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Posted: 10/31/2010 1:56:09 PM EDT
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I have a winchester model 70 heavy varmint in 308. I have been loading the COL as per book. My max COL was 2.810.
The way I measured my chamber was: I closed the bolt on an empty chamber I put a dewy one piece rod all the way to the bolt. I marked that with tape I took the bolt out I put a projectile in the chamber and made sure it was against the lands( I put pressure on it from the chamber side with a pistol rod and held it in place) I put the dewy rod back in and let it touch the tip of the projectile I marked that with tape Then I measured the distance from mark to mark. I came up with these measurements: Nosler 168 gr custom competition 2.842 COL sierra 175 MK 2.900 COL sierra 168 MK 2.846 COL Hornady 168 BTHP Match 2.864COL Do these sound right? How much should I back away from the lands? I dont want a pressure issue. Is this the right method of doing this? Any other input would be appreciated Thanks. |
| The cleaning rod has two problems. The first one is the bullet tip is inside the part that accepts a jag so you aren't getting an OAL that is accurate. The second problem is the part that's touching further down on the bullet (if it's touching at all) isn't touching the bullet where the lands touch it. Buy a Hornady Lock-N-Load gage system and a modified .308 case from them too. |
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I want them off the lands because I am afraid of pressure.
Right now the load I have is this: COL 2.810 Brass WRA 64,65,68 LC dont know the year trim to 2.005-2.007 Winchester LR primers Powder IMR 4895 39 grains Projectiles 175 sierra MK 168 sierra MK 168 nosler J4 CC I am getting under MOA at 300 meters. I am averaging .75 and .85 MOA I wanted to see if I moved the projectile closer to the lands if the groups will tighten a bit. I want to take this out to 500 meters Borderpatrol I am using the male threaded end. It is hitting the tip of the projectile. |
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Quoted:
Are you doing this using just a bullet in the chmaber or an entire cartridge? For the OTMs (open tip match) bullets, using the truncated meplat tip as a basis for measurement to set "jump to land" injects an additional tolerance of bullet tip to ogive. The FMJs and Plastic tipped bullets seem to have a tighter tolerance in that relationship than the OTM, at least in my experience. 
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I was just using the projectile. The diagram makes sense because I was pushing from the chamber end to keep pressure on the projectile to measure it. So the ogive was touching the lands.
So now my question is how much do I set the projectile back so I can have minimal jump but not create exessive pressure? |
| Recently, what I've started doing is taking a deprimed, unloaded, resized case and sticking a bullet into the mouth of the case and loading the empty case with the bullet into the chamber of the rifle as far as it will go. I intentionally attempt to come into contact with the rifling in the barrel and this (so far) has resulted in the bolt (on my bolt action hunting rifles) refusing to completely close (IOW, the bolt is slightly out of battery). After that, I remove the case and bullet (with is now stuck firmly into the empty, deprimed, case) and I measure the overall length of the empty cartridge with the bullet stuck in the neck of the case. I did this the other day with a 180 grain hornady spbt and an unprimed winchester case and it came to an overall length of 3.135" in my Model 700 PSS rifle. Currently, I'm loading my .308 winchester 180's out to 2.9" COL but I may start loading them longer at an even 3" in overall length. BTW, my next test loads for my .308 will be using the aforementioned 180 grain hornady btsp's with Reloader 15 powder. |
For about $35 you can get the right tool and be done, their are several made I went with the Hornady OAL gage but you will soon find out that even superior quality bullets vary in length due to tip irregularities so you will need a comparator insert to check OAL from the ogive and while your at it you might as well get the headspace gage so you can measure how far your bumping your brass 
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