Recently I have had 3 primers go off in the primer seating location on my Hydro Mec, there has not been anything in the priming tool eg. a ball of shot and the primers are unmarked, this does not happen in my 336 or my Mec Jnr,
I think I have solved the problem as it has only started since I started using Fiocchi 616 primers,
I have noticed that in certian shells these primers are hard to seat with the Spring Loaded primer punch on the Hydro often seating late in the stroke and seating with a consiserable bang as the shell finally thumps down.
I think the problem lies in the 616 being all steel and oversize, the steel binds in the primer cup and at the last minute relaeses causing considerable shock which I think is setting the primer off.
In the 366 and the 600Jnr you feel the pressure on a tight primer and increase force and it goes in, but at a controlled rate.
With the 366 and the Jnr the primer seating function is not directly over the powder drop tube, so there is no real risk of setting off the powder in the drop tube or the powder bottle.
After changing undies three times now, I have decided to stop using Fiocchi 616 primers with my Hydro in hulls known to have tight primer pockets
I recently purchased a spring loaded primer seating tool for my 366 which I have not fitted as yet and now it will probably stay in the box
I've been reloading on Mec machines (7) since 1976, using most commonly available primers, foreign and domestic, without ever detonating one. This includes a 650, four grabbers (in each gauge) and a hydraulic 9000 and an electric 9000. HOWEVER..., in some hulls, once-fired where the primer pockets haven't been stretched by reloading, Fiocchi primers will pop in instead of just press in with the pressure of the ram. Although never firing one it is disconcerting and makes me a little nervous. The solution for me has been to use Cheddite primers which are somewhat bell-shaped and reach their full dimension in the last third or so of their length. These never pop in, seating gently, and make life a little less stressful. I believe all will agree that Fiocchi, Cheddite, and Winchester primers can be used interchangably with most normal pressure loads. The Federal hulls with their own primers seem worst when loading with the other above-noted primers as the original Fed primer are maybe 0.002" smaller in diameter, somewhat compounding the problem you are having. It could be too that you have somewhat excessive pressure on the seating ram and could back off a little with that.
Just my experience....
When my 9000 had a shell carrier with worn slots it allowed the deprimed hull to migrate outward as it left the resizer. When that happened the primer pccket was not properly centered and it would snap into place when the primer was installed....always a -pucker- moment. Off course its all over but the shouting by the time you hear it. I now give the hull over the primer/powder station a little push in as I load the next shell in the resizer. Ken
If you use the oversize eurotrash primers for the SECOND reloading of hulls when the primer pocket is stretched out a little they go in great, esp. on a MEC progressive machine.
I know this sounds like a PITA and why not use Win. primers and forget about it
but I enjoy screwing around with diffrent hulls,loading tools and components.
I stopped using Fiocchi's and switched back to Winchester. I figured it was worth the extra $3/1000 to avoid the FTF's. Never had a bang on the reloading bench, must've scared the [email protected] out of you!