243 winchester oddity

[eric 270 wsm]

I have a strange problem reguarding a 100 gr sierra game king and 95 grain sst hornady both when shoot out of my sons remington 770 has a 1/2 point of impact differance, but out of my 700 the 100 gr has a 4 inch lower point of impact still with a 3/4 inch group for both bullets. this is at 100 yards. what gives

 

[DrMike]

You are likely witnessing differing tolerances on the barrels. Hence, you have differing pressures generated with the same amount of powder burned and thus, differing velocities. Consequently, this causes the differences int he POI you observe. Have you chronographed these loads from the two rifles?

 

[JD338]

Every barrel is different.

JD338

 

[6mm Remington]

Dr. Mike and JD338 are both correct in their response. In your son's Model 770 you are very fortunate to have two very different bullets of different weights to almost the same point of impact, and grouping about the same! How your Model 700 responded to the two bullets would be what I would consider as more typical of the everyday factory rifle that most of us shoot.

Even with two identical Model 770's in the same .243 Winchester chambering and shooting the exact same loads as you currently are would very likely show the same result as what happened with your Model 770 and the 700 when they were compared. The different bore dimensions and smoothness, how the action and barrel mate up to the stock, and the harmonics are all going to be different if even only slightly. This will make a difference.

I'll give you an example of how even really small changes, let alone having two completely different rifles, can make a difference. One of the most accurate rifles that I own is a Ruger #1B single-shot in 30-06. It's favorite load is the 165 gr. AccuBond with Winchester cases, 57.4 grs. of IMR4350, and Federal 210 primers. I can shoot 1/2 inch to about 3/4 inch groups at 100 yards every time with this rifle if I do my part.

If I only change primers in this equation, and I have, and use CCI large rifle primers with everything else being the same, I will have two different groups at 100 yards. The Ruger will shoot them in the same group of about 1/2-3/4 of an inch, but the two groups will be about 3/4 of an inch away from each other at 100 yards. I will have one 3 shot group with the Federal primers that is right where my rifle is sighted in. The CCI load will be about 3/4 of an inch away in it's own little group. My experience has shown that for the two groups to be the same size roughly and to only shoot 3/4 of an inch away from the other load is actually more of an oddity than the norm. I think this rifle is able to do this because the bedding is stable and was done correctly and the barrel on this particular factory rifle is a very good one.

Just my 2 cents worth.

 

[eric 270 wsm]

this i understand what is strange is the 4 inchs just looks like a lot.

 

[JD338]

Barrel harmonics. The vibration is different. Changing the barrel length and or weight will have an effect on accuracy and point of impact. The very reason why target shooters will use a bull barrel.

JD338

 

[Antelope_Sniper]

this i understand what is strange is the 4 inchs just looks like a lot.

This is not unusual at all, especially when change bullet designs. The Hornady is a true spitzer, where the Sierra uses a curved ogive.

I've seen the point of impact move 12" just by changing primers, let alone bullets.