Shiloh Rifle Forums

I’m working on an article on the BACO JIM410410M1 bullet (408.7gr using 16:1 alloy) in the Browning .40-65 BPCR 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. 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 chrono provided SD, I included it although it should not be taken as an indication of accuracy.

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 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

As I commented, the standard deviation numbers should not be taken as an indication of accuracy due to other factors 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.

Wayne

how many shots per load?

BFD wrote: ↑Thu Jan 17, 2019 9:15 pm how many shots per load?

I would have rather shot 10/load but only had enough bullets to shoot 5/load. BTW, I wiped between shots.

Wayne

It's hard to say that the variation in SDs is meaningful with so few shots.

WAYNE:
Don't forget that you have TWO variables here. Not only charge weight, but amount of compression. When the compression doesn't vary, e.g., in a muzzle loader, I see around 6-8 fps/grain of Swiss 1.5Fg, using moderate loads.

CHRIS
RGChristensen

I looked for that diminishing return some talked about a while back. I went up to .500" compression in my .50-2.5 and never found it, it slowed down the velocity but never to a point were it did not stop. I went with a .54 caliber muzzle loader up to 210 gr and it never went to zero but the loss of velocity was not as pronounced as a compressed load in the cartridge rifle with major compression.
I did not go higher because the recoil got to my upper limits

BFD wrote: ↑Fri Jan 18, 2019 7:02 am It's hard to say that the variation in SDs is meaningful with so few shots.

I agree. I probably should have left the SD data out of the chart but it does pretty well track my results from prior accuracy testing with at least 10 shots/load over various shooting conditions and also from many matches. 61grs seems to be the best accuracy load with 67grs being the 2nd best.

Wayne

Wayne,

Velocity is dependent on the energy in the powder, which imparts energy on the bullet. Given the same bullet and same expansion ration (same OAL), one would expect velocity to increase with the square root of powder ratio. I checked the top and bottom loads-taking the square root of 68/59 and multiplying it by the velocity of the 59 gr. load and got a number within a few fps of the 68 gr. load. So, within this range, the powder is transmitting the same percentage of its energy to the bullet.

Adding powder adds energy, but energy increases as the square of velocity, resulting in velocity increasing as the square root of the powder ratio.

I have found the Kidwell Money bullet in my Shiloh likes to be pushed hard, and so I kept increasing powder until I got the best accuracy at ~0.175" compression.

Clarence

Hi Clarence,

I don't have time to think about your comments as I'm heading to our deer lease for the last weekend of the extended season. I'll get back to this thread when I return & give your comments some thought. Thanks & have a good weekend.

Wayne

I actually did basically the same thing as Clarence . The energy in the powder is a function of the mass. In theory the energy should vary linearly with respect to the weight of the charge, and not the velocity. There are plenty of reasons for the powder to impart it's energy to he bullet less than perfectly so I'm not surprised that the graph is not extremely close to being linear.

Chris.

Clarence wrote: ↑Fri Jan 18, 2019 2:51 pm I have found the Kidwell Money bullet in my Shiloh likes to be pushed hard, and so I kept increasing powder until I got the best accuracy at ~0.175" compression.
Clarence

Clarence,

As I noted in my opening post, there are two, what I'm referring to here as "accuracy nodes", in my 16-twist Browning with the bullet and Swiss 1.5Fg. The higher 0.223" compression or accuracy node has repeatedly resulted in lower SD than the lower one at 0.067" of compression but the shot pattern opens a little worse at 500 meters with the higher compression. I've noted similar results with other bullets in the rifle including the Kidwell Money Bullet. But it just may be due to the heavier recoil or the point the bullet drops down to subsonic velocities. Regardless, since the lower velocity load has sufficient energy to reliably take down the rams, I see no advantage of going with the heavier load other than time-of-flight and a little flatter trajectory.

I may try the same experiment including accuracy testing with my Shiloh Sharps .40-65 with 14.5-twist bore using the Kidwell bullet which it seems to like.

Wayne