Bucking the pellet trend!

[Bobson]

I am curious if anyone else has come across the same scenario as I have.

When I first got my rifle I used a chrono at a rifle club to test the output and my average fps was 725 with a hw100 with exactly half a cylinder of air using JSB Exacts of the .177 variety. This lead me to think the rifle's energy at the muzzle was around 9.85 FPE. Since then I believe this was not the correct reading.

I have just bought a combro chrony and my curiosity of how my rifle would like other pellets lead me to buy some Bisley Magnums @10.5 ish grains.

When testing these two different pellets through the combro here are my findings (I did 3 sets of 10 pellets of each type to get these averages with a haaf cylinder of air).

JSB Exact Diablo .177 @8.44 grains
786.8 FPS
11.6 FPE (This is more what I was expecting from the rifle!)

Bisley Magnum .177 @10.5 grains
678.5 FPS
10.74 FPE

This seems to buck the trend as most of what I have read, people report to have an increase of anywhere from 0.2 to 2FPE energy when using Bisley Mags!!!

I understand that my rifle must just not like Bisley Mags. I thought the more pointed tip may have played a part in a lower reading from the combro so I tried micro adjustments of the combro's alignment with no noticable change in the readings (apart from one "bad" reading which is reasuring).

There was a noticable drop in POI with the Bisley Magnums but my trusty hw100 is still stupidly accurate with both types of pellet.

Has anybody else experienced this with their rifles?

Rob.

[MrGreengrass]

Yes i have too ...these 8.6 grain Polymags are a bit more powerful than with the 10.5 grain Crosmans...R17 with BSA barrel......must be a barrel\pellet diameter or a pellet hardness thing ..one may spread the base and grip better\faster..Obturation i think it is called....in your case also the AA'S have thinner skirts...optimum obturation...

[junglie]

I've found this to be true in .177 & .22 about jsb's v's bisley mags in my pcps & my sons R10, springers are a different story though, usually the lightest gives the highest ft/lbs, try h&n green in them & you may have to de-tune to stay legal.