Pressure Signs

[M1barker]

I shot some of my "pet" load today and it appears I may have gotten some pressure signs on my brass. The gun is a Rem 700. The load is 44.5 grains varget under a 175gr SMK seated to 2.84. It was roughly 32 degrees today, and this load had never given me pressure signs before. The brass was on its 3rd firing. What do you think? Is my load still safe?

 

[shoot4fun]

LC brass is thicker so pressure would be higher (that is if you may have just switched over to LC). Otherwise, it may be that you FP hole is oversized and primer is flowing back into it. This is a quite common issue with R700.

 

[BuzzBoss915]

Without looking up the load, I'm assuming you have an accurate scale and it's not labeled a "max" load....I see some cratering, not especially serious. I see slightly flattened corners on your primers, again not as bad as it gets, BUT. I wouldn't go any higher, and you might want to back off a half a grain, just because. My personal attitude is that I never push a load, I never look for trouble, the "gain" is not worth it. However, I don't like that type of cratering around the firing pin but have been reading that Remington is doing that shit intentionally, for whatever reason? You don't mention the primer, which is kinda curious? Are they Winchester, by any chance? BB

 

[M1barker]

I worked my way up safely to this charge for my gun. Believe it or not, ALL my primers look like that, no matter what load. I was more worried about the smooth markings around the edge of the base of the brass shown primarily in the bottom two rounds. The primers are CCI 200. Scale used was hornady magnetic scale with each charge weighed and verified.

 

[bigedp51]

On your bottom two cases you can see that the brass was just starting to flow into the ejector which indicates high pressure. The bolt face on the 700 has a beveled firing pin hole, so the primer flowing into the bolt face is normal.

Below is Quick load data, Lake City 7.62 cases have 2.0 grains less case capacity than commercial cases and you have to adjust for this with loading manual data.

Standard commercial case, 44.5 grains of Varget, 60,161 psi chamber pressure.
(max rated chamber pressure 60,191 psi)

Lake City case, 44.5 grains of Varget, 66,234 psi chamber pressure.
(and over max pressure by 6,043 psi)

NOTE: Military Lake City cases are also harder in the base than commercial cases are and the ejector mark on the base of the case indicates much higher pressure than would normally be assumed)

Question, where did you buy or get the Lake City cases?

The reason I ask is Federal loads 7.62 ammunition with LC marked cases that failed quality control inspection at Lake City. These cases can fail for weight/volume, hardness, case wall uniformity, etc.

Weigh your three cases pictured and check case capacity in grains of H2O and you might find your problem. The top case in your photo does not show signs of brass flowing into the ejector, this case should have more case capacity or the base is harder.

Duplicating NATO cartridges (cloning)

M118 7.62 mm Special Ball LR, 175 Sierra MK bullet, 2580±30 fps, 42.5 grs. of Varget, LC cases

 

[M1barker]

Biged,

Thanks for the pressure info. I will check the volumes on cases with and with out the ejector marks as soon as I get back to the house. At what charge weight with the LC brass does it yield safe pressures? The brass was purchased online from a brass distributer as once fired surplus. I can't attest to where it was from but I do know it was once fired due to the crimped in primers.

 

[bigedp51]

I was lazy and didn't want to upload two more photos to photobucket for the .308 so as an example below are .223/5.56 cases with the maximum case capacity and minimum case capacity. I shoot mixed brass for practice and load 25 grains of H335 in my blasting ammo. The max chamber pressure below is approximately 50,000 psi and the minimum is 44,000 psi, with the same powder charge. Max rated chamber pressure is 55,000 psi so all the mixed ammo is well below max pressures and good enough for 100 yards or less.

Bottom line, case capacity can have a "BIG" effect on chamber pressure and the reason "WHY" they say start low and work up.

 

[918v]

I have found Varget to show pressure signs in the cold as well. Interesting. Maybe it's inverse temperature insensitive