Effect on cartridge pressure when seating a .308 bullet closer to the lands?
- Thread starter MCMXI
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1858,
I agree, your brass looks fine. Try the 43.5gr load and see what that does for you.
Don
I agree, your brass looks fine. Try the 43.5gr load and see what that does for you.
Don
NCsmitty, Afy and Don, thanks very much for the feedback. I plan on following the OCW method once the barrels are broken in. Yesterday, I wasn't really doing any load development as such but on the other hand, I didn't want to "waste" ammunition by sending it downrange without getting something in return. I'm sure once I start neck-sizing (after I've shot my way through all 200 Lapua cases), I'll see further improvements. This has been my experience on my other rifles, but that said, I've never had such a high-quality barrel/chamber before so who knows.
Don, I'll try the 43.5gr loads next weekend and will post another photo if you can bear it.
Thanks.
Don, I'll try the 43.5gr loads next weekend and will post another photo if you can bear it.
Thanks.
Ridgerunner665, I've read through this thread again and I have a question about the photo that you posted of the cases with the ejector marks. What action where they fired in? I'm curious since I've been looking at the ejector on the bolt face of the Remington 700 action that I have to see what pattern might appear on the case head at high pressure .... the impression left by your ejector looks a lot bigger. Also, the Remington ejector is just a spring-loaded pin which I assume pushes the case away from the bolt face as the bolt is opened. If the case pressure is getting too high, is the Remington ejector going to leave an easily identifiable mark?
I need to make a correction to an earlier post ... I spelled Krieger as Kreiger ... sorry about that.
Thanks.
I need to make a correction to an earlier post ... I spelled Krieger as Kreiger ... sorry about that.
Thanks.
Ridgerunner665
Member
Remington 700 (SPS Tactical)
The "mark" gets more visible as the pressure increases...but if you pay close attention you will feel the bolt lift get a little "sticky" before the mark gets as bad as those in the pic.
The "mark" gets more visible as the pressure increases...but if you pay close attention you will feel the bolt lift get a little "sticky" before the mark gets as bad as those in the pic.
Ridgerunner665
Member
The marks on the brass in that pic were not caused by excessive pressure...I got in a hurry and left case lube on those brass, which causes excessive bolt thrust (no grip on the chamber walls)...but the mark looks the same whether its caused by pressure or bolt thrust.
Some may argue that excessive bolt thrust does not exist in that form...I have done some "experimenting" since that happened...and I can assure you, even with very low pressure, slick brass will get you ejector marks.
Some may argue that excessive bolt thrust does not exist in that form...I have done some "experimenting" since that happened...and I can assure you, even with very low pressure, slick brass will get you ejector marks.
Ridgerunner665 said:
That's a VERY good point ... and thanks again for the tip about bolt lift. I wonder if excessive pressure in a trued action would be easier to detect. I had both 700 actions trued by Krieger and they're noticeably smoother and more positive so hopefully any "sticking" will be more obvious.
Thanks.
Ridgerunner665
Member
It would probably make a small difference, dont really know for sure though...Mine has been trued too.
Howard Roark
Member
The length of the bearing surface of the bullet also makes a differance in pressure. I can shoot the same load in my .260 with a 142gr SMK jumped 10 thou and a 140gr Berger jammed 10 thou into the lands. The Berger has a much shorter bearing area to give resistance.
Clark
Member
In a 308 the charge [needed to reach the threshold of short brass life] gets higher, very slightly as the bullet is seated longer, until it gets jammed into the lands, and then the threshold drops ~ 2 grains.
Jammed into that lands has the classic advantage of better accuracy and the disadvantage of a pressure spike and unfired rounds when ejected may leave the bullet stuck in the lands and spill powder all over the chamber and action. The following cases fired will have imprints of powder sticks. This is called "leprosy" and having that on your cases is the mark of shame. If you jam into the lands on hunting trips, you should take a cleaning rod.
Flirting with shame, I have worked up some lengths for bullets and my individual guns, where the bullet is "semi-jammed into the lands". This length gets the pressure spike and accuracy boost, but can be extracted without leaving the bullet in the throat.
Jammed into that lands has the classic advantage of better accuracy and the disadvantage of a pressure spike and unfired rounds when ejected may leave the bullet stuck in the lands and spill powder all over the chamber and action. The following cases fired will have imprints of powder sticks. This is called "leprosy" and having that on your cases is the mark of shame. If you jam into the lands on hunting trips, you should take a cleaning rod.
Flirting with shame, I have worked up some lengths for bullets and my individual guns, where the bullet is "semi-jammed into the lands". This length gets the pressure spike and accuracy boost, but can be extracted without leaving the bullet in the throat.
uh-oh
Member
I like the advice in this thread since I am a greenhorn in .308 loading.
I don't have much to add to this thread, but I need to state the Ideal Gas Law would not apply to any firearm cartridge. A fired cartridge would have pressures in the realm of supercritical fluids and plasmas. A serious model would require some heavy duty programming for various components (like Quickload). I know this as a Chemical Engineer who had to write some programming code for several models for relatively simple multi-component systems as part of my coursework.
I don't have much to add to this thread, but I need to state the Ideal Gas Law would not apply to any firearm cartridge. A fired cartridge would have pressures in the realm of supercritical fluids and plasmas. A serious model would require some heavy duty programming for various components (like Quickload). I know this as a Chemical Engineer who had to write some programming code for several models for relatively simple multi-component systems as part of my coursework.
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