7 mag reloading conundrum?

[pyroducksx3]

I was testing 7 rem Mag loads today and had something weird happen. I was testing 140 gr Berger vlds and working my loads up. I started with the all loads .010 off the lands so oal to ogive was 2.650", all loads are using h1000. First load was 67 gr and velocities were 2715, 2732, 2743. Load 5 69.8 gr velocities 2930, 2930, 2956 and no pressure signs. Load 6 70.5 velocities 2982, 2969, 2969 no pressure signs. So everything is looking good. Test load 7 at 71.2 velocities at 2048, 2020, 2048 what the heck is happening? Test 8 to see it's 72 gr and velocities are 2290 and 2271 I didn't shoot the third because I wanted to make sure I loaded these correctly. Got home pulled the bullet and sure enough 72 grains. So what happened? The only thing I can think of is these 140 gr bullets have such a small bearing surface (.265) that when I seat them to .010 off the lands there isn't much in the neck to allow the pressure to develop properly, maybe 40% of the bearing surface is in the neck, is this logical at all? The 150 swift I measured had a bearing surface of .515 and easily allowed for long seating depth with plenty on bullet being seated. Also I use a redding neck bushing and size all brass so there is .002 (.282 ID) neck tension. Any help on understanding what happened would be appreciated. I'm thinking of going to 160 AB or 168 bergers because I'm thinking this must be a bearing surface issue. Thank you for any help in helping me learn something

 

[7stwnut]

Maybe your chrono is jacked up? I shoot the same bullet/powder combo out of my 7STW and with 84 grains I get a little over 3,200 fps.

 

[desertbull]

Seems like you should be getting higher velocity with 67 grains of H1000 and 140 grain bullets.

My 162 grain SST's are 3000 FPS with 68 grains of H1000

 

[4bycamper]

Could your problem be H 1000 being too slow for 7mm light bullets?
Do you have another powder like H 4831 to try with the 140 s ?

H 1000 should work great behind 160 AB and 168 vld.
At least it does for me.

 

[pyroducksx3]

I'm not sure it was the chrono. I was getting 3009 out of a 270 with 140 gr sst's in their superformace ammo, 2478 out of a 300 savage with 150 ballistic tips and 40.5 gr ogIMR 4895, 813 fps with my 45 acp, 950 fps out of my 10mm glock 29, 1109 with my .22 lr and 2354 fps in a 303 British with factory 180 gr bullets the box said it would get about 2400 fps. All the reading from the chrono seemed good. I'm pretty sure there is a reason why I'm not getting the velocity I should, and not a chrono problem, I'm thinking it has something to do with the bullet not bring seated deep enough but this is just my reasoning and I don't have much experience or knowledge to back this up. I'm hoping somebody with both will be able to shed some light on this. I though the chrono might be bad also , like maybe it means 3290 instead of 2290 but it chronoed the 270 at around 3000 fps just fine. I'm learning that the equipment when it is functioning reliably ( as it seemed to read everything else just fine) is not lying and if it's telling me something is not acting right there is a reason why and not that it is broke.

 

[pyroducksx3]

On hodgdons website it list the 140
Noslers partition (note I was shooting Berger vlds but) going I think around 3030 over 70 gr of h1000. I got 2982, 2969, 2969 with 70.5 gr of h1000 with no pressure signs do this is close to book but I was hoping to push em a little harder. What really throws me is why the velocity dropped to 2048 when I went up to 71.2 gr

 

[AZShooter]

I realize you had other rifles with their velocities reading correctly. Did you shoot any of them right after getting low readings?

I firmly believe the low readings WERE your chronograph. Sun angle can change readings. Were you starting to shoot later into the afternoon? Was one skyscreen shadowed? Were there partial shadows across one or both screen openings? Battery in good shape? There is no way you suddenly lost that much velocity.



Go back another day with the same load and just in case put in a new battery. Shoot with equal light on both screens. Repeat the same load, bet it reads fine.

 

[pyroducksx3]

We were facing NE, I started shooting at 12 and these last two groups were shot between 3:20 and 3:45. The sun did come out at around 2:30. The only thing shot between these groups through the chrony was my dads 357 mag and he was testing his HSM Bear loads and those chroned at 1132-1116. Theses two groups shot great but the velocity drop confused me. I will shoot them again the next morning I can get to the range.

 

[rscott5028]

Muzzle blast can throw off the chrony. So, you might want to set it out a little farther if possible and in addition to the other cautions about changing sunlight. Some people go so far as to use an umbrella over the chrony to maintain consistency.

Also, there's a big gap between your loads. try dropping down to .5 gr or smaller step size in that mystery range to see if/where it begins to fall off.

Like others, I don't think the velocity dropped like that when you increased the powder. ...unless perhaps you had good neck tension with the earlier loads and then had poor neck tension with the latter loads.

-- richard

 

[Camshaft]

A velocity drop that big would be noticeable in the recoil and report of the rifle. If no change in these factors were noticed that it is definitely a chrono issue.

 

[pyroducksx3]

I will recheck the loads over the chrono as soon as I can. We were having muzzle blast issues earlier so we kept moving the chrono out until everything worked, it ended up about 20-25 feet away from the bench. I was going up in .7 gr loads (1%) at a time. The loads shot great, I dont have the targets in from of me but they were between .6 and .7" at 100 and there was no noticable change in recoil or sound report. And neck tension wasn't an issue, I used the redding competition neck sizer and and rechecked the ID (they measured at .282 before I reloaded the brass. At first I thought I was getting pretty low velocities but after looking at hodgdons website I was just a little slow maybe 50 fps to what there info says for the 140 nosler partitions. Also the chrono was a new competition electronics prochrono digital, so the batteries were freash as well. I was hoping to get 3100-3200 is that realistic in a 7 rem mag with a 24" using 140 berger vlds? I saw that someone had posted they were getting a little over 3200 with an stw and 85 gr of h1000 so maybe Im not not far off of where I should be. I didnt realize that the chrono could throw that far off a number. I got errors earlier and everything else seemed to read clean so I figured it would throw an error if it had a problem reading. The other thing that made me doubt that the chrono could be throwing errors was that it read the strings consistant, I figured if it was reading poorly the numbers would be all over and not close but in the 2000 and 2220 but Im learning so thanks for the info that the chrono can be flakey even if it appears to be functioning correctly.

 

[Sackett]

I really like IMR 4350 in my 7mag loads...140gr Ballistic Tips at 66grs...145gr Grand Slams 64grs...these loads pattern best in my 7mag.

 

[Tikkamike]

I have to agree sounds like a chrono issue. People usually dont read directins (not saying you dont) but my suspicion is that you are way too close to the chrony. the directions on mine say 12-15 feet away and most people do it at about 6 feet from what I have seen. I have excelent results with my machine i take about 5 paces out and set up my chrony , thats about 15 feet. . muzzle blast will jack up your readings almost every time.

 

[pyroducksx3]

I have to agree sounds like a chrono issue. People usually dont read directins (not saying you dont) but my suspicion is that you are way too close to the chrony. the directions on mine say 12-15 feet away and most people do it at about 6 feet from what I have seen. I have excelent results with my machine i take about 5 paces out and set up my chrony , thats about 15 feet. . muzzle blast will jack up your readings almost every time.

I appreciate the help but you must not have read the tread all the way. I started I about 15 feet and it was reading fine with the .22, pistols and the savage but started shooting the 270 and rem mag and it started throwing errors so I moved it back until it worked. Ended up at about 20-25 feet. It was reading fine and then these last two groups were way low. I believe/understand though that this is still probably a chrono issue but it is most likely from the changing light conditions (brightness or sun moving) and not from muzzleblast. Hopefully sunday I will be out and can recheck these loads.