6.5-284 High pressure

[Glenn Powell]

I have a cooper 6.5-284 that after 3 firings of the same brass, it shows high pressure s and hard bolt closing. The brass has a shinny ring on the base after just chambering and closing the bolt, after firing there is brass flow into the ejector slot . All brass is full length resized(hunting ammo) and bullets are not on the lands. 49g H4350, 130 Accubond, Norma brass CCI No.200 primer. I get no pressure signs the first two loadings and it shoots great! What is going on? Do I need custom dyes? All the measurements I am capable of taking show brass is sized properly, I can't get the shoulder though.

 

[fivering]

What is your loaded OAL?
How much are you setting the shoulders back when you re-size?
How accurate are you when weighing powder charges?
Do you seat your bullets to engage the lands, or do you have some jump?

I am at max pressure when shooting 140 molyed bergers engaging the lands with 48 gr H4350.
You might just be loading a little hot.

 

[Glenn Powell]

I am off the lands, how much I am not sure, every charge is trickled on a balance beam scale, I don't have the equipment to measure shoulder bump, but maybe I do, how do you measure it?. Cartridge length is 3.044, Norma chamber, not the Winchester, High pressure would show its ugly head after the first loading not the third, right? I would hate to load down, they shoot so good, 1/2 inchers are hard to let go of. :'(

 

[coreydelong]

Do you set up your press to where the shellplate touches the die, or sits off the die a bit? If you are off the die just turn the die in till it just contacts the shellplate. I do not like to overcam my press.

I have two shellpates... one is my standard for regular FL sizing without bumping the shoulder. The other is 0.002" thinner and is what I use to bump the shoulder back when brass gets tough to chamber.

By coincidence I have a Lyman shellplate and a RCBS shellplate. The RCBS is 0.002" thinner. Measure your current shellplate thickness and spec one out till you get one a tad thinner or wet sand one down on a piece of glass with 1200 wet sand paper.

Just check along the way and stop bumping when your bolt closes without resistance.

 

[mytwo60]

Sounds like you need to trim your brass.

 

[XTR]

That ring in front of the web is the brass telling you it's about to pop the base off.

I'm guessing here but if you are pushing the shoulder too far back each reload the case is stretching forward every firing and the stretch happens just in front of the web. Cut a case in half and look at the thinning ring on the inside. You can often feel it with a bent paper clip.

Does the ring look anything like this:

That's a 308 case that told me it was done.

 

[Glenn Powell]

Don't see any ring on the web the, brass "looks " fine. I have started a new batch of brass, I have fire formed them, full length sized, trimmed, and turned the necks. I am hoping they last a bit longer, I am trying 120 TSX, this go round, and they shoot just as well, not near as hot. 48.5 H4350. But I do like the accubond, 5deer with 5 shots last year, and the farthest any ran was 30 yards.

 

[harloe]

You should have some way of measuring headspace to see if you're actually bumping the shoulder back at all.

I like the rcbs precision mic for this. Even though though (I don't think) rcbs doesn't make one for a 6.5x284 its possible a different caliber could be easily adapted. If it's of help see http://bulletin.accurateshooter.com/2010/07/adapt-308-precision-mic-for-6br-family-and-6-5x47-cartridges/

Reason for gravitating to headspace as a possible issue is; I had a similar sounding problem with my 6.5x47. After 3-4 firings it was hard to close/open the bolt and no amount of body sizing seemed to help. Adapting my 308 precision mic so I could at least see relative measurements showed that I wasn't bumping the shoulder back.

 

[racesnake]

Glenn...You may have some soft brass. I had this same problem (kinda). with Norma brass (Mine chambered hard after the first firing). I switched to Lapua and the problem disappeared. Don't know for sure what was happening but I guessed that it was the Norma brass.
Dave