RA4 BC vs G1 BC?

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Each projectile shape (e.g. domed diabolo pellet, boat tail slug, etc.) has a characteristic drag coefficient that varies with its velocity. Plot it and we get a drag profile. Here are the popular "standard" drag profiles plotted in Hawke's Chairgun software:
drag profiles - Chairgun.gif


Without getting too deep in the weeds, we can infer Patriot is saying their Javelin slugs have a drag profile that is somewhere in between the G1 (black) and RA4 (yellow). With this information, you can use ballistics software like Chairgun or Strelok to predict the trajectory, wind deflection, etc. under different conditions...to within some margin of error. Gets you in the ballpark at least.
 
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Seeker said:
RA4 is the same as G1 at the speeds below 1400FPS. Source:

RSI - Exterior Ballistics Basics

RSI's overview of ballistic coefficient basics, or B.C.'s made simple.
www.shootingsoftware.com
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I have seen that, but it does not agree with many other sources. I am not sure if it is correct or not, not having the history of RA4.

The fact is that neither G1 or RA4 are suitable for slugs, particularly as speeds get above 900 ft/sec, the shape of the drag curve is wrong. Many manufacturers like to use G1 or RA4 because, at high muzzle velocities, they give artificially high BC values, good for marketing. The SLG0 drag curve is unproven but getting to look better as more data becomes available.
 
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Ballisticboy said:
I have seen that, but it does not agree with many other sources. I am not sure if it is correct or not, not having the history of RA4.

The fact is that neither G1 or RA4 are suitable for slugs, particularly as speeds get above 900 ft/sec, the shape of the drag curve is wrong. Many manufacturers like to use G1 or RA4 because, at high muzzle velocities, they give artificially high BC values, good for marketing. The SLG0 drag curve is unproven but getting to look better as more data becomes available.
Click to expand...
Will the SLG0 be available in Strelok Pro? IMH experience, with Airgun slugs under 1000 fps, the G1 and RA4 work out almost identical firing solutions.
 
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When shooting less than 100yds, slugs don’t slow down much, so no real need to have a constant BC vs velocity.

In a perfectly matched drag model, the BC will be the same regardless of velocity. When shooting slugs at high muzzle velocities (~1000+fps) and long distances where the velocity falls off significantly, RA4 is a better match than G1, for many slugs.

Using G1 to report the BC of a high sectional density slug measured at >950fps will give an exaggerated BC value.
 
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Centercut said:
Gotcha... For me, shooting the .25 Altaros BT 49.5 grain at 885 fps, and at 100, 200, and 300 yards, the BC profile of 0.21 G1 and RA4 are almost identical. And using the G7 profile and BC of 0.111 (as recommended by the slug manufacturer) correlates almost exactly with the 0.21 of the G1 and RA4 profiles.
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At 885fps, you are below the steep part of the curve where the drag coefficient rises rapidly.

When you get further up into the transonic region, the drag models diverge significantly.
 
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Scotchmo said:
At 885fps, you are below the steep part of the curve where the drag coefficient rises rapidly.

When you get further up into the transonic region, the drag models diverge significantly.
Click to expand...
Cool. Thanks. Maybe that's why Altaros recommends about 900 fps for their BT slugs? I shot the 49.5 grain .25 caliber at 885 FPS at LDs on Sunday across the canyon out to 152 yards in very windy conditions. It started off just breezy but quickly built-up after noon. The interesting part was that the POI didn't change much even at 152 yards, and I experienced just how good a G1 BC of 0.21 (confirmed) "bucks" the wind... Even got a snapshot on a ground squirrel at 143 yards and hit first shot.
 
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Centercut said:
Cool. Thanks. Maybe that's why Altaros recommends about 900 fps for their BT slugs? I shot the 49.5 grain .25 caliber at 885 FPS at LDs on Sunday across the canyon out to 152 yards in very windy conditions. It started off just breezy but quickly built-up after noon. The interesting part was that the POI didn't change much even at 152 yards, and I experienced just how good a G1 BC of 0.21 (confirmed) "bucks" the wind... Even got a snapshot on a ground squirrel at 143 yards and hit first shot.
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Its cool to experience this first hand isn't it?!
 
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Yesterday I tried the 22 cal Altaros (edit 32.3gr smooth) very briefly. It was 5 mph wind when I arrived at the location and 15 mph by the time my friend and I left an hour later. It was the last 10 minutes when I shot at 100Y. If I had used pellets my group at 100Y would have been 6 inches wide but instead it was 2" wide by 1.1" of vertical. BC, BC, BC.....
 
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Centercut said:
Will the SLG0 be available in Strelok Pro? IMH experience, with Airgun slugs under 1000 fps, the G1 and RA4 work out almost identical firing solutions.
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Not that I am aware of. If you know how you can always add it yourself as I believe Strelok Pro can take custom drag laws.
 
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