7mm Rem Accumark Load Testing

[Autorotate19]

I went to the range today to try out Jerry Teo's method of load development. I did everything the same as he describes except I shot three shot groups instead of two. I started at 69.5grs and worked up to 73.5grs with retumbo. I used once fired winchester brass, rem 9.5 primers, loaded to a coal of 3.668 which is magazine length. It puts me .069 off the lands. I used berger 168 vlds. I shot at 200 yards with about two minutes between shots in groups and then let the barrel get cold in between loads.

69.5grs - 3.9"
70.grs- 2.7"
70.5grs- .9"
71.0grs- 1.3"
71.5grs- 5"
72.0grs- 5.4"
72.5grs- 2.4"
73.0grs- 3.1"
73.5"grs- 1.8"

At 71grs and 73.5 grs two were touching with the third opening them up. At 73.5 grs I had no pressure signs whatsoever. I think one node is at 70.5 and the other one is somewhere above 73.5 grs. I think Im going to bump it up and see if they tighten up before I get too much pressure.

So those of you that use a method of load testing similar to this, is it normal that in .5grs of powder difference a group can go from 1" to 5"? Seemed kinda weird that it would open up that much so suddenly. I used a lead sled to keep human error to a minimum. Also do you guys have a lot of success finding a good long range load with this kinda method?

O and can anyone give me an idea of what kind of velocity Im getting at 70.5grs with a 26" barrel. Thanks

 

[Topshot]

I would say that you can not tell much from one 3 shot group of any particular powder charge. Too small a sample. Could be the load, could be wind, could be you, could be seating depth, could be a number of things.

Now if you repeat this whole experiment 3 times and get more data. Then you will have a better idea of what is going on. But this is an expensive exercise and is wearing out your barrel.

With "big cartridges", I have given up on this process due to the large number of shots involved. I now forget about accuracy and just work out where my maximum charge weight is. Then back off 1 grain and play about for an accurate load by adjusting seating depth.

If I can not find an accurate load at this charge weight by adjusting seating depth, I then back off the powder charge by 1 grain, and try again, starting with using the most accurate seating depth from the higher powder charge.

 

[Pdvdh]

I think you're methods and interim conclusions are on the money. I've been through the process and ended up with a good consistent load of 74.6 gr Retumbo in my 24 3/8" barrel. I get about 3050 fps MV with the 168gr Berger VLDs and Federal 210 primers.

Not sure what you'd be getting for MV @ 70.5gr Retumbo. I don't have any recorded velocities at that low of a powder charge. I'd say you're close to a good consistent load at 74 gr. You'll probably hit max around 75 - 75.5 gr, but if you continue to move up in 0.5 grain increments you should be safe. I think Retumbo is about the best powder going for the 7mm Rem Mag with the 168 VLDs.

 

[Autorotate19]

I just read his article and read the thread on it and there was tons of good reviews so I gave it a shot. I also liked the idea of not playing with seating depth and just using one variable. I have already did the berger test of seating depths and this one shot the best. There was absolutely no wind today so thats out of the question. I obviously wont go do it all again but Im going to load up some more up to probably 75.5 grs and play around in the 70.5- 71 gr area. I'm not the type to mess around too much so if I go back to the range and 70.5 shoots the best thats probably going to be my hunting load. It seems like in this reloading game a guy could drive himself crazy pretty easy with all the different variables and things to try. It just seems odd that one load could shoot so good and .5gr later 5" group. I guess it could be me or anything but it just seems like a huge step. Anyone else had an experience like this? Thanks for all the input and help!

 

[Pdvdh]

Your group sizes do vary a bit more in size than I've experienced. You'll learn more based on your next outing.

 

[Autorotate19]

Do you think it could be the bergers are that finicky about being jumped and the velocity they like?

 

[Pdvdh]

I load my VLDs into the lands about 5-10 thousanths inch. I load them single shot style as they're too long for the magazine. Dunno what to say other than shoot them again and if you repeat the performance at what appears to be the sweet powder charges you'll begin to confirm those are loads your rifle likes.

 

[Autorotate19]

Will do. I would have tried that but with this being a hunting rifle I didnt want a single shot and I dont want to deal with two different loads etc...... If it didnt like the bergers I would of just tried something else. Hopefully its a repeat performance next time. I appreciate the help!

 

[Topshot]

It just seems odd that one load could shoot so good and .5gr later 5" group.

There is no way that a change of 0.5 grains of powder is going to do this in a 7mm Mag.

I would be looking to some other cause for such a large change in your group size.

Also why have a 7mm mag if you are going to shoot it at 280 Rem velocities.

 

[Autorotate19]

Im going to bump it up and find my max and see how it shoots there. Berger told me the max with retumbo was 70 grains so I figured that was a good place to start. Thanks for the input.

 

[Pdvdh]

There is no way that a change of 0.5 grains of powder is going to do this in a 7mm Mag.

I would be looking to some other cause for such a large change in your group size.

Also why have a 7mm mag if you are going to shoot it at 280 Rem velocities.

Never say never. It took 1.0 grain to open the group from 0.9" to 5.0". You show a steady progression of improvement, to deterioration, and then back to improvement in group sizes. Only way to know if these results are for real or not is to see if you can duplicate good groups at the apparent optimal powder charges. You may find your highest MV optimum charge around 74-75 grains. You may peak out on pressure before getting to 75.5.

 

[Autorotate19]

Another thing that is kinda bothering me is at 73.5 grs its pretty compressed... Im worried as I go higher im going to run into issues.

 

[Pdvdh]

My COAL is 3.456" and I have no problems at this bullet seating depth with 74.6 grains Retumbo.

You must have a typo in your first post. At 3.668" COAL the bullet would just about fall out of the case neck. I think you meant 3.368"? A little compressed powder probably won't hurt anything. But at that deeper seating depth you may have an overly compressed load. Since I'm not seating that deep, I don't know. See how it goes.

Loading single shot style for LRH really hasn't proven to be a handicap for me. I load Nosler Accubonds or Barnes TSXs for carrying in the magazine and closer range shots. When the animals out at 400 yds or farther, I load my long range VLD accuracy loads one at a time. The farther the animal is away, the more time you'll have to load single shot style without compromises.

 

[roninflag]

i would try again with WLRM primers; or cci 250