Range Report Need advise.

[serzant]

I am new to the LD shooting.
Here is the my amberassing range card from the last F-T/R match at Quantico (11/08/2009). I was especially disappointed about the last 3 shots in the 1000 yard relay (group 3), it seamed as the bullets just dropped: all 3 shots landed at exactly 6 o'clock, but went lower and lower. What could cause it?
Here are some things that i already checked:
-Parallax was out of wack by 1 moa,
-scope, action, or bipod were not loose.
I circled couple of good groups at 800 and 900 yards just to show that the factory Black Hills load was NOT a main issue IMHO(10 ring is 10" and x-ring is 5").
I would really appreciate your advise based on practical experience.
Thanks in advance.

 

[Sig685]

Re: Need advise.

Tell us about the conditions, what is windy? If so, where was the wind coming from, was it coming from behind you or in front of you?

Also, tell us about the barrel of the rifle, and actually about the rifle itself. What contour is the barrel?

 

[serzant]

Re: Need advise.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sig685</div><div class="ubbcode-body">Tell us about the conditions, what is windy? If so, where was the wind coming from, was it coming from behind you or in front of you?

Also, tell us about the barrel of the rifle, and actually about the rifle itself. What contour is the barrel? </div></div>

The wind was mild, sunny day about 70 F. Range 4 at Qtco is bisected by birms every 100 yards and sometimes wind bounces off, which I don't have enough experience/ability to see.
The rifle is Remi 700P .308 26" heavy barrel (government profile?) which was fire lapped with Tabbs bullets.
I had an FTF immediately prior to the drop, but the same round fired later. I noticed some clime as the barrel got hotter and compensated by holding off lower. However, as the drop occured, the last round fired was held off high to 8 ring at 12 o'clock and still plopped in front of the target. I am loosing my mind thinking of the cause.

 

[ChadTRG42]

Re: Need advise.

I'd look at the ammo. What's the ES and SD on this ammo out of your rifle? It could be the velocity running lower which caused the low impact. As some rifles get dirty and hot, different things might be happening with the velocities. Have you chrono'd the ammo with a hot dirty barrel vs cool?

 

[Sig685]

Re: Need advise.

We are talking about a rather large drop going in one direction at the end of a 22 round string. I'm thinking the barrel or the receiver was heating up and starting to droop. I think it's also very wise to consider a problem with the ammo, or the combination of this ammo and the this rifle.

To go from an X to a 9 then 7 then 5 then clean miss low, we are talking several MOAs drop within a few shots.

What I would suggest is to set the rifle at 100 or 200 yards, with a powerful scope and then take 30 rounds. Warm up the rifle with 5 rounds. Let it sit for 20 minutes, then shoot 25 rounds at the rate of 1 every 30-45 seconds aiming at the same dot on the target. If the 25 round stay together, then you had an ammo problem but if it starts to go down by the drops you listed, you have a rifle problem.

At least, this is what I would do.

 

[Jerry m]

Re: Need advise.

+1 on Sigs advise. See where it is shooting at 100 or 200.

How many rounds down the tube? Could you have blown a chunk of rifling?

A change in the light, like a cloud shading your target will make you shoot different, but not miss.

Good luck

Jerry

 

[serzant]

Re: Need advise.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jerry M</div><div class="ubbcode-body">+1 on Sigs advise. See where it is shooting at 100 or 200.

How many rounds down the tube? Could you have blown a chunk of rifling?

A change in the light, like a cloud shading your target will make you shoot different, but not miss.

Good luck

Jerry </div></div>

Jerry, the rifle is 8 weeks old, I bought it brand new and had 200-220 round down the pipe including 50 Tabbs lapping rds. I will definately try Sigs suggestion. I went cheap on the rail and have EWG alluminum... Perhaps as the chamber heats up it causes the front end of the rail to expand and lift the front of my scope, which would lower the POI. I will follow the routine Sig suggested and see if I can replicate the problem. I did not clean the barrel since the match, thinking that I will do it at the range to see if it could be carbon buildup that caused the issue. So the plan is: 5 rds, then cleanup, then 5 more, then 20 minutes cool down, then 25 shots in 30 second increments. Thankfully, I'm off on Friday, Anything else I should do or check before the range?

 

[ChadTRG42]

Re: Need advise.

Actually, I wouldn't clean it at all. Sometimes cleaning it can cause issues. Also, most rifles take about 150-200 rounds for the barrel to really come in.

 

[Greg Langelius *]

Re: Need advise.

Climb/drop can usually be associated with barrel heating, but its consequences can be counterintuitive. Rather that trying to bust my skull figuring out the problem in the middle of a match string of fire; I try to approach it from the directions of what I can/can't do about it.

First, I slow down my firing cadence, to allow heat levels to equalize between the inner core and outer surface of the barrel.

This equalization is the best strategy you can employ to cope with the interactions of heat differences and internal stresses, and their effects on POI drift.

Next, I pay heed to the fact that a cold cartridge contains less heat energy than a hot one, and that any added heat energy produces a hotter volume of gas and increased pressure. While this contributes to vertical dispersions, it is no slamdunk that this means a higher impact. More to it than that. No need to compute the effect, it's enough to simply know that vertical POI displacements occur.

The way we cope with this is to reduce the cartridge's cooking time in a hot chamber. My technique is to advance the bolt so the cartridge is half in/half out of the chamber, providing minimal contact area that can conduct heat. I then go through all the steps of assembling/preparing the shot until I'm ready to actually fire. From then, it's time to step up the tempo. I close bolt, settle crosshairs, and dispatch the round. If it can get 'er done in under 15 seconds, I extract the round, set it aside to cool, and start over with a cool round.

Finally, I engage in barrel heat management. I test my loads in a barrel that's up to match temp. I start my match string with several heater rounds, then get down to the business of getting the sighters into the desired POI. Once they're there, I check the barrel temp with my hand, fire two more sighters, and immediately fire my first scoring round. From that point on, no scope adjustments are made. It takes some faith, but flyers occur; and changing the zero (or 'chasing the spotter') will nearly always lead to frustration and unnecessarily dropped points.

If a trend develops, I shift my POA to compensate.

My best guess, POI shifts have at least half their origin in environmentals shifts. Unlike barrel stresses, they will shift back and forth randomly, while barrel stresses will follow a repeatable pattern. If you ever intend to be able to sort these out, you need to learn the latter, and get them down pat.

Greg

 

[Rapidrob]

Re: Need advise.

After seeing your target,go ahead and do the test Greg and others have mentioned. But from my experience on the range,your score really indicate you got hit by wind. This is where your spotter really needs to dope the wind (mirage ) and note the range flags.
Your earlier score dont point to bad ammo or rifle problems.
My club shoots out to 600 meters every Sunday,rain or shine. While not 1,000 yards,we do see some very interesting bullet flights as conditions change,even on a dead calm day.
Were you shooting with any High Masters? What did they notice that day? My two cents.