ES% and big bores

[shorty]

What Kind of ES% do you guys like to see with .357 cal for accuracy out to 50 yards? Would it be the same as smaller calibers ?

I am starting to notice that the ES% is more critical for accuracy when throwing an 35 cal vs 22 cal unless it's just in my head.

I know I am throwing them slow but this is what I was doing to not be an air hog.

3000psi
600 fps up to 635 and back to 600 fps for 17 shots for a nice 70 fpe backyard target shooting tune.
Ending 2500psi

I see a full 1.5" vertical string with 5.5% ES. With the 22 running 21.14 barracudas at a 5.5 ES% I see less than a half inch at 50 yards.

What's going on here ? For some reason I can't wrap this around my head. I know it's a heavier projectile but gravity is gravity.

[rsterne]

The difference is likely barrel harmonics.... Few guys tune big bores for a long shot string, the most common tune for a hunting rifle is 2 shots at full power, or 3 in as shallow a curve as you can get.... and then the rest declining.... For target work, you would tune the same as any other PCP, with a 3-4% ES being good to about 50 yards....

Bob

[Tofazfou]

IMO, looking at your numbers of 600-635-600, i can see why your get 1.5" of vertical string.  600 fps to 635 is a lot if you just look at those two numbers.

Case in point, i recently shoot my guns reg'd.  I shot various 5 shot groups.  each group had a different speed.  such as 775 fps on average for one group of 5 shots.  the next group might have had a speed of 805 or even 815 fps.  The groups at just these two speeds were totally different in referrence to where the shots HIT while i was aiming at the same CENTER MASS.  So if i started with the 1st group which has a speed of 775 and after the 1st shot, i increased the speed to 800+ fps for the 2nd shot, the 2 shots would have hit far apart.  Lets just say, 1.5" apart.  If the 3rd shot speed then drops back down to 795 fps on the 3rd shot then i would expect it to also hit somewhere different than either of the 1st 2 hits.  Making for a bigger group.  This can happen LEFT to RIGHT or UP to DOWN or 45 degrees in between N,E,S,W.  IMO, your bell curve starts and peeks and ends too drastically (600-635-600 over 17 shots).  Every big bore i owned, if if 2 shots varied by more than like 10 fps, the shots impacted different areas on the target.

You can also WEIGH and SORT your ammo for better consistency (read Accuracy) to.

[shorty]

So the typical less than 3% ES then at 50 yards- same as any other caliber. Can't measure barrel harmonics ( not measurable ) so I guess that's out.

I guess it's safe to say "hunting" big bore at 2 or 3 shots (under 2% ES) would be general bigger game - larger than raccoon.
and
Less than or equal to raccoon at 50 yards with high shot count as long as the shot string is 3%ES or less due to the vertical stringing.


This kind of makes sense on how Hatsan and RAW did the .357 cal with the shot strings I am seeing lately.

[Bill G]

Another way to look at this would be with regard to the Kill zone.  How big is the kill zone of your prey?  This is sometimes called the point blank method.  Lets say that you are engaging a kill zone that is 3" in diameter.  What you want is all of your shots to hit that kill zone.  Chairgun will help you visualize this, so I recommend that you reference it if you have it.  You will want to choose a trajectory that crosses the line of sight twice.  Onece when it climbs trough and the other when it falls back through the line of sight.  This chosen trajectory should apex at 1/2 the kill zone diameter above line of sight/ POA.  So a 3" KZ would have a hit below POA at ranges closer than the near zero.  At ranges between near and far zero, the POI will be above the POA and beyond the far zero, below POA.  Now.... that was rubric for all intents and purposes.  What you have to do now is get that to match the normal vertical dispersion due to velocity deviation.  When said and done,  you'll end up with an established effective range*  Effective range is when your probability of a hit in the KZ is extremely high(IMO).   If I were to give advise, I'd say narrow that spread and make it easier on yourself.  Increase the fpe and tighten up the ES and ultimately I think you'll end up with a rifle that you are more confident in.  Once your confident in the equipment and know exactly what it does every time, Then it all about the shooter.  Become confident with yourself and you are officially all Zen'd up and shoot like Cedric.

IMO, the point blank method really helps establish a solid sense of confidence in the equipment.  We have all bought and sold AG's because, we didn't like them and weren't confident that they were shooting right and they may not have.  Looking back on it though, I have had some that I probably didn't give a chance. Remember, ES is tied to FPS, FPE, shot count ect... AG's are nothing but compromise and that is why we should have more than one.

Now if we could get our wives to understand this compromise thing, we'd be able to have more AG's.   hmmmm?

Bill   

[rsterne]

Excellent point, Bill.... A lot of the time, in practical situations, the ES is completely lost in the noise, and trajectory is the thing to worry about.... There are two situations where the ES is critical....

1. Where you are shooting for groups at a known, consistent range....
2. Where you are push PAST the far zero of your rifle, already fighting trajectory, and then the ES becomes an added complication....

Bob

[KnifeMaker]

please disregard.