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Gil P. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gil P. Quote  Post ReplyReply Direct Link To This Post Posted: August/18/2012 at 14:36
Sorry for the wait.

The first picture is a target with 45.9gr and 47.1gr charges of VV N550 powder. I am still using Winchester brass, 175 SMKs, and Fed 210M primers.
47.1gr charge seems to be more accurate than the weaker, 45.9gr charge. The two low bullet holes on group #1 (top left) I let the barrel cool down and the three above it I shot continuously. If I shot them all the same way, I imagine that group would be much smaller. I have more rounds loaded up with 47.1 gr of powder that I plan on shooting soon, so I will post those targets up when I can.

The second picture is a ladder test of the VV powder and the third picture is just some primers that dont seem to be showing signs of over pressure.

dfddd

ddddd

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Gil P. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gil P. Quote  Post ReplyReply Direct Link To This Post Posted: August/18/2012 at 14:45
Originally posted by Stevey Ducks Stevey Ducks wrote:

The .308 Win is probably one of the more accurate calibers.
 
Some items that sort of popped out - primer failed to fire, wind 15-20 mph (or about).
 
Primers that fail to go off sometimes are the result of excessive head space - the firing pin just does not set off the primer and excessive head space can result in poor accuracy. For some reason I have found that many lots of unfired or new .308 brass are a little short (base to shoulder or datum) and excessive head space results. Of course the primer could be contaminated by oil, solvent, or water. If fired cases have primers that appear to be totally flattened this indicates excessive head space provided pressures are in the normal range. The Rem 700 has a spring loaded plunger type ejector that shoves the round deeply into the chamber. Just a thought but might be checked out.
 
I try to test out loads on calm days - wind can really draw bullets away from their intended targets.
 
The .308 Win accepts a wide variety of powders H4895, IMR 4985, Varget, IMR 4320, TAC, Win 748. I have used all of these with great results. Your targets indicate that your combo is nearing what you want to do.
 
Check out the bedding in your rifle like actions screws tight without binding or bending the action (bedding screws can exert major tension on actions and actually bend an action) and try "free floating" the barrel - no contact with the stock. Epoxy bed receiver ring and recoil lug.
 
Last but not least - your barrel may not be so good - but it appears that your rifle is on the verge or producing good results. 


The primer didnt actually fail to fire, I simply forgot to load up the case with any powder.

What is excessive headspace, exactly? How can the cause primers to fail to fire?

The barrel is floated and the stock has an aluminum bedding block (B&C M40). I torqued the action screws to 65 inch pounds, Although I may try backing off a bit because I am using a Borka Torque driver to do it and it is said to over torque by around 4 inch pounds and that is turning it by the end of the knob, getting the most leverage instead of the turning it by the notch in the middle of the nob as specified by the instructions (which is what I do). So the action could be over-torqued.

What problems could be caused by the round being too far in the chamber? I dont think my bullets are touching the rifling and my pressure limits seem to be ok.
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Alan Robertson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Alan Robertson Quote  Post ReplyReply Direct Link To This Post Posted: August/23/2012 at 19:40
One other thing about your M700 action screws- the middle screw doesn't need to be torqued and shouldn't be. Just screw it tight and back it off 1/2 turn.

Really excessive head space might cause a primer to not light since the cartridge would be so far forward in the chamber that the firing pin would barely strike. Excessive head space means that your cartridge is too short to fit correctly in the chamber and will be moved forward to fit the shoulder at the expense of the head of the round not making contact with the bolt face. The most obvious symptom of this is excessively short case life with the cases forming a bright ring just above the head, or even suffering case head separation.


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jonoMT View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jonoMT Quote  Post ReplyReply Direct Link To This Post Posted: August/23/2012 at 20:12
I would give Varget a try. I haven't found that much variation in it from lot to lot, although if I've had to buy jugs from different lots I'll mix them. One thing I've noticed with any powder is that the .308 cartridge likes to be full. I have always seated to mag length or slightly over (2.81) and after safety testing run a 44.5 to 45.5 load (which is almost compressed).
 
Your groups with the 4895 @ 43.5 grains look good as far as vertical stringing go. As SVT mentioned, it might require stiffening up the stock. Something is causing the shift. Could be not getting the same sight picture every time, uneven trigger pull (make sure you're not past the pad on your finger tip...and mentally I've done better with this little trick: "press the button" rather than "squeeze the trigger". Forget about the noise and the recoil and think of the rifle as just another tool. You don't do all that much thinking when hitting a nail with a hammer.
 
Re: running a ladder test. If you do, set up a series of targets, e.g. 1-5. Separate your loads the same way. Shoot one round of load 1 into target 1, one of load 2 into target 2 and so on. That way the barrel is roughly the same temperature, air temperature is too and wind (unless it's really erratic) is the same as well. Let the barrel cool and cycle through the sequence until you've shot 25 rounds. Five loads is enough to test a 2.5 grain spread.
Reaction time is a factor...
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Gil P. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gil P. Quote  Post ReplyReply Direct Link To This Post Posted: August/23/2012 at 23:56
Originally posted by Alan Robertson Alan Robertson wrote:

One other thing about your M700 action screws- the middle screw doesn't need to be torqued and shouldn't be. Just screw it tight and back it off 1/2 turn.

Really excessive head space might cause a primer to not light since the cartridge would be so far forward in the chamber that the firing pin would barely strike. Excessive head space means that your cartridge is too short to fit correctly in the chamber and will be moved forward to fit the shoulder at the expense of the head of the round not making contact with the bolt face. The most obvious symptom of this is excessively short case life with the cases forming a bright ring just above the head, or even suffering case head separation.




Thanks for the info on the headspace. My cases have always had the bright ring just above the head, but the cases have been fired several times (5-6) without a problem.

My bottom metal doesnt have a middle screw.
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Gil P. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gil P. Quote  Post ReplyReply Direct Link To This Post Posted: August/24/2012 at 00:03
Originally posted by jonoMT jonoMT wrote:

I would give Varget a try. I haven't found that much variation in it from lot to lot, although if I've had to buy jugs from different lots I'll mix them. One thing I've noticed with any powder is that the .308 cartridge likes to be full. I have always seated to mag length or slightly over (2.81) and after safety testing run a 44.5 to 45.5 load (which is almost compressed).
 
Your groups with the 4895 @ 43.5 grains look good as far as vertical stringing go. As SVT mentioned, it might require stiffening up the stock. Something is causing the shift. Could be not getting the same sight picture every time, uneven trigger pull (make sure you're not past the pad on your finger tip...and mentally I've done better with this little trick: "press the button" rather than "squeeze the trigger". Forget about the noise and the recoil and think of the rifle as just another tool. You don't do all that much thinking when hitting a nail with a hammer.
 
Re: running a ladder test. If you do, set up a series of targets, e.g. 1-5. Separate your loads the same way. Shoot one round of load 1 into target 1, one of load 2 into target 2 and so on. That way the barrel is roughly the same temperature, air temperature is too and wind (unless it's really erratic) is the same as well. Let the barrel cool and cycle through the sequence until you've shot 25 rounds. Five loads is enough to test a 2.5 grain spread.


I may try Varget later on down the road, I may try you ladder test method with the VV N550 powder except with the same powder charge on each target. I think its a good way to take some of the mental pressure out of taking a shot.

I should probably get a front rest as well, ive been using a bipod until now.
Easy come easy go

Always remember that you are absolutely unique. Just like everyone else.
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