Anyone ever Chrono'd factory 338 WinMag loads out of a 20 inch Ruger M77?

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Northern Shooter

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I picked up a Ruger Guide Gun in 338 WinMag and topped it with a Leupold VX-5 with the CDS dial. One of the requirements for tuning the CDS is to know the exact velocity of your chosen load out of the barrel length used.

I'm curious if anyone has Chrono'd factory 338WM ammo out of a 20 inch Ruger M77 rifle? Leaning towards the Hornady 230 grain ELD-X but am also open to other suggestions.

Ive read that that velocity loss between the 24" and 20" barrels is fairly minimal with this cartridge.

Thanks,
 
If you're looking to get a CDS dial you're going to need to chrono your gun. Some guns are faster, some are slower, using someone elses data runs a very real risk of having useless data at longer ranges. I've got a 20" 7mm08 that goes as fast or faster than some reloading manuals using 24 and 26" barrels with the same load.
 
Suther said:
If you're looking to get a CDS dial you're going to need to chrono your gun. Some guns are faster, some are slower, using someone elses data runs a very real risk of having useless data at longer ranges. I've got a 20" 7mm08 that goes as fast or faster than some reloading manuals using 24 and 26" barrels with the same load.
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Good to know. I've considered picking up one of those new Garmin's for just that purpose. Just curious what others have been seeing out of similar rifles with the same barrel length.
 
Friend of mine up here had a Ruger 77RS 338 Win cut and crowned to 20 inches by Paul Rogan about 30 years ago. Paul also reinstalled the front sight, and replaced the recoil pad with a Pachmayr Decelerator.

We shot factory ammo over my Oehler before and after the change. That was along time ago, and I don’t recall the exact numbers, but I do remember that we were both surprised at how little velocity was lost in doing that.

He used that rifle for everything.

Ted
 
Why not? said:
Friend of mine up here had a Ruger 77RS 338 Win cut and crowned to 20 inches by Paul Rogan about 30 years ago. Paul also reinstalled the front sight, and replaced the recoil pad with a Pachmayr Decelerator.

We shot factory ammo over my Oehler before and after the change. That was along time ago, and I don’t recall the exact numbers, but I do remember that we were both surprised at how little velocity was lost in doing that.

He used that rifle for everything.

Ted
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That's along the lines of what I've been hearing as well. Apparently the general rule of 25 fps loss per 1" doesn't apply to Magnums, or atleast the 338.

I've seen others quote 10-15fps/inch.
 
I had a 20” 338WM; IIRC I was pushing it pretty hard to get 2650-80 with 225gr Hornadys. Super nice to carry around though. Considering that a box of ammo is $80 now, and filling up the truck can be $250, not owning a Garmin or even a $200 crappy chrono is a bit silly.
 
Northern Shooter said:
That's along the lines of what I've been hearing as well. Apparently the general rule of 25 fps loss per 1" doesn't apply to Magnums, or atleast the 338.

I've seen others quote 10-15fps/inch.
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The bigger the bore the less shortening the barrel length is going to impact velocity loss typically speaking. I'm pretty sure it has to do with the increased volume for the gases to expand behind the bullet due to the larger bore but don't quote me on that I haven't dug very deep into it.
 
You’ve got it right. It’s called “Expansion Ratio”.

It is the relationship between the case volume beneath the seated bullet and the volume from the same point to the muzzle.

Ted
 
With my 20 inch 338, the heavier the bullet the less velocity lost it seems.

If you can afford a double rifle, 458 win ammo and guided hunts you can afford a chronograph...
 
conor_90 said:
With my 20 inch 338, the heavier the bullet the less velocity lost it seems.

If you can afford a double rifle, 458 win ammo and guided hunts you can afford a chronograph...
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Those Garmin's aren't priced that bad, might pick one up when they restock.

No double rifle for me this year, I decided to go with the 416 bolt gun instead. I even booked domestic hunts for 2025-2026 instead of Africa.
 
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