MOA or bust
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Thank you to Rflshootr and fseaman for helping this neophyte better understand ballistics.
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28 Nos Flat Primers
- Thread starter Hikinghunter
- Start date
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johngibbs222
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- Joined
- Jun 15, 2012
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- 211
Slug the bore and check the size against the SAAMI drawings, also ensure the groove diameter is the same as or just a midge's dick bigger than the bullets you're using.
Also check the diameter of the case about 250 thou in front of the rim groove both before and after firing.
I had similar issues with a browning blr in 308. Polishing the chamber was the recommended fix, the bore was fine.
My rifle responded to that treatment but prior to it about 1 in every 20 rounds would give extremely sticky extraction as well as the tophatting phenomenon.
By the elimination process discovered that the factory brand of ammo I was shooting was a maximum sized cartridge and the chamber was a minimum sized chamber.
I now use peterson SRP brass without issue but my handloads are not yet at the DNE level but I've good accuracy, albeit 150 to200 fps down on the max loads.
These were reloads but factory ones were similar.
Also check the diameter of the case about 250 thou in front of the rim groove both before and after firing.
I had similar issues with a browning blr in 308. Polishing the chamber was the recommended fix, the bore was fine.
My rifle responded to that treatment but prior to it about 1 in every 20 rounds would give extremely sticky extraction as well as the tophatting phenomenon.
By the elimination process discovered that the factory brand of ammo I was shooting was a maximum sized cartridge and the chamber was a minimum sized chamber.
I now use peterson SRP brass without issue but my handloads are not yet at the DNE level but I've good accuracy, albeit 150 to200 fps down on the max loads.
These were reloads but factory ones were similar.Mike Matteson
Well-Known Member
I kind feel you are on the right track about the primers being seated. Been proven wrong before. Have to watch this.
MagnumManiac
Well-Known Member
Sure have, every load I have ever put through both barrels have gone over the Pressure Trace. Well within parameters of Max Pressure as by SAAMI.
Cheers.
Buttermilk
Well-Known Member
My 28 Nosler Hells Canyon LR doesn't do that.
Hikinghunter
Well-Known Member
Alright, based on what I'm hearing from @Rflshootr and @fseaman , it sounds like the maybe the factory headspaced my chamber on the long end of the 5 thou tolerance so I can cram any old dirty ammo in there 
, so while I'm in spec and nothing going to blow up in my face , it's going to take several rounds to fire form my brass out before it's a cozy fit in my chamber. Until then, expect to see flattened primers.
A bit annoying, as this rifle seems to hit its node at bergers's max powder charge of 81 grains of Retumbo, but I feel like loading more toward the bottom end until the flat primers go away. Getting nervous about pressure signs leads to flinching (ask me how I know)
All barrels should have a barrel nut. Would be nice to screw the barrel in a few thou and save unnecessary rounds down the tube fire-forming brass. These noslers are not exactly known for long barrel life.
, so while I'm in spec and nothing going to blow up in my face , it's going to take several rounds to fire form my brass out before it's a cozy fit in my chamber. Until then, expect to see flattened primers.A bit annoying, as this rifle seems to hit its node at bergers's max powder charge of 81 grains of Retumbo, but I feel like loading more toward the bottom end until the flat primers go away. Getting nervous about pressure signs leads to flinching (ask me how I know)
All barrels should have a barrel nut. Would be nice to screw the barrel in a few thou and save unnecessary rounds down the tube fire-forming brass. These noslers are not exactly known for long barrel life.
You don't know that until you test with a no-go gaugeAlright, based on what I'm hearing from @Rflshootr and @fseaman , it sounds like the maybe the factory headspaced my chamber on the long end of the 5 thou tolerance so I can cram any old dirty ammo in there
A bit annoying, as this rifle seems to hit its node at bergers's max powder charge of 81 grains of Retumbo, but I feel like loading more toward the bottom end until the flat primers go away. Getting nervous about pressure signs leads to flinching (ask me how I know)
All barrels should have a barrel nut. Would be nice to screw the barrel in a few thou and save unnecessary rounds down the tube fire-forming brass. These noslers are not exactly known for long barrel life.
Hikinghunter
Well-Known Member
There's 5 thou between a go and no-go guage. I'm not saying it's out of spec, I'm saying that "spec" is a very broad range of values. If my brass needs to grow that much, I'm posturing that the rifle was headspaced toward the upper end of the allowable range. Is what it is, just wish I could tweak it a little to a tighter tolerance.
Go and no-go vary by maker. Not always .005". Good luck
tomcat818
Well-Known Member
Yes, I agree that you are bumping the shoulder back too far. I agree with the other reply about not bumping shoulders unless your fired brass will not chamber smoothly but take it a few steps further:
1st - Decap and tumble brass (if you clean your brass)
2nd- make sure your chamber and brass is free from all debris and oil
3rd - test chamber your case if it chambers with normal force then test a 9 more to verify. If they all chamber smoothly your'e good to go do not bump shoulder back. *It's a good practice to have a headspace comparator so you can measure them for variance as well if you find more than .035" variance chamber or measure them all. I do this primarily for final loads I'm going to hunt with to make sure I don't have a failure to chamber in the moment.
4th - If after 2-3 firings your cases no longer chamber after steps 1&2 then first measure case OAL to see if you need to trim once your cases are trimmed or at or below recommended length chamber them and if they won't chamber then it's time to bump the shoulders. I measure headspace for reference purposes at this point and bump them .002" (need a consistent way to accomplish this) and test and if they chamber smooth and easy your're good to go. Proceed to primers, powder, and bullets.
Having just looked at your fired Peterson brass again it looks to me like the firing pin craters are shallow and less concentric than they should be. I would expect firing pin craters to deeper and more pronounced the more you bump the shoulder back and potentially pierced primers and case head separation with more extreme headspace gaps. Have you had any failure to fire or hang fires? Have you taken the bolt apart to clean and inspect? Recommended firing pin protrusion in primer cap is .045-.055" it doesn't appear you are getting that. Could be weak or damaged firing pin spring or debris slowing down firing pin down allowing the primer to back out slightly then extrude when the brass flows.
I know people who every 100rds or so break the bolt down expect, clean, and lube. Probably not a bad idea
1st - Decap and tumble brass (if you clean your brass)
2nd- make sure your chamber and brass is free from all debris and oil
3rd - test chamber your case if it chambers with normal force then test a 9 more to verify. If they all chamber smoothly your'e good to go do not bump shoulder back. *It's a good practice to have a headspace comparator so you can measure them for variance as well if you find more than .035" variance chamber or measure them all. I do this primarily for final loads I'm going to hunt with to make sure I don't have a failure to chamber in the moment.
4th - If after 2-3 firings your cases no longer chamber after steps 1&2 then first measure case OAL to see if you need to trim once your cases are trimmed or at or below recommended length chamber them and if they won't chamber then it's time to bump the shoulders. I measure headspace for reference purposes at this point and bump them .002" (need a consistent way to accomplish this) and test and if they chamber smooth and easy your're good to go. Proceed to primers, powder, and bullets.
Having just looked at your fired Peterson brass again it looks to me like the firing pin craters are shallow and less concentric than they should be. I would expect firing pin craters to deeper and more pronounced the more you bump the shoulder back and potentially pierced primers and case head separation with more extreme headspace gaps. Have you had any failure to fire or hang fires? Have you taken the bolt apart to clean and inspect? Recommended firing pin protrusion in primer cap is .045-.055" it doesn't appear you are getting that. Could be weak or damaged firing pin spring or debris slowing down firing pin down allowing the primer to back out slightly then extrude when the brass flows.
I know people who every 100rds or so break the bolt down expect, clean, and lube. Probably not a bad idea
tomcat818
Well-Known Member
That's true and I know of 2 smiths that will add shims as to limits the bolt play to .001" in a precise action.
Rflshootr
Well-Known Member
The same reason I described in post #23. Factory ammo is short just like your new brass.
Rflshootr
Well-Known Member
Add shims where?
Rflshootr
Well-Known Member
If you look at the SAMMI Specs, you will see that there is a chamber drawing and also an ammo drawing for each cartridge. The head space on the ammo is always shorter than the minimum head space on the chamber so it will always chamber. Both the chamber and the ammo has a minimum and maximum tolerance. So, and I'm not saying this is the case of your situation, but, it is possible that a chamber could be made to the long side of the tolerance, and the ammo could be made to the short side of the tolerance, which in that situation, the brass would have to grow much more to fill the chamber than if the chamber was on min and the ammo on max.
With that being said, even with the ammo on max, and the chamber on min, there is still clearance built in so that they will fit together. So as an example, if you had .004 tolerance on the chamber, and .004 on the ammo, plus .002 clearance from min to max, then it would be possible to have .010 total clearance on a virgin piece of brass whether it is in factory ammo or brass as a component.
As a side note, even when you get your headspace on the brass corrected, if you are shooting max or near max loads, you could still get top hatted primers. It also depends on the amount of chamfer around the primer pocket on the brass you are using. When you slam that little thin piece of metal with 55K-60K psi, the metal is going to stretch and fill in any space where it isn't supported.
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