Bullets rising at 150??

[jhalcott]

Today I was shooting a 30-06 with 311291 and 311041 bullets. 26 & 28 grain charges of 4759 powder and CCI 200 primers with a 3x9 scope. OFF sand bags I was pretty much zeroed at 100 yards. Groups in the 2 to 4" range and a bit right of center due to the wind. When I moved out to 150 yards, I hit HIGH by several inches. Enough to miss a clay pigeon on the berm!? This was with BOTH powders. I had a friend spotting while I did the shooting. What could cause the bullet to rise another 4-6 inches from a 100 yd zero? Hornady gas checks were used on all bullets Estimated velocity was near 2000 fps,but not chronoed. Wind was switchy, almost straight at me and then crossing left to right.

[handyrandyrc]

Your 100 yard 'zero' is the first zero as the bullet passes above the line of delineation (is that the right term?). You will have another 'zero' as the bullet drops back down through -- probably out at 300+ for that load.

Remember, a bullet fired completely level with the ground will never rise above that point. Most of the time, we have our barrel set to shoot ABOVE level, in comparison to the sights.

[mooman76]

Zero at 100 yard with an .06 the bullet is still rising. I used to zero mine at 25y and it would hit 2" high at 100 and right on at 200 if I remember correctly and then back to 300 it would be a few inches low. This gave me a good medium for a hunting zero.

[303Guy]

I was pretty much zeroed at 100 yards. handyrandyrc , jhalcott is saying the rifle is zeroed at 100 yds. The bullet shouldn't be rising by 150. It should be dropping off from 100 yds onwards. I sounds like the head on wind was actually causing 'lift'. But it would have to be gusting upwards!


Calculated Table
Range Drop Drop Windage Windage Velocity Mach Energy Time Lead Lead
(yd) (in) (MOA) (in) (MOA) (ft/s) (none) (ft•lbs) (s) (in) (MOA)
0 -1.5 *** 0.0 *** 2000.0
10 -0.9 -8.8 0.0 0.0 1974.2
20 -0.4 -2.0 0.0 0.0 1948.6
30 -0.0 -0.1 0.0 0.0 1923.2
40 0.3 0.7 0.0 0.0 1897.9
50 0.5 0.9 0.0 0.0 1872.9
60 0.6 1.0 0.0 0.0 1848.2
70 0.6 0.8 0.0 0.0 1823.6
80 0.5 0.6 0.0 0.0 1799.2
90 0.3 0.3 0.0 0.0 1775.1
100 0.0 0.0 0.0 0.0 1751.2
110 -0.4 -0.4 0.0 0.0 1727.0
120 -1.0 -0.8 0.0 0.0 1704.0
130 -1.6 -1.2 0.0 0.0 1680.8
140 -2.4 -1.6 0.0 0.0 1657.9
150 -3.3 -2.1 0.0 0.0 1635.2
20 Mar 2009 21:43:57, Calculated by JBM[jbmtraj-5.0.cgi]

[JSnover]

handyrandyrc , jhalcott is saying the rifle is zeroed at 100 yds. The bullet shouldn't be rising by 150. It should be dropping off from 100 yds onwards.

Only if the highest point of its flight happened to be at 100 yds. It begins to drop as soon as it leaves the barrel, that's why we have to angle the barrel up a little for the bullets flight path to intersect the line of sight. At 2000 fps, the bullet has not yet reached it's peak at 100 yds.

[303Guy]

Only if the highest point of its flight happened to be at 100 yds.Quite true, but the ballistic calculations show that for a zero of 100yds, that is the highest point.

(It is hard to see in the data presented. Maybe it will be clearer to look at only the 100yd and 110yd figures).


muzzle -1.5in 2000fps
100yds 0.0in 1751fps
110yds -0.4in 1727fps Hope this helps clarify.

Of course, it the scope were mounted higher then the figures would be a bit different. My scopes are 2" high on all my rifles!

[JSnover]

You're not wrong but there are always variables. With iron sights the line of sight is much closer to the bore, so the angle formed between the sights and the bore centerline will be smaller. In that case your figures might be right on. Mount a scope with some nice big lenses and the line of sight can be two inches above the bore, so we'll have to increase that angle in order to zero the same weapon at 100. Look over your figures, you'll find the highest point is actually 60-70 yards but the bullet is only .6" high.

[303Guy]

Yup. We are on the same page. Somehow I don't think we have the answer for [Bjhalcott][B]. I checked the calculations for wind effect but it would take a gale to actually lift a bullet (although I have had it - shooting at 200m with a tail wind into a cliff face down a gouge. The wind had to flow up the cliff face at the end of the gouge. This lifted my 22 hornet bullets! Or at least, reduced the drop). Perhaps we should ask what the group size was at 150yds?

[44man]

The key was said in the first post, "Pretty much on at 100." He may have been a little high and due to the groups size it would be hard to measure. A little high at 100 and the highest point is still down range some.
A high mounted scope adds to it because the barrel is angled up more. I hate those see through rings for that reason and mount a scope as low as I can get it.
Then we have to know if the boolit itself has gone unstable before 150. They could be fliers.
Bullets can not rise once they leave the muzzle, a certain wind might keep drop down from normal but will not blow a bullet UP and it takes a heck of a wind at just the right angle.
A very flat shooting bullet can still be angled up if zeroed at 100 too. The sight in distance is not always the high point of trajectory.
If you zero at 25, it will still be rising above the sight line beyond 25 and will drop through the line of sight downrange again and this can also happen if sighted farther away.
Charts do not tell the tale, only shooting does.

[JSnover]

- shooting at 200m with a tail wind into a cliff face down a gouge. The wind had to flow up the cliff face at the end of the gouge. This lifted my 22 hornet bullets! Or at least, reduced the drop).

Ha! I guess that would do it. 200 meters is where it starts to get interesting. Some people get focused on 100 and don't give a lot of thought to what happens beyond that. Jhalcott just found out there's more range in that '06 than he thought :-D

[montana_charlie]

Your 100 yard 'zero' is the first zero as the bullet passes above the line of delineation (is that the right term?). You will have another 'zero' as the bullet drops back down through -- probably out at 300+ for that load.
Wrong.
With a 30.06-like rifle and a sight height of 1.5" above the bore, zeroed at 100 yards, the first time the bullet passes the line of sight (LOS) is when it is rising. That occurrs at about 25 to 30 yards.
The bullet crosses the LOS again at 100 yards as it falls below the sight picture.

The Mid-Range Trajectory is the high point of the bullet's arc of travel. That high point is somewhere near 70 yards when the rifle is zeroed at 100 yards.

The table posted by 303guy clearly illustrates these figures.
Red shows the bullet crossing the LOS (twice), and blue shows the mid-range trajectory high point.

0 -1.5 *** 0.0 *** 2000.0
10 -0.9 -8.8 0.0 0.0 1974.2
20 -0.4 -2.0 0.0 0.0 1948.6
30 -0.0 -0.1 0.0 0.0 1923.2
40 0.3 0.7 0.0 0.0 1897.9
50 0.5 0.9 0.0 0.0 1872.9
60 0.6 1.0 0.0 0.0 1848.2
70 0.6 0.8 0.0 0.0 1823.6
80 0.5 0.6 0.0 0.0 1799.2
90 0.3 0.3 0.0 0.0 1775.1
100 0.0 0.0 0.0 0.0 1751.2


The key was said in the first post, "Pretty much on at 100."
I fully agree.
A 4" group at 100 yards could mean the rifle is sighted (as much as) 4 inches high. That condition would result in the rifle being (pretty close to) zeroed at 300 yards.

Such a setting would place the high point of the arc of travel out between 150 and 200 yards. A drop table calculated for a 300-yard zero would nail down the exact point.

CM

[44man]

Every bullet, velocity will give different results. Just because a rifle is sighted at 100 does not mean it is the high point in trajectory, it could be before 100 or after 100, plus you are setting scope height at 1-1/2" only. The chart gives an approximation only. I have never seen a single gun in my life that exactly equals a chart.
Reading a chart is like the guy that buys a new rifle, gets the dealer to mount a scope and bore sight it and then the jerk goes hunting without taking any shots.
Same with a loading manual that says a load gives 1900 fps and you only get 1750. Or your rifle is tight and you get 2000.
Shooting the gun at all ranges will tell you and nothing else will.

[kir_kenix]

44man, you are very right about letting the rifle tell the story. I've chrony'd a load, inputed the BC, altitude, pressure guestimates, and had the load shoot 8-9" lower at 600 yards then what the computer said it would. There are just too many variables to rely on "statistics" "computer reading" and "graphs".

Another problem is that bullet manufacturers seem very optimistic about their given BC (I know, bc's are dependent on elevation etc...but "close enough" is usually sufficient to get realistic drops...). Everything Sierra or Lupua seems to be very dead on, but I've found that the A-max (Hornady) bullets don't seem to shoot as flat as they should.

I have also experienced "lift" while prarie dog shooting. I believe that this is actually a combination of mirage and a stout headwind, but it does make it appear as though those 40 grain v-max's are shooting higher at 400 yards then 200.

Anyway, I just wanted to chime and throw my experiences out there too. There are just way to many variables to ever nail down with any certainty what is going on with your given load at a given distance. Doesn't mean I'm going to give up trying tho lol !

[Larry Gibson]

jhalcott

Today I was shooting a 30-06 with 311291 and 311041 bullets. 26 & 28 grain charges of 4759 powder and CCI 200 primers with a 3x9 scope. OFF sand bags I was pretty much zeroed at 100 yards. Groups in the 2 to 4" range and a bit right of center due to the wind. When I moved out to 150 yards, I hit HIGH by several inches. Enough to miss a clay pigeon on the berm!?

I'm betting those 28 gr loads of 4759 were running 2100-2200 fps. I'm also betting your '06 has a 10" twist. If I won those two bets the that load is pushing 155,000 RPM give or take. That load was considerably over the RPM threshold and probably accounts for the 4" groups. On top of that the group dispersion at longer range will be non-linear as your shooting indicates it was. Consider a 311291 zeroed at 100 yards with a scope 1.5" above the bore wil hit about 3" low at 150 yards then two things are happening. First; "pretty much zeroed" may not have been really the zero. Second with the non-linear dispersion of your bullets that they were hitting high may just be because of the group dispersion caused by the higher RPM.

This was with BOTH powders. I had a friend spotting while I did the shooting. What could cause the bullet to rise another 4-6 inches from a 100 yd zero? Hornady gas checks were used on all bullets Estimated velocity was near 2000 fps,but not chronoed. Wind was switchy, almost straight at me and then crossing left to right.[/QUOTE]

Both pwders? You only mention 4759?

I'll suggest backing the 4759 off to 20 gr and work up in 1/2 gr increments until 1850-1900 fps is reached. A 1/2 gr filler of dacron will also improve consistency of ignition. You should reach the target velocity with good accuracy before you hit 23 gr of 4759. That target velocity range should give you a good accurate load that is below the RPM threshold and will have linear dispersion as the range increases. Thus your accuracy and point of impact will be commenserate with what it should be.

Larry Gibson

[303Guy]

A high mounted scope adds to it because the barrel is angled up more. I hate those see through rings for that reason and mount a scope as low as I can get it.
I am the other way round. I like mine high! Helps me with my long neck and it can extend the point blanc range a little. And if sighted correctly, it enhances high or low angle shots ie those taken into trees. Makes for serious longer range down hill shooting error though. Besides, who actually shoots up into trees? Not with heavy cast bullets anyway! (Or any other heavy bullet that could fall on someones head! I wouldn't want a 'light' bullet falling onto my head either.)

[Hipshot]

A rifle is ALWAYS "ON TARGET" twice during it's bullets flight. The first time is when the bullet comes UP to the line of sight and then again when it comes back down to the line of sight. Some determining factors are velocity, how far the sights are above the center of the bore and yes even how tight the rifle is held !

Hip

[rbuck351]

I'm not sure if it could be done with that bullet load combo, but if he managed to get the first cross over point (first zero) at 100 instead of 25/30 like normal it may very well be several inches high at 150. And the higher the scope the easier it would be to do.

[mooman76]

A rifle is ALWAYS "ON TARGET" twice during it's bullets flight. The first time is when the bullet comes UP to the line of sight and then again when it comes back down to the line of sight. Some determining factors are velocity, how far the sights are above the center of the bore and yes even how tight the rifle is held !

Hip

That's not always true. I have a rifle that's not on target even once!:groner:

[snaggdit]

Mooman, I got a few of those too!

[Larry Gibson]

I'm not sure if it could be done with that bullet load combo, but if he managed to get the first cross over point (first zero) at 100 instead of 25/30 like normal it may very well be several inches high at 150. And the higher the scope the easier it would be to do.

Come on guys....these are cast bullets in the 2000-2200+ fps range. Check the ballistic tables. If zeroed at 100 yards the bullet crossed LOS at 30-40 yards and had a MRT of .8-.9" at around 60 yards. If thus zeroed the bullet's trajectory was going down at 150 yards.

Using 311291 at 2200 fps the only way for the bullet to first cross the LOS at 100 yards is if the scope is about 4.5" above the bore. I seriously doubt jhalcott's scope is mounted that high. Even so, it it was and the bullet first crossed the LOS at 100 yards that's the only place it crosses becuase it is then falling and would hit about 1.5" low at 150 yards. The figures are going to be more out of wack if we reduce the velocity. Simply put; jhalcott's rifle was not actually zeroed at 100 yards and/or the group dispersion from exceding the RPM threshold was causing the rounds to hit high at 150 yards.

Larry Gibson

[bobk]

+1 what Larry said. The "first zero", at any range cannot have an ACTUAL drop that exceeds the sight height above bore center.

Bob K

[rbuck351]

What Larry and Bob say is quite true, but the man said it was zeroed at 100 and hitting 6 in high at 150, and the only explanation of that would be with a very high scope mount and first cross over at 100. I didn't set the parameters nor do I believe them to be accurate.

[jhalcott]

WOW!! I didn't want to start a forest fire with that question. I don't mount my scopes any higher than neccessary to clear the front bell. This ones is about 1 1/2" above the bore<Centerline to centerline. The powder was the same but the AMOUNT was different(26 and 28 grains). The groups were hitting just right of the bullseye and 6 shots from each charge and bullet weight were shot at 100 yards.The 26/311041 was the tightest group at 1.658" The 26/311291 went 2.325". The 28/311291 went 2.985" and the 28/311041 went just over 4"! ALL but one of the remaining rounds that were shot at 4 inch clay birds on the 150 yard berm went high. Meaning I aimed at the center of the bird and the bullet hit at LEAST 4 inches higher than that. ONLY ONE hit lower than the bird. As I intended to reload the ammo ,I simply shot it up for practice and fun. What confused me was the first 3 tries all hit high. So I just kept on aiming at the same spot . I could see the dirt plumes as my buddy told me where the bullets were hitting. I generally do NOT hunt with a load until I've shot it at the longest range I will use it. I fully expected the FN's to drop a good bit MORE than the RN's. They did not do this . They all hit in an 8-9" circle above the bird.

[Larry Gibson]

jhalcott

Well something else is afoot then. The fact is, as I originally posted, if zeroed at 100 yards with the scope 1.5" above bore the center of the group at 150 yards would hav been about 3" low. Now consider this; based on you and your buddy seeing the dirt "plume". Most berms are slanted and they have a harder packed bed of dirt under a loose bed of dirt. It is quite possible the bullets were hitting low, penetrating the loose dirt only to errupt behind the clay giving the appearence of the bullets hitting above the clay.

The only way to know for sure is to load the same loads up and double check the zero at 100 yards then put a large paper target up at 150 yards and really see where the bullets are hitting. My bet, based on physics and ballistics, is with the 100 yard zero they will be hitting low.

Larry Gibson

[303Guy]

Hey, Larry has a point! In my days of 44mag shooting, it became apparent that high shots would get higher as one tried to 'correct' the error by shooting lower. Actually, what we were seeing was the ricochet hitting the bank behind the target! Good one, Larry!:drinks:

[BD]

Lets think about this a minute.

Unless I've lost my memory, virtually all of the the common hunting rounds from 6.5x55 up through 300 win mag, that I ever helped sports to sight in, have had the "close zero" in the 20 to 30 yard range, this includes iron sights, scopes and scopes with see through rings. Put them in the center at 25 yards and you're on the paper at 100. When you zero a rifle farther out, say to 300 yards, the "close zero" actually moves in more, and you're printing a fraction high at 25 yards.

The only way I could see getting the "close zero" out to 100 yards would involve something like a .220 swift with a scope hieght above bore around 4". That's not the case, so something else has to be going on.
BD

[bobk]

To hopefully add to the old rule of thumb, sight your iron sight (0.7-0.8" above bore) 2200FPS loads at 20 yards, and your scoped 1.5-.175" above bore, 2800 FPS loads on at 30. Minute of deer, every time. Got to be exact, though, which is actually harder with the scope, due to the close range parallax. And I do wonder if parallax was the cause of the original problem.

Bob K

[Ben]

Whenever I read an article that someone " says " that the bullet is " rising ", I want to always suggest some other phrase.

When a bullet leaves the bore it IMMEDIATELY is affected by gravity and begins to drop, even if the bullet is traveling 7,000 fps.

It is true that in most cases we elevate the axis of the bore so that we can zero our rifles at 100 yards. This causes the bullet to travel in an arc, passing through the line of sight two times.

Through all this however, the bullet is constantly being affected by gravity and is NEVER rising.

Ben

[rbuck351]

Once again, everyone is quite right, what was originally stated can't be happening. So it, as has been suggested,is time for paper at 150. Then you will know what is really happening.

[mpmarty]

An interesting demonstration of this was performed for a bunch of us many years ago.
A series of paper targets were set up at twenty-five yard intervals for two hundred and fifty yards. A surveyors transit was used to draw a line on each target, horizontally at exactly the same elevation. A shot was fired at the line on the twenty-five yard target and "mapped" as it transited each target behind it. This was with a "Ma Duce" in single shot mode. The fifty caliber bullet did exactly as is described here. Penetrated the line at the first target and rose to it's mid range maximum then began dropping. It never exhibited any unusual deviations from the force of gravity.

[jhalcott]

Yes sir , A new batch is being prepared and a 2 foot x 2 foot backer will be set at 100 yards 5 shots will be used and marked. THEN it will be set at 150 yards for 5 more shots will be recorded. MAYbe i'll even go shorter like 25 and 50( not sure yet).
As for seeing the plume , my buddy (John) was using a 20x60 spotting scope . He said he could actually see the bullets hitting the berm. This is not the first time I've shot this gun with cast or jacketed. It IS the first time I noticed this "RISING BULLET" thing.

[bobk]

Be sure to take special precautions to avoid yeast contamination. :mrgreen:

Bob K

[Gohon]

Shooting off sand bags with wind strong enough to blow bullets left or right isn't the most accurate way to know what is going on. Pretty much on at 2-4 inches also says shooter control was not at it's peak. Target zeroed means the bullet was on it's way down and strikes on the second crossing line of sight. As Larry said, physics and ballistics dictate the bullet will never rise again. My best guess is you were actual 3-4 inches high at 100 yards, bullet still rising to 5-6 inches at 150 yards and actual target zero was out at 270-300 yards. there is no other explanation for the bullet to still be rising at 150 yards. Scope height, bullet and load, and target distance are all variables that are consistent and can be taken into account. But a solid rest and consistent shooter control is a must if you want to be sure what is going on.

[44man]

I just dug up an old chart I made years ago by actual shooting. Zeroed at 100 yd's my bullet was 1-5/8" high at 150 and still 1/4" high at 200.
The 100 yd zero and 150 as the high point is the longest place this can happen, never with a farther sight in distance.
If you read all trajectory charts they only show 100 zero and 200 yd drop and what you can't see is what the bullet height is at 150. A flat shooting rifle CAN be higher at 150. However it will only be a small amount and most calibers will show a drop. You need high velocity and a high BC bullet.
4" high at 150 still leads me to believe the center of the 100 yd zero was much higher at 100 or light conditions affected the shooter.
Sighting in at 100 with either the sun high in your face or high behind your head will show a drastic elevation change if shot at 150 or farther in opposite sun conditions, some very high and others very low. The same with the sun to your left or right which will change windage if shot opposite.
This is why shooters can take sighter shots at BPCR shoots because as the sun changes during the day, sight corrections need to be made.
If you do my locked down scope test you will be amazed at how far out of center the cross hairs are as the sun changes position. They will rise and rotate in a circle to come back to center as the sun goes down and the distance out of center is HUGE. You are shooting where the target IS NOT WHERE YOU SEE IT.
A valid test MUST be done under the same conditions. You can not sight in at 100 in the morning and shoot 150 in early afternoon or sight in during the late afternoon and shoot 150 at noon. Time is of the essence! Light and mirage can blow you away! [smilie=b: It can be a WHOLE lot more then 4", from 10" to a foot from where you see the target.
Please guys, do the test, you will learn stuff you don't want to know! :bigsmyl2:

[montana_charlie]

I just dug up an old chart I made years ago by actual shooting. Zeroed at 100 yd's my bullet was 1-5/8" high at 150 and still 1/4" high at 200.
Was that done with an M-16-style rifle with a scope mounted on the carry handle?

You can not sight in at 100 in the morning and shoot 150 in early afternoon or sight in during the late afternoon and shoot 150 at noon. Time is of the essence! Light and mirage can blow you away! It can be a WHOLE lot more then 4", from 10" to a foot from where you see the target.
I check my scope adjustment prior to the start of deer season. I don't pay any attention to the time of day when I do this.
Usually, the rifle will hit exactly where it did the year before, and I don't know where the sun was last year, either.
I make sure the group is two inches high at 100 yards, and I expect my 7mm Rem. Mag. to still be 'on target' at 300 yards.

During the season, I will take a shot at morning, noon, or dusk with no regard for where the sun is...as long as it is not in my eyes. My kills usually happen at ranges between 150 and 200 yards, and they are always one-shot kills that impact exactly where I expect them to. I have never had any problem with the few 300-yard kills I have made.

I think your contention that a 100 yard sight setting can be off by as much as 10 inches at 150 yards...just because the sun is in a different place...is a 'mirage' in itself.

CM

[Gohon]

http://i42.tinypic.com/51rgv9.jpg


Not to argue but how is it even possible?...............I can't see how it is physically possible and I don't believe in magic bullets.

[44man]

Was that done with an M-16-style rifle with a scope mounted on the carry handle?

I check my scope adjustment prior to the start of deer season. I don't pay any attention to the time of day when I do this.
Usually, the rifle will hit exactly where it did the year before, and I don't know where the sun was last year, either.
I make sure the group is two inches high at 100 yards, and I expect my 7mm Rem. Mag. to still be 'on target' at 300 yards.

During the season, I will take a shot at morning, noon, or dusk with no regard for where the sun is...as long as it is not in my eyes. My kills usually happen at ranges between 150 and 200 yards, and they are always one-shot kills that impact exactly where I expect them to. I have never had any problem with the few 300-yard kills I have made.

I think your contention that a 100 yard sight setting can be off by as much as 10 inches at 150 yards...just because the sun is in a different place...is a 'mirage' in itself.

CM
It was shot with a .300 Weatherby with a max load. Actual paper measurements. I would set targets every 50 yd's to 550 yd's and shoot one after the other with the same sight picture for each to measure drop. This rifle was super accurate, holding sub 1/2" groups at 100. All measurements were taken to the center of the groups.
And yes, your POI can be far off if wind is blowing a mirage added in to light changes from sun position. Do not question results until you do a fixed scope test under calm and also windy conditions. You will find there are times you are not shooting anywhere near where the target actually is. The same thing happens with open sights but it is far easier to see with a scope.
Fix a scope on center of a target at 200 yd's at first light. Look through it every 15 minutes all day and record where the cross hairs are. Please do it! You will sit with a gun to watch the scope because you will be sure someone is moving it.
Why is it so hard to understand that POI follows the sun and mirage adds (Or subtracts) to the problem?
If you really want to blow your mind, try it at 500 to 1000 yd's. You will understand why it takes years of training to make a good sniper. Maybe twice as long to make the spotter.

[303Guy]

Do not question results until you do a fixed scope test under calm and also windy conditions. You will find there are times you are not shooting anywhere near where the target actually is.Actually, it is not about disagreeing of disbelieving, it is about; "Say What!":shock:
This is a totally new revelation to me and would explain my apparent crap shooting or inexplicable rifle not shooting 'like it did last week-end'! I still don't understand how all this happens but I shall be re-reading your posts to try get my head around it! I had two occasions to place 'blame' on sunlight - first was shooting an open sighted 357 carbine and getting vertical stringing which I put down to sunlight reflecting off the top of the open sights causing sight hight error the second was the same thing with a 44mag - also sunlight glinting off the flat topped open sights, resulting in a hight error! (Missed the vital spot!)
And yes, your POI can be far off if wind is blowing a mirage added in to light changes from sun position.These are the conditions in which I was shooting crap! Mmmm..... !
Look through it every 15 minutes all day and record where the cross hairs are. Please do it! You will sit with a gun to watch the scope because you will be sure someone is moving it. Well, thinking about it, why shouldn't 'lensing' play a role? Light is bent by gravity, air density, even glass lenses! I already knew about the 'mirage' effect of a hot barrel so why not changing sun angle and changing air temperature and air tempreature distribution? Mmmm.... wind would do it!

[jhalcott]

Larry I'd like to hear more about this RPM thing. Both of my manuals show 4759 going as high as 31 and 31.5 grains in the 30-06. Both the 311041 and 311291 are started at 20 grains and going 1650 or so fps. They max out at 31(291) and 31.5(041) with a velocity of about 2325 fps. Lyman 47th edition used a universal receiver when testing their loads. I am using a Remington 700 classic. It seems you are saying that Lyman's manual is giving bad info to us reloaders. Why would they give us data to reach 2300+ fps IF we can NOT do it? They even list loads with different powders (and bullets) 100 to 200 fps faster.!

[Larry Gibson]

jhalcott

I never said the Lyman manual was giving bad info or that you can't get that velocity. You can. However, if you read the fine print in the Lyman manual you find the "accuracy loads" are based on the most uniform internal ballistics. With rare exception do they shoot for group with their pressure barrels in the Universal receiver. Many, many loads listed do give very fine internal ballistics. It's just that their accuracy leaves a lot to be desired.

You can "search" for RPM threshold and you will find a lot more than you want to read. For regular cast bullets like 311041 or 311291 (most nose bore riders regardless of caliber or cartridge) there is an "RPM threshold" of 120-140,000. This means that given a particular load (based on alloy, design, fit, lube and acceleration among numerous things) somewhere within that threshold the centrifugal force of the RPM will have a greater affect on the defects caused during acceleration by obturation and will overcome the static rotational stability and the bullet will begin to follow an outwardly increasing spiral, i.e. accuracy lessons in a non-linear manner as the range increases.

With a 10” twist barrel the RPM threshold runs from about 1670 fps up through 1950 fps. Once again, depending on the load somewhere in that range is where velocity will start to lesson because of the RPM threshold. Now those are not hard and fast numbers. A "threshold" is not a "limit" as many here continually want to think. The threshold can be lower and it can be higher. To get it higher takes some doing and tweaking of your casting and loading process. I can push 2300 fps with 311291 and have the first five shots stay accurate to about 2-3 moa. If I shoot anymore of that load before cleaning the barrel about round 7 or 8 the groups get larger very quickly (10 shot groups run 4+ moa) and open up in a non-linear fashion as range increases. That velocity is above the RPM threshold for that load with that bullet and the loss of accuracy is very noticeable. Conversely I can load that same 311291 to 1850-1900 fps and it will shoot inside 2 moa all day long without cleaning the barrel. The goups also open linearly at longer range whether I've fired 5 shots or 100 shots. That load with that bullet is under the RPM threshold and the consistent accuracy demonstrates that.

A recent test i ran (at Bass Ackwards request to prove or disprove the RPM threshold theory) was to test 311291 out of a 10" twist barrel at 1912 fps (136,400 RPM) and at 2500+ fps (179,400 RPM) with targets at 50, 100 and 200 yards. Bass's hypothesis was that if the higher velocity/RPM load's (well above the RPM threshold) groups opened in a linear fashion the same as the lower velocity/RPM load's (within the RPM threshold) then the RPM theory was bunk.

I ran the test using the same rifle for both loads. 10 shot groups were used at each range for each load. The barrel was cleaned between each string and 2 foulers were fired prior to the test string.

With the 1912 fps (136,400 RPM) load the groups were;
50 yards; .7"
100 yards; 1.3'
200 yards; 2.5"

You can see here the group increases in a very linear fashion as the range increases with the load that is under it's RPM threshold.

With the 2500+ fps (179,400 RPM) the groups were;
50 yards; 2.55"
100 yards 4.7"
200 yards"14.5"

You can see the obvious non-linear dispersion as the range increases. You can also see that the 100 yard group of this load which is above the RPM threshold is nearly twice as large as the 200 yard group of the load that is within the RPM threshold. Actually the 50 yard group here is larger than the 200 yard group of the previous load that was within the RPM threshold. You can also see why I don't lend much credence to 50 yard groups with such loads and always test this type of load at 100 yards and then confirm at 200 yards. Obviously the RPM theory is not "bunk", it is real and you've seen the results of it not only with my example but with your own loads.

This is a brief explanation. There is a lot more to it. I've gone over it numerous times so you might sift through a "search" of my posts regarding the RPM threshold for more detailed information.

Larry Gibson

[leftiye]

Well guys, flame me if you want. I don't like the Lyman cast boolit manual for anything. As Larry said, they don't even shoot groups when testing. For my tastes, all of their information is usually so conservative as to be useless. With a universal reciever in the proper setup groups would be automatic.

Larry, I think you've hit on something there - perhaps it's the bore rider design??????