Could I be losing 350-400 fps in my rifle vs factory ammo published data

[Fursty]

So here is my challenge. Shooting. Remington 783 7mm mag with Bushnell Trophy XLT scope with DOA reticle.

Zeroing rifle at 100 yds and then using Ballistic calculator and bullet published velocity and ballistic coefficient to figure bullet drop. (Using Ballisitic AE App)

Then adjusting turret for bullet drop and shooting at 400-500 yd targets.

Shooting Federal Fusion 150 gr 3050fps .509 bc. And Hornady 154 gr SST 3100 fps .525 bc.

The results have me always low at the 400-500 yard targets. When I use the ballistic calculator to find my true velocity, I come up with 2712 fps on the Federal ammo and 2791 fps on the Hornady.

So it is not the ammo as tried two kinds with same result.
Brand new range finder so I suspect it is ok but not verified.
I verified the scope with a yard stick on the wall, stationary scope and adjusted the turret to see that the clicks match the expected vertical distance change.

Is it possible to lose 350-400 fps from the gun?

 

[the444shooter]

It's possible, because some 7mm Mag factory barrels have some notoriety for being "slow," but what I would think is more plausible is that you're inputting the wrong BC for at least the fusion ammo. There's no way that a 150gr Fusion load is .509 G1 BC.

Not sure about the Hornady, though. Good luck figuring it out!

 

[RT2506]

You have to shoot any ammo in YOUR rifle over a chronograph to see what velocity it actually is getting. Factory ammo is notorious for greatly exaggerating velocity. The way they do it is shoot it in a tight chamber pressure barrel that is about 30 inches or so long. Your millage will differ greatly.
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[Dr. Vette]

A couple of thoughts -

How low are you shooting compared to what you expect?

What power scope are you using?

I would recommend using their 200 yard dot as your sight in point, if not the 300 yard dot. Then, go closer and further from there. I suspect that you will find your results are much better than zeroing at 100 as they recommend and attempting to go out to further distance.

 

[JakeL]

You can usually count on factory ammo to be 5% slower than actual stated velocity. But your BC values are also probably a problem.

Federal lists the fusion 150 load for 7mm rem mag at 3050. I would guess actual will be more like 2900-2950 with a 24-26" barrel. (Pure guesstimating). Then they claim a BC of .509 for the bullet, that seems very optimistic to me. The sierra gameking boat tail spitzer bullets usually have about as high of a BC as you can get with a soft nose bullet (like the fusion is). Sierra also has a decent reputation of giving pretty accurate BC values for their bullets. They state that their 7mm 150 gr gameking has a BC of .436. Try inputting a BC for your fusion bullet around .42-.43 and a velocity of 2900-2950 and you should be getting closer.

With the hornady round I suspect it's the same deal, velocity is probably about 2950 and the BC is probably more like .500 than .525.

Hopefully that helps.

 

[Fursty]

Per the Federal Fusion Website and Ballistic Advanced Edition App, the BC of the Fusion is indeed .509

I am trying to find a chronograph to test the velocity.



The scope is a 12x.

I am not sure what to expect from my shooting. My 100 yd shots seem to be all over the board even using a led sled, but my 400 yard shots are many times as tight as my 100 yard shots at least vertically.

 

[JakeL]

I see it listed there, but inaccurate BCs are listed by manufacturers all the time. And especially for a bullet like the fusion which isn't offered to handloaders, federal could easily by fudging numbers.

 

[JakeL]

I also just checked, the .277 150 gr fusion bullet is listed with a BC of .471. Almost definitely the .284 150 gr fusion bullet will have a lower BC than the 150 .277.

Basically it looks like the 7mm fusion bullets are listed with falsely inflated BC values. I have no reason other than common sense to believe this, so if others know better they can post. But if it looks like a duck, and quacks like one, it probably is. It looks like the BC is lower than .47, and it's shooting like it's lower than .47...

 

[Fursty]

So how do you verify the bc?

 

[JakeL]

That requires an accurate chronograph. What I would do is just shoot a bunch at various ranges and then plug numbers into a ballistic calculator until they fit. I think if you try a muzzle velocity around 5% lower than listed, then subtract 25 fps per inch your barrel is shorter than 26", then use a BC around .43, you will hopefully find the ballistic charts are making sense and matching up to your bullet drop results. Hopefully...

Or if you have a friend with a chronograph that simplifies things.

 

[RT2506]

His rifle only has a 24" barrel.

 

[Dr. Vette]

You can usually count on factory ammo to be 5% slower than actual stated velocity.

That's quite a broad statement. I've had factory velocities virtually match what is printed on the box when I test them. My latest one was Winchester PowerMax in my 270 Win Vanguard where the printed data is 3060fps, and I got 3055+ using my MagnetoSpeed chrono. That's close enough for me.

In the end, he needs to use a chrono to verify his velocity and then go from there.

 

[JakeL]

That's quite a broad statement. I've had factory velocities virtually match what is printed on the box when I test them. My latest one was Winchester PowerMax in my 270 Win Vanguard where the printed data is 3060fps, and I got 3055+ using my MagnetoSpeed chrono. That's close enough for me.

In the end, he needs to use a chrono to verify his velocity and then go from there.

You're right. It is a broad statement. But I'd say it's true at least 75% of the time. Without a chronograph guesswork is the best we can do.

 

[WildRose]

Per the Federal Fusion Website and Ballistic Advanced Edition App, the BC of the Fusion is indeed .509

I am trying to find a chronograph to test the velocity.



The scope is a 12x.

I am not sure what to expect from my shooting. My 100 yd shots seem to be all over the board even using a led sled, but my 400 yard shots are many times as tight as my 100 yard shots at least vertically.

It's not that high.

Try a BC of around .470 and a velocity of around 2900 and see how that works.

Manufacturers are notorious for inflating BC's and velocities and BC's are not static they change with velocity.

Also check your scope height by measuring center of the bore to center of the scope tube with a ruler or tape. That can make a big difference as well.