7mm rem. mag. 175 gr. PSP

[MontanaRifleman]

Humidity actually has almost no affect on external ballistics. Altitude and pressure have the biggest effect followed by temp.

I ran some numbers using and MV of 2900 ft and a BC of .52 (same as the Nosler Partition which is like a PSP) With a 320 zero @ 5000' altitude the bullet is 4.3" high @ 100 yds, 5.6" high @ 175 yds and 8.4" low @ 400 yds.

You might want to shoot and check your drops again, because to get the trajectory you are describing, you need an MV of voer 3300 fps which just isnt possible with a 7RM shooting a 175 bullet.


Mark

 

[eric2381]

I've chronied Federal blue box 175gr. 7mm rem mag ammo and gotten 2650fps from a 24" barrel.

I shoot alot of the 175gr. Hornady IL at 2900fps out of one of my 7mm RM.

To me, your data seems strange....

 

[MontanaRifleman]

I've chronied Federal blue box 175gr. 7mm rem mag ammo and gotten 2650fps from a 24" barrel.

I shoot alot of the 175gr. Hornady IL at 2900fps out of one of my 7mm RM.

To me, your data seems strange....

Whose data?

 

[soundwaves]

lm going hunting tomorow. so l will check again. l will shoot 100 yards 200 yards and 300,400 yards l dont know l might be wrong? but l clearly checked 3inch high at 100 yards and dead on at 320 yads. l might have done a mistake when shootin? but dont think so. any way we will see tomorow

 

[eric2381]

Of the original poster, sorry. If I remember right, I was 4.4" high at 100 to be bang on at 300.

I keep mine 2" high at 100 yds, and it kills very well to 300, without using holdover.

 

[liltank]

The warmer and more humid the weather the better a bullet will fly. I'm not sure why, I can remember reading it some where that humidity helps a bullet fly better. If you play with humidity setting you will see this change in your ballistics. I could be backwards, it has been a while since I have read that article.

Tank

So this humidity thing was bugging me. I decided to run the numbers through JBM to see if my theory held weight and whether or not that I have in fact read an article discussing this very issue. So all things being equal; Baro, temp, altitude, I just changed the humidity to see what effect it changed on velocity and flight. Here is what I came up with:


Rifle is an assumed load because I was crunching numbers for another thread:
338 Norma 2750fps 300grnSMK

First the numbers
75 degrees temp, 100%Humidity, 1000' elevation, Baro 28.82 (close enough)
39.55 MOA 1506fps 1510 ft. lbs 1340yrds

Same as above except the Humidity is changed to 30%
39.04MOA 1505fps 1508 ft. lbs. 1330yrds.

So as you can see, all things being equal which can happen in PA except the humidity, a more humid environment allows for better ballistics. Can somebody explain this?

Tank

 

[soundwaves]

hahaha l dont know Tank l guess when it is humid the air is wet so the bullet must get slippery and glide throgh the air **** man so if my theory is right the ballistics must be way better in the rain hahaha