Is there a maximum effective distance for pellets.. Yes! And it can be predicted

I l8ke what you're doing ! On GTA there are a couple of very informative threads of similar research. It's extremely interesting.

My own experiences are that at 17.7 twist, the 177, 10.3s and 8.4 pellets are stable past 150 but of course, not very useable because of wind. The 22 cal 25.4s have stayed stable out to 289 in 1 in 17.7"... the farthest I've shot them. The 18.1s have been good to 200, though wind is a big issue. The 25 cal 33.4s fall apart after 220 so are very bad by 289.... 1 in 30" twist. The 30 cals seem to be stable at 289, but blow in the wind so much more than the 25 and 22 cal, I don't shoot them much.... 1 in 30" twist.

The one I'm VERY interested in is the 177 16.1s. They seem PHENOMENAL at 50 and really good at 75 but by 100, there are many fliers... 1 in 17" twist. I would really like to try different twist rates but LW has only 17.7, 20 and 30 twist rates but the slow ones are only available in 16 mm. I would have turn them down to 15mm and that affects the bore diameter a little. So... In order to keep it simpler, it would really be good to know if it needs faster or slower twist than 17.7

Anyway, I'm following your research with great interest. Thanks much for sharing.

Bob

Click to expand...

Hi Bob,

I've done some calculations but I didn't know your specific scenario so I came up with some myself. The pellets used were .177 8.44 grains, 10.34 heavies and the 16.2 monsters, twist rate from 1:12 to 1:40 and calculated at sea level conditions.



First a comparison at a muzzle velocity of 250 m/s, then the monsters at 275 m/s and as a last comparison all three .177 pellets for heavy varmint benchrest class.

To make things clear: the calculations I've done approximate the downrange velocity at which the pellet will go into the danger zone of destabilization for a given muzzle velocity. A translation has to be done to convert these values to a downrange distance but I didn't do that because I don't know the used BC values of these pellets (and it's a boat load of work ).



Here is the excel sheet I made to get an overview of all of them next to each other:




And the graphs of all of them (from left to right in the table):

JSB 8.44 grain @ 250 m/s:



JSB 10.34 grain @ 250 m/s:



JSB 16.2 grain @ 250 m/s:



JSB 16.2 grain @ 275 m/s:



JSB 8.44 grain for Heavy Varmint BR:



JSB 10.34 grain for Heavy Varmint BR:



JSB 16.2 grain for Heavy Varmint BR:



@azrover: can you check if these values correspond with your experience? otherwise I can tune it a little to make a better fit. Haven't done much with .177 pellets so all info is welcome



If someone wants a custom curves let me know and please provide the following information:

Pellet weight and length, muzzle velocity, environmental conditions (ambient pressure and temperature) and preferred twist rate range.

@peaceful_ruler If I do a quick translation of the JSB 8.44 grain at 250 m/s (around 13 fpe by heart) with a twist rate of 1:17.7 it should keep them stable to at least 85+ meters (used a BC of 0.019 and sea level conditions). From then on they enter what I would call the 'danger zone for instability' and self-destabilization becomes likely -> read spiraling is likely to start somewhere past the 85+ meters.

For 14 fpe I would go for the 8.44 grains or 10.34 grains JSBs, just check which one groups best because they should remain stable to 60 meters without problems if you don't have clipping or other (air)gun related issues.



If someone has tested values of instability for the 8.44 at this speed let me know and I can correct the tuning factor for the calculations. Haven't done much testing on .177 for this, mostly .22, .25 and .30. The hard part about this destabilization is that with some pellets it starts really fast and they go completely out of control while others get a slight spiraling motion which gradually builds before they go out of control