Do you weigh your charges.  (Likely you do.) If not you might have an occasional light load thrown by the powder measure.

Hi S.S. 
         Do you have any of those loaded rounds (fixed) left in your cartridge box from the shoot ?

   If so, I would recommend that you set up your chronograph and record the M.V.'s and calculate the standard deviations.  If you are finding that the inconsistencies persist throughout the entire batch of remaining rounds left over from the match, you might want to back track the loads by disassembling them and weighting the power charges and comparing the actual weight against each other.

If you find no fault with the powder weights, then look at the primers as the source of the problem.  I have used primers that have absorbed moisture from being improperly stored at home and as a result have given me a similar problem.

One other inquiry, have you ever enlarged the flash holes in your cases w/ a drill ?  Some folks do that and upon cleaning and re-use the cases they become co-mingled, that is, the factory size flash hole diameter cases get mixed in with those which have the larger diameter holes.

Good luck in identifying the problem area/s. 

C.M.M.

It resembles an ignition problem, try to eliminate that varible first in your process of elimination.

  S.S. Shooter:

   Would I be correct to assume that you shot this past weekend at Shippensburg ?  Or was it at the Fairfax Club ?  Besides the difficulties you've described, how did you do otherwise ?  Mark it up to EXPERIENCE and give it a try next time out after you've gotten to the bottom of your variations.

Good luck
C.M.M.
.

Did shoot at Shippensburg (cool and breezy). BP only. Rem LR primers. Shoot Rem cases at 200/300m and Starline at 385/500m.

6.3 PRIMER TESTS
C. Dell

"I have been told many times down through the years that if a gun has a light hammer fall the groups fired with that gun will string up and down. I had always assumed that this was true as the persons reporting this effect were very respected men who had done a lot of really serious shooting.
Back before the primer shortage developed I had made a test rig to test primers all by themselves (a stand alone test of primers). Basically I was able to hit primers with a very repeatable force and was determining how much force it took to reliably fire them as well as the velocity that they would impart to a specially made pellet. Results were determined by measuring the velocity of the pellets about fifteen feet from the muzzle of the test rig.
This testing was discontinued when the supply of the desired primers for testing dried up.
These tests have not at this time been resumed. Two observations were, however, made from the data collected at that time. One: the observed average velocities were not affected by how hard the primer was hit. Second: about one primer in five regardless of make or grade was to a noticeable amount deviant from the group average. This took the form of either being significantly higher OR lower in velocity than the average.
These properties were discussed with various shooters during the time that supplies of the various primers were not available. I was often asked if the same results would be observed if I were actually shooting cartridges loaded with powder and bullet. There was at that time no practical way that I could test this idea. As a result the question was left hanging with no real answer.
Recently a method was conceived that would readily permit study of this as well as other questions. I had a spare Douglas 32-40 barrel blank with a 1-12 inch twist that could be devoted to a test program. A breech system was devised that would permit various firing pin impacts on the primer to be studied. It is not a fast sy

joeb33050 - thanks for Dell's report. Do wish his testing had been a bit more exhaustive and covered both larger cases and BP, but backs the thinking that if the primer goes off at all it is complete.