7mm Mag ladder / IMR 4831

T

TackDriver284

Handloader
Feb 13, 2016
2,559
2,139
Resumed load development for the 7 Mag using IMR 4831, last time out, velocity was on the low side. 65.5 grains gave me only 3080 fps at 90 degrees, book max shows 65 grains as 3250 fps. Wanted to do a ladder to see if I can get some velocity. So here goes the ladder today at 75 degrees with new Nosler brass.
Edit: Forgot to add the bullet,,, 150 grain Ballistic Tips
Gr. FPS
65.9 3075
66.3 3093
66.7 3110
67.1 3114
67.5 3144
67.9 3173
68.3 3175
68.7 3193
69.1 3250
69.1 grains has a large velocity jump, a little hard bolt lift, plus a swipe on the case head with a noticeable ejector mark on the head which I used a magnifying glass when I got home. That is pressure right there. Also round #2, 4, 5, 6, 7 and 8 has a very faint ejector mark, just hard to see.
Is it possible that the headspace of the virgin brass caused the very slight ejector marks from round 2, 3 to 7? The virgin brass headspace measures at 2.104" while the fired cases measured at 2.114", that is .010" headspace. It may cause enough blow back to hit the bolt face to make those very slight ejector marks. I'm pretty sure case #9 has some pressure signs and rounds 1 to 8 does not have any swipe. Opinions please, if any.
Thinking to try 67.8 to 68.7 in 3 round charges and with .3 increments. 66.7 - 67.1 may show something.
 
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Just me, and everybody has to work with what they're comfortable with, but based on your description and your velocity nodes, I'd load some up at 68 on the button and try it. If you're getting zero noticeable stiffness on the bolt lift, and no case swipe, I wouldn't worry about a faint ejector mark that is hard to see...........especially since it's showing up way way down the list on the powder charge and more importantly on the velocity comparison of what the book says is max.
 
Like others have said 68gr for 3175fps is right about where I would expect a 7mm rem mag to be. 3150fps with a 150gr and 3250fps with a 140gr. Noslers load data showing 3250fps with a 150 seems on the hot side but rifles vary.

Belted cartridges headspace between the bolt face and the belt on fresh brass so I doubt headspace is an issue. Now, I have seen that oil in the chamber will produce ejector marks on case heads even on lower level charges. Might be something to check out next time?
 
A few years ago I was looking for a new load for my 7mm mag. I tried both IMR 4831 and IMR 4350 using a 175 grain Hornady bullet. My results were a lot like you describe along with pressure swings. Followed 2 years later testing my 300 Winchester Magnum and 180 grain Hornady bullets. I don't like loads that are inconsistent, especially concerning pressure. So I dropped the IMR 4831 from my powder choices.
I ran some tests on imr 4350 and had none of the problems I had with imr 4831. In the end I worked up some very accurate and hot loads for both calibers. I took my 300 to N. Colorado and at 400 yards sent a bullet through both shoulders for a dramatic kill. I also have found some lighter loads I use for whitetail deer around home. IMR 4350 is my powder of choice.
 
TackDriver284 said:
Resumed load development for the 7 Mag using IMR 4831, last time out, velocity was on the low side. 65.5 grains gave me only 3080 fps at 90 degrees, book max shows 65 grains as 3250 fps. Wanted to do a ladder to see if I can get some velocity. So here goes the ladder today at 75 degrees with new Nosler brass.
Edit: Forgot to add the bullet,,, 150 grain Ballistic Tips
Gr. FPS
65.9 3075
66.3 3093
66.7 3110
67.1 3114
67.5 3144
67.9 3173
68.3 3175
68.7 3193
69.1 3250
69.1 grains has a large velocity jump, a little hard bolt lift, plus a swipe on the case head with a noticeable ejector mark on the head which I used a magnifying glass when I got home. That is pressure right there. Also round #2, 4, 5, 6, 7 and 8 has a very faint ejector mark, just hard to see.
Is it possible that the headspace of the virgin brass caused the very slight ejector marks from round 2, 3 to 7? The virgin brass headspace measures at 2.104" while the fired cases measured at 2.114", that is .010" headspace. It may cause enough blow back to hit the bolt face to make those very slight ejector marks. I'm pretty sure case #9 has some pressure signs and rounds 1 to 8 does not have any swipe. Opinions please, if any.
Thinking to try 67.8 to 68.7 in 3 round charges and with .3 increments. 66.7 - 67.1 may show something.
Click to expand...
Just my opinion TD, but the velocity node at 67.9 - 68.7 is where I would be working myself. The speed is right on the right spot at nearly 3200, and I'd almost bet a dollar that if you shot some groups around the middle of node you might have a quick load work done, minus a little seating depth adjustment.

I wouldn't sweat the case marks myself on your lower than 3200 FPS charges. With new cases you're getting alot of case head smash into your bolt and if your ejector is sharp at all, it'll leave prints. Reshooting those charges on fired cases will tell you much more.

It does look like you're onto a good load with the 150 BT at nearly 3200.. Giant killer in my book right there!
 
SJB358 said:
Just my opinion TD, but the velocity node at 67.9 - 68.7 is where I would be working myself. The speed is right on the right spot at nearly 3200, and I'd almost bet a dollar that if you shot some groups around the middle of node you might have a quick load work done, minus a little seating depth adjustment.

I wouldn't sweat the case marks myself on your lower than 3200 FPS charges. With new cases you're getting alot of case head smash into your bolt and if your ejector is sharp at all, it'll leave prints. Reshooting those charges on fired cases will tell you much more.

It does look like you're onto a good load with the 150 BT at nearly 3200.. Giant killer in my book right there!
Click to expand...
Yep Scotty, I have loaded 12 rounds, 67.8, 68.1, 68.4 and 68.7 with the same ogive I used. Just waiting to put this rifle on the bench.
 
I think SJB238 is right in this. One reason is I have done extensive testing of seating depths and nodes and my findings lean towards his.
When I start looking for new loads with new powders I will load up 3 rounds at each charge weight that interests me. I then fire them and look for signs of pressure. If one that I want shows little pressure then I will start fiddling with bullet seating depths until I find the most accurate load.
 
As for the marks on the case head.....If that were the only signs of pressure I'd be inclined to use them for hunting. If any other signs start showing up then I would consider stopping and backing up a grain or so. Reason is the pressure signs we look for were the best we had years ago and today the factorys have better methods to check for pressure.
When we see signs like a shiny case head what that really means is you may be loading high pressure rounds already. So you must proceed with caution. It's never wise to tickle the dragons tail.
 
Loaded a lot of 7mm magnum. IMR 4831 never ended up being the best powder in any loading I had. H4831 with 120gr Nosler Ballistic Tip was a screamer though...very accurate, fast and deadly.
 
SJB358 said:
Did you ever run them?
Click to expand...
Yes Scotty, 68.4 and 68.7 shoots .4 -.5 MOA roughly. I'll use 68.4 grains until I finish the box of 150 BT that I purchased from nhenry. Probably switch to the 2 boxes of 140 BT that I have until all brass is fireformed before I do any tweaking.
 
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