Home Forums Hunting & Shooting Long Range Hunting A WTH moment with 300gr bergers

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".