over pressure and no idea why? need help

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tylerbeck

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I have been shooting the same load through my 6.5 CM for the last 600 or so rounds.
39.9 g of H4350, lapua brass with the small primer, cci 400 pushing a 143g eld-x traveling at around 2750

Ive never seen pressure signs of any kind, its just not that hot of a load. never even had a sticky bolt.

Did up 200 rounds yesterday and now my pressures are off the charts. Blowing primer pockets, very tight bolt. way to hot.
I figured I must has a component problem. pulled the bullets, new powder, new primers and same issue.
Even though Im getting crazy pressures signs, I'm not getting faster bullet speeds.
I cannot figure out what changed.

My only though left is that the primer pockets are just loose and leaking out the back.

Any ideas, I'm at my wits end.
 
Do you have a way to check for build-up in your rifle's throat? Also, is it possible that your brass has grown too long? Either has the effect of crimping the bullet - can't get going as easily as in the past, and would cause pressures to rise. Regarding primer pockets - you would feel that the primer seats much easier than it used to, if the pockets were enlarged.
 
tylerbeck said:
I have been shooting the same load through my 6.5 CM for the last 600 or so rounds.
39.9 g of H4350, lapua brass with the small primer, cci 400 pushing a 143g eld-x traveling at around 2750

Ive never seen pressure signs of any kind, its just not that hot of a load. never even had a sticky bolt.

Did up 200 rounds yesterday and now my pressures are off the charts. Blowing primer pockets, very tight bolt. way to hot.
I figured I must has a component problem. pulled the bullets, new powder, new primers and same issue.
Even though Im getting crazy pressures signs, I'm not getting faster bullet speeds.
I cannot figure out what changed.

My only though left is that the primer pockets are just loose and leaking out the back.

Any ideas, I'm at my wits end.
Click to expand...

What rifle do you have?Please don't tell be Bergara, I am having similar problems but pressure signs with low velocity in Alpha Brass.
 
You are only guessing that the pressure has increased significantly ("and now my pressures are off the charts.") , as for most people, only their Chrony can give a reliable estimator of pressure, and you report that your MV's are unchanged. However, you're wise to find out what's happening - since there is a change.

Since your load seemed fine in the past, you naturally look at what might have chnaged. Has the outdoor temp increased significantly where you are?

As mentionned as far as what can chnage, I'd look at the length of you brass and trim as required, and as this seems to be many-fired brass, perhaps the primer pockets are just loosened. Tight bolt - do you neck size or partial-full-length size? If so, maybe it's time to full-length size.
 
Exactly. Not nearly enough information. Probably related to one or more of the following. How many times reloaded? How many times neck sized? Necks turned first? How many times shoulder bumped? How many times full length resized? Brass make? Trim to length?

Secondary but unlikely possibility: Copper build up in barrel?
 
Is it a new lot of H4350? I just started a new lot of H4350 a couple weeks ago and my 140 ELDM load went from exactly 2700 fps to just shy of 2740 fps. That's why I always buy larger amounts of the same lot now.

It's rediculous how much lots can vary sometimes. I had Retumbo in my 338 LM change from 2750 to 2820 and got a bit of heavy bolt lift between different lots.

Edit-missed the part where you said same velocity haha sorry.

Something I learned from Jerry from Mystic Precision is that with thicker brass like Lapua you can run into issues with not enough neck clearance which can drive up pressure. Especially with a bit of carbon build up on top of that. Simple quick check is make sure your bullets fall freely into your fired cases. Quick 10 second check will eliminate that at least..
 
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Curious, is accuracy suffering as well? Almost sounds like excessive copper fouling in the barrel, and/or build up in the throat as mentioned above. Wipeout is pretty great if you can find it.
I've had the long brass issue pop up in a SAAMI minmum spec chamber, but only caused hard extraction, to the point half the rim was being ripped off the case in a semi auto, primers looked fine.
Possible headspace issue developing? Which rifle?
 
Thank you or all the suggestions. This is a Christionson LR Mesa. i had check the brass length, COL and head space. No change on dies.

Finally tried new brass and no issue. Back to 1/2 inch groups at 200.

My current theory is that my primer pockets are getting loose. Maybe the loads are hotter than I had though, but never has any issue before. 5th firing of brass and I think they finally gave out. Allowing some pressure to pass back though the flash hole, around the primer. was even burning out the primer pocket. this was pushing the primers and making the bolt sticky. Its all I can come up with, nothing else was different.

Regardless the new brass has fixed the issue.
 
tylerbeck said:
Thank you or all the suggestions. This is a Christionson LR Mesa. i had check the brass length, COL and head space. No change on dies.

Finally tried new brass and no issue. Back to 1/2 inch groups at 200.

My current theory is that my primer pockets are getting loose. Maybe the loads are hotter than I had though, but never has any issue before. 5th firing of brass and I think they finally gave out. Allowing some pressure to pass back though the flash hole, around the primer. was even burning out the primer pocket. this was pushing the primers and making the bolt sticky. Its all I can come up with, nothing else was different.

Regardless the new brass has fixed the issue.
Click to expand...

That's not very many firings, and it must be pretty high pressure to do that. I'd think that you should be having other fatigue issues before that one.

What happens if you push the primer out without resizing? Does the brass go back to chambering and extracting easily?
 
Brass cases vary in hardness in the base and in thickness of the flash hole web.

The simple truth is you are pushing that brand of brass beyond its elastic limits, meaning reduce your load.

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Example below the Federal cases on the left have a thinner flash hole web, and the primer pockets will stretch out of shape much faster than the case on the right.

cYeTsDp.jpg


Simple Trick for Monitoring Pressure of Your Rifle Reloads
http://www.hodgdonreloading.com/reloading-education/tips-and-tricks/simple-trick-monitoring-pressure-your-rifle-reloads
 
tylerbeck said:
Thank you or all the suggestions. This is a Christionson LR Mesa. i had check the brass length, COL and head space. No change on dies.

Finally tried new brass and no issue. Back to 1/2 inch groups at 200.

My current theory is that my primer pockets are getting loose. Maybe the loads are hotter than I had though, but never has any issue before. 5th firing of brass and I think they finally gave out. Allowing some pressure to pass back though the flash hole, around the primer. was even burning out the primer pocket. this was pushing the primers and making the bolt sticky. Its all I can come up with, nothing else was different.

Regardless the new brass has fixed the issue.
Click to expand...

since new brass resolved your issues, compare new vs old... focus on the neck thickness and I suspect that it is over 16 thou now. New brass would be around 14 to 15 thou. I prefer to be around 12 thou for my 6.5 Creedmoors.

If you do not outside neck turn AND continue to do this through the life of the case, brass flow can increase neck thickness to the point it jams into the chamber... ie no room to open to release the bullet. Big big big pressure spike.

Do the test that Longboat suggested.... if tight, you just found your problem area.

The load you are using should not be that hot unless you got a crazy fast lot of powder. My SWAG would be neck thickness.... resolve it now or the problem will show up in about.... 5 firings :)

Jerry
 
As Jerry said, it might be a combination of the neck getting thicker walls over time and a tight chamber.
I checked the neck wall thickness on a few of my 6.5 Lapua brass on the weekend, at 4-5 firings they're all 0.014-0.0145".
My rifle is a Savage, not a Christenson, so I can't offer any comparison. I don't neck turn, at least not yet.
Now, here's an odd question.. by any chance were you shooting in the rain when this happened?
 
tylerbeck said:
I have been shooting the same load through my 6.5 CM for the last 600 or so rounds.
39.9 g of H4350, lapua brass with the small primer, cci 400 pushing a 143g eld-x traveling at around 2750

Ive never seen pressure signs of any kind, its just not that hot of a load. never even had a sticky bolt.

Did up 200 rounds yesterday and now my pressures are off the charts. Blowing primer pockets, very tight bolt. way to hot.
I figured I must has a component problem. pulled the bullets, new powder, new primers and same issue.
Even though Im getting crazy pressures signs, I'm not getting faster bullet speeds.
I cannot figure out what changed.

My only though left is that the primer pockets are just loose and leaking out the back.

Any ideas, I'm at my wits end.
Click to expand...

Using FCDs?
 
Boomer said:
Something that has yet to be mentioned is your scale. Do you use check weights to ensure its accuracy and repeatability?
Click to expand...

Good thinking! Always important. Backchecking charge weights I do all the time as I have multiple scales, but a necessity if you don’t. If a balance scale, check for the balance beam sticking due to possible buildup of grime on the knife edge as well. Blowing primers is a definite sign something’s wrong.
 
Mystic Precision said:
since new brass resolved your issues, compare new vs old... focus on the neck thickness and I suspect that it is over 16 thou now. New brass would be around 14 to 15 thou. I prefer to be around 12 thou for my 6.5 Creedmoors.

If you do not outside neck turn AND continue to do this through the life of the case, brass flow can increase neck thickness to the point it jams into the chamber... ie no room to open to release the bullet. Big big big pressure spike.

Do the test that Longboat suggested.... if tight, you just found your problem area.

The load you are using should not be that hot unless you got a crazy fast lot of powder. My SWAG would be neck thickness.... resolve it now or the problem will show up in about.... 5 firings :)

Jerry
Click to expand...

^^^^^^ This. Measure the thickness of new Lapua and compare it to 5X fired. Lapua brass have thick necks to start with if you have a tight chamber you will start to have problems unless you start neck turning. Ask me how I know.:;)

If you don't want to neck turn Winchester brass is an alternative. It's a couple thou thinner in the neck.
 
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