I have been getting my big gun ready to go shoot an elk, but am having a duhhh moment for some reason. I am loading 140grs of H50BMG in a 338-408Ct improved. Most everyone else in running 142grs. I shot one case 11 times and primer pockets are still tight so I know I am not way over pressure. The guys running 142 are reaching sppeds in the 3300 fps range. Here is my issue, it only takes me 11 MOA to get to 800 yards. Which id the .818BC is correct means my bullet should be running 3400 fps.

I know there is no way I am at 3400 fps. When I first realized that 11MOA was perfect for 800 I decided that my 100 yard zero must be off. This afternoon I confirmed my 100 yard zero, no problem there maybe 1/4 MOA high. My sight height is correct. My enviromentals are correct as downloaded and check via kestral. I am accounting for the 2 degree downslope.

I decided it must me the scope dialing. So a couple minutes after I confirmed my 100 yard zero I dialed up 20 MOA then shot at the same target. Using my NPR2 reticle the 2nd bullet hole was exactly 20MOA higher than the first.

I decide to try my 600 hundred yard target elevation was perfect there.

It has to be something simple I am missing. Any ideas?

If I do not find something soon I am gonna start tweaking BCs because I know this load is actually running 3200 avg.

I would re chronograph the load

I wouldn't even worry about it.

Just shoot and confirm drops as far out as you can and record them with pencil and paper. Go into your ballistic program and play with the velocity number till the program outputs the same drop values you recorded in actuality.

I think when you have done that, the velocity figure you have determined works with all the important parameters in sophisticated ballistic software is more accurate than most readings you'll get over a chrono

True enough no disagreement here

After I read this I knew I had nothing to offer....


w

+1

I have to do the same with the 300 Scenar out of my Lapua. I know my velocity is 2715, but have to run 2750 in software to match real world. Oh well.

I would say the drop shows the true velocity. Too easy to get bad chrono readings n my experience unless the lighting is perfect

I will admit that this thing is rough on chonos but having a 200 fps error, I do not think so. I only fired one round at 600. If I shoot there again and it is good there has to be another reason but that is where I am going to start this morning. Besides the primers would be falling out of the case at 3400 fps.

I have run into something similar with this gun before causing me to run stepped G1 BCs. I had hope that I would not have to go through that again, not that I mind the range time.

+1 on the real fire come ups, I always confirm as far as I have room to shoot and tune from there.

Just curious how long is the barrel, and what kind of crony?

I would, too if that velocity hadn't been the consistent average of hundreds of rounds of the same ammo in a half dozen + rifles through an indoor ballistics lab, an oehler 35, and two personal chronos over several years time. What I don't know is how the manufacturer arrived at their ballistic coefficient. I know they now use Doppler, but did they when that bullet was designed? I can also tweak my data to arrive at real-world numbers by manipulating the BC. What effect does temp have on the powder used (most field shooting was during warmer months) etc.... ? That likely caused fluctuations so there could be a velocity differential there. Still, hundreds of rounds of ammo in multiple rifles over a several year period and through several different chronos and they all have exactly the same error? Maybe, but I doubt it. Regardless, by truing my data to match observed conditions I have good dope for the next shot. How I do it doesn't really matter.

When I find inconsistencies between yardages I tweak BCs. But when your consistently hitting dead perfect on your drops at 4 yardages there is no reason to tweak them I guess. I found a very slight dialing issue. It is 1/2 inch over when dialing 20 MOA. I think I corrected for it.

I found one click of the scope adjustment at my 100 yard zero. Other than those two things which allowed me to reduce velocity to 3370 and match my drops.

I took the gun over to the place where I shoot a mile this afternoon. I drove down to 1400 and dropped a milk jug, then pulled down to 1760 and set up a 4x4 sheet of corrugated plastic.

I then drove back to the firing line and started setting stuff up. It was then that I learned a very important lesson. Load your own stuff in the truck. I had a pile sitting there ready to load when my nephew came in. I asked him to load the stuff up for me. He did pretty good only leaving my bipod and rear bag sitting on the table. The targets were already set up and I did not have time to go hime and grab a bipod and for a change there was not one in the truck. I took my coat off and just leaned over my bedcover to shoot 3 shots, one at 1400 and 2 at 1760. The jug was pretty safe. I could not see the hit or find the bullet impact. I was not hopeful driving up to the target. I actually hit the damn thing both shots. Both shots were about a MOA from center and 1 MOA from center. But the elevation was close enough that I am going to go with what I have since I am not planning on shooting anything nearly that far.
I will go shoot a few times when I get to NM. If things are looking like I hope I might would if all things were perfect shoot a tad past 1K. It will take a lot more shooting of this load before my confidence gets back to the point it was a couple years ago with this gun.

Sounds like it's shooting well.

Eddy- Are you running G7BC or G1? It sounds like you have got it somewhat figured out and shooting to what your drops indicate. Just curious.

G7 it is just weird having to use a velocity I know is wrong. When I took classes I do not think a professor would have applauded me for changing a constant V in this case to match the outcomes. I have shot it across my magneto speed and my oehler, I have read posts from others loading the same componants, my primer pockets are not expanding, I have no pressure signs, the velocity is not 3370.
It works perfectly here, or as close as I have had one work, but it remains to be seen what it will do with a huge swing in temp humidity altitude and pressure.

That was my first thought. On my '06 shooting 230gr Bergers, there was a big difference in the calculated velocities when using the G1 vs. G7 BCs.

Maybe a better than calculated BC???

I am running a G7 BC. I have seen some odd stuff in the past with the really high BC bullets with high velocity. It is almost as if neither G1 or G7 form factors work. But the crazy part with this one is it does "work" in actuality, is just wrong in theory. But in application it is working as well as anything I have ever seen.

Before running the bergers I was running a custom 265gr bullet that had a derived G1 BC of .88 below 3000 fps and .92 above 3000. I knew that it was not the theoretical or "real" BC of the bullet but those were the numbers I was forced to use to make things work. I sent some of the bullets to Bryan Litz and he told me at one time he figured based on modeling the BC was around .87. Later he changed that to .7 something after shooting the bullet. The only way I could make that bullet "work" was by using the stepped BCs. At least this one is "working" without having to resort to stepped BCs.

I just cannot figure why I only have these problems with this particular rifle. With G1 BCs the bullet was kinda wonky you were never exactly in the middle, not off much, maybe an inch or three at the most, but never in the middle. But I trusted what I was using because I had taken it all over the US hunting and knew based on experience it would be close no matter where I went or the conditions.

I just used this same bullet in a 338 lapua and never had a minutes problems out to 1400. The only difference is about 400 fps velocity differences between these rounds. I shoot the 230 bergers at 3200 fps and they work pretty well using a G7 BC with very little if any fudging, until I get way out there.

I argued for days on another site that the only way to shoot long range was to do the shooting and make it work, but I guess I was not as used to manufacturer's BCs being pretty close back then. I think it was that argument that makes me feel so wrong fudging this velocity nearly 200 fps. I guess I should just adopt my old theory but modified. I used to think BCs don't mean anything, meaning they are just the number I have to derive to make my DOPE work. I guess now I can say velocity doesn't mean anything. I probably work up drop charts for 15 or so rifles a year and sometimes do it for a couple different bullets for several of those guns. It distresses me when I have issues where I cannot find a reason for something like this.

I do not think I can make the predictions meet the drops by changing the BC in this case because they are matching so closely. I would end up having to use a stepped BC again if I did. I am going to try and roll with it.

Eddie maybe it's just "better" in real life than it is on paper.

I know that's not cold comfort for someone looking for answers....but....just one of those "things".

EddyBo, if you change the BC and then have to run a stepped BC you are barking up the wrong tree! Tight primer pockets along with a crono reading are at least 2 indicators that your velocity is on. You have already confirmed the BC in another rifle shooting at slower velocities.

With all the Data you have you have at least mathematically proved what it is not.

From a mathematical standpoint this is what I believe to be the missing equation. It is BULLET ARC! An easy mathematical test will confirm. Even though your rifle printed one in high at 100 yds this will not take into account the changed duration of Bullet Arc that occurs especially in a high BC bullet pushed at 3200. Not to mention the bullet Arc can respond differently in differing barrels.

Try changing the point of impact figure at 100 yds to 2" high and so on and see if your charts don't line up near perfect. If they do then you will have proven from a mathematical standpoint the missing equation. Less than 2 minutes on your computer will confirm.



Shod

What is your level of training in mathematics and physics? I'm having trouble following you.

YUP!

I took the minimum required to get my degree so I could get on with law school. But I took a half semester of crash cal. Had to drop it before ruining my gpa

Here take e=mc2 say a certain amount of energy is released from the reaction say the theory does not work out for some explained reason. Do you just fudge the mass? All of it over my head anyway. The only thing bcs are to me is the number I have to use to get a desired result. Instead of changing the constant In the theory I want to know why m does not equal mass. Does that make sense? Hard to relae what I am saying on a phone and sober

Conversational description:

Often times the coefficients c in a math model for some unknown quantity q are not really constants, but are themselves variables which depend on q. This presents a kind of logical feedback loop which is not always easy or even possible to decouple. If the variable coefficients c(q) are nearly constant for a range of different values of q, then it may be reasonable to substitute constants c in the model and still keep acceptable accuracy. But change q enough and the approximating constant c being used instead of the variable quantity c(q) may need to be revised.

Uhhhh okay. I will just shoot when I get there. If it works it works.

EddyBo, the flight pattern of a bullet apon exiting the muzzle is not a constant. For instance. A rifle with a 200 yd zero will produce 2 intersections of the scope line of sight and the bullet flight. If the scope is 1 1/2 " above the barrel the bullet exits the muzzle 1 1/2" below the line of sight. Somewhere around 50 yds the lines will cross basically achieving zero. At 100 yds you might be 1" high. Again at 200 the lines intersect again achieving zero.

You can run the same bullet and load threw the different rifles both with a 200 yd zero. Will the first intersection appear at the same distance. The answer is not nessasarily. The reason behind this is Bullet Flight Patterns. When a bullet exits the muzzle it responds somewhat like a curve ball and can be effected less or sometimes more depending on whether the bullet exits at the top of or bottom of a pressure node.

A little about bullet flight pattern......When a bullet exits a muzzle it first curved downward then curves upward. How drastically the bullet curves upward can sometimes under the right circumstance be effected to a much greater degree though it doesn't happen that often. Because bullet intersection varies at the first point of impact means you can not rely on the scope height measurement. The scope height measurement is simply a trajectory figure. When bullet flight patterns are in effect throwing a sharper......in this case....upward curve ball....the trajectory is greater than the scope height figure you are useing. The scope height figure cannot be relied apon. Physics however and BC's can.


Change your scope height figure and when you put in the number that identifies the true trajectory your chart will fall into perfect alignment to way out there.

Shod

Just like I thought...

so I should now fudge this instead of velocity? That is not what Brian litz said a couple years ago when we argued this to death on another forum.

Fudge what? My post above was in response to a bunch of gobblety gook I didn't get.

If you're referring to scope height, just make sure you input an accurate number. Measure the scope tube diameter, divide by 2, measure bolt diameter and divide by 2 add both to the measurement between the scope on the gun and the bolt in the raceway

Make sure all of your inputs to your program are accurate in the atmosphere department.

Jordan and I were comparing output on 3 rifles and couldn't achieve the same output. When we got on the same page atmospherically with some of the other variables turned off, we jived.

Then you could also calculate the precise BC of the bullet fired from your rifle, which can vary between rifles with the same projectile. Chronograph close, chronograph far, then calculate. (Multiple shots at each range)

I've never gone to that extent but have a friend who does. I find that if all inputs are precise, simply adjusting the velocity figure will allow my program to output drop data that will match my actual shooting.

Same here. I just use software to give me approximate come-ups. Then after dialing at all the distances out to 1,000...I record the actual numbers and print them on my cheat sheets. Just too many variables to be an exact science...for me, anyway.

Eddybo....

1. You know your velocity figures are accurate.
2. You know your bullets are not magic and somehow have a BC rating that exceeds everyone else.
3. You know the changes in weather you are entering are accurate.
4. You've tried to adjust all of the above and none of it has fixed the problem.
5. The reason is because the issue is an angle of trajectory issue that is caused by bullet flight pattern.

I only need three numbers and I can accurately do the adjusted and accurate trajectory computation for you in two minutes or less and the proof in the pudding is I will produce for you an extremely accurate and reliable chart.

What do you have to lose?

All I need is

1.Scope height
2. Velocity
3.Advertized BC ( not Brian blitz)
4. How many minutes you dial at a given yardage in the field. ( not what it says on paper.

The proof will be that my chart will jive with everything you have come up with shooting in the field and it is accurate and reliable.

No Stepped Charts!!!

Shod

Shod I have done this chit hundreds of times. I have had this issue twice both times with this rifle. I ran down to the southern most part of the ranch we are hunting today and shoot out to 1640. Bastid put a cold bore shot dead center of a rock about a foot across with 4moa of windage dialed. It just pisses me off when chit ain't right and this chit ain't right even if it fuggin works perfect.

The gratuitous rifle cell phone shot.

I would shoot this one past 1k at a deer but am limiting the wife to about 700 on an elk.



The nephew is good to about 800 with my wizzum

Ooops svrewed that up my fingers might be drunk. Big hum is my 338 the other is the 280a! My wife is using. This is the wizzum the nephew is using.

we got within a mile of some elk today but they got off the property before we could close the gap for them.

EddyBo,

That is a fun photo. What magnification setting did you use?

Sierra lists different BC's depending on velocity. Is it possible Berger has not tested that bullet at 3300 and indeed your true BC is actually higher than advertised? Then as it decelerates the BC decreases. In order to accurately map this then a stepped BC may be needed.

60 through my antique kowa with a cell phone.