Reloading Question

[Summitthunting]

Was shooting my dads 7mm Rem Mag the other day with the chronograph and the loads averaged 200 fps slower than book data. The barrel length is the same as the book test rifle and the load was a max load. I pulled a few bullets when I got home and verified the load. I usually get within 50fps of load data, anybody have any ideas?

 

[jryoung]

Could be a combination of a "slow barrel" and or generous book data. I only use book velocity for a benchmark knowing that most often those numbers could be a touch generous.

You are using the same bullets correct?

 

[tarheel]

Might be heat or barometric pressure variances, but you'd think that influence would be nil at the muzzle to trap distance you're shooting. Ammo might be getting hot???? I keep my ammo shaded and cool in the heat of the summer, but have never done any real scientific research on varying conditions, just read such.

 

[BuzzH]

How did it shoot other than the velocity woes?

 

[1_pointer]

Did you calibrate the chronograph in anyway? I've read of folks using 22lr to do so.

 

[wgiles]

I seldom get velocities as high as the books would suggest. My barrels are shorter and my chronograph is cheap and old. I just look for consistency in velocity and repeatability on the target.

 

[Summitthunting]

Used the same bullet as book, accuracy was 2" at 100yds, the gun shoots 130's much better than that. Trying 160 accubonds, have not calibrated the chronograph. The only reason I'm trying to match velocity is for the Ballistic plex scope. Thanks for the reply's.

 

[Solohuntr]

couple things I can reflect on, ammo laying in sun getting hot will produce higher velocities, cold will reduce, using differnt brass will change MV also, and the differnt barrel lenghts seem to change MV some also,, my 2 cents tossed on pool

 

[canvsbk]

Lots of variables here. Temperature, primer lot, powder lot even the rifle's bore quality. I have a .25-06 that's always "fast" and yet the same model gun in a .30-06 for me cronies "slow" every time. I wouldn't worry about it too much. Watch for pressure and work up......

 

[Ben Lamb]

Used the same bullet as book, accuracy was 2" at 100yds, the gun shoots 130's much better than that. Trying 160 accubonds, have not calibrated the chronograph. The only reason I'm trying to match velocity is for the Ballistic plex scope. Thanks for the reply's.

This sounds more like it's the twist of the barrel not liking the bigger bullets. Do you know what twist rate you have? If it's slow, then you're stuck with the lighter bullets.

 

[danr55]

THis is a loaded subject. I've been loading ammunition for almost 35 years and I've never matched any velocity found in any reloading manual. I'm usually slower than published velocities. You can improve the velocity by lapping the barrel but you have to account for chamber variations. There is also humidity barometric pressure, ambient temperature, altitude (all of which can affect the burn rate of most powders) as well as the action and reaction of the bullet after it leaves the barrel. Even if you match the components as listed in the manual exactly, it's still a crap shoot. What you should do is record your average velocities for each load and compare from loading to loading to see if there are any significant changes. That will tell you when it's time to scrub the barrel and maybe run a lapping rag through it to clean up and rough spots. Throat errosion can play a significant part in muzzle velocities. So there are all kinds of variables that have to be considered. THat's one reason that one size fits all bullet drop compensators are generally not among my favorite toys.

 

[sbhooper]

Every barrel is different with every load. If you got within 200 fps, then I would say that is pretty good. Don't worry about the velocity as much as accuracy. Take the info that the chrono gives you and put it in a ballistics program to figure out your drop.

I had two Savage 7 mags that were completely different rifles. I finally found a load with 175 grain Hornadys (or Partitions) that shot well in both rifles. The velocity was quite a bit different between them, however.

I don't think that I have ever matched book velocity. The Speer manual that I have has been the closest to what my chrono says. There are just too many variables in the company testing vs your own rifle, powder, casing, bullet, primer, weather etc., etc.

I have had the most consistent results in my rifles with RL22 powder for the lighter bullets, and RL25 for the heavy hitters. Excellent velocity and accuracy for both.

 

[Foxtrot1]

I have had the same issues with alot of the loads that I have tried. The only powder that has consistently gotten close to the velocities published in the reloading manuals is Ramshot Big Game. I have heard that some chronographs will report lower velocities if they are placed too close to the muzzle when testing. I am not sure about that. I usually just try a variety of powders/load combinations until I find one that works with the rifle and has the best combination of velocity and accuracy. I usually test 4-5 powders in each rifle I load for, and the velocity of each max load varies dramatically with each type of powder. In my 30-06 with a 22" barrel and 150 grain Hornady Interbonds, a max load of Varget produces 2700 fps, and max load of Big Game produces 3050 fps. The max load of Big Game will group about a minute of base ball at 100 yds, but by backing down 2 grains, my rifle will shoot 2950 fps, and about 1/2-3/4 MOA with the same bullet.

 

[BobT]

Most of the quoted velocities you see in the manuals are corrected to actual muzzle velocity. If you place your chronograph 15 feet from the muzzle for instance, and don't correct to actual MV that will account for part of the difference. The rest of the difference is just in the variables the previous posters mentioned. The numbers I pay close attention to are the extreme spread and the standard deviation, they let me know how uniform my load is.

As far as the ballistic plex scope, the only way to know for sure what it will do is to shoot the different yardages and see. I have been working with a Minox ballistic reticle lately and with the rifle (.25/06 115 grain Noslet BT) zeroed at 300 yards I am dead on the aiming points at 350, 400 and 500, almost 4" high at 100 and for some reason I have yet to fire this combo at 200 so I don't have a clue where I'm hitting there. BUT this only works at maximum magnification which happens to be 20x on this particular scope. To actually validate a second focal plane ballistic reticle takes a lot of shooting, don't trust what the chart that came with it tells you.

Bob

 

[JGRaider]

I'm kind of surprised many here state they can't get the velocities the manuals claim. I find the reloading manuals today have done a great job of watering down a fantastic cartridge in the 7mm Rem Mag. I haven't had any trouble safely exceeding published velocities. For instance, in my rifle, this on a Tikka 695 7mag, I can easily get 3050fps with 71.5 gr of Retumbo and a 168 VLD H, 3/4 MOA. In another 7mag, this a Hill Country Rilfe with a 26" bbl, I've safely averaged 3180fps with 69gr H4831SC and Nosler Ballistic Silvertips. It's a 1/2 MOA load in that HCR. I think it's a matter of seating depths (it's all about the pressure), and matching the bullet with a powder your rilfes like. They each have their own personality.