Just got into reloading. I finished shooting my first 100 rounds of new Hornady 6.5 creedmoor brass. I bought a hornady headspace comparator kit so that I could check my once fired brass and attempt to bump the shoulder back 0.002" as many people suggest for a bolt gun. What is interesting is that comparing my once fired brass vs a piece of the same brass after I full length sized using a rcbs die set up as per the manual (screw die down until just touching shell holder) and the size difference is only 0.001" or 0.002". I expected to have to back off my die but that wasn't the case. Is this normal? Does the brass not expand enough after one firing to accurately measure headspace? Does my tikka just have a tight chamber? My load is 40 grains of H4350 with Hornady 140 eldm and it shot amazingly well for my skill level (0.31"-0.39" 5 shot groups) Thanks.
Full length sizing once fired brass question
- Thread starter Jessejames107
- Start date
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- Western Manitoba
Well, I am probably way out of touch, but it is your rifle and your chamber that will tell you what it likes to shoot - despite what you comparitor might say. Set your die to get your bolt closing with a hint of resistance - you are then sizing as close as possible within your chamber for that brass. If you have that in place, kinda do not worry about the sizing issue for a carton or two of primers (1,000 or 2,000 rounds). By then you will have chased through all the rest of the details that higher end bench rest guys have shown to matter - in their $2,000 barrels that they change out reasonably often. I do not play in that league. I have found that sizing to create minimal headspace room, and with really small run out numbers on the loaded rounds, get me as good of groups on target as I can do with my gear - while still having fun. In the end, for most of us, the groups on the target tell us what is working and what is not. Sometimes, it turns out the main issue, is actually the "nut behind the bolt"...
Every rifle is different but you are light on the charge. I would size 5 rounds without bumping the shoulder. See if they are different after the second firing, than your other ones. I would set your bolt for zero touch to find headspace. ( take apart your bolt to truly find it ) My 6.5 I went with only the comparator, however I am on firing #10 with Hornady brass, so I must not be too far off the disassembled bolt headspace number. I shot 140 Berger's with 41.1gr of H4350.
OP - You may have mis-read your die instructions. Most die manufacturers, including RCBS, suggest you turn the die in a bit after touching the shell holder. On my RCBS dies, it says 1/8 to 1/4 of a turn. What you have done is to partially resize the case, to your benefit, it appears!
Watched a good video on this the other day.
https://youtu.be/htvk1UYOXm8
https://youtu.be/htvk1UYOXm8
When you full length resize the case is squeezed in diameter and the case shoulder will move upward in the die. Then as the die approaches the shell holder the die starts pushing the shoulder back down. I would say your die and chamber are a good match and your case shoulders were not pushed back excessively.
When the case is fired it springs back from the chamber walls and becomes smaller than chamber dimensions. And when you resized the case you bumped the shoulder back .001 or .002 and shorter than the chamber. The next time you fire these cases just measure them again and bump the shoulders back .001 or .002.
When you full length resize the amount of shoulder bump will be the head clearence when the cartridge is chambered. And when the shoulder bump is not excessive you should not have any case stretching that can cause a case head seperation. And when the shoulder bump is not excessive the case can stretch and contact the bolt face and be within the elastic limits of the brass and spring back.
Below is a example of a .303 British catridge being fired in a Enfield rifle at the max military headspace of .074 and the case stretching. With the headspace at .074 and a rim thickness of .058 you will have .016 head clearance. And even if the headspace is at the minimum of .064 you will have .006 head clearance. And this is why you are better off just neck sizing the .303 British with excessive headspace.
Below is a posting by Kevin Thomas who worked in the Sierra ballistic test lab and now shoots for Team Lapua USA. In this posting is my favorite full length resizing expression. "The cartridge should fit the chamber like a rat turd in a violin case".
