Wowzer! Can .5 grain make that big of a difference?

[CB11WYO]

So I rebarreled my 300 RUM to 7mm RM a bit over a year ago. At that time I worked up loads with Berger 180 VLDs and 66, 67, 68, 69, 70 grains of Retumbo. (whole grain increments, not half grain... that'll be important later... ) 68 seemed to be a clear winner (about 3/4 MOA) but since then it just hasn't shot as tight as I thought a custom rifle ought to.

Fast forward to this last weekend...

I decided to do a simple ladder test, just to see if I could squeeze anything more out of it. I loaded one round each of 67 thru 71.5 grains, in .5 gr increments this time lightbulb, put out a target at 400 yards and went to work.

The results seemed pretty clear! (see pic) 67, 67.5, and 68 (shots 1, 2 & 3) went under 1" at 400 yards... I'd say there's a node there then. I was kinda excited to say the least. So to test it further I loaded up 3 rounds each of 67, 67.5 and 68 and went out to shoot for groups. 67 and 68 weren't anything special (maybe 3/4 MOA) but hey now look at 67.5! (see pic) 3 shots in under 3/4 INCH CTC at 400 yards! That's like .16 MOA!!! Man I'm super excited and really hoping this ain't a fluke... had to go back to work this week but come this weekend I'll be out putting the 67.5 gr load through her paces at longer distances just to be sure! Looking like .5 grain might make some difference after all. It took a so-so hunting rifle and turned her into the best shooter in my safe pretty much .

 

[newmexkid]

Hope it continues to work out for you. Isn't it nice when things fall into place?!

 

[Corey Schwanz]

Its amazing what one little thing can do to a group size. With all the variables we have to deal with, its a wonder we ever get good groups, haha.

Looking great from here!!!

 

[Bginvestor]

well, if you shoot at least 40 more rounds, you'll have a good statistical value to stamp on the gun... good luck

 

[bikehe]

Its great when we see tight groups like that. I just spent quite alot on a custom action and did ladder testing and round robbin. I thought best I would get was 3/4" at 100 and the group size was shooter error. Then I changed seating depth by only .002"and man did that change things completey. My groups went to 1/2" at 200 yards. At first I thought it was a fluke but have now consistently repeated the same result for around 50 shots. Best thing now is when I do have the odd flyer I know it was me that sent it in the wrong direction before even looking at the target. Ive very quickly learnt to record and measure everything to the finest detail.

 

[flashhole]

Outstanding, can you share some details on your gun?

 

[CB11WYO]

Outstanding, can you share some details on your gun?

Well sure...

Trued Rem 700 action, 28" barrel, Shrewd brake, HS Precision stock, Leupold VX-III LR 8.5-25x Running the 180 Berger Target VLDs at about 2900 fps.