The original Mythbusters did ice, leather, bamboo and wood cannons. All worked to the extent that it would fire a projectile, but the ice cannon failed when they increased the powder charge to get the projectile fast enough to cause damage to the target. Only the wood cannon was considered strong enough to withstand multiple firings and they finally got it to fail by plugging the barrel.
As mixdenny stated, the key is tensile strength. Pycrete may be as strong as concrete, but it’s still far below steel or iron. You can break shatter concrete or pycrete with a hammer, but properly tempered steel or iron will just dent.