grouping question

[truckie]

I am reloading for a 280 rem. I am using 46.3 gr of IMR 4350. and a 154 gr bullet. Groups are good but, why am I two inches low at 50 yds. and three inches high at 100 yds. I do not have a chronograph so fps is unknown. I do not understand the five inch difference between 50 and 100 yds   Help!

[Grumulkin]

Five inches does seem like a BIG difference.  I don't have a reloading manual handy so I can't check what velocity you should be getting.  In my opinion, lowish velocity and/or a high mounted scope could explain your results.

[Lone Star]

Measuring group center is only accurate if the groups are relatively small.  Five-shot groups are far better than 3-shot groups in finding the true group center.  You may find that the actual trajectory difference is a lot less than 5 inches in just 50 yards.  What size groups are you getting at 100 yards?  How many shots in the groups?



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[jhalcott]

 truckie, i am curious about this load. MY books show a load slightly heavier as a starting load. You MAY be getting a reduced velocity from 46.3 grains of 4350 powder. As low as 2350 fps. Since you do not have a chronograph this is ONLY a guess. Do you have a loading manual that gives this load? You do not state the cartridge overall length, OR the firearm used. If it is a Handi rifle I'd stop using this load till I could verify it from PUBLISHED information. I have a bolt action 280 and really enjoy it. It is very accurate with loads it likes. Deer groundhog and other critters have met their end from it. 
  Hornady 4th edition ,Page 279 shows a start load of 46.8 grains of imr 4350 as giving 2500 fps ansd a MAX load of 54.7 grains as giving 2900 fps.
  the col of the RN is 3.243" and the SP as 3.345"  the gun used is a Remington 700
  the 2350 fps info was from another source.!!