100yd vs 500yd groups

[coop2564]

How many of you have had a nice sub MOA 100yds group with a load, but at say 500yds it would not hold the sub MOA grouping under ideal conditions? What did you attribute the inaccuracy too?

And have you had that same bullet hold MOA at 500yds with another powder, primer, etc?

Reason I ask have friend that said he was using xbrand powder got .5moa 5 shot 100yd groups with ES of only 17 avg. yet his 500yds groups in light wind good conditions were 7 inches. Yet he went back to old load (same day/conditions) with another powder that also shot .5 moa at 100 and it held a 4.5" 500yd group yet had almost same ES of 16 avg. (new load 110fps faster) and using same brass, primer, coal. Old load was tuned only for best 100yd group and he started with that same coal with new load got same .5moa group at 100yd so he thought he would be good to go, but he did not try to do any further tuning with new load. Since his ES was virtually same and 100yd groups were same, bullet same he thought down range accuracy should hold too. Thoughts?

 

[LaHunter]

could be the loads, could be the shooter, could be the light wind mentioned. It may be worth while to check at 200, 300, and 400 also. At 500 yards, a 5 mph 90 degree crosswind will push my 7mm mag 160 grain AB about 7.5-8", so it doesn't take much wind to move your POI at that distance. Then add in a little variability of the wind speed and direction, and you can see your horizontal spread open up.

 

[midnightmalloy]

Parallax in the scope and proper shoot execution play a huge role the farther out you go. Also it's best to report "group size" at distance in the height and width of the groups. This makes it easier to diagnose the problems.

 

[gohring3006]

Lots of factors.
Load just isn't quite there.
Parallax in the scope, can play a role, but you mentioned the old load shot very well, so that's out.
One thing to consider, SG and twist rates are looked at for stability, but dynamic stability is often the problem, for instance muzzle exit pressure can upset bullet stability, and it probably won't be noticed at 100 yards, at 500 it will be. This has been observed with certain powders by Doppler, I even read a report where certain types of rifling can affect muzzle release with certain powder/bullets. To shorten this story up, your load sucks for that barrel.

 

[Gunpoor]

One think you don't mention is bullet. Some polymer tipped bullets suffer tip deformation during flight from friction heat, therefore the longer the air time the more deformation which affects accuracy. I tried Hornady SST bullets and thought they would yield better long range accuracy with their higher BC but was disappointed and switched back to the BTSP.

I will say if your friend is using the same bullet in both loads that is surely not the variable he is looking for. I don't know why it won't hold it's accuracy further down range, but I think he should use what has worked in the past. I am a firm believer of the old adage " If it ain't broke don't fix it". But again, that is just me. FWIW

 

[Wedgy]

That is the whole reason we stretch it out before we call a load "good". I've never seen a good 1,000 yard load shoot poorly at lesser yardage but have seen plenty great 100 yard ones fall apart on their way down range.

 

[coop2564]

That is the whole reason we stretch it out before we call a load "good". I've never seen a good 1,000 yard load shoot poorly at lesser yardage but have seen plenty great 100 yard ones fall apart on their way down range.

True. The bullet is a 143gr ELDX 6.5x284 power IMR 4831 old, new is Retumbo. Everything else is the same.