Max grain weight?

I have a Beeman Kodiak in 177 and 22.
I mostly use the 22 (squirrel and small game) 
I have read, somewhere, that a heavy grain pellet would damage the piston in a Springer.
With that in mind I was wondering if someone knows what the max grain weight could be used in a Springer? 
I am looking to use a weight no more than 25gr. and trying to keep the gun alive in the process.

Thanks in advance
 
I'm not 100% sure, but i don't think a heavy pellet would damage the piston, only wear out the spring faster, but on the other side, a to LIGHT pellet will cause piston slam, and that is not god, you will damage the seals, don't know if it will damage the piston, maybe it can get bendt, i'm regularly use Jsb 10.34 in my 177 's cause they are the most accurate and my hatsan 125 in 25 likes the Jsb 33.95 mk2 the best, if the spring got worn out faster, i just change it, no drama. 
 
The theory is, and I'm not sure I buy into it, is that the pellet is so heavy that it prematurely slows the piston mid stroke. This in turn, shocks the spring while having a large load still and can cause spring failure. Then when the piston makes full travel and it still has pressure against the face, it bounces and hit the end of the tube twice.
 
"coop709"The theory is, and I'm not sure I buy into it, is that the pellet is so heavy that it prematurely slows the piston mid stroke. This in turn, shocks the spring while having a large load still and can cause spring failure. Then when the piston makes full travel and it still has pressure against the face, it bounces and hit the end of the tube twice.

Correct, and then there's the issue of heat. Pressure builds up extremely fast, causing the air to heat up to temperatures that could potentially melt your seals and piston head at prolonged exposure.
 
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"Jonnes"
"coop709"The theory is, and I'm not sure I buy into it, is that the pellet is so heavy that it prematurely slows the piston mid stroke. This in turn, shocks the spring while having a large load still and can cause spring failure. Then when the piston makes full travel and it still has pressure against the face, it bounces and hit the end of the tube twice.

Correct, and then there's the issue of heat. Pressure builds up extremely fast, causing the air to heat up to temperatures that could potentially melt your seals and piston head at prolonged exposure.
A valid point for sure, Jonnes, one that I never considered.