What happened to my dope?

[kingzero]

So I had some cases I needed emptied so I took a buddy out to to shoot steel and water jugs at 500 yards. He has never tried to honestly hit anything past 100 so I figured he would have a good time. We get set up at a new spot and range the target at 487. Shooter told me 7.6 minutes so I dialed 7.5 and for a 6mph quartering wind. First shot hit about 1" low of center on a 10"x10" plate.....perfect. I send another round and hit the plate right on the lower edge......ok I yanked it. Third and fourth shots were just under the plate.....***! I dial up 1 minute and am back in the middle of the plate. It stayed there and we continued to shoot and bust steel and water bottles.

This is a proven load and have shot it to 775 yards. The rifle recently made a trip to Northern NM and was subject to sub zero temps. I never had a chance to shoot it up there so im not sure of how it would have performed. I did a velocity calibration and it showed a loss of 140 fps. I am not too concerned right now because I don't plan on shooting these loads again. I needed to empty some cases for new load developmet. I just dont understand what happened. I double checked all the data in Shooter and checked the atmospheric inputs that Shooter input against my Kestrel (station pressure) and everything was good.

Ideas????????

The load was

260 Remington
42.5gr H4350
120gr TTSX
2900 fps.

 

[MMERSS]

I noticed you didn't mention if you conducted another zero after your stated difficulties. This may be a good place to start if not already conducted.

 

[kingzero]

I noticed you didn't mention if you conducted another zero after your stated difficulties. This may be a good place to start if not already conducted.

I did not attempt to check or rezero the rifle as these were the last of the loads and zero will change with the new ones.

 

[cabelas90]

is it posable that you got a few tenths of a grain off in lodeing causeing the drop in fps?

 

[kingzero]

is it posable that you got a few tenths of a grain off in lodeing causeing the drop in fps?

Nope, I trickled each round and half were from the original batch and the other half were loaded right before I went to NM. They all shot the same asside from the first 2 shots.

 

[MMERSS]

Conduct a new zero with new reloaded ammo and see what happens. A good "confirmed" zero is a sound first step with establishing your parameters before conducting long range shooting and with troubleshooting problems along the way.

 

[kingzero]

Conduct a new zero with new reloaded ammo and see what happens. A good "confirmed" zero is a sound first step with establishing your parameters before conducting long range shooting and with troubleshooting problems along the way.

Thats the plan. I just dont know why the first round hit its mark and the next 2 dropped so much and then settled in. I will have to shoot more and see what happens.

 

[BCMAG2]

Is the powder you are using temperature instable....could the subzero temps in NM have altered its chemistry?

 

[BrentM]

I was thinking temp sensitive powder issue but your first round was ok etc.

Have you checked the head space of the brass? I was neck sizing only for a while but all of sudden my DOPE was off and I was getting pressure signs. I found my brass HS needed to be set back and once I did that all was good again.

 

[kingzero]

Powder is H4350 so it should be pretty temp stable.



I was neck sizing only and that trip was the 4th firing on the brass. They were getting a little sticky so I planned on FL sizing them before new load development.

 

[Canadian Bushman]

When is the last time you cleaned the barrel?

 

[kingzero]

I had cleaned the barrel at the end of October and it had 25 rounds through it between then and the shooting session yesterday. All 25 were spot on from 300 to 775.

 

[BrentM]

Powder is H4350 so it should be pretty temp stable.



I was neck sizing only and that trip was the 4th firing on the brass. They were getting a little sticky so I planned on FL sizing them before new load development.

OK, I am willing to bet this is your issue. The HS is gone and needs to be set back. I had this same problem. I body size and neck size separately and it working out fanastically for me now. My body die sets the shoulder back exactly .002 from my tighter fitting brass.

 

[Canadian Bushman]

I was kinda thinking copper fouling but that doesnt fit.