6.5 284 reloading mystery??

[ebb]

Have you trimmed the cases lately? If the case OAL in too much it will jam into the part of the chamber that gets smaller ( ahead of the area for the neck ) and try to crimp the bullet in the case. This will cause pressure to go way up.

 

[lightman]

I had pressure problems with H-4831 when The seasons changed from Winter to Summer. And yes, give that bore a scrubbing with one of the mild abrasives!

 

[hogpatrol]

+1 on the carbon. Can you access a borescope from someone? Yes, you'll be forever with a nylon brush removing a hardened carbon ring. Some have suggested a bronze brush in a section of cleaning rod spun in a hand drill at slow speed.

 

[jig4bass]

The brass I was using was not over length but just for good measures I tried new brass and got the same results, after scrubbing the throat with what I had the pressure has went down but I am ordering some iosso bore cleaner to give it a good scrubbing, do high pressure loads cause more carbon build up? I was over max load for about 180 rounds...

 

[jlow]

The brass I was using was not over length but just for good measures I tried new brass and got the same results, after scrubbing the throat with what I had the pressure has went down but I am ordering some iosso bore cleaner to give it a good scrubbing, do high pressure loads cause more carbon build up? I was over max load for about 180 rounds...

The length of the case neck can have different effects. As mentioned earlier, case neck that are too long can be forced in when chambering, causing a crimp on the bullet and high pressure. That does not appear to be your problem.

However, cases with too short necks can expose more of that area that Donovan illustrated where the donuts tend to form and may result in a higher chance for donuts related problem, so that should also be avoided.

 

[Homerange]

Oh and I'm currently nylon brush would I hurt anything using a bronze brush?

Years ago I went to nylon brushes but was never really happy with results. Better chemicals now available do help but in the last few years I've gone back to phosphor bronze brushes for all scrubbing duties. Here in NZ phosphor brushes have never been cheaper and IMHO their use prevents problems like yours. Sure be careful with them around the muzzle crown and use a rod guide if you're worried about damaging the leade but for hunting rifles I don't bother.