Is 2820 fps too fast from a factory 24' 6.5CM RPR barrel? Blown primer?

[mustang-cars]

Here's my load:
Hornady 1x fired brass from my rifle
H4350 42.6gr
CCI BR-2
ELD-M 140's
,020 off the lands
2820fps average over a Magnetospeed on a 90 degree day
sd/es 7.9/25
1/4'-1/2' groups at 100
RPR with factory 24' barrel. Round count 1000
Charges weighed with Chargemaster


I've fired 35 rounds of this load no problems. Went shooting when it was 50 degrees out, so much cooler than when load was initially checked. I didn't re-verify speeds in the cooler weather though. Fired 9 rounds with great accuracy at 550 yards. 10th round right on target. Extremely hard bolt lift and round wont extract. wait 60 seconds and brass extracts easily. Primer is blown out. Fire 2 more rounds after that, no problems, Never had hard bolt lift or extractor/ejector marks. Some of the primers look a little flat some look great so I don't really think that's an indicator. Bad primer pocket? Bad primer? Load too hot?

 

[nexusfire]

If you are not seeing sign of pressure on your other rounds I would not worry too much about it.

 

[FCS]

Case with different capacity?
Case that had some media stuck inside, changing case capacity?
Bad charge, higher than setpoint, from RCBS?
Bullet with different ogive profile, was closer to lands or touching lands, causing different pressure curve. I'd jump a little more than 20 thousands as ELD-M should / does handle jump just fine. Little more jump also gives you more wiggle room unless you are sorting bullets by ogive with a comparator. I've seen almost no variation in a box of Hornady and I've seen 0.035" variation in box of Hornady bullets.
Field / tactical rifle I start @ 0.040 of jump and increase if needed to get accuracy.
F T/R or F-open rifle I might run closer to lands but those are being fed sorted bullets.

I agree with nexusfire, if a one off with no other fired rounds showing pressure signs, wouldn't worry too much.

 

[918v]

Maybe you should do an oal test and find a good one farther away from the lands.

Also check your case length vs your chamber length. Your chamber could have pinched the neck against the bullet causing a pressure spike.

 

[mustang-cars]

I use a Forster micrometer seating die. They seat of the Ogive I believe so theoretically speaking the variations in the bullets shouldn't matter?

 

[FCS]

Ogive still matters because no seater die seats bullet by stem making contact right where bullet goes to full diameter. Every seater die has a stem that pushes somewhere on the ogive of bullet.
Theoretically if the stem in seater die seated bullet right where it went to full diameter, then you wouldn't have to worry about bullet to bullet, lot to lot variation.
Unfortunately, in reality, there is no seater die set up that way. Lot to lot, heck even within a single lot, variation in ogive, transition shape and where bullet actually goes to full diameter matters.

Even using a comparator, unless it is exactly the diameter as bullet, you can run into the same issue. If comparator is exactly same diameter as bullet, it creates other issues but I digress.
Been there, done that. I've put bullet into lands at same comparator length when I didn't verify new lot # of bullets for actual OAL that touched lands in chamber.
If you sit down and do the trig, you'll see just how easy a slight variation in the ogive/transition shape can easily put you into lands at same comparator length.

Back to the original question, I don't think that 2820 is too fast. I do think there was a variation in case capacity, either factory difference or some media was stuck in case, that caused a volume difference. Volume difference changed leading edge of pressure curve, which changes burn rate, which caused a one off, pressure issue. Just my working hypothesis at momement.

 

[mustang-cars]

That was some good info. Thank you

 

[lte82]

Mic the OD of a new case and fired case right above the extractor groove. I'm finding some factory rifles have generous chambers, and when paired with hornady brass that is sometimes smaller than SAAMI spec the brass stretches a lot at the case head causing premature loosening of the primer pocket even when well under max pressure.

 

[demonjigger]

I have heard others are having problems with Hornady brass in the primer pockets...

 

[mustang-cars]

I was doing load development with the same Hornady brass that had the primer blow but with a different rifle. I've had 2 blown primers today with lower charge weights. Pretty sure I have a bad lot of Hornady brass mixed in.

 

[NewsShooter]

I've got three 6.5's, one is a 24, and two have been re-barreled, all run about 2800 to 2820, loads have been from 41.7 to 43.0 depending on the barrel and powder lot. Currently shooting 140 ELDs at 2810, hornady brass is on the 7th firing, only tossed a few for loose primer pockets. Shot some FGGM 6.5 with 130's yesterday, chrono'd from 2900 to 2935. Shot Ok in my rifle, shot pretty much one hole in my buddy's rifle. I also get over 2800 with Hornady factory ammo in a 24 inch barrel.

 

[Greg Langelius *]

Straight answer, yes.

You are running more than a whole grain over Hornady's published (Hornady Handbook of Cartridge Reloading, Tenth Edition) maximum charge, and getting signs of overpressure including hard bolt lift and a blown primer. Of course your are, that load's too hot.

if you backed the load down to Hornady's actual published maximum load of 45.1gr of H-4350, I strongly suspect there would be no legitimate reason for your post.

Loading manuals strongly caution against running hot loads for genuinely good reasons.

Don't do it; and the rest of you should be advising against it as well, instead of trying to blame other causes. Maybe everything you say is correct about those other reasons, which is a large part of why max loads might seem conservative. They are conservative because they include a necessary safety margin. But it is precisely because those other reasons you cite do eventually, inevitably occur that published maximum loads are set where they are. If you are setting up a condition where any occasional component variation can create an unsafe condition you're doing it wrong.

In order for such a condition to be safe all the time, components must be as expected every time. Such perfection does not exist, so a safety margin is necessary.

I shoot the .260 from a 28" barrel and get 2850fps. The additional case capacity of the .260 should account for a minimum of 50fps more than the 6.5CM, and the additional 4' of barrel length should account for another minimum of 50fps of velocity aver the CM in a 24" barrel. This would drop my adjusted velocity down to 2750fps which is precisely where Hornady says the 140ELD-M should be running in a 6.5CM. I am running 43.5gr of H-4350, and I may have understated the estimated adjusted velocity of my load by as much as an additional 100fps.

When you start getting a 6.5CM within 30fps of a .260 with 4 more inches of barrel length, you are really overstoking your loads. Back them off before the accumulated excess stress causes sufficient metal fatigue to create a catastrophic failure. When one primer goes, others are pretty sure to follow. Even if they don't go, the overpressure for each round is incrementally eating away at the statistical mean time between failures that your rifle is designed to sustain safely. When a barrel fails from a hot load, it's not that one cartridge that caused the failure. It's the preceding several hundred hot loads that set up the failure as inevitable. Running hot loads and counting on luck to ensure your safety is just plain illogical.

Get your loads back to within the published limits.

Greg

 

[FCS]

I was doing load development with the same Hornady brass that had the primer blow but with a different rifle. I've had 2 blown primers today with lower charge weights. Pretty sure I have a bad lot of Hornady brass mixed in.

Keep brass segregated by component lot # or by lot # of the ammo the fired brass came from. I suspect you are correct, you have brass that was either stressed by factory load or that has weak / soft case head out of the bag/box.

 

[usafa77]

I see a load of 42.6 from the OP. Well under max.

 

[mustang-cars]

The other rifle blew a primer at 42.2gr

 

[CJS-6.5]

One thing to remember is that at 90 degrees that barrel and chamber is smoking hot after 9 rounds. Did you let the tenth round sit in the chamber for longer than a few seconds? If so that could have caused the blown primer.

 

[Mike Casselton]

Everything Greg said.

I'll also add this.
If you are charging directly from a powder measure (which I've always done) you could have had the powder bridge in the drop tube.
This would cause one charge to be a bit low and the next one way over maximum charge.
I use a clear drop tube to make sure that all powder is dispensed into the case.
I also check all cases at the same time to see if any look different from the rest.

Make sure your scale is accurate and reads properly.
Playing around with over max loads is not smart.
If you've ever ran loads through a test barrel and watched how pressure can skyrocket once max is reached, you wouldn't take chances

 

[mustang-cars]

Loading from a chargemaster. Checked charges randomly with a beam scale. Downloaded a bunch to 41.3gr two days ago. Out of 15 there were 2 that showed ejector marks. Still showing hot at 1gr less charge. If you look in the "reloading depot" of this forum you will see that 42.5gr of H4350 in Hornady brass is an extremely common node for 6.5CM. 41.3 is a ways away from that.

 

[mustang-cars]

Oh and CJS-6.5. The 42.6gr load was tested when it was 90 degrees out with success. The primer blew when it was 50 degrees out. I just think the brass cant handle it. Maybe it's because I have a little larger chamber or maybe it's because the brass is inconsistent and there's some bad pieces mixed in.

 

[rduckwor]

I think you found a one-off for an unknown reason. I have consistently run 43Gr H4350 behind a 140 AMAX or 140 ELD-M in Hornady brass without issues for the past 18 months. The brass has at least 10 loads on it and the pockets are getting a bit loose on several pieces. Seems to me you load should be fine as it is below max. The drop in temp is a variant that simply serves as a confounder in this mystery.

RMD

 

[CJS-6.5]

Oh and CJS-6.5. The 42.6gr load was tested when it was 90 degrees out with success. The primer blew when it was 50 degrees out. I just think the brass cant handle it. Maybe it's because I have a little larger chamber or maybe it's because the brass is inconsistent and there's some bad pieces mixed in.

 

[CJS-6.5]

Yes that can make a big difference. The chamber in my Savage is .095 longer than my Rpr and and the Savage shows pressure signs way sooner.

 

[CJS-6.5]

The throat is longer I mean.

 

[Fishkat]

I'm a speedaholic, however I've learned better. Be careful, blown primers and sticky bolt are telling you something. Here is a good article to take a look at www.primalrights.com/library/articles/understanding-pressure

 

[mustang-cars]

I think you found a one-off for an unknown reason. I have consistently run 43Gr H4350 behind a 140 AMAX or 140 ELD-M in Hornady brass without issues for the past 18 months. The brass has at least 10 loads on it and the pockets are getting a bit loose on several pieces. Seems to me you load should be fine as it is below max. The drop in temp is a variant that simply serves as a confounder in this mystery.

RMD

What velocity are you getting out of that load? Barrel length?

 

[Rebelirons]

I've had issues with Hornady fired brass. Blown primers, separated case heads and inconsistent speeds. I tossed all my Hornady and bought Lapua brass and haven't had an issue yet. That's just my experience. Make sure you're checking everything during the reloading process and go from there.

 

[mustang-cars]

I've been checking everything pretty thoroughly in my opinion. I bought 2 cases of prime to shoot and then I'll try and reload with that brass.