Posted: 8/13/2016 2:17:45 PM EDT
|
I'm trying to work up a load for <=600 yards for my 308 (R700 AAC-SD, 20" barrel, Nightforce 3.5-15, thunderbeast suppressor). I hit the range this morning with 50 rounds with 10 different powder charges (IMR 4064). The projectiles were 175 SMK seated to .065 from lands. Groups 1-9 were shot round-robin after 2 sighters (not shown). Finally, for the last group of the day, I shot a 5 shot group using 168gr FGMM to see how accurate I was holding. I'm not sure how to interpret this information other than my rifle seems to like the 168gr projectiles better. Should I re-do the entire test using 168gr SMK, or pick a specific powder charge range? Can the horizontal stringing from group to group be from the load or is that the shooter? Don't know why the text got resized down so small... group sizes range from .54 MOA (168 FGMM) to 1.7 MOA (group 6). All were shot at 100 yards with light breeze from 11 oclock. Also, I did not have time to let the barrel cool to ambient between groups. I took a break between groups, but the barrel temp was variable (and mostly climbing steadily) throughout shooting.   |
|
You have a node down near 39.0 gr.
You may have a node way down at 37.8 gr. You have an antinode spanning 6-9. You should be getting the 175 SMK up to the 2625-2650 range for the long range node to show up. If you have not seen any pressure signs, I suggest to walk the charge weight up into the 43gr range watching pressure along the way. |
|
Quoted: You have a node down near 39.0 gr. You may have a node way down at 37.8 gr. You have an antinode spanning 6-9. You should be getting the 175 SMK up to the 2625-2650 range for the long range node to show up. If you have not seen any pressure signs, I suggest to walk the charge weight up into the 43gr range watching pressure along the way. The bolt was ever so slightly harder to unlock at 41gr...although it could be a perception thing as I am admittedly gun shy (heh) about approaching full power charges. I'll run another group through at 41gr and slowly take it up from there. I was hoping my accuracy node was a little higher velocity than the ~2400 I was getting at 39gr. Thanks for the feedback. |
|
Quoted: You have to redo all the test with 168 gn. bullets, if you want to see the performance of 168's with different loads. but your 68 gn group looks so nice you might not need to make any changes to the load you have unless you change powder primers or cases. It came out pretty dang nice. Only problem is that was the factory stuff :) |
|
Hodgdon's website has 4064 ranging from 41.5-45.6gr for the 175gr SMK.
I'd say that you were just getting into the good powder range when your loads stopped. I don't think you would run into a dangerous situation with under loading a bulky stick powder like 4064, but staying within manufacturers recommended load data is generally good for accuracy as well as safety. As far as a sticky bolt lift, how was the brass prepared for this load development? Previously fired in this rifle and neck sized only? Purchased new and loaded up without any sizing or trimming? As I've started to delve into precision loading for a bolt gun as well (same rifle, in fact, just with a Titan-Ti vice a TBAC can) I have started to note that brass preparation can really have an impact compared to what I was doing with a .223 AR. |
|
Quoted:
It came out pretty dang nice. Only problem is that was the factory stuff :) Quoted:
Quoted:
You have to redo all the test with 168 gn. bullets, if you want to see the performance of 168's with different loads. but your 68 gn group looks so nice you might not need to make any changes to the load you have unless you change powder primers or cases. It came out pretty dang nice. Only problem is that was the factory stuff :) Ups. |
|
Quoted:
It came out pretty dang nice. Only problem is that was the factory stuff :) Quoted:
Quoted:
You have to redo all the test with 168 gn. bullets, if you want to see the performance of 168's with different loads. but your 68 gn group looks so nice you might not need to make any changes to the load you have unless you change powder primers or cases. It came out pretty dang nice. Only problem is that was the factory stuff :) Ups. Have you made some reloads with 168? You might have some shell, neck, or other problems with your 175 reloads. At 100 meters groups should be very very nice. |
|
Military brass will hit maximum pressure around 40.5 to no more than 41.0 grains of IMR-4064 with 175 grain SMK's. You didn't say what brass you're using, keep my post in mind if it's Lake City or IMI brass. Military brass averages close to 179 grains empty and unprimed. Winchester commercial brass weighs closer to 155 grains empty and unprimed. Huge difference in internal capacity.
I usually start my load development "jump to rifling" with 168 or 175 grain SMK's at .030". It's close enough to get good accuracy without spiking pressure. What's your current OAL"? You don't need to touch the rifling with Sierra Match King bullets, they fly just fine when jumped. They usually fly great when seated to magazine length. If your going to feed them from a magazine you need to develop loads that fit. That usually means no longer than 2.810" to 2.830" depending on what your magazine will accept. I shot my AR-10 this week @ 200 yards using 40.5 grains of IMR-4064, Winchester large rifle primers, 168 grain SMK's seated at 2.810" in Lake City 7.62x51mm brass. It shot a 2" group @ 200 yards and I feel fine with that. I will adjust the charge to see if I can get some improvement. This is my generic accuracy load that I know will feed, function and perform acceptably well across a number of different rifles. I can safely go as high as 41.5 grains of IMR-4064 using these components. Velocity is around 2500 fps from my 21" barrel. If you want more speed you need to switch to Winchester or Lapua brass, it can safely hold more powder without spiking pressure. |
|
One more thing, I can't shoot orange dots as well as simple black bulls eyes. I'm color blind, so that may play a roll in my experience. The orange dots seem to disappear with my vision.
Quartering a simple black bulls eye into a "pie" is easy and repeatable in my experience. |
|
Quoted:
One more thing, I can't shoot orange dots as well as simple black bulls eyes. I'm color blind, so that may play a roll in my experience. The orange dots seem to disappear with my vision. Quartering a simple black bulls eye into a "pie" is easy and repeatable in my experience. I have a similar problem with orange dots on tan remanufactured paper. To create a point of reference, I mark the center of the orange bullseye with a black Sharpie marker. If I can see the dot, I can put crosshairs on it. |