longer then 1500 yards but I did not understand how it would actually loose ground to the slower bullet with the same bullet?

Hey, I am a rifle maker, not a ballistics expert, will leave that to you boys to figure out!! /ubbthreads/images/graemlins/grin.gif

Good discussion!!

Kirby Allen(50)

 

[bailey1474]

[ QUOTE ]
Guys, I know that it may not sound right, but i would listen to what he (triggerfifty) is saying. This is his specialty and he has the real world experience to back it up. Velocity is not everything. Bullet caracteristics are more important than starting velocity. His facts are based on very accurate calculations and proven with on the range testing.

Hes been there, done that and then some so listen up!

[/ QUOTE ]

No one, including myself will deny that bullet characteristics are more important than velocity. However, I'm not seeing how a slower, identical bullet will ever catch a faster, identical bullet. I also fully understand that a "300 yd headstart" the faster bullet has doesn't equate to a 300 yd supersonic advantage but it does have some advantage.

 

[1doug]

[ QUOTE ]
By the way, where can I get ahold of some of those 270 gr pills to try out

[/ QUOTE ]

Kirby the lm-105 bullets that i linked to can be had from Lutz. They were @ 1 a piece plus shipping from germany with a 300 bullet minimum. I would be willing to split some with some one if they wanted to try them.

The lost river bullets triggerfifty mentioned are not the same.We all know that the LRb's require a special bore diameter to work, and i am not willing to spend 5-600 dollars to be proven wrong about them. I am willing to try the LM-105 and see if i can get them to shoot. The LM-105's have external drive bands that will seal up better than shooting a solid bullet.The Lm-105 have @ 1.0 bc and require the 7 twist in a 338 lapua to stabilize. the 338 AM might push them fast enough to stabilize them. My guess would be @ 3650 with thw 270 grain LM-105's

d-a

 

[Fiftydriver]

Dakor,

One question, why would you add moas into the ring system and still expect to have to dial in the same 110 clicks as you were before when using a standard 0 cant mounting system??

Also, I do not use clicks to determine BC, never have. I use bullet drop numbers. Generally bullet drop data from multipule ranges. THese ranges are generally 100 yards, 500 yards and either 800 or 1000 yards depending on the rifle.

I use the muzzle velocity in conjuntion with 100, 500, 800 and or 1000 yard actual bullet drops to get an accurate representation of my bullets actually flight over 1000 yards.

Then I plug the data into Exbal including temp, humidity, angle of shot if any, height of scope and finally an estimated BC value to get started.

From there I will tweak the BC until the generated ballistic model matches as closely as possible to my actual bullet flight.

For the conditions I shoot in, everything is a fixed variable for that time frame except the BC. I adjust this until I get the model to match actual bullet flight.

Is this the true scientific BC value, certainly not and I have stated that hundreds of times here on LRH. The numbers I use are BCs developed from bullet drop data and nothing else.

Frankly BC is a meaningless term. All we want is a number so that we can develope a drop chart that accurately predicts out bullet flight path over the range we will be shooting. This system works very well for that. Plenty of ballistics experts would not agree with this but MANY critters can attest to its success as well.....

No flame taken, and no flame directed at you but I do not use clicks to determine BC, just actual bullet drop.

Have a good one, /ubbthreads/images/graemlins/grin.gif

Kirby Allen(50)