Signs of overpressure in my rifle?

ArmedGinger

ArmedGinger

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I've been hunting with the M40A1 and been packing some Hornady Precision Hunter, a 178gr ELD-X with me and realized I haven't tried shooting the gun with this ammo yet. I've used it in my other guns to great effect.

Took a shot with it and hit just right of dead center at 100 yards. Opened the bolt and it didn't eject off the bolt. Well that was weird. So I tried another two rounds. All holes were touching but all failed to eject.

I pulled the bolt out and noticed this:

0n1aSRQ.jpg


It's a little hard to make out but the words from the end of the brass are imprinted into the end of the bolt face. I also noticed the ejector hole was plugged with brass.

Took a look at the end of the casings and noticed that pieces were shaved off the brass by the ejector hole.

L8xj1Kd.jpg


These are definately signs of over pressure but I'm not entirely sure why. I have had no problems with the Federal Gold Medal Match 175gr SMK before and I even tried a couple afterwards and had no issues.

Both the Hornady and the Federal state they are the same FPS, 2600 fps so why is one giving me over pressure signs?
 
The distortion into the ejector hole could be from overpressure; softer brass could also be a factor. I would certainly not use that ammunition/brass in that rifle.
 
Ok I just remembered the rifle does have an Obermyer Chamber which is slightly tighter tolerances than the regular .308 win chamber. But not enough to cause over pressure issues.

Now I talked to my boss, the head gunsmith, and he said he has seen the marks left by ejector holes before on Hornady brass before. Be believes that Hornady brass is softer than the Federal brass (his personal opinion). He doesn't believe it's an over pressure though issue since there are no bulged primers at all.
 
Just because the muzzle velocities are the same, doesn't mean the pressure curves, and therefore the max pressure reached, are the same.

Flattened, cratered primers AND ejector swipe. Sure looks a tad on the warm side to me.

One thing to check if you have a bullet comparator is if the length to ogive of the ELD-X is longer then the Federal. It might be being jammed into the lands and increasing the pressure.
 
Could be headspace issue but usually those types of imprints would be from excessive headspace not tight headspace?

Resize brass and test primer pocket and see if loose.

These are hanloads?

You might have pushed shoulder too far back.

Try resizing brass so you only bump shoulder back enough to close bolt smoothly.(or with slight resistance).

As stated above

Make a dummy shell with bullet and black marker trick and measure your oal to where bullet engages lands.( If you don't have comparator)
 
coyoteking said:
Those primers are cratered. Along with the ejector marks, that is definitely a sign of over-pressure.
Click to expand...

The Federal factory ammo do show signs of cratering although from my understanding that may be signs of a poor fit of the firing pin to the firing pin hole. The Federal ammo does no show any signs of the ejector marks at all.

350 Mag said:
These are hanloads?
Click to expand...

All factory.

Alpheus said:
One thing to check if you have a bullet comparator is if the length to ogive of the ELD-X is longer then the Federal. It might be being jammed into the lands and increasing the pressure.
Click to expand...

OAL is the same between the Federal and the Hornady
 
ArmedGinger said:
OAL is the same between the Federal and the Hornady
Click to expand...

Could still be jamming since the bullet profiles will be different.

If your seating die seats off the ogive, you can use it to find out. Screw the seater out and then slowly screw it back in while alternating between the two rounds. When you bottom out on one of them, record the number of turns/clicks until it bottoms out on the other one, and you can tell at least if there is a significant difference between the two.

Very odd, especially since you went back to the Federal afterwards and it was fine, so not likely a carbon ring or something similar.
 
Alpheus said:
Could still be jamming since the bullet profiles will be different.

If your seating die seats off the ogive, you can use it to find out. Screw the seater out and then slowly screw in back in while alternating between the two rounds. When you bottom out on one of them, record the number of turns/clicks until it bottoms out on the other one, and you can tell at least if there is a significant difference between the two.
Click to expand...

I don't reload yet, these are all factory loads.
 
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