Diminishing returns of powder vs. velocity

Discussion of BPCR loading techniques, SAFETY, Case Cleaning and Prep, Indexing, BP Choice, Primers, Wads, Compression, Drop Tubes, Vibration, Load Testing, etc.
TexasMac
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Diminishing returns of powder vs. velocity

Post by TexasMac » Fri Jan 18, 2019 12:34 am

The following should be interesting to you Browning .40-65 BPCR owners. I’m working on an article on the BACO JIM410410M1 bullet (408.7gr using 16:1 alloy) in the Browning with Swiss 1.5Fg & needed some velocity data vs. powder capacity. I thought I’d share the data. I did not shoot for accuracy, only over a chronograph to determine average velocities for each load. 5 shots were fired with each load and I wiped between shots. A chart with the data is below. BTW, it’s always been my rule-of-thumb not to compress Swiss 1.5Fg more than 0.1” for best accuracy, which is not confirmed or unproven by the chart

Since the chronograph provided standard deviation data, I included it even though it should not be taken as an absolute indication of accuracy due to other factors also affecting accuracy. Although, with that said, the two lower SD values in the chart do coincide with the best two accuracy loads for my rifle with the 410410M1 bullet.

Another observation: if you do the math you’ll note that the changes in compression are about 0.026” per grain. This is due to the Browning chamber having a constant diameter 0.5” long neck resulting in each additional grain of powder being compressed the same amount. In chambers such as the Shiloh .40-65, the neck has a constant taper resulting in more compression required for each additional grain of powder assuming the bullet seating depth does not change.

Wayne

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NRA Life (President's Council) Member, TSRA Life Member, NSSF Member
Click on http://www.texas-mac.com/index.html to my home page containing information on my Browning/Winchester BPCR book & associated articles.

rjmelehan
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Re: Diminishing returns of powder vs. velocity

Post by rjmelehan » Mon May 18, 2020 2:07 am

"BTW, it’s always been my rule-of-thumb not to compress Swiss 1.5Fg more than 0.1”
for best accuracy, which is not confirmed or unproven by the chart..."


My Swiss also likes .12 compression in a 45-70...
Wayne, was a drop tube used to load the cases... ?

Further, do you have any idea at what distance your 1300fps loads, in general, go subsonic.

TIA

Bob

TexasMac
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Re: Diminishing returns of powder vs. velocity

Post by TexasMac » Mon May 18, 2020 9:24 am

rjmelehan wroteCOLON
Mon May 18, 2020 2:07 am
"BTW, it’s always been my rule-of-thumb not to compress Swiss 1.5Fg more than 0.1”
for best accuracy, which is not confirmed or unproven by the chart..."


My Swiss also likes .12 compression in a 45-70...
Wayne, was a drop tube used to load the cases... ?

Further, do you have any idea at what distance your 1300fps loads, in general, go subsonic.
TIA
Bob
Bob,
I used a drop tube and have no idea when the 1300fps loads dropped to subsonic velocity.
Wayne
NRA Life (President's Council) Member, TSRA Life Member, NSSF Member
Click on http://www.texas-mac.com/index.html to my home page containing information on my Browning/Winchester BPCR book & associated articles.

DirtySteve
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Re: Diminishing returns of powder vs. velocity

Post by DirtySteve » Sat Mar 20, 2021 8:29 pm

Thanks for posting this..!
Dirty Steve
Forsyth, MT

Brent
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Re: Diminishing returns of powder vs. velocity

Post by Brent » Sat Mar 20, 2021 8:54 pm

rjmelehan wroteCOLON
Mon May 18, 2020 2:07 am
"BTW, it’s always been my rule-of-thumb not to compress Swiss 1.5Fg more than 0.1”
for best accuracy, which is not confirmed or unproven by the chart..."


My Swiss also likes .12 compression in a 45-70...
Wayne, was a drop tube used to load the cases... ?

Further, do you have any idea at what distance your 1300fps loads, in general, go subsonic.

TIA

Bob
Bob, that is really easy to find out using the JBM on-line ballistic calculators, if you know your bullet's BC or can make a SWAG about it.
I'm not from here, I just live here.

Plainbase
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Re: Diminishing returns of powder vs. velocity

Post by Plainbase » Sun Mar 21, 2021 11:18 am

Wayne, my accuracy load for a 400 grain bullet in my Browning 40-65 is only 53 grains of Swiss 1 1/2 with essentially no compression.
Plainbase

rjmelehan
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Re: Diminishing returns of powder vs. velocity

Post by rjmelehan » Sun May 02, 2021 2:22 pm

Brent wroteCOLON
Sat Mar 20, 2021 8:54 pm
rjmelehan wroteCOLON
Mon May 18, 2020 2:07 am
"BTW, it’s always been my rule-of-thumb not to compress Swiss 1.5Fg more than 0.1”
for best accuracy, which is not confirmed or unproven by the chart..."


My Swiss also likes .12 compression in a 45-70...
Wayne, was a drop tube used to load the cases... ?

Further, do you have any idea at what distance your 1300fps loads, in general, go subsonic.

TIA

Bob
Bob, that is really easy to find out using the JBM on-line ballistic calculators, if you know your bullet's BC or can make a SWAG about it.
Brent,
Thanks for the input

I sent my bullet drawing to Richard F. Gunn some 20 years ago.
He was kind enough to offer his observations on the design.
Richard estimated my BC G1 to be about .40.
He even recommended some modifications which would bring the transonic BC up to about .50

I hope Richard see this post, I would like to thank him again..!

Over the last 20 years life and other limitations have prevented me from doing much in the way of BPCR
shooting. Now that I have the time and where with all I plan on getting back into the sport.

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Brent
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Re: Diminishing returns of powder vs. velocity

Post by Brent » Sun May 02, 2021 3:43 pm

Sadly, Dick Gunn passed away some years ago. I can't say for sure but certainly at least 5. Must be a fairly whole thread I suppose but I didn't see a Date on it
I'm not from here, I just live here.

DRCook
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Re: Diminishing returns of powder vs. velocity

Post by DRCook » Fri May 07, 2021 3:00 pm

14 yrs ago

this is an exerpt from the post and his obit
Dr. Richard F. Gunn, D.C., age 60, of Stratford, died suddenly on Saturday, October 6, 2007, while visiting relatives in New Hampshire. "Doc" was the beloved husband of Marguerite Duffy Gunn.
http://bpcr.net/forum/viewtopic.php?t=1689
drcook = david r, not dr. but thanks for the compliment :)

Brent
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Re: Diminishing returns of powder vs. velocity

Post by Brent » Sat May 08, 2021 9:34 am

My but time races past.
I'm not from here, I just live here.

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