I've built a 280 AI on a VZ-24 action, and have noticed an interesting phenomenom. The standard 280 Remongton rounds I am fireforming to 280AI are making tighter groups than the subsequently reloaded 280AI rounds.

I used a 175 grain Sierra SP in both loads and seated the bullets to the same length. Even used 61.0 grains of H870 in both and got the same results. Some of the standard 280 groups were amazing: one was 0.24" and two less than 0.6" for three shots. The rel;oaded 280AI would do 0.75" at best.

I can imagine that the "crush" chanbering of the 280 Remington might be a reason. It is definitely harder to close the bolt on them.

My question then has anyone else seen this, and deos anyone have a better theory as to why it is happening?

Fireforming loads are often very accurate. I have shot some very small groups when forming brass for a 6PPC. I believe that when altering the shoulder, from say 28 degrees to 40 degrees, the pressure curve is flattened resulting in a change in barrel harmonics.
I believe that, once you've formed your brass, you will be able to get those small groups again by doing a ladder test.

Eddie nailed it!

quote:

Eddie nailed it

I have numerous AI and full shoulder forward blown out wildcats. I've had numerous that would group very well while forming. I don't recall any grouping as well with the exact same load after forming. On the few I tested before and after forming the same load gave lower velocioty after forming. Simply work up a new load.

Strange things happen. I was working up a 25-06 plains game load with 85gr Barnes X flatbased bullets. I planned on taking loads in once fired cases, thinking they would give greater accuracy than brand new factory bulk cases. Wrong! I ended up using new cases that only had the necks chamfered. Don't ask me why these proved to be the most accurate. But they downed 6 springboks at ~300 yards each.

When you resize the brass, try moving the shoulder just enough to get the brass for fit the chamber with .001" of headspace, so the firing pin can push the case forward.

Try seating the bullet long so that it jams into the lands, but not so far that the cartridge cannot be pulled out with the bullet stuck behind in the lands.

Try not using an expander ball.
De cap the case some other way. Cases bent with an expander ball can be straightened with another firing.

Try chamfering the inside of the case mouth so the bullet does not get scratched or pushed off center.

Seat the bullet half way, give the case a half turn, and finish seating the bullet.

Make sure there is no Copper fouling in the bore.

Make sure the scope mounts are tight to the receiver.
Make sure the rings are tight to the scope mounts.
Make sure the rings are tight on the scope.
Make sure the stock is tight to the action.

Practice dry firing and make sure the cross hairs stay on the bullseye. Squeeze the trigger with thumb on top of pistol grip. Do not pull the trigger against the shoulder.

Return the rifle to the same position in the rest for each shot.

Hold the rifle the same way for each shot.

Let the barrel cool between shots. Be consistent in times between shots. Feel the barrel to check that it is not too hot to hang onto. Do not leave a live round in a hot chamber for a minute.

If the target looks blurry, adjust the objective. If still blurry, reduce the magnification power of open exit pupil. As the afternoon wears on, it can get darker and your pupil gets larger, so the scope has less usable power.

Make sure there is no wind. If the wind is 3 mph, shoot at 50 yards instead.

Be satisfied with .75".

My VZ24 257 Roberts Ackley improved will shot sub .5 moa with 72 and 75 gr bullets, but averages .75" with 100 gr bullets.

When you get home from the range, measure all group sizes, and type up a report. Staple the targets to the write up and file it.

Next time you are about to reload for that rifle and or cartridge, read the last write up first.

Begin each reloading session with an objective and a plan based on needs and the experience of the write ups. In the write ups, discuss if your goals were met.

If someone at the range goes into a long bs session, use your plan and goals as the excuse to get away from him and back on task.