Why is my bolt stiff to push?

Make sure it is well lubed and there is nothing inside the bolt blocking the piston.

Done that, problem persists.
Really stuck here guys. Don't want this one to die...

I've never heard good things coming from mixing Pdi and Laylax parts...so that could be your problem. Could you give us a parts list?

Hey! I don't know if this will help much, but on my Bar-10 I had a problem with a stiff bolt push. After opening her up and looking for the problem, I found that my spring guide stopper was rubbing against the cylinder, creating friction and little tiny metal shards that flew everywhere. I sanded the slot on the bottom of the cylinder to make it ever so slightly wider, and it fixed the problem right up.

Open her up and see if theres any sign of excess friction between the sears and the cylinder. Check on the outside of the cylinder to see if its rubbing there.

Just don't go sanding willy nilly without being sure.

Hope that helps.

Okay quick update time guys, as I've opened her up and had a good long nose around inside without finding anything wrong.

The PDI sears are both fine without any wear.
The Laylax red piston is also wear free.
No rubbing marks or little metal (or even plastic for that matter) shards flown around...
As Vindi says its prob' the 45degree angle giving me grief.

Ho-humm... *shrugs*

Perhaps your piston head is too wide? Or not lubed enough?

I am currently having close to the same problem check out this thread, it may help! http://www.airsoftsniperforum.com/phpBB/phpBB3/viewtopic.php?t=1745

Like nate said, it is practically the same problem he is having. I am going to agree with Vindi as well. Most likely the sears and the piston are not compatible. Perhaps the trigger box sears are set at a different angle than the piston sear, and causes the stiffness when trying to push the bolt in.