257 Roberts Ackley Improved load development

[RiverRider]

Maybe I should read more carefully then. Going back for a second look!

 

[ScreaminEagle]

Ok I got a chance to go to the range today and shoot my ladder test through the chrono. I started with 49gr of IMR4350 and went to 52.5gr. At 52.5gr I had hard bolt lift and extractor marks.

Results were as follows:
49gr- 3142fps
49.5gr- 3277fps
50gr - 3323fps
50.5gr - 3350fps
51gr - 3386fps
51.5gr- 3395fps
52gr- 3453fps
52.5gr - 3499fps

I'm actually pretty close to what quickload predicted. I think I'm gonna stay in between 51.5gr and 52gr. Those three were real close together. Should stay in the mid 3400fps range. What are your thoughts?
Steve

 

[DrMike]

Sounds like a plan, Steve.

 

[ScreaminEagle]

Sounds like a plan, Steve.

You think 3400fps is good?

 

[DrMike]

I would be content!

 

[ScreaminEagle]

Ok ill play with seating depth a little, but it wont take much. This pacnor barrel is a shooter. I shot that ladder test at 300 yds, you could have covered the spread with a softball!

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[baltz526]

Older I get the less I worry about max velocity. I would try the 50gr load at 3300fps. Little less brass abuse, still plenty fast.

 

[DrMike]

Older I get the less I worry about max velocity. I would try the 50gr load at 3300fps. Little less brass abuse, still plenty fast.

That extra 50 fps or so seldom makes any difference in the field. Accuracy is where the action is.

 

[jason miller]

I've read from a source I trust that hard bolt lift and ejector marks on the brass are a poor indicator of pressure and that they often don't show until 70k+ psi. If it were my gun, I'd stick with whatever gets 3300ish fps in the individual rifle as a max; since quickload is predicting approximately 62k psi. Brass gets pretty short-lived when you exceed the standard 60-65k psi range...

 

[jason miller]

And as always, thanks Dr. Mike for running the numbers. I enjoy your posting of them even when it doesn't apply directly to a cartridge I work with. Pretty interesting stuff.

 

[ScreaminEagle]

I loaded up two strings of five with 51.7gr of powder. Should be over 3400fps. That charge should be in the middle of a nice accuracy node. I dont burn through rounds enough to worry about brass life. Plus i have hundreds of once fired 257 bob brass. Gonna shoot at 300yds over the chrono to check for accuracy and standard deviation.

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[brians356]

If you have a steady hand, you can zero your scale and drop the water in with a pipette until you form a concave meniscus. This is called "maximum case capacity, overflow."

DrMike, didn't you mean "convex" meniscus?

Brian

 

[DrMike]

If you have a steady hand, you can zero your scale and drop the water in with a pipette until you form a concave meniscus. This is called "maximum case capacity, overflow."

DrMike, didn't you mean "convex" meniscus?

Brian

Yes, I did. That is what happens when you get old and the brain begins to turn to applesauce. :?

 

[jason miller]

In his defense, he did correct it to convex in a later post...

 

[brians356]

257 Roberts Ackley Improved (40 degree shoulder)
100gr Nosler BT
IMR 4350
Steve

FYI

For 100-grain bullet and IMR 4350:

The current Sierra book lists max 48.0 gr @3200 fps (26-inch barrel.)

A really old Hornady book: 50.0 gr @3100 fps (24-in barrel.)

Brian

 

[ScreaminEagle]

Well I had the day off today and decided to hit the range. I had ten rounds loaded up for the Ackley using:
100gr Nosler BT
51.7gr IMR4350
CCI 200
seated .015" into lands

I got and average of 3451fps with an SD of 17.41 My groups aren't quite where I want them to be, but I think I can take care of that with seating depth. My question is, what is everyone's experience with then BT? Specifically where do they like to be seated? Thanks
Steve

 

[JD338]

That will be a flat liner.

JD338

 

[ScreaminEagle]

That will be a flat liner.

JD338

You think an SD of 17.41 is ok?

 

[DrMike]

Oh, yeah, you can be pleased with that sort of accuracy, Steve. I believe that load will hunt.

 

[SJB358]

Very nice SE!

Yeah, I would think around .010-.040" would have you in the spot for BT's.

Great speed man. That is screaming!