A Note for John Kepler - Slower Bullets Hit High

[tenntex32]

...........all things being equal, using open sighted milsurps, with powder charge weights being the only variable, I usually see the slower loads impacting higher than the faster loads. This is when firing at 100 yards for group size comparisons. I see different things going on when I back out to 250yds.(range max) Keep this in mind, if the rifle recoils in the slightest, which I would assume all do, then you are getting some barrel movement. If you are shooting off a front rest the rifle usually has no where to go but rearward and up.

Dale

[Jim Tarleton]

Thanks, TennTex. I guess I am seeing something more clearly for the first time. In my 50+ years of shooting all kinds of firearms, I have obviously seen it before, it just didn't sink in. I repeated my test yesterday, with exactly the same results. It has now sunk into my thick head.

Jim

[Jim Tarleton]

Just to add to the evidentuary list, I was shooting my K-Hornet with 12 grs 4227, 40 gr V-Max, grouping dead on the Bull (2" to 4" groups). I switched to loads with 24 grs 2400, 40 gr V-Max, and the shoots printed on the target above, 7" higher with a velocity of 2750 fps versus the 3080 fps for the faster rounds. One nice change, the slower rounds grouped in a 0.83"group versus the much larger groups for the faster rounds. Looks like I don't need the speed. I will go with the accuracy.

I scanned the target, but the file is too large to post (1.7 mb). I also developed a target that is easy to see in dim light for us old goats. Can't post that either.

A 7" (1.5" to the left) rise in trajectory at 105 yards (I had to move my shooting bench back 5-yards to get in the shade) is just amazing to me. It also looks like my little K-Hornet doesn't like max or near-max rounds. This has been a frustrating rifle in which to find an accurate load. Part of the problem has been my desire to take advantage of that extra capacity. I would have been just as well off leaving it as a Hornet.

I might note that the second most accurate load is my fireforming load of a case full of 4227 behind the 40 gr V-Max (12 grs IMR 4227) - 1 1/2" MOA. They are quick to load - just dip the case in a bowl of 4227 and fill her to the top. That same load in the K-Hornet case shoots like a 410 at 100 yards. Go figure.

I haven't tried Lil'Gun because I can't find any. Anyone got any good K-Hornet loads?

I use this rifle to shoot cottonmouths from a deerstand that sits on Burgaw Creek behind my house. It rips them apart like a handgrenade. It is more fun than deer hunting.

Jim

[Jim Tarleton]

Good Lord! That was 10.5 grs of 2400! Criminy, my fingers don't hit the right keys anymore.

Jim

[rayg]

Good Lord! That was 10.5 grs of 2400! Criminy, my fingers don't hit the right keys anymore.

Jim

I never have that froblem, Ray

[Patrick Chadwick]

Sounds like a case of "bad vibrations". The bullet is exiting the barrel at a time of maximum whip. The whip timing depends on the longitudinal shock waves travelling down the barrel, being reflected back to the chamber, reflected again etc etc. And such a "resonance" load is very sensitive to small changes.

You need a load that avoids the resonance points. If you are in the valley between two resonance peaks, then the POI will only change very slightly with load variations, but if you are around one of the resonance points, then the POI can vary quite sharply. It is difficult to find the best load, but easier to find a couple of bad loads and then pick a value in between. Run a series with varying loads from your fire-forming load up throught your bad load to the specified maximum safe load. The best load is that range where the group position varies least from one load step to another. That may be difficult to tell, but plotting a graph of group size and position against load will show it up. For instance, with my M1917, with 46 or 49 gn of N140 the grouping is about 3 times larger than anything in the range 47-48 gn. Same method ought to work with your Hornet (much smaller loads, of course!)

Patrick

[Jim Tarleton]

Sounds like a case of "bad vibrations". The bullet is exiting the barrel at a time of maximum whip. The whip timing depends on the longitudinal shock waves travelling down the barrel, being reflected back to the chamber, reflected again etc etc. And such a "resonance" load is very sensitive to small changes.

You need a load that avoids the resonance points. If you are in the valley between two resonance peaks, then the POI will only change very slightly with load variations, but if you are around one of the resonance points, then the POI can vary quite sharply. It is difficult to find the best load, but easier to find a couple of bad loads and then pick a value in between. Run a series with varying loads from your fire-forming load up throught your bad load to the specified maximum safe load. The best load is that range where the group position varies least from one load step to another. That may be difficult to tell, but plotting a graph of group size and position against load will show it up. For instance, with my M1917, with 46 or 49 gn of N140 the grouping is about 3 times larger than anything in the range 47-48 gn. Same method ought to work with your Hornet (much smaller loads, of course!)

Patrick

This is what I have been doing lately, with excellent results. I have my groups below 1 MOA now. I discovered this rifle doesn't like loads near 3000 fps.

This is my shooter and my range officer. Misbehave on my range and Sabre will BITE! My grand daughter Ashley is a better shot than I am.

The target is from my WWI USMC A5 sniper rifle. It can still put them in the black. There are actually two groups on the target, and is the result of having to change scope adjustment.

Jim

[303carbine]

I experinced the same thing with my .303, I loaded up some 216 grain Norma and took some factory 180 KKSP for my No1Mk111 and fired a few sighting shots.
The heavier bullets did indeed hit higher on the target..6 inches higher at 60 yds. Both are accurate, I just have to remember where they print on paper when I use the No1Mk111 for hunting.

[Bill H]

The "slow bullets hit higher" effect is true for handguns, but not always true in rifles.

For example, I am experimenting with a Ruger number 1 in .300 h&H, and 200 grain bullets impact several inches lower than 180 grain bullets.

I believe it is safe to say that any individual rifle has it's own personality, and the result is not always predictable.

[Dave Waits]

It has to do with 'Dwell-time' of the bullet in the barrel. Hard to quantify as the differences are in milliseconds. Just as a heavier bullet with the same charge will print higher due to longer time in the barrel(Dwell-time) because of the lower velocity and more inertia two bullets of the same weight loaded to different velocities will print at different vertical points of impact.

Using a Garand as an example, .008 changes point of impact 1-inch at 100 yards(Actually 1.08"). A few milliseconds longer in the barrel can cause a raise of elevation of as much as four or five inches due to the longer stretch of recoil. You're hardly moving the barrel upwards at all to achieve this. Less than 1/2 of an inch.