Newbie trajectory validation

[adamg1986]

Hey guys, been on this site for a while now but had a few questions so I thought id join up and get some expert answers. Ive been a hunter all my life and have always liked a challenge so for the last couple years ive been trying to get into long range shooting. My first attempt at a long range gun was a ruger m77 mkII boat paddle stock 270. After many bullet and powder combos later. I gave up on it. I could never get it to group less than 1.75 moa with my best loads. So I moved on to better things. I bought a Browning A-bolt 7mm rem mag a couple months ago, bedded the action, free floated the barrel, put a 6-18 leupold on her and have slowly been acquiring stuff to reload for it. Finally got everything I need and have been working up loads for it and let me tell you this thing is a dream to load for. Most loads are sub moa. My best group so far is a .181 3 shot. That is the load that I thought id use to stretch her legs with. I don't have a chronograph yet so I am cross referencing my load book with others online to estimate my velocity. This morning I set up a milk jug at 550 yards, dialed in 7.5 minutes, which I thought would be really close fired 2 shots, still no water bomb. Headed down range to see what was going on and to my amazement, I was around 9 inches low. So I go back and dial up to 9 moa, fire off and water goes everywhere, dead center. Ive been playing with the numbers to see what is going on and it seems like my velocity is way below what it should be. My scope height is around 1.75. My 100 yard group was 2.185 inches high. And I thought my velocity would be around 2950. The load Im using is 66gr of H4831sc under a 168gr berger vld. I think I have a 26 inch barrel as its over 26 inches from bolt face to muzzle. Anyhow I just thought id check with you guys to see what you thought. Thanks for your time.

 

[Shortmagman]

According to my Sierra Infinity ballistic program, a 7mm 168 grain Berger VLD with a velocity of 2800 ft/sec needs to be 8.85 inches high at 100 to be dead on at 550 yards. So you are probably not getting the 2950 ft/sec velocity that you think. Your 9 moa is about perfect for just over 2800 ft/sec.. I also checked with the Hogdon web site and they show that 65 grains of H4831 under a 170 grains bullet produces just over 2800 ft/sec.. I don't know the barrel length but I think again that you are in the 2800 ft/sec neighbor hood.

 

[yobuck]

going from memory which is dangerous for me, we were about 8 minits from
a 100 yd zero to 500 yds with a 162 hornady in the 7 mag with same load as you. but whatever it is it is so if your happy with the load thats it. try a few
more distances and write down the data by way of minits it took. then go to
jbm or one of the others for your chart. tweeking velocity numbers to match
actual shooting results is common even with a chronagraph.

 

[adamg1986]

Thanks for the reply guys. After searching the net for more load data I'm realizing that I'm not to far off from where I'm supposed to be. I'm tickled with the accuracy of my load but a little disappointed in my velocity but it doesn't really matter I guess. As long as I can hit what I'm aiming at. What do you guys think of retumbo? I'm out of h4831 and if I was to switch powders, now would be a good time. I like the fact that h4831 is not temp sensitive so I may stick with it. How's retumbo with temperature changes?

 

[Shortmagman]

I think that Retumbo would be a great choice. According to Hodgdon, Retumbo works great with the heavier bullet in a 7mm Rem Mag.. It is also not temperature sensitive so you are not giving up anything but according to the data you should be able to gain some velocity using Retumbo over H4831.

 

[cohunter14]

Thanks for the reply guys. After searching the net for more load data I'm realizing that I'm not to far off from where I'm supposed to be. I'm tickled with the accuracy of my load but a little disappointed in my velocity but it doesn't really matter I guess. As long as I can hit what I'm aiming at. What do you guys think of retumbo? I'm out of h4831 and if I was to switch powders, now would be a good time. I like the fact that h4831 is not temp sensitive so I may stick with it. How's retumbo with temperature changes?

You might get a little more velocity with Retumbo, but with how your load is grouping do you really want to mess with it? What are your end goals with this gun? Are you hoping to be able to shoot a certain animal at a certain distance? These are all things to consider. Is it really worth changing powder and (probably) increasing your group size to gain 100 fps or so? New load development also comes with increased cost and increased rounds down the tube. Again, just some things to think about...

 

[adamg1986]

Well I just shot at 600 and 700 yards this evening. I think Im going to stick with the H4831.My velocity is around 2770 I guess. At 604 yards I dialed 10.5 minutes and got a 2 inch group about an inch and a half low. I dialed for 600 so that might explain why I hit a bit low. I couldn't range 700 yards so I ROUGHLY ranged 100 yards further from where I was shooting. I only shot once at 700 but I hit around 2 inches high. After getting back home and looking at a ballistics chart, Im surprised that I got that close at roughly 700 bc 5 yards closer or further than 700 results in over 2 inches of difference either way. Guess I got lucky. Ive shot guns and hunted all my life but this is by far the furthest Ive ever shot and It feels awesome to be able to hit that far out. The only bad part is that I just shot the last of my H4831. How much difference could I experience from a different lot of powder?

 

[Beluebow]

Well I just shot at 600 and 700 yards this evening. I think Im going to stick with the H4831.My velocity is around 2770 I guess. At 604 yards I dialed 10.5 minutes and got a 2 inch group about an inch and a half low. I dialed for 600 so that might explain why I hit a bit low. I couldn't range 700 yards so I ROUGHLY ranged 100 yards further from where I was shooting. I only shot once at 700 but I hit around 2 inches high. After getting back home and looking at a ballistics chart, Im surprised that I got that close at roughly 700 bc 5 yards closer or further than 700 results in over 2 inches of difference either way. Guess I got lucky. Ive shot guns and hunted all my life but this is by far the furthest Ive ever shot and It feels awesome to be able to hit that far out. The only bad part is that I just shot the last of my H4831. How much difference could I experience from a different lot of powder?

I'd be looking for some H4831,,,two inch groups out of a Browning A-bolt at 600 yards is nothing to sneeze at.