Good Evening:

My latest toy is an 80's vintage W'by Fibermark in 7 Mag. This gun is an oddity in that it has McMillan stock and a 20' LW barrel.

After significant load development, the gun prefers 120 gr. NBT over 66 grns of I 4350 and shoots them very well.

I chronoed this load today and found four different speeds: 2956, 2982, 3016, and 2996.

Thee spread between the four is 60 fps. Is this significant?

I'm a very careful loader, and I'm curious about the spread.

Thanks,

Bob

Did you keep track of the accuracy? What was it?

Mick:

Since I've been shooting the 120 BT's the accuracy is consistently sub MOA @ 100 yds. I haven't played w/ this load beyond that distance.

The largest bullet I'ver shot is 140 gr, and accuracy ranges between 1" and 1.25".

You may have answered my question for me by asking yours. If the accuracy remains good, it stands to reason thet 60 fps is not relevant, at least not at the muzzle.

Good question.

Thanks,

Bob

You can drive yourself nuts over this stuff sometimes. I think you have a handle on what you’re doing.

quote:

Since I've been shooting the 120 BT's the accuracy is consistently sub MOA @ 100 yds.

60fps might have impact at longer ranges.

Guys:

Thanks for taking the time to reply.

Bob

What will you use the rifle for? If it just range plinking, you are fine. if it is for hunting, then you are way below optimal velocity as you should get (with 120 gr bullets) at least 3400 fps in a 7mm W'by mag if not 3500 fps.

If you plan to use it for hunting Mule deer, elk etc. I would suggest that you try something like 160gr Accubonds which should do 3100 fps comfortably.

Good luck.

Yep even with a 20" that is a touch slow.

The load I use, 66 grns I 4350, is the redline via Nosler's manual. I could likely crank it further by using another powder, but this one is accurate as hell.

I'll continue to play.

Thanks again for your input.

Bob

In the what's worth department I had to slow IMR 4350 down to 94% of normal burn rate to reduce the velocity to 3000FPS. I've always found Nosler velocties to be optomistic at best. In a 24" QL calls the 66grs as 3254 compared to Nosler's 3348 in a 20" QL calls it 3090@56500psi. To get the velocity down to 3000 I had to reduce burn rate and pressure was 51000.

If it were mine I would believe I had a slow lot of 4350 and would continue to work up until I saw and issue. If you are happy with accuracy and velcoity leave well enough alone. My wife's 7x57 gets over 100fps more velocity adjusted back for her 22"

The 20" barrel may be an inhibitor but I get @2900fps with 160's. I am not a light for calibre kinda guy and usually the reason folks use light bullets is so they can brag about how fast they are going but it looks like you're kinda snookered in both departments.

Maybe your correct. I'm a light for caliber bullet guy, but I'm sure this load will kill anything I'm shooting at. The recoil's not bad, and the load is accurate.

I loaded some today w/ 70 grns of RL 19, so we'll see how that works.

Again, your input is much appreciated. I'm going to have to play w/ the chrono more, that was very enlightening data.

Best,

Bob

Bob, take your favorite accuracy load and weigh the charges. If that's the spread you get then that's it! I honestly doubt that you will notice accuracy differences due to 60 fps in a rifle that groups 1", even at long ranges, but, if you have access to say, 4-500 yard ranges, try it. With your barrel length and the lighter bullets you may want to try a faster powder. I am starting to develop loads for my 7mm Rem Mag using 168 gr. Berger VLDs and when I have an accurate load, plan on trying it at 5-600 yards, just for grins.
Peter.

quote:

I honestly doubt that you will notice accuracy differences due to 60 fps in a rifle that groups 1", even at long ranges, but, if you have access to say, 4-500 yard ranges

YOu are probably correct the drop is only about 3/4" more for the slower bullet. In looking at the data if that is the the only 4 tested showing the 60fps spread I would question the lower velocity reading.

Thanks guys.

I only tested four, so mechanical error is a possibility.

Bob