Pressure Problem

[v63800]

Having problems with a new build 7 saum.
Bore scope shows the case neck well short in the neck leaving me to think i have a chamber problem.Looks like it has .040-.050 to the end of the neck.
Fired cases also have a lot of carbon down to the shoulder junction.
Mild load 54.3 2209 (4350) behind a berger 184 popped a primer.
Case measures 2.0180

 

[ebb]

If it popped a primer it was not a mild load in your rifle. Is it designed to be a no turn neck? Maybe check neck clearance just to be sure.

 

[mac86951]

What's the freebore look like? I've seen a rifle that needed a throat cleanup when one land was longer than others as an alternate suggestion. Maybe a chamber cast would help ID issues?

-Mac

 

[Link]

Following to see what the smiths say about the picture ;]

 

[Alex Wheeler]

Based on that picture you have .020" gap at most. Perfect in my opinion. I would not want it any closer.

 

[Bc'z]

Carbon ring or shadow in the picture?

 

[Straightshooter1]

Having problems with a new build 7 saum.
Bore scope shows the case neck well short in the neck leaving me to think i have a chamber problem.Looks like it has .040-.050 to the end of the neck.
Fired cases also have a lot of carbon down to the shoulder junction.
Mild load 54.3 2209 (4350) behind a berger 184 popped a primer.
Case measures 2.0180

I don't think you really have that much of a gap above your case mouth as the bore scope makes everything look much, much bigger that it really is. The gap looks pretty normal to me and not much different from what I saw when I took a picture like that in my Krieger .308 chamber. Here's that picture that you might compare:

 

[Coyotefurharvester]

Just measured one of my fired brass, 2.028(deprimed, not sized) trim length is 2.025 but I never go to book trim length. Just looked at my 2002 sendero, looks like your pic. Don't run more then 0.003 headspace. Your cases can be left longer. I have around 300 rounds on my rifle( no rifle big game hunting in my area).

 

[Ggmac]

looks normal ! pressure is excessive if your cases are new or near new . Every rifle is different. Check neck clearance , powder age and density,bullet weight , and check your scale

 

[v63800]

Based on that picture you have .020" gap at most. Perfect in my opinion. I would not want it any closer.

thanks Alex

 

[v63800]

Carbon ring or shadow in the picture?

Bc,z, definitely a shadow. cheers

 

[dkhunt14]

Having problems with a new build 7 saum.
Bore scope shows the case neck well short in the neck leaving me to think i have a chamber problem.Looks like it has .040-.050 to the end of the neck.
Fired cases also have a lot of carbon down to the shoulder junction.
Mild load 54.3 2209 (4350) behind a berger 184 popped a primer.
Case measures 2.0180

By popping a primer, do you mean blanking or a hole in primer? Too short of headspace can cause blanking. The firing pin drives the case forward and pressure slams it against the bolt face. If the firing pin bounces and touches the primer, it will punch a hole. Matt

 

[Ksmirk]

What brass are you using? I got a surprise when I couldn't find Winchester brass for a 7-08 and picked up some PPU, same load and pressure! guess I had an brain fart moment as the PPU brass had less capacity..... it worked great when I backed off the load 1.5gr just something to think about.

 

[searcher]

If you actually had the primer pop out of the pocket using a truly mild load - excessive pressures can build up when using too little of a very slow burning powder - which some call "pre-detonation". Extreme cases of undercharged loads can dismantle a rifle quite nicely.

If you did not undercharge below the book minimum starting load- the culprit is most likely a shoulder being pushed back much too far, allowing the primer to simply be pushed out the rear of the cartridge case, thus giving the illusion of overpressure.

If you are not sure whether you have pushed back the shoulders too much, and If you have a Hornady measuring tool for your dial caliper - I'd measure an unfired, un-sized piece of brass or a loaded factory ammo cartridge and compare them with your sized brass. If your sized brass is more than a few thousandths shorter - I'd look at that as a contributing problem if not the entire problem, as the shoulders are getting pushed back tool far in the sizing process.

An alternative is to choose another powder out of the manual, do a mid-range (no more) load, and seat the bullet no more than .002" off the lands. That will allow the case to more fully blow out upon being fired before taking your measurement for shoulder setback - and should help to contain the primer in the process of case "blowout".

Once a case has the shoulder pushed back too far - it can otherwise take a number of firings for the shoulder to fully move forward. This can result in a lot of 'false' readings as you try to navigate what should be a proper shoulder setback.



Good Luck!

 

[v63800]

If you actually had the primer pop out of the pocket using a truly mild load - excessive pressures can build up when using too little of a very slow burning powder - which some call "pre-detonation". Extreme cases of undercharged loads can dismantle a rifle quite nicely.

If you did not undercharge below the book minimum starting load- the culprit is most likely a shoulder being pushed back much too far, allowing the primer to simply be pushed out the rear of the cartridge case, thus giving the illusion of overpressure.

If you are not sure whether you have pushed back the shoulders too much, and If you have a Hornady measuring tool for your dial caliper - I'd measure an unfired, un-sized piece of brass or a loaded factory ammo cartridge and compare them with your sized brass. If your sized brass is more than a few thousandths shorter - I'd look at that as a contributing problem if not the entire problem, as the shoulders are getting pushed back tool far in the sizing process.

An alternative is to choose another powder out of the manual, do a mid-range (no more) load, and seat the bullet no more than .002" off the lands. That will allow the case to more fully blow out upon being fired before taking your measurement for shoulder setback - and should help to contain the primer in the process of case "blowout".

Once a case has the shoulder pushed back too far - it can otherwise take a number of firings for the shoulder to fully move forward. This can result in a lot of 'false' readings as you try to navigate what should be a proper shoulder setback.



Good Luck!

searcher
i think you hit the nail on the head
cheers

 

[searcher]

Excessive carbon on the case below the neck is another sign of possible underpowered load not burning hot enough. I had that happen on a 7 MM Rem. Mag loads and others when I was working up mild practice loads. Huge kick, sign of overpressure, lots of carbon. Hard to want to increase the powder charge when one has those signs, yet sometimes that is exactly what is needed. Go slow and incrementally.

 

[EWM]

Hi. Had the same probline
Free bore needs to be 220 +& neck needs to turned at the base of shoulder

 

[v63800]

Hi. Had the same probline
Free bore needs to be 220 +& neck needs to turned at the base of shou

just checked a loaded round .3165 at the top of the neck, down towards the shoulder where the pressure ring sits i'm measuring .319 so essentially i only have .001 clearance on a .320 neck.
necked down 300 saum brass. could the brass get thicker with the necking down process
good call EWM