OCW and OBT Load Development

[Dr. Vette]

Dr. Vette...

Give me some load and rifle info for one of your known good loads.....powder charge, bullet, oal, barrel length, and chrono'd muzzle velocity....and I think I can show you what you want to see.

Or it can be a known bad load....just any load, with a measured muzzle velocity.

I did this one using the OCW method.

7mm Weatherby Mag, Mark V stainless, 26in barrel
150 Barnes TTSX
75.0gr H-1000
3.359 COAL (actually 2.760 base to ogive with my comparator)
MV 3060 fps

How close did I get?

 

[Ridgerunner665]

You're testing me giving me the Weatherby, lol...long freebore...I added .378" to your OAL of 3.359" for a total of 3.737"...3.737" is the actual combustion chamber size when freebore is included, and freebore has to be for QL to work with Weatherby rounds...

OBT for a 26" barrel at node 5 is 1.33 milliseconds...QL says you're at 1.302"...well within 3%, and about as accurate as any prediction is capable of being...you're on node 5...node 4 (1.20 milliseconds) should be just above 3,200 fps, and should be within reach, easily.

Cartridge          : 7 mm Weath. Mag.
Bullet             : .284, 150, Barnes 'TTSX' BT 28476
Useable Case Capaci: 83.317 grain H2O = 5.410 cm³
Cartridge O.A.L. L6: 3.737 inch = 94.92 mm
Barrel Length      : 26.0 inch = 660.4 mm
Powder             : Hodgdon H1000

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.66% 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

-06.7   92    70.00   2845    2696   41469  12038     96.4    1.436
-06.0   93    70.50   2866    2737   42372  12126     96.7    1.424
-05.3   93    71.00   2888    2778   43294  12212     97.0    1.412
-04.7   94    71.50   2910    2820   44231  12295     97.3    1.400
-04.0   95    72.00   2931    2862   45208  12376     97.5    1.384
-03.3   95    72.50   2953    2904   46199  12454     97.8    1.371
-02.7   96    73.00   2975    2947   47216  12530     98.0    1.356
-02.0   97    73.50   2996    2990   48256  12603     98.3    1.342
-01.3   97    74.00   3018    3033   49322  12674     98.5    1.329
-00.7   98    74.50   3039    3077   50414  12741     98.7    1.315
+00.0   99    75.00   3061    3121   51533  12806     98.9    1.302
+00.7   99    75.50   3083    3165   52681  12867     99.1    1.288
+01.3  100    76.00   3104    3210   53857  12926     99.2    1.275
+02.0  101    76.50   3126    3254   55062  12982     99.4    1.262  ! Near Maximum !
+02.7  101    77.00   3147    3299   56298  13034     99.5    1.249  ! Near Maximum !
+03.3  102    77.50   3169    3344   57566  13083     99.6    1.236  ! Near Maximum !

Results caused by ± 5% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 5% relative to nominal value:
+Ba     99    75.00   3148    3300   56922  12685     99.9    1.246  ! Near Maximum !
Data for burning rate decreased by 5% relative to nominal value:
-Ba     99    75.00   2960    2918   46537  12697     96.3    1.363

 

[Dr. Vette]

You're testing me giving me the Weatherby, lol

Well you asked... :mrgreen:

...long freebore...I added .378" to your OAL of 3.359" for a total of 3.737"...3.737" is the actual combustion chamber size when freebore is included, and freebore has to be for QL to work with Weatherby rounds...

OBT for a 26" barrel at node 5 is 1.33 milliseconds...QL says you're at 1.302"...well within 3%, and about as accurate as any prediction is capable of being...you're on node 5...node 4 (1.20 milliseconds) should be just above 3,200 fps, and should be within reach, easily.

Interesting. It appears that you tweaked the QL to match my data?
Is that correct?

I had previously wondered about trying for the next node, but as I went up to 77(?) grains I didn't see improvement and I don't recall seeing speed like you have listed, so stayed with the 75.0.

I may ask another one tomorrow if that's OK.

 

[Ridgerunner665]

Tweaking is usually required...yes...but in your case here, all I did was add the freebore (.378" according to SAAMI) to the OAL...and it matched.

Ask away...happy to help.

Measured case capacities will make it more accurate...if you have measured them.

 

[SJB358]

Tweaking is usually required...yes...but in your case here, all I did was add the freebore (.378" according to SAAMI) to the OAL...and it matched.

Ask away...happy to help.

Measured case capacities will make it more accurate...if you have measured them.

Great info RR665.. I will have to fool around with that a little on my boys 300. I just got the 210 ABLR's as well, so those long suckers are going to get all the length the magazine can handle.

I'll have to run some checks adding the .378 into the OAL and see what I come up with..

 

[Ridgerunner665]

Tweaking is usually required...yes...but in your case here, all I did was add the freebore (.378" according to SAAMI) to the OAL...and it matched.

Ask away...happy to help.

Measured case capacities will make it more accurate...if you have measured them.

Great info RR665.. I will have to fool around with that a little on my boys 300. I just got the 210 ABLR's as well, so those long suckers are going to get all the length the magazine can handle.

I'll have to run some checks adding the .378 into the OAL and see what I come up with..

I believe it is .361" in the 300...

Also, if you seat longer than SAAMI oal...subtract the difference from .361".

If shorter than SAAMI, add the difference to .361".

 

[SJB358]

Got it. Makes sense. I'll give it a shot.

 

[Dr. Vette]

Tweaking is usually required...yes...but in your case here, all I did was add the freebore (.378" according to SAAMI) to the OAL...and it matched.

Ask away...happy to help.

Measured case capacities will make it more accurate...if you have measured them.

89.84gr with slightly rounded meniscus of water.



If I might, how about this one?

FC cases
270 Win using 140 AB
COAL 3.380
H4831SC powder
24 inch barrel
F210M primers
67.7gr capacity

speed 3035, 3064, 3071 and best accuracy but still not as good as what the rifle will do with factory ammo
-.03 seating speeds were 2994/3020/3033
-.06 seating speeds were 2994

I can't get this one to be repeatable and essentially gave up on it.
So, if the calculations can give any hints I'd be happy.

additional info
57.5gr 2933/2937/2915
58.0gr 2961/2946/2943
58.5 2998/2985/2844
59.0 2994/2994/3028
59.5 3006/3027/2986

 

[Ridgerunner665]

Now that one isn't so simple...I can offer a theory or two...but no promises.

You're either experiencing erratic ignition or chrono troubles...could be either one....no way to know which without more chrono data.

The load is on the node, or very close to it...so its one of the components that the rifle doesn't like...if I had to guess, I'd say brass (I never liked Federal, but thats a personal opinion)...could also be the bullet, you mention factory ammo but not what specific factory ammo (bullet)

 

[Dr. Vette]

Now that one isn't so simple...I can offer a theory or two...but no promises.

You're either experiencing erratic ignition or chrono troubles...could be either one....no way to know which without more chrono data.

The load is on the node, or very close to it...so its one of the components that the rifle doesn't like...if I had to guess, I'd say brass (I never liked Federal, but thats a personal opinion)...could also be the bullet, you mention factory ammo but not what specific factory ammo (bullet)

The rifle - both of my Vanguard 270 Winchesters, in fact - LOVE the Winchester PowerMax 130gr factory loads. Easily under an inch at 100 yards and continue Sub-MOA to 400 yards at 3000+ fps. So I know the rifle can do it.

However, the 140 AccuBond Home brew won't do it repeatably. Got 0.74 inch group once with the 60.0 load but can't repeat it. I don't recall how sunny it was or was not the day I was shooting and of course that messes with the accuracy of the Shooting Chrony.

All brass is trimmed to the same length, primer pockets are trued and flash holes are reamed. For the set of different COALs I even sorted them to have all the bullets of the same length to the ogive and all the brass of the same weight.

 

[Wyo7200]

Nice! Should cut the search time down for finding a powder that can fill the case and be "on" an OBT node.

 

[Wyo7200]

Three more confirmed loads. Will update my post above and maybe post pics.

 

[Wyo7200]

Dr. Vette,

This is what I'm getting in QL based on the velocities you provided. Like RR665 said, you're on node 4. I'm starting to see how OBT also shows which bullet weights may not be the ideal- such as a 180gr AccuBond out of a 16" barrel.

+00.0 106 60.00 3051 2893 63548 11834 96.5 1.104 ! Near Maximum !
+01.0 107 60.60 3084 2957 65915 11938 96.9 1.086 !DANGEROUS LOAD-DO NOT USE!

I'd drop it down to 56.2 and get on the 5th node.

+00.0 99 56.20 2839 2506 50621 11077 93.5 1.224

Or try another powder that will fill the case and be within the 5th node. (Didnt get any suggested powders with the 60gr charge that would hit the 4th node)

Powder type Filling/Loading Ratio Charge Charge Vel. Prop.Burnt P max P muzz B_Time
% Grains Gramm fps % psi psi ms
Alliant Reloder-25 105.9 58.9 3.82 2941 99.5 49977 11990 1.224
IMR 7828 103.8 56.4 3.66 2897 95.0 49787 11843 1.224
Winchester WXR 103.2 57.1 3.70 2921 96.8 51018 11964 1.224
Vihtavuori N165 103.0 57.0 3.69 2845 97.5 51861 10704 1.224
Accurate 3100 102.5 57.4 3.72 2895 99.3 54301 10906 1.224
Vihtavuori N160 102.3 54.9 3.56 2814 95.5 51622 10516 1.224
Hodgdon H4831 102.0 55.5 3.59 2841 94.4 50696 11032 1.224
Accurate MAGPRO 100.9 60.0 3.89 2928 93.2 51063 12321 1.224
Ramshot Magnum 100.6 61.3 3.97 2892 97.4 50275 11553 1.224
Alliant Reloder-22 100.5 56.9 3.68 2922 97.0 50964 11961 1.224
Vihtavuori N32C Tin Star 100.0 27.9 1.81 2175 100.0 63975 4247 1.224 ! Near Maximum !
Vihtavuori N560 100.0 57.1 3.70 2927 94.8 50482 12256 1.224
IMR 4831 25_06 98.7 52.9 3.43 2885 99.8 53053 10728 1.224
Norma MRP 98.7 57.6 3.73 2953 98.2 50707 12282 1.224
IMR 7828 SSC 98.2 56.4 3.66 2897 95.0 49787 11843 1.224
Hodgdon H4831 SC 98.0 55.5 3.59 2841 94.4 50696 11032 1.224
IMR 4831 97.8 52.4 3.39 2882 99.9 53144 10616 1.224
Alliant Reloder-19 96.7 54.1 3.51 2874 96.8 50958 11307 1.224
Winchester Supreme 780 96.2 56.7 3.68 2841 96.7 51389 10817 1.224
Hodgdon Hybrid 100V 95.1 51.5 3.33 2849 100.0 52037 9982 1.224
Hodgdon H4350 94.2 51.6 3.34 2826 97.8 51654 10472 1.224

 

[M7025-06]

I'm glad I found this thread.

I've been doing more research into OBT. I seem to be having some issues with developing a consistent load for my 280 & 25-06. I can find a load that will shoot sub moa one day, go to retest it on the next trip out, and it prints like a shotgun.

 

[Wyo7200]

I know your pain. Care to let us know what you've tried so far?

My dad uses 139gr GMX in his 280. He nailed a goat from 400 yards and it went through both shoulders and was lodged in the skin- mountain goat was laying down. The GMX retained 95 or 98% of its weight.

 

[M7025-06]

I know your pain. Care to let us know what you've tried so far?

My dad uses 139gr GMX in his 280. He nailed a goat from 400 yards and it went through both shoulders and was lodged in the skin- mountain goat was laying down. The GMX retained 95 or 98% of its weight.

Anywhere from seating depth, adjusting powder charge up and down in 0.30 gr. increments, to cleaning the bore a little more often. With the 280...I'm hoping the new stock (that has since been bedded) is the ticket to a little more consistency, that and I've swapped my RCBS full length/seater dies and Redding neck dies out for a couple of sets of Lee Collet neck dies and Redding body dies.

I had a load with the 280 that shot a 0.635'' 3-shot group one morning and the best I've done since then is 1.5'' (all at 200 yds). It's not even a consistent 1.5''...someday's it's a tad under that, others it's 2.5''+.

So with that...I've been digging into this OBT a little more hoping to find something that'll give me consistent results for both rifles (280 & 25-06). I've been playing around with QL along with some different powders to see what I can find. My go-to for both rifles has been R-22.

Sorry to high-jack the thread.

 

[Wyo7200]

Have you adjusted the weighting factor to represent an overbore cartridge in QL? It defaults to .55 for 25-07 and I found that changing that made my estimates match my real world data more accurately.

 

[M7025-06]

I did...i leave it set at 0.33.

I usually adjust the powder burn rate (no more than 5%) up or down to get QL to match my chrony readings.

 

[SneekeeMT]

Ok guys,
So I worked up my first OCW loads last week and got them to the range today. Can you guys please help me interpret the results and suggest which charge weights might be my OCW?

The first is on my Remington 300 RUM. notice the 100.5 grn and 99.9 grn loads are swapped. I somehow got the rounds out of order in my round-robin.
Bullet: Hornady 208grn A-max. Powder: hodgdon 50BMG. Remington Brass, CCI primes.
http://i265.photobucket.com/albums/ii20 ... 5yqlny.jpg


The second is on my Ruger .280 rem
150 grn NABLR, IMR7828ssc, nosler brass, Fed 210 primes

http://i265.photobucket.com/albums/ii20 ... mx2ovs.jpg


<a href="http://s265.photobucket.com/user/sneekeedanno/media/2015-02-07%20004.1_zpsw6ah4r4t.jpg.html" target="_blank"><img src="http://i265.photobucket.com/albums/ii202/sneekeedanno/2015-02-07%20004.1_zpsw6ah4r4t.jpg" border="0" alt=" photo 2015-02-07 004.1_zpsw6ah4r4t.jpg"/></a>

 

[DrMike]

Unless I'm missing something, your .280 load jumps out at you. The 300 RUM may take a little more exploration, though the full power load looks quite promising.