Home Forums Hunting & Shooting Hunting Rifles Help with trajectory

I have recently had my Remington ADL 7mm Mag rebarreled as the previous barrel was absolutely shot out. After some initial problems, the new barrel is now shooting very well - 3 shot 1 inch group any time I care to shoot the range. This is my working rifle, a go to gun that has to perform on deer etc all year round and 1moa is more than adequate for game. I was down the range today, sighting in some new loads for another rifle and thought I would try the 7mm Mag at 300 yards. Many of us sight in our rifles at 100 yards and then assume that published trajectory tables are sufficient for the long range stuff - not so apparently!
I am loading 70gns of 4831 behind a Sierra 140gn boattail projectile. I assume this load is giving me approx 3000-3100fps, its right up there near max [maybe over] but there have never been any signs of pressure. I usually have the rifle printing 3 1/2" high at 100 for a 300 zero, allowing shots to 400-450 provided the shooter does his part. First 3 shot group at 300 yards was about 7-8 inches low, so I gave the scope 6 clicks up and tried again - 3 shot, 3" group, but still 6" low!
I've got no problems shooting a rifle knowing its printing 6" low at 300, but on checking all the trajectory charts I have at home, 3 1/2" at 100 should be printing dead on at 300 - any ideas as to what may be happening?
Unfortunately I didnt have the time to check it at 400, but I did take the scope back down 6 clicks to return to the original setting. Looks like I may need more time at the range.
As an aside, I ran out of Magnum primers so used Std Rifle primers for a batch of reloads. Both loads grouped 1 moa, exactly the same point of impact at 100. Obviously no need for Mag primers in this rifle.

A chronograph and Federal 215 primers are your friends, also make sure your scope tube isnt in a bind in the rings inhibiting accurate tracking.

Also, RL-22 and IMR-7828 are all things religious 7mm Remington Magnum.

Gunner

Mmmm.......where to start

First,the rule is you don't know(and can't assume) what your load is giving for velocity unless you chronograph it.(This goes as well for the effect of switching from a magnum to a standard primer.Sometimes it will have an effect on velocity and deviation, and sometimes it won't.)

Second,IF your load is in the 3000-3100 range with a 140,and you are zeroed 3.5" high at 100, you should be about POA at 300 yards,maybe slightly low, but not 6, 7, or 8" low;more like 2" app.

Third requires questions, and is a bit tricky to explain. When going from 100 to 300 yards, are you changing anything? ie,are you shooting from the same exact rest and shooting the same way? Is your barrel floated or bedded? Is your scope mounted in medium, high, or low rings?

I have seen your situation before.

Can't go further without knowing your velocity....it is possible that (despite the load),you may not be getting the velocity you think. I've shot many 7 RM loads doing 3150-3250 with a variety of 140 gr bullets,and from a 3" high zero at 100,I am POA to 1" low at 300; 8-10 low at 400,and about 25" low at 500,depending on the bullet.

Those chronograph numbers do make a difference,maybe not in killing stuff, but certainly when you are trying to reconcile published load, velocity,and trajectory figures.As you know, they do not always line up..

I suspect you may not be getting the velocity you think,but I could be wrong....anyway we are guessing without that number.

Gotta edit this...was thinking about it...it has been awhile since I shot a 280 Remington and 140's,and they gave mostly about 3050 with a 140 gr bullet...(which is about what the OP thinks he is getting),and these velocities are really not that fast from a 7 Rem Mag with 140's....from a 3" high zero at 100 yards, bullet drop was about 4" at 300 yards,or 2-4" less drop than what the OP seems to be getting.It could be other things as well, but velocity still needs to be checked.I would look for something in the 3200 fps range with that bullet;then trajectory will be about what the OP thinks it should be.

Even with a chronograph you don't really know..... but you have a better idea.

Trajectory is ultimately the trump card..... it is what it is. If you are running 3k-3100 with a 140..... and you are indeed 3" high at 100..... and 6"-8" low at 300..... you've got yourself a problem with something(s).....

3250-3350 shouldn't be a problem for a 7RM with a 140.... I too believe you're not getting what you think you're getting (somewhere in the 2800fps range would fit your trajectory better). The new barrel will require new loads..... and more/less powder could be required to reach previous velocities.... looks like in this case it's more.

Also, the mag/standard primers will have an effect as well..... I've seen identical loads produce 100+ fps difference switching from reg to mag primers.

The difference you are seeing is not due to velocity or charts being off unless there is something very wrong. It would take a difference of 500 to 600fps to drop you 6-8 inches lower at 300 yards. As Bob pointed out, you have a scope issue, barrel contact issue, or a zero issue.


What type of scope are you using and what is the average group size at 100 and 300 from that rifle and load? Not best groups, but average including all rounds fired, even the "fliers"?

Guessing has never been Bob's mo either.....One thing I'll ad is you may have a parallax problem too. What kind of scope are you running?

Handloading without a chrono is a fool's errand.

I vote parallax or simple rifle mounting difference. I can make the same thing happen if I use the same bag/front rest set up between 100, 200, 300 simply by changing the angle of face and eye to the scope by "scrunching" down into the stock. Took me a little while to realize that simple problem. I really only identified it when shooting at prairie dogs at varying ranges from a bipod. The only variable I could isolate was what I described. Once I adjusted my prone bipod stance to be more consistent, the POI became much more consistent also.

Now when range shooting, I adjust the bags or front rest to ensure a consistent mount of the rifle between the ranges I will shoot. It works for me, but since everybody mounts and looks through their rifles and scopes differently, it may take a different approach for you.

Gee, if handloading without a chronograph is a fool's errand,I wonder how the millions of rounds were loaded, shot accureatly, even for bench rest shooters, prior to the mid 80's or so when chronographs became the more popular.

Since the OP adjusted his scope 6 clicks and if it was 1/4 min adjustment,it should have moved POI 5.5 inches at 300 yards and didn't elevation wise, that should have been a clue then.I assume if he has already shot out 1 barrel in the 7 mag , he should be some what a proficient shooter.

I have two old Weaver V-7's that need tapping on the tube with a woden handle to settle it in. They have been that way for over 40 years, but once zeroe, willhold thier zero and shoot less than 1" at 100 if the rifle is capable of it.

Prior to that a Model 88 Winchester wore an $18 Bushnell that would shoot just as well ,but it did not have self centering reticles back then.

Some guys make all this gack way too hard an do not think about the obviuos problems first. A chronongraph is a nice toy and maybe required for some loading chores,particularly in the top end of max loads, but they certainly are not a "MUST HAVE" when the scope isn't functionly properly.

Checking my Hornady manual, 66.7 gr is max for a 139 gr bullet in a 7mag for IMR4831. Velocity is listed 3200 fps.
An older Lyman list 67.5 gr of 4831 and 3100 fp. An even older Lyman manual lists 73 gr max with a 145 gr bullet at 3261 fps. With 70 gr/ 140 gr bullet the OP is certainly getting more than 3200 fps, unles he has a grossly over sized barrel.

Hi guys, just wrote a big long reply and lost it so will start again.
Bit of history, the rifle was given to me about 20 years ago by a very good friend and gun enthusiast, as a work rifle - I am a fishing and hunting guide here in NZ. The rifle was 2nd hand, but refurbished when I got it. History unknown.
At the time, not knowing as much as I do now, I decided a light projectile going really fast was what I needed, so after some experimentation settled on 70gn's 4831 pushing a 140gn Sierra projectile. This load did every thing I asked of it right up until I wore the barrel out, a case of if it aint broke, dont fix it. It would consistently group 3 shots 1moa.
For clients I would tell them to aim centre mass out to 300, and give 3+ inches beyond 350. For myself I would simply aim it at the animal, crosshairs where I wanted it, gun goes off, animal falls over, end of story. Head shots at 150 were common. It was my go to rifle for nearly everything, I hunted maybe 30 - 40 days per year, it shot literally hundreds of animals, none complained and I certainly didnt cos everything fell over. Because it was my go to rifle, I was extremely confident with it, only had to aim it and it went off and killed what I was aiming at.
When sighting in with clients I would send a shot down range at 100 and if it went the same place as last time I left it alone. Sometimes I would send one down at 300 and if it did the same thing, again I left it alone. Never had to alter it. I have had a 3-10 Weaver Grand Slam on it for most of those 20 odd years and never had a problem.
Until I tried the new barrel at 300!
After missing a couple of animals, I had the barrel checked and it was shot out, so had it rebarreled with a new 24" stainless barrel that matched the old barrel profile. Initially it wouldnt group, so the gunsmith rebedded it and solved the grouping problem. Now I can pick it up and confidently shoot a 3 shot 1 moa group again.
I know I need a chrony to find out exactly what speed it is doing, but realistically after checking several ballistic charts and based on the previous barrels performance, 3000 - 3100 isnt out of the question. I will have access to a chrony in a couple of weeks so will know a bit more then.
The rifle is still the same old wooden stocked rifle, with a Weaver Grand Slam on top, nothing fancy but it works. The only thing thats changed is the barrel. I'm even using the same load I have been using for the past 20 years and it groups - 1moa at both 100 and 300. Its just the trajectory thats got me beat.
When I shot it on the range, bluebird day, very little breeze, prone position off a big heavy bag, butt supported. The target remained in the same place, I moved from 100 to 300, but for all intents an purposes my shooting position was the
same. The only change was that targets I used at 100 were a 11/4" white dot on a black background and at 300 a 21/2" white dot on a 12" red circle background. Next time I will use a white dot on a black background for both.
So, next step is a chrony just to see what speed we are getting, but honestly a few hundred fps shouldnt make that much difference. I will check the mounting screws etc and the action screws, but a 1moa at 300 group does kinda say that all is okay in that area.
Now to open another can of worms, if I need to sort out a new load, I may as well get the maximum out of my 7mm Mag as possible. I need a high BC projectile around 160gn's, going as fast as is necessary for a flat trajectory, but not so fast as to knock the shooter around. I need to kill cleanly at close range, and out to 450 or beyond if necessary - I'm open to suggestions. Doesnt need to be rocket science, doesnt need to be travelling at warp speed, just needs to be simple. After all the last load worked for 20 years without changing, now for another [wiser] 20 years.
Cheers, Al

Did you copy and paste this or make it up on your own. This [bleep] is gettn' good

Just had a look at my ammo cabinet and found some Win 175gn and Hornady factory loads, so will try them out to see the results. At least until I have a chrony.

I don't know if anyone mentioned this, but when using theoretical trajectories, isn't there an assumption of how high the line of sight is above the barrel? Could it be angles would change with various scope heights and screw with the theoretical trajectory?

Yes, a difference between the actual scope height and that used for the calculations can throw off the results. So can altitude and other factors.

Every rifle is a bit different. Find an accurate load for rifle using a bullet that fits the animal hunted. Shoot off a bench rest with bags at targets set at 100, 200, 250, 300, and 350 yards. Its the only why to know what the rifle is doing. The scope then can be adjusted to get the best point blank range for the size of the aminal hunted. For big game rifles I start out with the site set for about 2 1/2 high at 100 yards. Varmint rifles at about 1 1/4 inch high at 100 yards.