JSB Exact Beast Diabolo .177 Cal 16.20 Grains Pellets

[K.O.]

I was thinking about like 1/3 harder/more energy needed : since I am at 805 fps with 14.3g(558 w/26g so I am over ported for the 14g-16 pellets) and think I can get to 830-850 fps with 14.3g

22 is~ .038 in²
.177 is ~.025 in²

.038 x.66 = .025 so yep I guess I am down about 4-6 fpe (not the full 1/3 (7-8 fpe) because the air in the .177 stays a bit ahead on pressure/velocity longer

if starting at 1600 psi @ barrel port 5" into the barrel the .177 has a 165 psi advantage at 1061 psi so lets just say 10% more energy, at 24" into the barrel the .177 has a 130psi advantage at 465 so lets call it 30% and yes now it is wasted but it shows the .177 does make up a bit in the barrel because its smaller bore...

so 16g .177 at 18 fpe+ (711+)fps does seem do-able

Holes in my logic...  ?

well in force felt the .177 does gain on the .22 but even with a .242 valve the .22 does stay ahead...

to make it easier to imagine 16 grains is close to 1 gram which is  ~ 1/453.6 of a pound...

So 1500 psi @ barrel and a .242 c.i. valve


                                        Pounds force felt @
                                10"         20"           24"

.177                            18.29       12.16        10.729

.22                              21.59       13.4          11.63
--------------------------------------------------------------------
.22 advantage               3.3        1.24           .90

with .37 c.i. valve

.22 advantage               5.22      2.33          1.08


hmmm...

[K.O.]

My big question about using a real heavy weight like the beast has to do with the porting...

My (has been know to be wrong) say go big or go home... Slightly over bore size to ensure the bore is the restriction...

but at 7.9g it has been shown that keeping the charges velocity up matters most and a .125-.140 transfer port does best...

but what about 10.3g

and  13.4g

and   16.1g


now honestly biggest I can go is .140 by ~.216 with a .220 t-port sleeve and that has almost the area of the bore at .02375...

but is that big necessary... or does the weight of the charge need to be a little less and the velocity a bit more...

So how about it porting for pellet weight the algorithm any thoughts... ?

[rgb1]

These two shots represent the minimum and maximum spiral I am seeing. As posted previously, the
MV is 885, LW barrel (1:17.7 in), target paper at 65 yd. Crazy things start to happen at approximately
45-50 yd with this rather long pellet (.310 in)..........very likely a dynamic stability issue.

   http://104.131.46.156/nextcloud/index.php/s/G4ZndvpOylrnvUm


                                                                                                                                Ron

[rsterne]

The heavier the pellet, the larger the ports need to be to flow enough air at a given pressure to get into the 900s.... More FPE (ie heavier pellet) requires more air, be that pressure or flow, and/or a longer barrel....

Bob

[K.O.]

unable to read the avi. just get black...

[rgb1]

Kirby, and others who have occasional problems with playback.........download and install
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                                                                                                          Ron