Over pressure?

[Russ661]

180g Hornady GMX over 76g of Reloader 26 and fired with a Federal 210 primer. This case had been fired 1x before. Velocity @ 15 feet was 3174 out of a 24 inch barrel, 1 in 10 twist. Bolt lift was heavy but the case came right out with no issues. I think I will back it off half a grain and see what happens. Oh yea, I seated the bullet .020 off the lands. Temp at the range that day was about 45°F.

 

[cohunt]

I'd say either slightly over pressure or too much induced headspace from over sizing

How much are you bumping the shoulder?

 

[Deleted member 107796]

Other than the heavy extractor mark, the firing pin mark isn't cratered and the primer isn't flattened excessively.

 

[Russ661]

I'd say either slightly over pressure or too much induced headspace from over sizing

How much are you bumping the shoulder?

This brass was full length sized for the first loading and neck sized only for this loading. I did not attempt to set back the shoulder. This is the first time I have had heavy bolt lift.
Funny thing about this is I shot 10 rounds loaded exactly the same except I used a 195g eld-m bullet and got zero pressure signs. Velocity averaged 2990fps.

 

[cohunt]

Alliant book shows 3099fps with 79.2 grains of re26 is listed for the barnes 180 tsx as max.

3174 seems fast for a tipped monolithic bullet, they tend to have higher engraving force than lead core bullets, thus showing higher pressures and slower speeds

Are you sure that speed is accurate? I dont have a hornady book, maybe someone else can see how the GMC compares to other bullets of same weight in the hornady book

 

[Russ661]

Alliant book shows 3099fps with 79.2 grains of re26 is listed for the barnes 180 tsx as max.

3174 seems fast for a tipped monolithic bullet, they tend to have higher engraving force than lead core bullets, thus showing higher pressures and slower speeds

Are you sure that speed is accurate? I dont have a hornady book, maybe someone else can see how the GMC compares to other bullets of same weight in the hornady book

Velocity was measured using my ProChrono with fresh batteries about 15 feet from the muzzle; if it is off I have no way of knowing.
ETA: Fired, unsized brass fits easily in the chamber under a closed bolt which makes me think bumping the shoulders back won't help with the pressure issue.
The simplest answer is usually the right answer and in this case it just sounds like I need to back it down some, don't you think?

 

[L.Sherm]

I would.

 

[jjmp]

Yes !

 

[just country]

morning, why r u using a large rifle primer, instead of a
215 or other magnum primer? magnum cartridges use
large amounts of powder. justme gbot tum

 

[Greyfox]

I'd back off the charge given you have three potential indicators. Stiff bolt lift, ejector mark, flattened primer.

 

[Creedmoor shooter]

Back off. No sense in playing with fire

 

[fmuguira]

Ditto, back off.

One other thing I ve encountered is sometimes your pressure will slightly decrease if you move the bullet back from the lands. At .020 from touching you re pretty close with a monolithic; but if the accuracy there no reason to introduce another variable.

 

[Russ661]

morning, why r u using a large rifle primer, instead of a
215 or other magnum primer? magnum cartridges use
large amounts of powder. justme gbot tum

Some recipes I've seen use a large rifle rather than a magnum primer so I thought I'd try it.

 

[jpretle]

You have brass extruding into the ejector hole of the bolt face.
Back it down.....