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Discussion Starter #1
I was testing some M118LR this weekend with my suppressor and could not help but I noticed the cases were damaged.

I'm going to make the assumption that the rather nasty gash on the cases is due to the suppressor. They are coated in varying degrees of gas adhesion to the case.

The additional blowback caused by the suppressor is likely causing the cases to hit something on the way out. I've tried to film this but the case is ejected far too fast for me to record it with my iPhone or my digital camera. There is no obvious impact points around the Receiver or scope mount to point the way to the damage point.

So before I rent a high speed camera, anybody have any idea what is causing this?

The "clean" case was fired without the suppressor.

BTW, the M118LR was clocking in at around 2781 - 2849 FPS.

Thanks in advance!

Bryan
 

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My guess would be oprod or around the rear sight. But with a scope mount, idk.

Maybe try putting chalk all around the possible ejection route, and see where it's scuffed off after a few rounds?
 
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My regular loads for one of my match conditioned M1As gets those marks, that is how I count the number of firings on the cases. I believe they are hitting the corner on top of the op rod, the area is getting shiny.

2781 - 2849 FPS appears to be high, do you have a ported and vented plug?
What chronograph do you use?
 

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Discussion Starter #5
That load a bit stout for a M1A, what year is the ammo?
The ammo is "Long Range M118 LC-12F274-141 Sub Lot B". Head stamp is LC 12 LR.

The load is 43.3 Gr of powder with a 175 gr Sierra 175 BTHP.

I was also clocking some Surplus German DAG and came up with similar numbers. The last round came out with 2938 on the Chrony. I noticed that the last of the 5 rounds always came out hotter than the first three. Guess that had a lot to do with the chamber heating up.

The tar around the bullet might have a bit to do with it. Similar to crimping to hold the round in while the pressures are building up, for just a micro second.

- Bryan
 

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Discussion Starter #6
My regular loads for one of my match conditioned M1As gets those marks, that is how I count the number of firings on the cases. I believe they are hitting the corner on top of the op rod, the area is getting shiny.

2781 - 2849 FPS appears to be high, do you have a ported and vented plug?
What chronograph do you use?
Only happens when I put the can on it, but my max load is around 42 Gr of IMR 4895 or 4064. Still working up the load.

The speeds were without a vented gas plug. Probably need to use it in conjunction with a Saldak grooved piston as I work up in the higher loads.

I'm using the Base line Blue Chrony with the LED lights, about 15 feet from the end of the barrel.

-Brayn
 

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A suppressor is not going to cause extra blowback or increased pressures. In fact it is allowing the gas to expand and be redirected inside it.
If your issue is a pressure related one, like the others I'd be suspect of the ammo.
Have you tried regular NATO ball with the suppressor and gotten case problems?
 

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A suppressor is not going to cause extra blowback or increased pressures. In fact it is allowing the gas to expand and be redirected inside it.
If your issue is a pressure related one, like the others I'd be suspect of the ammo.
Have you tried regular NATO ball with the suppressor and gotten case problems?
Suppressors do cause a lot of gas to vent rearward, especially to vent around the shell casing. It is not unique to the M14. In stoner pattern rifles it is bad enough to where they have designed charging handles with side gas vents. Certain suppressors are better in this regard by their design. However regardless of suppressor used you will see higher movement speed of the moving parts, piston, operating rod, bolt. Use of a vented or adjustable gas plug can help with this. Some suppressor users advocate using an m3 breech shield from a blank firing kit or a full length rail scope mount.
 

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Only happens when I put the can on it, but my max load is around 42 Gr of IMR 4895 or 4064. Still working up the load.

The speeds were without a vented gas plug. Probably need to use it in conjunction with a Saldak grooved piston as I work up in the higher loads.

I'm using the Base line Blue Chrony with the LED lights, about 15 feet from the end of the barrel.

-Brayn
The reason I asked about the Chrono, one time we were on the range doing some load, one guy had Chrony, a CED Millennium, and an Oehler. The CED and Oehler agreed on the reading, the Beta Chrony registered about 70-100 FPS higher on any load we tested.
 

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The suppressor shouldn't cause that kind of brass damage. Back pressure isn't normally that great. I will point out that M118LR tends to create higher pressure in gas guns. It was loaded to be used on bolt actions and the load coupled with the bullet ogive tends to do that when fired in the M14. If you load your own keep the velocity down to about 2500 FPS.
 
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