Plusgas won't really penetrate into the threads, at least not until you've undone the bolt a bit. Concentrate on getting a really good fit with the M14 into the bolt; clean the bolt if required. Then concentrate on getting a good purchase and angle of attack on the bolt.
The Plusgas helps a lot when you're unthreading the bolt, but I think it's a placebo effect for actually 'uncracking' the bolt initially.