causes of big ES spreads

[TackDriver284]

I would guess based on your speed you could go a bit higher, carefully of course. Did a bit of work last year with IMR 7977 (and IMR 4451 too) and the 154 gr Hornady, it is slower burning than 7828 and it seemed to work quite well in the limited work I did with it. Your plan of using RL 25 and Retumbo is a good plan and it sounds like guys using RL 26 are really liking it as well.

You are correct about 7977 being the slowest next to the 7828, I completely forgot about those Enduron powders which I got on my shelf as well. I never tried them and read good reviews about them as well. Once I run out of RL-25, I will jump to RL-26.

 

[SJB358]

I'd look up a little higher at around 66-67 grains of 7828. It's a slow powder and doesn't really burn efficiently till you get towards the top end with it. There's not many powders that are better than 7828 in the 7 RM with 160's.

The next culprit would be neck tension but it seems like you've got a handle on that.

 

[SJB358]

7828 and RL22 have usually ran pretty close, grain for grain over the years for me and my rifles. I haven't seen any problem with nudging up a load to attain book speeds. It's just certain lots of powder are slower than others. Bumping up a 1/2 grain at a time should get you into the good spot.

No sense in running a 280 with the big 7, unless you don't want the extra HP. :lol:

 

[TackDriver284]

7828 and RL22 have usually ran pretty close, grain for grain over the years for me and my rifles. I haven't seen any problem with nudging up a load to attain book speeds. It's just certain lots of powder are slower than others. Bumping up a 1/2 grain at a time should get you into the good spot.

No sense in running a 280 with the big 7, unless you don't want the extra HP. :lol:

Thanks Scotty. I sure don't want to be one of those slow pokes. :mrgreen: I'll be back with some good results next week.

 

[SJB358]

7828 and RL22 have usually ran pretty close, grain for grain over the years for me and my rifles. I haven't seen any problem with nudging up a load to attain book speeds. It's just certain lots of powder are slower than others. Bumping up a 1/2 grain at a time should get you into the good spot.

No sense in running a 280 with the big 7, unless you don't want the extra HP. :lol:

Thanks Scotty. I sure don't want to be one of those slow pokes. :mrgreen: I'll be back with some good results next week.

I said it sorta tongue in cheek, but the 7 RM really seems to do its thing when run up towards the top end and that's where it made its name. Looking forward to seeing your results.

What does QL show you for the specs you're getting?

 

[TackDriver284]

Scotty, checked QL after tweaking to my H20 case capacity ( 87.25 ) and velocity (2,930 fps) with the 64.5 grain charge, it shows that I have more room to push that 160 AB. I cannot rely on this data alone but I need to work my way up and find my max pressure. Looks like a hammer at max pressure.


Cartridge : 7 mm Rem. Mag.(SAAMI)
Bullet : .284, 160, Nosler AccuBond 54932
Useable Case Capaci: 78.192 grain H2O = 5.077 cm³
Cartridge O.A.L. L6: 3.330 inch = 84.58 mm
Barrel Length : 26.0 inch = 660.4 mm
Powder : IMR 7828 ?, Temperature: 85 °F

Predicted data by increasing and decreasing the given charge,
incremented in steps of 1.0% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step    Fill. Charge   Vel.  Energy   Pmax   Pmuz  Prop.Burnt B_Time
 %       %    Grains   fps   ft.lbs    psi    psi      %        ms

-10.0   87    61.20   2782    2751   41928  11556     97.4    1.476
-09.0   88    61.88   2813    2811   43293  11676     97.7    1.454
-08.0   89    62.56   2843    2872   44704  11791     98.1    1.432
-07.0   90    63.24   2874    2934   46162  11901     98.4    1.411
-06.0   91    63.92   2904    2996   47666  12006     98.7    1.390
-05.0   92    64.60   2934    3059   49225  12106     98.9    1.370
-04.0   93    65.28   2964    3122   50831  12201     99.2    1.350
-03.0   94    65.96   2994    3185   52499  12290     99.4    1.330  ! Near Maximum !
-02.0   95    66.64   3024    3249   54216  12373     99.5    1.310  ! Near Maximum !
-01.0   96    67.32   3054    3314   56000  12451     99.7    1.291  ! Near Maximum !
+00.0   97    68.00   3084    3379   57836  12523     99.8    1.273  ! Near Maximum !
+01.0   98    68.68   3113    3444   59726  12589     99.9    1.254  ! Near Maximum !
+02.0   99    69.36   3143    3509   61672  12648    100.0    1.236  !DANGEROUS LOAD-DO NOT USE!
+03.0  100    70.04   3172    3575   63681  12702    100.0    1.219  !DANGEROUS LOAD-DO NOT USE!
+04.0  101    70.72   3201    3641   65756  12749    100.0    1.201  !DANGEROUS LOAD-DO NOT USE!
+05.0  102    71.40   3230    3707   67900  12794    100.0    1.184  !DANGEROUS LOAD-DO NOT USE!

Results caused by ± 10% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 10% relative to nominal value:
+Ba     97    68.00   3213    3667   69673  12037    100.0    1.178  !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 10% relative to nominal value:
-Ba     97    68.00   2896    2980   46661  12460     95.6    1.397

 

[SJB358]

Yeah... that's More like it. That's sorta what I was thinking.

 

[TackDriver284]

Last week I had huge extreme spreads with IMR-4350 and 150 ABLR, so I retested with a different powder and bullets. Hit the range today to retest the 7 Mag but this time with RL-25 and Retumbo with the 160 AB. It was already so hot and mirage was bad when doing the ladder test with RL-25 at 300 yards, did not see any nodes, culprit could have been me and the mirage. So I'll skip the RL-25 report for now and get on with the Retumbo ladder test.

I never used Retumbo before and when seating the lowest charge, it was already lightly compressed. Loaded one round per .4 increments from 71 to 73.4 grain Retumbo, seated at 2.788 ogive ( .020" off lands). I reduced the range for the ladder test from 300 yards to 200 yards due to bad mirage. Distance could be too short for most. I wanted to see if there was a flat spot that I can relate to POI. Cleaned the barrel, fired 3 foulers and let cool. Picked out an old target that has been used, round one downrange, let cool 3 mins and round two down range and repeat while taking notes on POI and velocity.

Upon inspecting the target, it seems that # 3 and 4 is rounds of choice at velocity of 3,098 and 3,103 fps. Also there is # 5 and 6 with velocity of 3,125 and 3,152 fps which is fast for a 160 AB. After tweaking velocity and Ba rates on QL, it seems that 72.9 grains is maximum charge at 3,130 fps.

I think I'll try 3 round groups of 72 grains and 3 more at 72.8 grains. I am leaning on 72 grains BTW. What do you think?

I have a 26 inch barrel, my OBT is 3.3295 # 5 node, but its a slow node at 3,025 fps with 70.1 grains Retumbo. I am above that charge. Not looking for a one hole group, just a decent .5 MOA hunting load for this season. Should I try 70.1 grains as well according to QL? Won't hurt to try and deer won't know the difference. It will feel like a Thor's hammer.

Cartridge : 7 mm Rem. Mag.(SAAMI)
Bullet : .284, 160, Nosler AccuBond 54932
Useable Case Capaci: 77.713 grain H2O = 5.046 cm³
Cartridge O.A.L. L6: 3.290 inch = 83.57 mm
Barrel Length : 26.0 inch = 660.4 mm
Powder : Hodgdon Retumbo ?, Temperature: 85 °F

Predicted data by increasing and decreasing the given charge,
incremented in steps of 1.0% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step    Fill. Charge   Vel.  Energy   Pmax   Pmuz  Prop.Burnt B_Time
 %       %    Grains   fps   ft.lbs    psi    psi      %        ms

-10.0   91    65.70   2846    2878   43388  11352    100.0    1.464
-09.0   92    66.43   2876    2938   44902  11412    100.0    1.440
-08.0   93    67.16   2905    2998   46471  11472    100.0    1.418
-07.0   94    67.89   2934    3059   48100  11531    100.0    1.396
-06.0   95    68.62   2963    3119   49790  11589    100.0    1.374
-05.0   96    69.35   2992    3181   51543  11646    100.0    1.353
-04.0   97    70.08   3021    3242   53363  11702    100.0    1.332  ! Near Maximum !
-03.0   98    70.81   3049    3303   55253  11757    100.0    1.311  ! Near Maximum !
-02.0   99    71.54   3078    3365   57213  11812    100.0    1.291  ! Near Maximum !
-01.0  100    72.27   3106    3428   59248  11865    100.0    1.272  ! Near Maximum !
+00.0  101    73.00   3134    3490   61365  11918    100.0    1.253  !DANGEROUS LOAD-DO NOT USE!
+01.0  102    73.73   3162    3553   63550  11970    100.0    1.234  !DANGEROUS LOAD-DO NOT USE!
+02.0  103    74.46   3190    3616   65806  12020    100.0    1.215  !DANGEROUS LOAD-DO NOT USE!
+03.0  104    75.19   3218    3680   68142  12070    100.0    1.197  !DANGEROUS LOAD-DO NOT USE!
+04.0  105    75.92   3246    3744   70560  12118    100.0    1.179  !DANGEROUS LOAD-DO NOT USE!
+05.0  106    76.65   3274    3808   73065  12166    100.0    1.162  !DANGEROUS LOAD-DO NOT USE!

Results caused by ± 10% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 10% relative to nominal value:
+Ba    101    73.00   3240    3730   75825  11513    100.0    1.156  !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 10% relative to nominal value:
-Ba    101    73.00   2972    3137   48156  12514    100.0    1.383

 

[jimbires]

I'd be looking at 3 and 4 . you have flat velocity , and very little vertical between these two shots . it looks like the barrel is holding the position for bullet exit . you'll be able to tell more at a longer distance , when the conditions are right .

 

[TackDriver284]

I'd be looking at 3 and 4 . you have flat velocity , and very little vertical between these two shots . it looks like the barrel is holding the position for bullet exit . you'll be able to tell more at a longer distance , when the conditions are right .

I was thinking the same.

 

[Dwh7271]

Try loading 72 gr :grin:

 

[SJB358]

I was thinking 73.2 and 72 myself. Both of those look pretty good.

 

[TackDriver284]

Full sized and SS tumbled as well. Selected two charges of 72 and 72.8 grains of Retumbo and the 160 AccuBond. Range is 200 yards. 72 grains did not shoot well, but the 72.8 grain charges did somewhat OK, put two in one in the bullseye and one little flyer above it. It could have been me, the rifle is a Sako M995 custom featherweight 26 inch barrel / Nightforce NXS 8x32 and so light that you can barely make it sit still in the saddle of the bull bag.

I'll go back out and re confirm before settling down.

 

[desertcj]

I have seen loads on the lower end show larger spreads in velocity. Pressure=Velocity, so if you aren't seeing any pressure signs and your velocity is still comparatively low. Keep working up SLOWLY. You should see nice consistent incremental changes in velocity as you increase the powder charge. You may hit a spot where more powder doesn't add any velocity or very little. That is probably the zone where you want to be. If you see a noticeably larger jump in velocity in a given powder charge then the previous steps where showing, it's probably time to stop or even back down a few steps! I would expect to see over 3000fps with a 160gr in a 7mag.

 

[desertcj]

Oh, I would try 73.2gr and play with the seating depth. Based on those numbers. I'm no fortune teller tho!

 

[TackDriver284]

Oh, I would try 73.2gr and play with the seating depth. Based on those numbers. I'm no fortune teller tho!

Shot pretty good with 72.8 grains at 3,140 fps with the 160 AccuBond. Loaded up 10 rounds to check again this weekend. Pretty amazed at the speed.