stephentri
Well-Known Member
Hi just started loading for 6mmbr norna using new lapua brass mild load of 28grains N15O with 108g eldm get started noticed stiff to lift bolt, no pressure signs to be seen, could this be the way chamber has been left,
6mmbr stiff bolt
- Thread starter stephentri
- Start date
What do you mean by “could this be the way the chamber has been left”?
stephentri
Well-Known Member
Ment to say cut
That doesnt sound hot in the least
40gr of N140 was the standard load for 105gr AMax when i was running one
Whats on the side of the barrel?
Tight neck?
Should say if non standard
40gr of N140 was the standard load for 105gr AMax when i was running one
Whats on the side of the barrel?
Tight neck?
Should say if non standard
stephentri
Well-Known Member
It's a. 269 neck, brass is turned down to give a loaded round of .266 I did think this might be the problem and sacrificed 4 pieces of brass and turned them to .265 this made no difference, striped the bolt and chambered fired case,hard to close and open, I then bumped shoulder 2tho and bolt will close again open as normal, reloaded fired case with shoulder bumped bolt hard to lift, could it be reamer spec doesn't suit lapua brass,
You haven’t got much choice when it comes to the 6mmbr. It’s Lapua or nothing.
Are there any witness marks on the bullet from the rifling on the bullet? If you are jamming the bullet that will cause an increase in pressure.
Are there any witness marks on the bullet from the rifling on the bullet? If you are jamming the bullet that will cause an increase in pressure.
stephentri
Well-Known Member
No marks on bullet loading 10tho back throat was cut for 108g eldm
28gn N150 should be mild. Around 30gn is a near standard for this powder with 105-108gn match bullets. (I run mine with exactly 30gn with the 107gn Sierra MK.)
Are you full-length sizing? Even with new brass the shoulders may have been rather too far forward depending on the how the chamber was cut in a custom rifle. Slight resistance on chambering often turns into hard bolt lift and primary extraction after firing. (The giveaway for this problem shows up on the case-head face if your action has a button ejector as a part-circle inscribed around the case-head, the case being tightly held against the bolt until primary extraction has taken place.) This won't show up in chambering and extracting an empty unfired or sized case as there is no change to the brass caused by pressure. (If the ejector button is partly jammed and won't push back fully flush in the bolt-face, you get the same symptoms/marks and there's your cause.)
There can be lots of causes. My first 6BR had been chambered using a 6mm BR Remington (the original 6BR form) chamber reamer, not a 6mm BR Norma example and this causes such problems with Lapua or Norma cases which are marginally larger diameter than Remington examples. The Norma chamber is specified slightly larger in the lower case body area. It's unlikely that you have this problem now as I'd hope no gunsmiths here are still using the 'Rem' version. If it is the cause, you'll see witness marks on the lower case body just above the solid web. The real problem here though is partially stuck cases and hence pulling the bolt open after primary extraction.
It certainly sounds like a case to chamber fit problem, and it'd be worth giving fired cases a really good look-over using a quality magnifying glass looking for 'witness marks' from an over-tight fit somewhere. Nevertheless, apparently mild load or not, dropping the charge by a grain or even 1.5gn is a wise precaution just in case this chamber / barrel / bullet combination produces higher than usual pressures with that powder lot. If that cures the problem, there's your cause. If not, take it back to the gunsmith and get him to check everything out.
Are you full-length sizing? Even with new brass the shoulders may have been rather too far forward depending on the how the chamber was cut in a custom rifle. Slight resistance on chambering often turns into hard bolt lift and primary extraction after firing. (The giveaway for this problem shows up on the case-head face if your action has a button ejector as a part-circle inscribed around the case-head, the case being tightly held against the bolt until primary extraction has taken place.) This won't show up in chambering and extracting an empty unfired or sized case as there is no change to the brass caused by pressure. (If the ejector button is partly jammed and won't push back fully flush in the bolt-face, you get the same symptoms/marks and there's your cause.)
There can be lots of causes. My first 6BR had been chambered using a 6mm BR Remington (the original 6BR form) chamber reamer, not a 6mm BR Norma example and this causes such problems with Lapua or Norma cases which are marginally larger diameter than Remington examples. The Norma chamber is specified slightly larger in the lower case body area. It's unlikely that you have this problem now as I'd hope no gunsmiths here are still using the 'Rem' version. If it is the cause, you'll see witness marks on the lower case body just above the solid web. The real problem here though is partially stuck cases and hence pulling the bolt open after primary extraction.
It certainly sounds like a case to chamber fit problem, and it'd be worth giving fired cases a really good look-over using a quality magnifying glass looking for 'witness marks' from an over-tight fit somewhere. Nevertheless, apparently mild load or not, dropping the charge by a grain or even 1.5gn is a wise precaution just in case this chamber / barrel / bullet combination produces higher than usual pressures with that powder lot. If that cures the problem, there's your cause. If not, take it back to the gunsmith and get him to check everything out.
How the heck did you get 40gn of N140 into a 6mmBR case???? - that's >40% more than my standard load
(28.2gn N140 with a 107gn SMK).stephentri
Well-Known Member
Hi Laurie, I full length sized new brass and trimmed to length, problem is now fixed I have loaded up to 30grains no stiff bolt or pressure signs,
Thanks
Thanks
Typo!How the heck did you get 40gn of N140 into a 6mmBR case???? - that's >40% more than my standard load
30gr
What was the cause ?
stephentri
Well-Known Member
Like Laurie said shoulder of new brass to far forward , so I full length sized trimmed to length problem gone,
surely that would be stiff on close as well?
Trim length in a short neck chamber would drive pressures up though
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