Blown out primers and pressure signs

[dellet]

You need a good lesson in basics, before you get hurt.

Your max trim length for your chamber need to be at .010” less than factory spec to compensate for the short chamber.

Then you need to drop about 5% below minimum charge weight and work up your load. Your max load might make it to 5% less than book max, if you’re lucky.

Look at the SAAMI drawings and compare your measurements to the specs.

You do not have a 6.5 Creedmoor. You have a 6.5 almosta bomb.

Trying to shoot max loads in a chamber known to be short, because it won’t close on a Go-Gauge, is insane.

 

[mikehill85]

You need a good lesson in basics, before you get hurt.

Your max trim length for your chamber need to be at .010” less than factory spec to compensate for the short chamber.

Then you need to drop about 5% below minimum charge weight and work up your load. Your max load might make it to 5% less than book max, if you’re lucky.

Look at the SAAMI drawings and compare your measurements to the specs.

You do not have a 6.5 Creedmoor. You have a 6.5 almosta bomb.

Trying to shoot max loads in a chamber known to be short, because it won’t close on a Go-Gauge, is insane.

I took a look at my Go-gauge. It measures 1.5400" from the base to the shoulder. SAAMI spec is 1.5368" to 1.5438". My Go-gauge is seemingly not SAAMI spec. I will take it to a gunsmith to get them to check it with their gauges.

For the record I wasn't shooting it knowing it didn't close on my go gauge. I hadn't tested it until you mentioned too little headspace could cause this problem. It's not really something you should have to check on a factory rifle.

Anyway, I need to find out if my Go-gauge is the right dimensions now. I was looking on another forum and with the same Hornady comparator insert and the same set of calipers (Mitutoyo digital calipers) they were measuring 1.5335 as the base to shoulder dimension on their Go-gauge.

 

[Doom]

I took a look at my Go-gauge. It measures 1.5400" from the base to the shoulder. SAAMI spec is 1.5368" to 1.5438"

You are reading the cartridge not the chamber dimensions.

 

[M-61]

What is your case headspace, how much bump?

Chamber has the headspace not the case.
That ‘bump’? Well therein is a real possibility.

 

[dellet]

There is always some discrepancy with the comparator inserts. That’s to be expected. Your go gauge measures within about .0005” of how it should. You’re looking at the wrong specs, cartridge. You need to be looking at chamber. Circled below is chamber 1.541” min 1.551” maximum. The go-gauge should be say 1.5405-1.5415.



A comparator is no good for actual measurements, but great for making comparisons. Using the same insert and caliper the fires brass measures 1.5385”, the gauge 1.540”. That leaves .0015” difference. The Go-Gauge will not close in the chamber so we know the chamber is shorter than 1.540”. There is Probably than .001” clearance On your fired brass.

Maximum cartridge base to shoulder is 1.5438, minimum is -007” or 1.5368”.

If you look closely at the numbers, you can see that this is one of those cartridges that a maximum cartridge, will not fit a minimum chamber. Minimum chamber 1.541”, will not accept a 1.5438” case. This is why an answer of “it’s in spec” is useless.

we know you’re chamber is minimum base to shoulder, reasonable to assume also minimum overall. So your brass need to be 1.900 maximum. If your shoulder is also set back Less than minimum, your neck length will need to be even shorter. Case length from shoulder to mouth is determined by base to shoulder. The shorter base to shoulder is, the longer neck to mouth will be with the same exact overall length.

So not only are your outside measurements and tolerances at dangerous minimums, your internal capacity has been reduced. Thats your recipe for over pressure at low book loads.

 

[mikehill85]

There is always some discrepancy with the comparator inserts. That’s to be expected. Your go gauge measures within about .0005” of how it should. You’re looking at the wrong specs, cartridge. You need to be looking at chamber. Circled below is chamber 1.541” min 1.551” maximum. The go-gauge should be say 1.5405-1.5415.

View attachment 1654970

A comparator is no good for actual measurements, but great for making comparisons. Using the same insert and caliper the fires brass measures 1.5385”, the gauge 1.540”. That leaves .0015” difference. The Go-Gauge will not close in the chamber so we know the chamber is shorter than 1.540”. There is Probably than .001” clearance On your fired brass.

Maximum cartridge base to shoulder is 1.5438, minimum is -007” or 1.5368”.

If you look closely at the numbers, you can see that this is one of those cartridges that a maximum cartridge, will not fit a minimum chamber. Minimum chamber 1.541”, will not accept a 1.5438” case. This is why an answer of “it’s in spec” is useless.

we know you’re chamber is minimum base to shoulder, reasonable to assume also minimum overall. So your brass need to be 1.900 maximum. If your shoulder is also set back Less than minimum, your neck length will need to be even shorter. Case length from shoulder to mouth is determined by base to shoulder. The shorter base to shoulder is, the longer neck to mouth will be with the same exact overall length.

So not only are your outside measurements and tolerances at dangerous minimums, your internal capacity has been reduced. Thats your recipe for over pressure at low book loads.

Okay, thanks for that information. I didn't realize the Go-gauge was based on the chamber dimensions, but that makes sense.

I'll have a gunsmith take a look at it to see what they think. I checked online and some other people had issues with go-gauges from the same manufacturer not closing with factory rifles.

If I have to stay significantly under max load with this rifle I don't necessarily care because it shoots so well. The last time I shot it it averaged 0.4 MOA for 5-shot groups which is pretty good (for me anyway).

 

[Coyotefurharvester]

For cartridges I have HS gage for, I check my comparator bodies(than I know how "bad" they are). Can also zero off the error. and improve readability of your caliper(easier,quicker to determine a case is 0.001-0.002 different from the rest).

 

[rdremsek]

if it is fine with factory ammo and not with reloads your doing something wrong try full length resizing and see what it does

 

[mikehill85]

if it is fine with factory ammo and not with reloads your doing something wrong try full length resizing and see what it does

This is what I thought, and as I stated earlier, I wasn't bumping the shoulder back at all. I just just screwed my LEE FL Sizing Die down to touching the shell holder, not the extra 1/4 to 1/3 turn they recommend. That said, I'm not sure how not bumping the shoulder back enough would cause these random pressure spikes and it's not necessarily different than neck sizing only. Anyway, I am going to adjust the die to bump the shoulder back and proceed with caution.

 

[DLT]

if it is fine with factory ammo and not with reloads your doing something wrong try full length resizing and see what it does

That’s where I’m at with it also

 

[TTE]

I am getting blown out primers and other pressure signs 1.5 grains under maximum charge for multiple powders.

Maximum charge determined by who ? You or a reloading manual ?

 

[Stumpy1]

I didn't see it in the responses, but will a bullet drop freely into a fired case?
Too tight of a neck can cause this type of issue.
Even 'boogers' at the case mouth due to insufficient chamfering can cause high pressures.

Hope this is useful to someone.

Frank

 

[TTE]

This is what I thought, and as I stated earlier, I wasn't bumping the shoulder back at all. I just just screwed my LEE FL Sizing Die down to touching the shell holder, not the extra 1/4 to 1/3 turn they recommend. That said, I'm not sure how not bumping the shoulder back enough would cause these random pressure spikes and it's not necessarily different than neck sizing only. Anyway, I am going to adjust the die to bump the shoulder back and proceed with caution.

Just a reminder .... the cartridge drawing, the reamer, and the "bump gauge" were not made with the same reamer. There will be differences within all the measurements.

 

[dellet]

Bumping the shoulders back isn’t likely to change anything. The problem isn’t that the way you’ve loaded your cartridges appears to leave “0” headspace clearance, it’s that you haven’t compensated charge weight for a smaller capacity case and chamber.

If your bolt closes on brass the way you’ve sized it, there is no reason to change that. An easy check is to chamber a sized piece and measure it before and after, if it’s pushed the shoulder back, it’s a big problem.

There are multiple ways to double check headspace without a gauge. Adding a piece of tape to the case head and checking if it will close gets a measurement within the thickness of the tape. Inserting a spent primer and leaving it proud of the case head then closing that in the chamber having the bolt seat the primer them measure how much it sticks out is another.

You’re clearly new to this, no big deal, we all started there. Most of us, I know I have, have blown a primer or worse due to taking something for granted, trusting someone else’s load, including published data or just wanting to squeeze a little more speed out of a cartridge. It’s part of the process.

That said, we’re still missing vital load data.
Case trim length
Cartridge overall length
Cartridge base to bullet ogive if you can would be really helpful.

You stated that factory rounds don’t have a pressure problem. Measurements of those would be helpful if possible.

You said that you’re loading all bullets .020” off the lands. How did you determine this?
It take some time to develop the feel needed if you’re using most any tool. A .010” jam was really tough for me to feel. It’s only because the bullet stayed in the chamber after removing the tool that I discovered I was the problem.

The big issue is finding why maximum loads were fine, loads 1.5 grains lower were not. This clearly points to an assembly error. What were the maximum loads, and what might have been different about them?

Sooner or later the problem will be obvious, it’s either asking the right question, or getting the right answer. Sometimes it’s the same question asked a different way. Just keep with it.

 

[KMW 1954]

Another quick little exorcise since you say factory ammo doesn't present a problem.

Take a box of whatever factory ammo your rifle likes and also your comparator. Measure and record every round in the box for BTO and Base to Shoulder. Keep them in order back in the box. First look over these measurements and see just how much variance there is.

Next, take this box out and shoot it and again keep every case in the exact order to match the preshot measurements. This should give you and indication of where your chamber is after you have fired these..

Now measure these cases again and compare them to the measurements you had before firing. Then tell us what you've found.

I almost always shoot a box of factory rounds thru any new gun just to get a baseline. Every barrel is different. Each has it's own fingerprint.

 

[mikehill85]

Bumping the shoulders back isn’t likely to change anything. The problem isn’t that the way you’ve loaded your cartridges appears to leave “0” headspace clearance, it’s that you haven’t compensated charge weight for a smaller capacity case and chamber.

If your bolt closes on brass the way you’ve sized it, there is no reason to change that. An easy check is to chamber a sized piece and measure it before and after, if it’s pushed the shoulder back, it’s a big problem.

There are multiple ways to double check headspace without a gauge. Adding a piece of tape to the case head and checking if it will close gets a measurement within the thickness of the tape. Inserting a spent primer and leaving it proud of the case head then closing that in the chamber having the bolt seat the primer them measure how much it sticks out is another.

You’re clearly new to this, no big deal, we all started there. Most of us, I know I have, have blown a primer or worse due to taking something for granted, trusting someone else’s load, including published data or just wanting to squeeze a little more speed out of a cartridge. It’s part of the process.

That said, we’re still missing vital load data.
Case trim length
Cartridge overall length
Cartridge base to bullet ogive if you can would be really helpful.

You stated that factory rounds don’t have a pressure problem. Measurements of those would be helpful if possible.

You said that you’re loading all bullets .020” off the lands. How did you determine this?
It take some time to develop the feel needed if you’re using most any tool. A .010” jam was really tough for me to feel. It’s only because the bullet stayed in the chamber after removing the tool that I discovered I was the problem.

The big issue is finding why maximum loads were fine, loads 1.5 grains lower were not. This clearly points to an assembly error. What were the maximum loads, and what might have been different about them?

Sooner or later the problem will be obvious, it’s either asking the right question, or getting the right answer. Sometimes it’s the same question asked a different way. Just keep with it.

I measured the distance to the lands with the Hornady LNL OAL gauge.

See below for loads with blown primers and pressure. The case trim length was 1.9130" in all cases. I didn't record the COAL, because they are more variable than CBTO.

Primer: Remington 9-1/2
Brass: Hornady LRP
Bullet: 147 grain Hornady ELD-M
Powder: N555
Charge: 41.1 gr (max is 42.6)
CBTO: 2.2500"
Velocity: Unavailable

Primer: Remington 9-1/2
Brass: Hornady LRP
Bullet: 147 grain Hornady ELD-M
Powder: H4350
Charge: 40.9 gr (max is 41.8)
CBTO: 2.2620"
Velocity: 2,660 fps

Primer: Federal 210M
Brass: Lapua LRP
Bullet: 143 grain Hornady ELD-X
Powder: 6.5 Staball
Charge: 42.5 gr (max is 43.5)
CBTO: 2.2520"
Velocity: 2,717 fps

Primer: Federal 210M
Brass: Lapua LRP
Bullet: 140 SMK
Powder: 6.5 Staball
Charge: 42 gr (max is 43.0)
CBTO: 2.2530"
Velocity: 2,647 fps

Primer: Remington 9-1/2
Brass: Lapua LRP
Bullet: Berger 140 grain Hybrid Target
Powder: 6.5 Staball
Charge: 42.5 gr (max is 43)
CBTO: 2.1925"
Velocity: 2,711 fps

I measured some factory ammo:

Hornady Precision Hunter (143 grain ELD-X bullet).
CBTO: 2.1677"
Base-To-Shoulder: 1.5315"

Hornady ELD-M (140 grain ELD-M bullet)
CBTO: 2.1766"
Base-To-Shoulder: 1.5340"

 

[dellet]

Ok that’s a better start.

Take your hornady modified case off the tool and throw it in the garbage can.
Only sort of kidding.
Measure it and compare it to your sized brass. It will be different. You might as well be looking for the lands on someone else’s rifle.

Where the shoulder is placed determines jump or jam. So using brass sized for another chamber will change jump distance or jam depth. Your using someone else’s brass to determine your seated depth.

Load an inert round, no primer no powder with the bullet a little bit longer. This will not be as exact, but is quicker than stripping the bolt. Muzzle up, insert the inert cartridge into the chamber with finger pressure. Most likely the round will not fall back out, it’s jammed into the lands. Back into the press and seat it .005” deeper. Try again. Repeat until the cartridge falls out under its own weight.

That Hornady tool takes some time to get the feel of, and it’s not sized to your chamber. Better to make a case fired in your chamber. There a couple guys on the forum that advertise for that. Or you can buy a tap.

If the hornady case you have. Is longer base to shoulder, you can size that as you do normally and expand the neck back out to allow the bullet to slip in and out.

Also it’s rare to have different bullets have the same base to ogive touch point, it’s being Hornady they might have the same profile, but it’s a flag.

 

[mikehill85]

Ok that’s a better start.

Take your hornady modified case off the tool and throw it in the garbage can.
Only sort of kidding.
Measure it and compare it to your sized brass. It will be different. You might as well be looking for the lands on someone else’s rifle.

Where the shoulder is placed determines jump or jam. So using brass sized for another chamber will change jump distance or jam depth. Your using someone else’s brass to determine your seated depth.

Load an inert round, no primer no powder with the bullet a little bit longer. This will not be as exact, but is quicker than stripping the bolt. Muzzle up, insert the inert cartridge into the chamber with finger pressure. Most likely the round will not fall back out, it’s jammed into the lands. Back into the press and seat it .005” deeper. Try again. Repeat until the cartridge falls out under its own weight.

That Hornady tool takes some time to get the feel of, and it’s not sized to your chamber. Better to make a case fired in your chamber. There a couple guys on the forum that advertise for that. Or you can buy a tap.

If the hornady case you have. Is longer base to shoulder, you can size that as you do normally and expand the neck back out to allow the bullet to slip in and out.

Also it’s rare to have different bullets have the same base to ogive touch point, it’s being Hornady they might have the same profile, but it’s a flag.

Thanks for the suggestion. I will give that a try. Yes, it is possible the distance I measured to the lands are off and random variation in the CBTO dimension could explain the random pressure spikes if I am near the lands (i.e. some might be off the lands, some might be in the lands).

I also think it is interesting how short the base to shoulder dimension is on the factory ammo compared to my fired brass. I assume they size it on the low side to ensure it fits in pretty much all factory chambers.

On those two bullets with the same CBTO dimension, I made a mistake copying the information from my spreadsheet. They aren't the same dimension. It has been corrected now.

 

[243winxb]

What is the neck tension?
Minimum is .002"

If bullets move to soon on primer firing, there may be a 2nd pressure spike. Slow burn rate powders. Standard primers, longer then normal OAL. Are some comditions to avoid.

 

[243winxb]

I checked my powder charges with another scale (both give me the same value for my powder charges)

Is each & every powder charge hand weighed?
Is scale old type balance beam? Only 1 i would trust.