Question about heavy pellets for a .177

[Paul68]

I shot 10+ grain air arms out of my Air Hawk with stock spring for a couple months because they were extremely accurate before I got a chrony. The spring broke fairly quickly, I replaced it with an aftermarket spring and bent that one, and after I replaced that spring I did some chrony work and found JSB 8.44 gave just as good accuracy, and better at long range, while producing peak FPE. No problems since.

Basically, there is usually more than one pellet that will work well, and only a couple that will have the right weight and accuracy. You just gotta find em.

[rsterne]

When you want to compare pellets in different calibers, compare the Sectional Density.... which is the weigh in grains divided by the bore squared and then divided by 7000 (to convert the weight to lbs.).... Examples:

8.4 gr. in .177:  8.4 / .177 / .177 / 7000 = SD = 0.038
10.5 gr. in .177:  10.5 / .177 / .177 / 7000 = SD = 0.048
14.3 gr. in .22: 14.3 / .217 / .217 / 7000 = SD = 0.043

Therefore the 14 gr. in .22 cal is easier to "push" with the same air pressure than the 10.5 gr. in .177 cal but harder to start moving than the 8.4 gr. in .177 cal.... In addition, for the same powerplant (swept volume), once the pellet starts to move, the volume behind it in the barrel increases faster in the .22 than in the .177, causing the pressure to drop faster in the larger caliber.... The combination of these effects makes the .177 cal gun much more likely to see a spike in pressures and temperatures when you use a heavy pellet....

Bob

[pappa]

I shot 10+ grain air arms out of my Air Hawk with stock spring for a couple months because they were extremely accurate before I got a chrony. The spring broke fairly quickly, I replaced it with an aftermarket spring and bent that one, and after I replaced that spring I did some chrony work and found JSB 8.44 gave just as good accuracy, and better at long range, while producing peak FPE. No problems since.

Basically, there is usually more than one pellet that will work well, and only a couple that will have the right weight and accuracy. You just gotta find em.

I have found by long experience that .177 pellets at around 8.5gr gives me the best performance all around in all of my .177 rifles. Best in accuracy and killing power. Have NEVER had a problem with springs or seals since going this direction. Get the same performance in .22 with around 14.5 gr.

[Hanabata808]

When you want to compare pellets in different calibers, compare the Sectional Density.... which is the weigh in grains divided by the bore squared and then divided by 7000 (to convert the weight to lbs.).... Examples:

8.4 gr. in .177:  8.4 / .177 / .177 / 7000 = SD = 0.038
10.5 gr. in .177:  10.5 / .177 / .177 / 7000 = SD = 0.048
14.3 gr. in .22: 14.3 / .217 / .217 / 7000 = SD = 0.043

Therefore the 14 gr. in .22 cal is easier to "push" with the same air pressure than the 10.5 gr. in .177 cal but harder to start moving than the 8.4 gr. in .177 cal.... In addition, for the same powerplant (swept volume), once the pellet starts to move, the volume behind it in the barrel increases faster in the .22 than in the .177, causing the pressure to drop faster in the larger caliber.... The combination of these effects makes the .177 cal gun much more likely to see a spike in pressures and temperatures when you use a heavy pellet....

Bob

Wow! Awesome stuff right there! Thanks! 

[GunnerAl]

It's a real science. I wish I could truly throw some light on the subject but to be honest, what I think I know about it, probably just scrapes the surface. There "are" best pellet weight groups to shoot in the known calibres (.177 to .25) and it's better to stick with them..

Just remember, energy can't simply just appear and/or disappear. It has to be imparted or absorbed in one form or another. What does not come out the end of the barrel has to be absorbed somehow and since (once the rifle is cocked), the spring is the main source of much of this energy, that spring will pay the heaviest toll if that energy does not get transferred into its surroundings, like the pellet or recoil or whatever. If the spring cannot perform to its design specs, it will suffer. It will either get weak (which all springs do when they extend or compress over their lifetime) or it will suffer sudden failure, which is sort of the same as a lifetimes worth in a moment. Quality and technique of manufacture can make a difference but springs are just pieces of steel, which have mechanical limits...

There are some things which don't have to been known through scientific explanation. If we walk out onto a busy highway and just stand there, we know sooner or later we are going to meet with our maker. We also know that "on average", shooting heavier pellets is going to play merry h-e-l-l on the mainspring. My only suggestion is - stick to known accpeted pellet weights until you have a gun made for, or have components fitted and made for heavier pellets...