Over pressure?

[ar10ar15man]

back off, and a bit more if you change primers.
yes you should change primers
i use fed 215 with rl26 in a 300 win mag with230 bergers

 

[Jeffrey Van Zandt]

View attachment 125507

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.

https://www.primalrights.com/library/articles/understanding-pressure

 

[Jeffrey Van Zandt]

https://www.primalrights.com/library/articles/understanding-pressure

 

[Rick Richard]

https://www.primalrights.com/library/articles/understanding-pressure

Great article. Thanks for posting

 

[Wedgy]

One poster said monos have higher engraving pressure and one said monos like a longer jump than .020" but neither is true for the Hammer Bullets monos. They are insensitive to seating depth and their parabolic sides and softer copper have lower engraving pressure = higher velocities. They are the easiest bullets you will ever work up a load for. Read some of the Hammer Bullet threads.

 

[jebel]

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

I agree with the above.

One poster said monos have higher engraving pressure and one said monos like a longer jump than .020" but neither is true for the Hammer Bullets monos.

I also agree that Hammer bullets differ in these ways from other monos.

And you mentioned not finding the same pressure when you switched bullets. A different bullet can affect pressure. The butt end can leave more/less volume in the case, the material hardness being pushed down the barrel can differ, etc.

 

[aushunter1]

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

The was I see it, changing the CBTO or seating depth to just off the lands will increase the pressure & hence pushing the velocity up.
OP, have you tried(while working up) the proj seated deeper?

 

[vancewalker007]

I would make the same guess as the others on the mono bullet. That Hornady copper bullet is likely a lot like the many Barnes I've used. The tend to shoot better 50 or more off the lands and require a shade less powder charge. If this was shot recently I assume outside temp was not an issue. Summer in Phoenix I have had loads shoot hot that were not over pressure in March. I'd say back down to the next accuracy node seat it a little deeper and it should be fine.

 

[Wedgy]

I would make the same guess as the others on the mono bullet. That Hornady copper bullet is likely a lot like the many Barnes I've used. The tend to shoot better 50 or more off the lands and require a shade less powder charge. If this was shot recently I assume outside temp was not an issue. Summer in Phoenix I have had loads shoot hot that were not over pressure in March. I'd say back down to the next accuracy node seat it a little deeper and it should be fine.

Reloder 26 has been found to be very stable at lower temps but above ~84F it builds pressure very fast.

 

[vancewalker007]

Reloder 26 has been found to be very stable at lower temps but above ~84F it builds pressure very fast.

Yeah, air temps can cause issues for sure.

 

[Dirtrax]

Did anyone suggest weighing the offending case? If not...weigh the case. Measure the neck thickness. If only one round looked this way something about it was different. If the weight is the same check H20 volume. It could be a simple over-charge. Sorry I didn't have the patience to closely read every post.

 

[Russ661]

The case shown in the first post was the first (and last) round fired at that charge weight. I have since disassembled the remaining rounds I had made up: pulled the bullet, dumped the powder, resized the neck, replaced powder minus .5 grain (now at 75.5), reseated bullets to be .040 off the lands (was .020 off). When the weather breaks I'll make another trip to the range and give it a go. One thing I have noticed with this Norma brass is that it seems to be softer than some other brands, most notably R-P.