Looking at the numbers.... 7Mag, 150gr Bullets

[FiveInADime]

I was looking at the numbers for a 150gr Sierra MK fired from a 7mag at ~2800fps. It's not a great B.C. bullet (0.429) but to 1000 yards it looks plenty good. At 1000 it looks like it would be doing about 1900fps.

I have had good luck with 150s in both my former 7mm-08 and my 7mmRemMag for short and medium range accuracy and if I were to start shooting longer ranges it seems that 150gr. SMK at 2800 (a mild-load) could do everything I need it to.

Any flaws in my logic here? I know I could shoot the heavier bullets for less wind drift, but it seems I can always find the 150gr SMKs and they work well with powders like IMR-4350 which I can use in all of my rifles.

[Jimro]

You lose a lot of the advantage of the 7mm rem mag when you launch a bullet with a BC below 0.5 at 2,800 fps.

Realistically what you are proposing is little better than M80 ball from a 308.

But, if it is accurate for you at those ranges, that is really all that matters.

Jimro

[FiveInADime]

Originally Posted by Jimro

You lose a lot of the advantage of the 7mm rem mag when you launch a bullet with a BC below 0.5 at 2,800 fps.

Realistically what you are proposing is little better than M80 ball from a 308.

But, if it is accurate for you at those ranges, that is really all that matters.

Jimro

True. But does M80 ball reach 1000 yards supersonic? Isnt 1900fps quite a bit of velocity at 1000 yards?

I have zero experience beyond 500 yards, but I have a lot of experience AT 500 and under. I know this 150gr. MK was a popular bullet for rifle silhouette in the 7mm-08.

[Jimro]

The silhouette game is a different beast, and bullets that do fine at 500 aren't necessarily great bullets for 1000. The 308 168 SMK is a good example of this.

Also, 1900 is hugely optimistic performance for your proposed load. JBM puts that bullet at 1,147 fps at 1k when launched at 2,800 fps from the muzzle. Time of flight 1.724 seconds, 11 moa windage. The transonic region starts at mach 1.2, so about 800 yards for your proposed load. The 150 SMK may handle the transonic region very well, I don't know as I only reload heavy for caliber 175gr bullet in 7mm Rem Mag.

To give you a comparison, using the same meteorological data:

A 7mm 168 SMK at 2,800 fps muzzle has 1,417 fps remaining, and a 1.507 second tie of flight. 7.3 moa windage

A 175 SMK at 2,700 fps muzzle has 1,481 fps remaining, and a 1.591 second time of flight. 6.6 moa windage. The 180 SMK at the same velocity has almost exactly the same performance.

A Berger 180gr Hybrid at 2,700 fps muzzle has 1,536 fps remaining at 1k, with 6.1 moa windage. 1.474 seconds time of flight.

So I recommend the 175 SMK or Berger Hybrid for long range target work with the 7mm Rem Mag. All of the velocities I listed can be achieved below maximum loads with hodgdon's published data.

Hope this helps,
Jimro

[FITASC]

MY 700BDL prefers 140 and 160 grain bullets as to accuracy. I can get great groups with that 160 and 4350.

[FiveInADime]

The silhouette game is a different beast, and bullets that do fine at 500 aren't necessarily great bullets for 1000. The 308 168 SMK is a good example of this.

Also, 1900 is hugely optimistic performance for your proposed load. JBM puts that bullet at 1,147 fps at 1k when launched at 2,800 fps from the muzzle. Time of flight 1.724 seconds, 11 moa windage. The transonic region starts at mach 1.2, so about 800 yards for your proposed load. The 150 SMK may handle the transonic region very well, I don't know as I only reload heavy for caliber 175gr bullet in 7mm Rem Mag.

To give you a comparison, using the same meteorological data:

A 7mm 168 SMK at 2,800 fps muzzle has 1,417 fps remaining, and a 1.507 second tie of flight. 7.3 moa windage

A 175 SMK at 2,700 fps muzzle has 1,481 fps remaining, and a 1.591 second time of flight. 6.6 moa windage. The 180 SMK at the same velocity has almost exactly the same performance.

A Berger 180gr Hybrid at 2,700 fps muzzle has 1,536 fps remaining at 1k, with 6.1 moa windage. 1.474 seconds time of flight.

So I recommend the 175 SMK or Berger Hybrid for long range target work with the 7mm Rem Mag. All of the velocities I listed can be achieved below maximum loads with hodgdon's published data.

Hope this helps,
Jimro

I was using Nikon Spot-On's ballistic calculator. 1100ft above sea level. Don't know why it would be so far off?

[Jimro]

I was using Nikon Spot-On's ballistic calculator. 1100ft above sea level. Don't know why it would be so far off?

The most likely answer is the keyboard nut. Every once in a while I'll fat finger something and transpose a number, like 8200 fps for muzzle velocity instead of 2800, or hit the number keys one to the right of the ones you want, 3900 instead of 2800.

FWIW 3900 leaves 1765 fps remaining at 1k, so it is well within the range of error for a ballistics program that doesn't use the variable BC data published by Sierra for that bullet. In fact, plugging in the highest listed BC for the 150 SMK and running it against 3900 fps gives 1863 fps, so pretty dang close to the numbers you got.

Jimro

[FiveInADime]

Originally Posted by Jimro

The most likely answer is the keyboard nut. Every once in a while I'll fat finger something and transpose a number, like 8200 fps for muzzle velocity instead of 2800, or hit the number keys one to the right of the ones you want, 3900 instead of 2800.

FWIW 3900 leaves 1765 fps remaining at 1k, so it is well within the range of error for a ballistics program that doesn't use the variable BC data published by Sierra for that bullet. In fact, plugging in the highest listed BC for the 150 SMK and running it against 3900 fps gives 1863 fps, so pretty dang close to the numbers you got.

Jimro

No, I checked it a couple times. There must be some inherent flaw in the software. I typed it into JBM and got the same as you. Now I wonder how far off the "Spot-On" calculations ate for the BDC reticle.

Also checked Strelok and it pretty much matched JBM.

[Bart B.]

M80 ball ammo is used in British fullbore 1000 yard matches. Leaving at 2900 fps or faster from 28+ inch barrels, those 148-gr boattail bullets are well supersonic through the paper 1000 yards downrange.

I think your numbers entered weren't correct; assuming Nikon's software is good.

[Clark]

I average 3023 fps with 180 gr Berg VLD and Re22
I average 3356 fps with 150 gr Nos BT and H4350
I average ~ 3400 fps with 140 gr Nos BT and H4350
I average 3633 fps with 120 gr Nos BT and H4350
And I think I have killed animals with all of those.


Getting 2800 fps with 150 gr sounds like the beginning of a work up, not the product of one.

[FiveInADime]

Originally Posted by Clark

I average 3023 fps with 180 gr Berg VLD and Re22
I average 3356 fps with 150 gr Nos BT and H4350
I average ~ 3400 fps with 140 gr Nos BT and H4350
I average 3633 fps with 120 gr Nos BT and H4350
And I think I have killed animals with all of those.


Getting 2800 fps with 150 gr sounds like the beginning of a work up, not the product of one.

That's impressive Clark but I was actually trying for a light load using a moderate amount of powder for cost and practicality reasons. I never really shoot my 7mag mainly because my .260 or .243 are more enjoyable to shoot and cheaper to boot.

Also, I fear the factory Winchester barrel may not be a "hummer" judging by the amount of copper I clean out every time I clean it.

Edit: I figured out why Spot-On was giving me false numbers. It defaulted to the G7 model. When I changed it back to G1 everything was as it should be in agreement with JBM and Strelok.

[Jimro]

Yeah, a G1 BC of 0.7 translates down to something like a 0.25 G7 BC, so that would do it.

But bullet manufacturers can publish more impressive BCs using the G1 model, so they continue to do so, even to the point where Sierra publishes multiple BCs based on velocity. A single G7 BC covers all velocities for boat tail spiter bullets.

Jimro