Please Help Me Develop a Load for 145 GR LRX in 7 MM WBY Magnum

You have 3300 ft/sec as your goal and say you will stop at or close to this vel. I think that you should not assume that you will get there, but place more attention to pressure signs and not vel. You could max out before 3300 ft/sec or just sail on by.

cape cove said:

You have 3300 ft/sec as your goal and say you will stop at or close to this vel. I think that you should not assume that you will get there, but place more attention to pressure signs and not vel. You could max out before 3300 ft/sec or just sail on by.

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This is very good advice! Thanks for your reply. I will closely monitor every shot that I shoot today for signs of pressure.

Do you think that jumping by 0.5 grains with each shot I will be in danger? So far the biggest jump in velocity that I've seen in 0.5 grain increments has been 62 FPS when I made the jump from 2960 to 3022 FPS.

Also, with RL 22 when I was at 3300 FPS I showed no signs of over pressure. Why would that be different with H4831SC?

No 2 powders react the same. You can't just assume because pressure reacted in a certain manner with RL-22 that it will behave in the same manner with H-4831. Also, generally, when you are getting close to max pressure you will see a reduced # of ft/sec per .5 gr increase of powder. Always be viglant of pressure. I know that accuracy is important, but accuracy will not harm you, pressure will.

Duly Noted. So far I have seen a reduced number of feet per second two times. At 67.5 grains I was at 2999 FPS and at 68.0 grains it dropped to 2967 FPS. It dropped again at 68.5 grains to 2960 FPS.

From 70.5 grains to 71.0 grains it also dropped by 20 feet per second.

Bottom line, do you think it's safe to continue my testing with 0.5 grain increments noting that if I get to 3300 FPS or I show any signs of pressure I will then stop?

What are the chances that in a 0.5 grain increment jump the pressure will suddenly become extreme enough to cause me or my gun harm?

As long as you are capable of reading pressure signs I would continue going .5 gr at a time until you see slight pressure signs, then stop and reduce till all pressure signs have gone. If you are fairly new at this then I would read up on how to detect pressure. Till you have a good grip on pressure I would remain conservative and go by the manafactures data. What you have to remember is that you have a custom barrel and tighter twist than the factory. This changes pressure and in turn velocity. All Weatherby chambers have a generous free-bore, and with this you can use heaver loads than one could with no free bore. This is one of the ways Weatherby attains is high velocity.

OK. I'm going to read up on pressure signs. So far I've been looking mainly at the primers. All of mine look nice and round and not smashed after shooting. My embossed writing on the bottom of the case also looks distinct (not smashed). My cases don't have any splits anywhere.

Is there anything else I should be watching out for?

Ejector marks on the case head and a stick bolt lift are signs of pressure, as well as very flat primers and in some cases cratered primers. Case splits are in most cases not an indicator of high pressure, but of another problem such as improper case sizing, poor brass quality, etc.

OK. I will fire with extreme caution today. So far I could have lifted the bolt of my rifle with my pinkie each time and I haven't seen any unusual marks on the case heads when comparing them to all my previously fired cases. If I even feel an inkling of those things I will stop and not continue any further.

If I do feel or see any of those things then obviously I will stop my range time and back off when I load up for accuracy testing at a later date. I will be in touch tomorrow morning with the results.

I just got this email from Barnes so I'm changing my tactics. Once I get to 3200 FPS I'm going to stop and then do my ladder test from there. I no longer care about 3300 FPS.

The Email begins below:

Sorry about the phones, we have been slammed today. Your velocities are pretty close to what they should be, probably max out at about 3200 with H4831SC powder, you will get about 55-60 fps more with the 145 gr over the 150 gr. So you can go up a little. .5 gr, increments are fine but are small increments for a case capacity this high. You are not going to go from no pressure signs to damaging your gun in .5 grains of powder.


Wby is using proprietary powders and duplex loads, so don't compare your loads to their ammunition.





H4831 SC and RL 22 are different powders and should be treated as such, just because one gets a certain velocity does not mean the other will do it safely. 3300 fps is about what I would expect from RL 22 with a 145 gr. bullet at max charge. But I would expect to get about 3200 fps at max charge with H4831 SC.

chesspunker said:

Duly Noted. So far I have seen a reduced number of feet per second two times. At 67.5 grains I was at 2999 FPS and at 68.0 grains it dropped to 2967 FPS. It dropped again at 68.5 grains to 2960 FPS.

From 70.5 grains to 71.0 grains it also dropped by 20 feet per second.

Bottom line, do you think it's safe to continue my testing with 0.5 grain increments noting that if I get to 3300 FPS or I show any signs of pressure I will then stop?

What are the chances that in a 0.5 grain increment jump the pressure will suddenly become extreme enough to cause me or my gun harm?

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How long is your barrel? I am getting 3620fps out of a 140gr SST using H1000 in my 270 Wby (same case) 28" barrel.

I'm fairly certain my barrel is 24" long. I need to measure to be sure.

chesspunker said:

I'm fairly certain my barrel is 24" long. I need to measure to be sure.

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Hopefully you have at least a 26" barrel.

It's very possible it's 26". I'll need to measure to be positive. I know it's long enough to get what WBY says the speed should be on their factory ammo within 25 FPS. I've never considered it to be a slow rifle and when using RL 22 it actually seemed like a super fast rifle considering I got up to what Barnes Considers to be max speed of 3300 FPS with that powder way before getting close to the max powder charge they recommend.

Yesterday at the range my very first shot was 3225 FPS with 1/2 grain of powder over the max load on the Barnes recipe. The case showed no signs of pressure and the gun didn't seem to kick horribly, but the bolt did seem a tad bit heavier to lift than normal after firing. I may have just been paranoid, but since Barnes Bullets told me that with H4831SC Powder 3200 is about as fast as I want to go, I decided to stop there and make that my high limit. I'm going to the range on Monday to do a ladder test and find my flat spot. After that I'll load some groups at different lengths for accuracy testing.

Here is my plan:

I'm doing a ladder test for velocity on Monday and I'm starting with 71.3 grains of powder which should give me around 3100 FPS and I'm working my way back up to 73.5 grains which should be around 3225 fps in 0.2 grain increments. Once I determine the flat spot in velocity I'll load up several groups of three shots at different lengths.

I'm starting with the longest length that will fit into my magazine which is 3.370" to tip (2.796" to ogive). So far I've done all of my testing at that length so the muzzle velocities I've been sharing with you are from 3.370" long cartridges. I will then make my next groups 3.340", 3.310", 3.280", 3.250" and see if one groups better than the other. Does this sound like a reasonable plan? When I shorten the length of my cartridges do you think it will affect the muzzle velocity much? I don't want to shoot for groups with a chronograph strapped to my barrel because that might change barrel harmonics for me. Please comment.