I would guess muzzle blast. The 338s with the 300 are a little different to chrono than a 223. I like to be at least 20ft out with anything over 300WM class. My 300RUM even had issues with chrono placement. I usually run 8-10 YDS out. And yes I have blown a chrono into very small pieces with a 338 if anyone is asking.
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So here's an update for y'all. Today I went to test the loads that was suggested to me. 91.4gr and 92.2gr seated .010 off of the lands. First up was the 91.4grs. The chronograph was set at a distance of 15 feet and I was still seeing a lot of fluctuation in the velocity. The velocities were 2769,2815,2932. 163fps spread. This had me puzzled. I then moved on to 92.2gr and measured 2810,2824. After the second shot of 92.2gr i pulled the trigger, which was on safe, and noticed that I would push my shoulder into the rifle (anticipation). After noticing this I focused on squeezing the trigger. The result. 2859,2861,2861. and a .36" group. WOOF!! I'm happy with 2fps ES. Seems as though I hit a sweet spot
brentc
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Are you saying that differing shoulder pressure induces differing velocities? I have often wondered about this because according to physics it makes sense but its not something you hear a lot about. There has been some talk of this on here but nothing conclusive.
My ES shrunk on my 338s when I added weight to them. Makes some sense as the differing recoil velocities and interaction with your shoulder COULD cause this in theory anyway. I added a lot of lead to one 338 I had and my notes showed decreased ES BUT I never really put 2 and 2 together as the barrel had more wear, it was different temps and other variables were present.
From what I've found over the passed and from this outing is that "Yes, In fact it does relate to velocity". I did some work at 660yds to experiment with this. I shot 2 groups. One with my shoulder just touching the rifle and the second with my just pressing my shoulder on the stock. What I found is that the group that I pressed with was about .5MOA higher than the group that I was just touching the rifle
Shoulder pressure can also throw shots low or high for reasons other than velocity. This has been one of the things I have consistently wondered about for a while and not found much research on. If a rifle recoils 1" at 30 FPS x rifle weight BEFORE the bullet exits...then it would make complete sense that the velocity will be affected versus a rifle that recoils 2"x30 fps x lower rifle weight.
Throw a box of 22lr in a fire and the bullet stays put and the case flies off into the night. Makes me wonder if a similar affect isn't in place with lighter rifles OR a lighter HOLD.
dsculley
Well-Known Member
Little things like that are why I will believe my target over my chronograph. If you were pushing your shoulder into the rifle that also explains some of the groups. It is hard to shoot a good group without good form. Good thing the safety was on for that one shot! This is a case when recognizing the scatter node can be as well as/better than recognizing the accuracy node.
Glad things worked out for you.
Glad things worked out for you.
WildRose
Well-Known Member
Are you weighing each load individually or using a powder dropper measuring volumetrically? Stick or ball powder? What scale are you using?
WildRose
Well-Known Member
No, everything affecting velocity is happening between the bullet and the brass.
You can hang a rifle suspended by wires or paracord and pull the trigger remotely and it won't affect MV.
WildRose
Well-Known Member
That's not a change in velocity, it's a change in how the rifle moved.
We did a good thread on "managing recoil" a couple of years back, I'll see if I can dig it up.
It's a good read.
Every load of H1000 is weighed to 0.1gr with a Hornady LNL Scale and dispenser.
WildRose
Well-Known Member
Are you giving it plenty of time to warm up then calibrating and zeroing it each time as per instructions? That's what I have to do with my RCBS to get it to weigh accurately.
Your ES is all over the place so I'm running through all the things in my head that can effect it. Neck tension would be the next place I look along with primers. What primer are you using?
