It's a long time since I've been here lately - should have posted this question in September but I've been so busy I've not had a chance. That's a way of saying that I hope my memory of what happened / was said is correct.
I was at a BDS range day at the start of Sept. I was testing another of my .308 reloads - a 110gr SP on top of H335. I've shot lots of these rounds previously during load development and I'm currently trying to refine them further for accuracy. Certainly on that day in September, it was going well - three rounds through the same ragged hole at 100m was one of the targets I produced on the day in question.
Unfortunately, what should have been a successful day worthy of celebration was interrupted by the RCO saying that he wasn't happy with the amount of muzzle blast the rounds were producing. He feared a safety issue and asked me to stop using them and I did. Although I wasn't convinced that his assertion that a split barrel could result was correct, it would have been disrespectful to argue with him and one can of course never be certain that something untoward isn't happening, so erring on the side of caution, I stopped.
However, my doubt at his diagnosis was partly based on the fact that I've shot around 80 of these rounds previously without incident and partly because the behaviour of the rounds (i.e. excellent accuracy) didn't fit with his explanation of what he thought was wrong.
The rounds, propelling a very small bullet for .308, are short, loaded to a 2.580" OAL. The RCO feared that they were in fact so short, that they were allowing combustion gas to pass the bullet before it engaged the lands and exit the barrel in front of the bullet, which was causing substantial muzzle blast - more than one would normally expect. An alternative theory centred on worn out brass failing to expand to fit the chamber properly, allowing the same effect to occur.
In the event, I didn't want to argue with the RCO because I wanted to keep shooting using my other rounds. However, it was generally agreed during discussions after the event that if gas were passing in front of the bullet, several other signs ought to have shown that - notably, the rounds would exhibit "random" groupings due to interference with the gas cloud and noticeably lower power and recoil because the gas in front of the bullet would not be used to propel the bullet.
As I said above, the groupings these rounds showed were probably the best I have ever achieved with a reload and the recoil / behaviour felt exactly like any other full-power round. The brass was either on it's third or fourth firing. If the cases had failed to expand, I would have expected to see combustion residue on the outside of the case - these were not present.
I am therefore left to conclude that the substantial muzzle blast is simply a feature of the H335 powder and the fact that some quantity of it remains un-burnt as the bullet leaves the barrel. It is probably a little on the slow side for a 110gr bullet, but not substantially so. Conversation with trusted friends and some research online certainly supports this theory, but I am the only one of my acquaintance who uses H335, so I have no direct, corroborating evidence.
I am posting this in the hope that someone can either corroborate, or refute the idea that H335 is simply "a bit boomy" and either
a) reassure me that I need not worry about this particular situation, or
b) warn me about some effect and consequence I have not yet considered.
I would very much like to continue using this round now I've found it to be accurate, but I need to reassure myself and be able to reassure the RCO that whilst the muzzle blast is undesirable, it is not unsafe, if that is indeed the case.
With many thanks for any input you can give,