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Diminishing returns of powder vs. velocity (Read 2272 times)

texasmac Frequent Elocutionist Offline Posts: 2153 Location: Central Texas Joined: Aug 16^th, 2004	Diminishing returns of powder vs. velocity Jan 18^th, 2019 at 1:36am	Print Post
	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

	NRA Life (Benefactor & President's Council) Member, TSRA Life Member, NSSF Member, Author & Publisher of the Browning BPCR book
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Schuetzendave Frequent Elocutionist Offline Retired Ex-Shooter Posts: 4232 Location: St. Albert, Alberta Joined: Jan 28^th, 2005	Re: Diminishing returns of powder vs. velocity Reply #1 - Jan 18^th, 2019 at 3:39am	Print Post
	Wayne: What cases did you use in your test? What length of barrel did you use? What was your C.O.A.L.? Would also be very interesting to do the same test with Swiss FFg and FFFg to see what happens when you change to a finer powder. My groups would open up if I compressed Swiss FFFg more than .240". Dave


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Swede Junior Member Offline Posts: 55 Location: Karlskrona Joined: Sep 12^th, 2007	Re: Diminishing returns of powder vs. velocity Reply #2 - Jan 18^th, 2019 at 10:38am	Print Post
	When you increase powder weight you do not increase velocity 1:1 You do increase the energy wich is the product of the square of muzzlevelocity If you compare powder weight to muzzle energy you probably get a different answer... Probably a fairly staight line.


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texasmac Frequent Elocutionist Offline Posts: 2153 Location: Central Texas Joined: Aug 16^th, 2004	Re: Diminishing returns of powder vs. velocity Reply #3 - Jan 18^th, 2019 at 11:44am	Print Post
	Schuetzendave wrote on Jan 18^th, 2019 at 3:39am: Wayne: What cases did you use in your test? What length of barrel did you use? What was your C.O.A.L.? Would also be very interesting to do the same test with Swiss FFg and FFFg to see what happens when you change to a finer powder. My groups would open up if I compressed Swiss FFFg more than .240". Dave Dave, Remington cases reformed from .45-70 & trimmed to 2.120", 30" barrel, C.O.A.L. is 3.050. Also, .060" fiber wad, Fed. GM150M large pistol primers. Keep in mind I did not check accuracy during this testing. 61grs is the load I use with the bullet based on prior accuracy testing. 67grs has shown to be another accuracy point but the results were not as good as with 61grs. Wayne

	NRA Life (Benefactor & President's Council) Member, TSRA Life Member, NSSF Member, Author & Publisher of the Browning BPCR book
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JLouis Frequent Elocutionist Offline Posts: 10625 Joined: Apr 8^th, 2009	Re: Diminishing returns of powder vs. velocity Reply #4 - Jan 18^th, 2019 at 12:17pm	Print Post
	If not looking to achieve an increase in accuracy what exactly is the end goal that you are trying to achieve.

	" It Is Better To Now Have Been A Has Been Than A Never Was Or A Wanna Be "
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texasmac Frequent Elocutionist Offline Posts: 2153 Location: Central Texas Joined: Aug 16^th, 2004	Re: Diminishing returns of powder vs. velocity Reply #5 - Jan 18^th, 2019 at 1:31pm	Print Post
	JLouis wrote on Jan 18^th, 2019 at 12:17pm: If not looking to achieve an increase in accuracy what exactly is the end goal that you are trying to achieve. Sonny, I had run prior accuracy tests with 10 shots/load but with load increments of 2grs from 59grs to 69grs. From those tests I determined 61grs and 67grs were the two best loads based solely on target results. The accuracy tests (shot at 200 yds) were not shot over a chronograph since overhead extended baffles at the shooting line preclude the use of a standard chrono due to lack of sunshine. The recent test was only to determine the velocity over the same range of powder/compression although I did limit the test to 68grs rather than 69grs. The test was run at a different location on the range which provided the necessary sunshine for the chrono but the range was limited to 100yds which I do not consider a reasonable length to test accuracy since I shoot BPCR silhouette out to 500 meters. I prefer accuracy testing at 500 meters but my local range is limited to 200yds. Wayne
	« Last Edit: Jan 18^th, 2019 at 2:44pm by texasmac »
	NRA Life (Benefactor & President's Council) Member, TSRA Life Member, NSSF Member, Author & Publisher of the Browning BPCR book
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JLouis Frequent Elocutionist Offline Posts: 10625 Joined: Apr 8^th, 2009	Re: Diminishing returns of powder vs. velocity Reply #6 - Jan 18^th, 2019 at 1:52pm	Print Post
	Thanks Wayne and now I understand!

	" It Is Better To Now Have Been A Has Been Than A Never Was Or A Wanna Be "
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