What Happened?

[Captcurt]

I took my M18 Mauser 6.5 CM out for a ladder load with Win 760 and had pressure signs on my starting load. I had a sticky bolt lift and could see ejector marks on the 2 rounds that I shot. . When I got home I pulled bullets and checked powder weight on 2 different scales. All were dead on. Then I checked both case length and over-all-cartridge length. I thought that the bullet might have been contacting the lands, but when I checked that, I was .020" short. This has me scratching my head.

Brass new Hornady trimmed to 1.91
Fed 210 primer
41gr Win 760
Overall Length 2.80 with 130gr Sierra TGK

Book shows 46gr as Max.

 

[Docendo Discimus]

How do the primers look?
Weigh one of the pulled bullets and make sure they are correct and not mispackaged?
Was it really hot at the range? Did the cartridges sit in the sun before they were fired?

 

[Laphroaig]

This is a situation where some chrono velocities would give another piece to your puzzle.

I had a similar situation once where my starting loads were showing velocities way over what you'd expect for a max load. My problem was a short chamber and I was jamming into the lands. The chrono might have saved me and my rifle in that situation because I didn't see any other signs of over pressure and had planned to shoot some hotter loads in my ladder.

I now measure the length of my chamber when starting anything in a new rifle.

 

[Captcurt]

This is a situation where some chrono velocities would give another piece to your puzzle.

I had a similar situation once where my starting loads were showing velocities way over what you'd expect for a max load. My problem was a short chamber and I was jamming into the lands. The chrono might have saved me and my rifle in that situation because I didn't see any other signs of over pressure and had planned to shoot some hotter loads in my ladder.

I now measure the length of my chamber when starting anything in a new rifle.

I checked the chamber length and distance to leades. I have used the same load with a 143gr ELD-X with no pressure signs. The primers were flat. It really has me buffaloed. I think that I will leave the 760 alone and stick with the H4350 and R-17.

 

[LoonWulf]

I would check bullet diameter, and case capacity.
I would also confirm that the primer and powders used wernt something else.
Ive never seen 760 so dont know if it looks similar to 748 or cfe223 for example.

 

[AJC1]

When was the rifle really cleaned. Does the other load shoot good still.... first guess of unexplained pressure in a previously good shooter with an in spec load is carbon ring or other buildup.

 

[LoonWulf]

Just pulled up the hogdons data for 130s and 760. With the 130 ABLRs, which should be pretty comparable to the TGK's, they're running significantly lower.




Stabal is in the 44gr range if I remember correctly.


I can run the data on quick loads when I get home.

 

[LoonWulf]

Just ran the numbers, and QL think you should be running about 50Kpsi with that load as spec'd. Not something that Id expect would lock up an M-18 or leave marks on the brass. My loads are closer to 60Kpsi (theoretical/extrapolated) and dont show those kindsa pressure signs.....I agree with @Laphroaig this is where chrono data would be VERY helpful.

 

[troy fairweather]

Hornady brass has been butter soft the last few years, think there trying to not have guys load factory brass kind like what federal does. Was the sticky bolt from the ejector marks of the case expanded to much from to much psi. My m18 leaves marks pretty good even some with a warmer load using some nosler brass but bolt is still pretty easy to open even when up there in pressure. Mine is a 6.5 prc tho.

What other ammo have you shot

 

[FROGO207]

I am wondering what case volume is with those compared to your good shooting brass first off. The other thing is lack of velocity info. Might be a faster batch of propellant. Do let us know what you ultimately find.

 

[Bfh_auto]

I am wondering what case volume is with those compared to your good shooting brass first off. The other thing is lack of velocity info. Might be a faster batch of propellant. Do let us know what you ultimately find.

Plus one. My Hornady brass has been lower capacity and soft in everything except 5.56.