The UK's Finest Independent Forum for Shooters and Gun Owners. Est 2010.

Please remember this is my first developed load, the result of reading through the Hornady guide and based on the manufacturers data. I have no chrono (yet) but as a result of having the willies put in me elsewhere, I have a friend's chrono arriving in the post soon.

Okay.. I have a Browning X-Bolt Stainless Stalker rifle and wanted to create my own load based around a 70gn Nosler BT bullet, that's close to what I had used for all my foxing and a similar weight Sierra HPBT match round is also available for range days.

I opted to use VV's N150 powder as, from the load data on their site, it would cover everything from 70g up to 105gn (the latter of no use to me as it likely wouldn't stabilise but I may wish to create a soft point hunting load using 100gn bullets).

Using VV data I started at just under 10% below the minimum load for that powder, with that weight bullet. So the data states 41.9gn min & 45.5gn max.

I loaded four each at 38gn, 38.5gn, 39gn, 39.5gn, 40gn, 40.5gn, 41gn, 41.5gn, 42gn, 42.5gn. 43gn, 43.5gn, 44gn, 44.5gn. Headed off to the range.

Starting off at the low end with 38gns of N150 at 100 yards the groups were quite loose, as I hit 39.5gn the groups tightened up nicely, beyond that they opened up again. At 42gn (just 0.1gn over the recommended minimum load) the bolt started to stiffen up on extraction and the cases (I was using Federal brass, I now know they're a little softer) started to show marks from the ejector pin, small, round marks on the case head. At 42.5gn the bolt got stiffer, at 43gn very stiff and that's where I stopped.

Now, given that the tightest groups were at 39.5gn and there were no primer distortions, no stiff bolts, no marks from the ejector pin and that 39.5gn represents 94.5% of the minimum load am I making a huge boo-boo with my load here? Since then, I tried various case types and found that Winchester brass gave me bullet on bullet groupings at 100 yards, literally 5p groups over four shots. Up till now the best I could achieve with factory ammo was 1.5" - 2" groups at the same distance.

I also found a load on reloadersnest.com (I know, unknown data posted anonymously) for N150 that came very close to mine. This was with a Hornady SXSP 70 gn and 39.7gn of N150 with a velocity of 3018fps (load #9803). I know I need a chrono to see how fast the bullet is going but I just wanted to ask those more experienced their advice too.

Using the advice posted as a sticky I measured the case base between four cartridges. I don't have 70gn factory loads, but I do have 75gn loads.

So, Hornady with 75gn BT unfired avg. over four cases is .4637. Fired avg. is .4677

And Winchester with 70gn BT (my loads, twice fired and FL sized) unfired avg. over four cases is .4642. Fired avg. is .4676

Ummm, not sure what this tells me though!

Seems fine to me you appear to have safe load giving you acceptable accuracy that is an improvement on what factory gives you with acceptable case fill.

You don't state you col but based on 2.71" with that bullet and charge QL predicts the following:

Cartridge : .243 Win.
Bullet : .243, 70, Nosler BalTip 39532
Useable Case Capaci: 51.230 grain H2O = 3.326 cm³
Cartridge O.A.L. L6: 2.710 inch = 68.83 mm
Barrel Length : 20.0 inch = 508.0 mm
Powder : Vihtavuori N150

Predicted data by increasing and decreasing the given charge,
incremented in steps of 2.0% 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

-20.0 71 31.60 2335 847 22791 8182 86.4 1.383
-18.0 73 32.39 2391 888 24191 8463 87.8 1.354
-16.0 74 33.18 2446 930 25655 8739 89.1 1.327
-14.0 76 33.97 2502 973 27190 9009 90.4 1.300
-12.0 78 34.76 2558 1017 28813 9272 91.6 1.273
-10.0 80 35.55 2614 1062 30529 9528 92.8 1.247
-08.0 82 36.34 2670 1108 32344 9775 93.8 1.221
-06.0 83 37.13 2726 1155 34260 10012 94.8 1.200
-04.0 85 37.92 2782 1203 36285 10239 95.7 1.173
-02.0 87 38.71 2838 1252 38423 10454 96.6 1.143
+00.0 89 39.50 2893 1301 40682 10656 97.3 1.113
+02.0 90 40.29 2948 1351 43066 10845 98.0 1.083
+04.0 92 41.08 3003 1402 45584 11020 98.5 1.055
+06.0 94 41.87 3058 1453 48244 11180 99.0 1.027
+08.0 96 42.66 3112 1505 51054 11324 99.4 1.001
+10.0 98 43.45 3166 1558 54023 11452 99.7 0.975 ! Near Maximum !

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 89 39.50 3042 1438 48103 10658 100.0 1.027
Data for burning rate decreased by 10% relative to nominal value:
-Ba 89 39.50 2701 1134 33432 10123 90.5 1.212

Sorry, I forgot to add COL. I used Nosler's data for 70gn BT for that, which is 2.680" (and it seems to work fine, adjusting either side didn't seem to make a lot of difference).

Thank you for that info Dromia. From that I guess my load is between 2701fps and 3042fps with an average of 2893fps. I need to check over the Chrono when I get it I guess, just to make sure.

Oh, and my trim length is an average of 2.036" (I use the Lee trimmer at the moment until funds allow something better).

Revised QL prediction with an oal of 2.680", predicted velocity for 39.5 gn charge 2902 fps.

Cartridge : .243 Win.
Bullet : .243, 70, Nosler BalTip 39532
Useable Case Capaci: 50.976 grain H2O = 3.310 cm³
Cartridge O.A.L. L6: 2.680 inch = 68.07 mm
Barrel Length : 20.0 inch = 508.0 mm
Powder : Vihtavuori N150

Predicted data by increasing and decreasing the given charge,
incremented in steps of 2.0% 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

-20.0 71 31.60 2341 852 22934 8181 86.5 1.380
-18.0 73 32.39 2397 893 24348 8461 87.9 1.351
-16.0 75 33.18 2453 935 25827 8737 89.2 1.324
-14.0 77 33.97 2509 979 27378 9006 90.5 1.297
-12.0 78 34.76 2566 1023 29019 9268 91.7 1.270
-10.0 80 35.55 2622 1068 30754 9523 92.9 1.244
-08.0 82 36.34 2678 1115 32589 9768 93.9 1.225
-06.0 84 37.13 2734 1162 34528 10004 94.9 1.197
-04.0 86 37.92 2790 1210 36577 10229 95.8 1.169
-02.0 87 38.71 2846 1259 38742 10442 96.7 1.139
+00.0 89 39.50 2902 1309 41028 10642 97.4 1.108
+02.0 91 40.29 2957 1359 43443 10829 98.0 1.079
+04.0 93 41.08 3012 1410 45995 11002 98.6 1.050
+06.0 94 41.87 3067 1462 48691 11160 99.1 1.023
+08.0 96 42.66 3121 1514 51540 11301 99.4 0.996 ! Near Maximum !
+10.0 98 43.45 3175 1567 54552 11427 99.7 0.971 ! Near Maximum !

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 89 39.50 3050 1446 48525 10633 100.0 1.023
Data for burning rate decreased by 10% relative to nominal value:
-Ba 89 39.50 2710 1141 33705 10119 90.6 1.208

Brilliant! Thank you Dromia.

So, a slightly loitering load for the 70 grainers as the lowest on Nosler's site is 3093fps. Not sure if 200fps makes that much of a difference and I suppose, if my barrel prefers it, then stick with it?

Someone mentioned to me about barrel harmonics, I'm not sure whether or not this is true, but they mentioned finding the right load that suited the barrel and created the optimum harmonic for accuracy. I guess, if it's a little slower and a little lower that's just what that particular rifle prefers.

It'll be interesting to see how the real world data compares!

Interesting that QL is giving Near Maximum warnings at the same load as had a stiff bolt.

Personally I would have stopped at 42 gns.

Looks like the Vihtavuori data is a bit hot.

Did you cross reference the data with any other sources like Nosler?

I tried, Nosler didn't have any data for the N150 with the 70gn (see here: http://www.nosler.com/nosler-load-data/243-winchester/). I did look at a few other places to see if I could get at least something close to 70gn but the closest I found was the reloadersnest.com load #9803 (which I was super cautious of, and which stated 39.7 gns and 3018 fps).

They do give data for a 55gn bullet though, which is 41-45gns. Given the rule of thumb that as bullet weight goes up, powder charge comes down (correct me if this is totally wrong) I think I'm about on the money. I agree though, the VV data does look a bit toasty doesn't it! I'm glad I took the other chaps advice and stopped when I saw the ejector marks on the case. Hopefully, four rounds at 42.5gns won't have done any lasting damage