I shot my .458 Lott for the first time this weekend, both factory and handloads. Hornady 500-grain factory loads kicked like a mule, however all primers came out of the chamber with just a dimple, no distortion.

My handloads, on the other hand, showed slight flattening and distortion. Thing is, the primers showed the problem with all loads: 82 to 85 grains IMR 4320. No stickybolt with any of them.

I feel like this is more a situation with my dies oversizing than over-pressure.

What do yo think?

I agree.

Neck size a case and see if the primer stays rounded on the shot. JMO, Dutch.

Slight flattening of a primer is nothing to worry about. But what part of your case is distorted? I don't think I've ever heard that term used before in this context.

Are you using a chronograph to judge your factory loads against your handloads? If not, by what means do you make comparisons?

Dave,

No distortion on the case. Just some slight distortion on the flattened primer. I've heard it described as primer "flow". But, still, very slight.

Different brand of primers?

Hunter,
When you speak of "distortion", are you referring to what is also called primer "riveting"? If the face of the primer appears to be larger than the body, the primer comes out looking somewhat like a flattened rivet. If this be the case, you might have a little more chamber pressure than you want.
I do a lot of research in high pressure load development and I've learned a lot just from the primers. As a matter of fact, that's the first thing I check when the case comes out of the chamber. If the primers are somewhat flattened, you're in no danger, just at the higher end. If the primers are riveting or "flowing", as you put it(by the way, good description!), you might want to back off on your powder charge, switch to a slower powder, use a lighter weight bullet or decrease the bullet seating depth. All these factors can affect chamber pressure. One thing in particular to watch for: A perforated primer! If the primer has a blackened hole where the firing pin indents it, likely the chamber pressure is over 60K and that's TOO hot!!

Hope this driveling helps in some way!

Puncher

You are kind of near the upper end for your load...what I found the useful range is:

IMR-4320 From 64.2 grains to 85.0 grains
Federal 215 Primer

Back'r'down to around 80.0 and work-up in 0.3 grain steps.


Case "A" is slightly undercharged, case "B" is slight overcharged, and case "C" is rediculously overcharged.

quote:

I feel like this is more a situation with my dies oversizing than over-pressure.

Quote from Metallic Cartridge Reloading 3rd edition:

"Unless you are completely familiar with the gun and the primers used, never suspect you can look at the primers in a fired case and make any reasonable or usefull pressure judgements based on any visible characteristics of that primer."

You might have a slight headspace problem that can't be corrected by sizing die adjustment because your straight-wall case must headspace off the belt unlike belted bottleneck cases which can be made to headspace off the shoulder.
A chronograph would be useful in working up your loads. It is more than just a single bullet speedometer.

Flattened primers can occur with a safe pressure load.

What happens is that you might have a slightly long headspace. The firing pin drives the case forward until it contacts the sholder or belt and ignites. Pressure pushes the primer out until the case slams back and flattenes it.

Observed this once in an old 32-20 carbine, which isn't a high pressure cartridge by any stretch of the imagination.

Just something else to look at.

I use a Chrongraph, and 84-grains of IMR 4320 comes very, very close to factory-load velocity with little variation between shots.

My strings, however, are very, very short (ouch!).

I have noticed over the years that my big bore rifles have more tendency to distort primers than my smaller bores, even though loads are well within the "safe" range. I think it's because the big bores tend to have oversized chambers.