Last winter when the temperature was in the 50's, I worked up a very accurate load for my 375 H&H with Swift 300 grain A-Frames. It was 78 grains H4350 (book max is 79.5) with Federal GM215M primers. Velocity was very consistent, averaging about 2507 fps. Last week when it was in the 70's, I loaded a couple of the same loads, same can of powder and tray of primers and my velocity went to 2575. And POI shifted down 3-3.5 inches. My practice load of 64 grains IMR-4064 also increased from 2345 to 2443 and POI went down about the same. Am I going nuts or is this normal? I just ordered a set of calibration weights for my RCBS 5-0-5, just to see if it was the scales. Any ideas? I am loading for a trip to Mozambique and it can easily be in the 90's or hotter.

try the load without the mag primer when it's hot.
i use mags with 4895 when the temp drops below 32*,it is a tad different but not enough to have to resight the rifle.

Yes, it is normal for pressure to increase in hot weather and decrease in cold weather thus higher velocity with same load in hotter temperature than colder. The higher velocity will cause the load to stike lower than the zeroed slower velocity because bullet is exiting muzzle at lower point of barrel rise due to higher velocity.

Lamar,

Thanks for the idea. I'll try some Federal 210's this weekend.

quote:

Originally posted by db1234:
Last winter when the temperature was in the 50's, ...Last week when it was in the 70's, ...POI shifted down 3-3.5 inches. .... Am I going nuts or is this normal? ....

Hey db, If your rifle has a Termite Food stock(aka wood) the problem could be due to the moisture content changing. That causes the Termite Food to flex(warp and warp some more) as the amount of water inside it changes.

I would suspect "warping" instead of a 20deg temp change having any "noticable" effect on the Point-of-Impact. I'm not using a 375H7H, but I am using a good bit of H4350 in other Cartridges. A lot of my Hunting Loads see temperature variations from 45deg<->125deg and none of them move that much.

Regardless of what the Termite Food fans say, it is the way that material works. Some is worse than others, but if it is Termite Food - it constantly changes (warps).

Best of luck to you.

Hot Core,

My main concern was the velocity change, because it seemed excessive. H4350 is supposed to be fairly insensitive to temperature. But, 75 fps change and 3" seems like a lot. You're not seeing near that much change in different temperatures? Thanks.

quote:

Originally posted by db1234:
Am I going nuts or is this normal?

When you got the load you liked, 78gr of H4350, how many shots did you take to achieve the average velocity? 3 shots when it was in the 50's and another 3 shots when the temp rose into the 70's?

A change in velocity of 68fps should not produce POI changes of 3" to 3.5"

quote:

Originally posted by DBird:
Hot Core,

My main concern was the velocity change, because it seemed excessive. H4350 is supposed to be fairly insensitive to temperature. But, 75 fps change and 3" seems like a lot. You're not seeing near that much change in different temperatures? Thanks.

Personal opinion from my limited experiance is, the "extreem" powders are fairly stable from room temp down to around zero/10* F. They do however show some variation above this.
I`ve heard tell the cartridge they are loaded in can also cause some to vary more then others. IMO that`s due to differences in the pressures these cartridges are loaded to.
I would stay with the mag primer simply due to the large powder charge and run another magazine full down range to see if maybe the chrony was fibbin` or reading off slighty due to a change in sun light.
I`ve run loads over my chrony before that when clocked again a week later were +/- 50 fps average quite regularly.
The change in POI? I have to go along with HC and look at a bedding issue or loose screw somewhere before blaming ammo...
Have a great hunt!

Hey db, I know folks have gotten tired of me saying - a chronograph can be misleading - but, that is why I'm not a big fan of them.

The first problem we have is I pretty much quit using a chronograph of any type back in the `80s, so my data is very dated. Second, I do not know if 75fps variance in a Case the size of a 375H&H is bad or normal.

I found that "for me", if I forget a chronograph exists, and focus on the best accuracy which is closest to a Safe MAX Load, while observing the Pressure Indicators(CHE & PRE), Load Development goes smoothly. Once I found that, then I used to chronograph the Load. Now it has evolved to the point that I realized knowing the exact velocity is pretty much worthles, "for me".

The bottom line "for me" is if the Load is accurate and the Pressure is OK, then the velocity is not a concern, nor the variation in the velocity. Maybe some of the Big Bore folks will jump in and be able to tell you if 75fps in your Load is something to be concerned about.

Dave(onefunzr2) would be a much better source of info about normal Variation between shots than I am, or any of the other folks that use a chronograph.
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I would be REAL CONCERNED about a 3" shift. I've never been to Africa and don't see it ever happening, but from what I've read(again dated info), I seem to remember large Humidity changes over the course of a week. I've lived the majority of my life in the High Humidity of the Southeastern USA and it is indeed difficult for "some" Termite Food stocks to remain stable.

If I talk to someone else, they often say their rifle's Point-of-Impact never changes even though they have a Wood Stock. I'm reluctant to say they are pulling a clinton on me, and yet that is just not normal for the sponge effect of Cellulose(wood).

If it is not Pillar Bedded, you might look into getting that done locally, if you are determined to stay with Termite Food. If you have a Synthetic Stock on it now, then Ol' Joe could be on to the problem with "a bedding issue or loose screw".

If you are using a Redfield Style Scope Mount, that could also be the problem. The Rear Rings tend to "Tear Through" the Lateral Adjustment Screws as the Scope slips forward through the Front Ring. That gives you all kinds of goofey Group Shifting(voice of experience).
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You might consider going up and using the "Find" Button and see what other folks have been using in their 375H&Hs. I've seen a few threads on them in the past. And you may find more info on the Big Bore Board.

I completely understand your concern with a $$$HUGE$$$ Hunt coming up. Best of luck getting the issue(s) resolved.

Last winter I worked up the accurate H4350 load and then ran 10 shots through the chrono and all were within 15 fps, which I thought was good. The lower POI is consistent with higher velocity, but 3" seems excessive for a 20-25 degree change. I only ran two loads of H4350 through the chrono last week because I was worried about pressure. But those two shots were touching, less than 1/2" center to center. And my practice load was grouping about 1"-2", which is normal for that load. To complicate things, I had just gotten the gun back from Hill Country Rifles in New Braunfels last winter for accurizing which included pillars and glass bedding, so I feel pretty good about that. I am not necessarily scared of 2575 fps, but I don't want it jumping to 2650 and moving another 3" when I need it most. Also, Hill Country put Talley Quick Detach rings and mounts on it, and the decent grouping with the practice loads makes me think that's not the problem.

Last winter, Federal GM 210M's were almost as accurate as the GM215M's and my notes show the same 78 grains of H4350 with 210's were within 5 fps of the 215's. I guess I'm going to try Federal GM210M's this weekend and see what happens.

Thanks for all the ideas. This is actually much more enjoyable than buying a box of factory ammo, sighting it in once and forgetting about it.

quote:

Originally posted by db1234:
I only ran two loads of H4350 through the chrono last week because I was worried about pressure.

Statistically speaking, data from only 2 shots isn't worth crap. Good luck sorting out your so called problem.

quote:

Originally posted by db1234:
...I had just gotten the gun back from Hill Country Rifles in New Braunfels last winter for accurizing which included pillars and glass bedding, so I feel pretty good about that. I am not necessarily scared of 2575 fps, but I don't want it jumping to 2650 and moving another 3" when I need it most. Also, Hill Country put Talley Quick Detach rings and mounts on it, and the decent grouping with the practice loads makes me think that's not the problem. ...

Hey db, Being able to rule out things that could be wrong is what it is all about.

I do agree with Dave that 2-shots is not nearly a large enough Sample Size. Even when you shot the 15, it might just be Random Selection that caused the variation to be smaller. But, it dosen't matter if the accuracy is there.

1. Did you change jugs of H4350 during the process?
2. And I was wondering about Neck Tension. I can see changing jugs of Powder spreading the Velocity and the POI. But I doubt Neck Tension would change POI that much.
3. Are your Cases from different manufacturers?
4. Are you cleaning your Barrel?

If you are concerned about Pressure, then (as always) I'd recommend you measure CHE & PRE. But, as Dave implied, you are going to have to take more than 2-shots for your data to be significant.

quote:

Last week when it was in the 70's, I loaded a couple of the same loads, same can of powder and tray of primers and my velocity went to 2575. And POI shifted down 3-3.5 inches. My practice load of 64 grains IMR-4064 also increased from 2345 to 2443 and POI went down about the same

The fact 2 different loads composed of totally different components makes me more certain the change in POI isn`t load related. The fairly consistant change in velocity also makes me doubt a change in the loads performance.

I`d try chronoing my loads with the sun at the same relative height and make sure the screens are level to the line of sight. If your screens fold, be sure to extend them fully for each setup. I found once with my Pact screens I was getting a odd reading and found the "ball detent" had slipped and the sensor was ~ 1/2" closer to the center of the rod then it should be.
HC (I hate to admit it at times ) has offered some good ideas about where to look also. A change in any of the component lots or going from a FL sizer to a neck sizer can make a difference.
One more place to look is the stock its self. I had a small crack ~ 1/2"-3/4" develope behind the trigger guard of a Sauer M200 that caused both a change in POI and group size. It wasn`t noticable at 1st glance and took me a week or two to figure out. Actually a fellow shooter was the one that found it
A 375 will certainly shake things up or move them. You might even find your grip on the rifle or change in where you rested the forearm is partly to blame. I hate to infer, but even the best of us at times has a bad day and gets a little jerky

Hot Core,

1. Same can of powder
2. I had resized the cases several days before and the neck lube may have dried. Would that make any difference?
3. All same cases, bought at same time.
4. Barrel cleaned religiously, with solvent and copper remover.

Ol Joe,

Could be the chrono. I'll reset it up this weekend and see what happens. And I'll go over the stock and mounts good. I was probably using a lead sled originally, and have gone to a front and rear benchrest type of rest, so that could affect POI.

I'm even wondering if my RCBS 5-0-5 could have gotten out of calibration. I didn't think that was possible with a scale- but do you know if they can?

Thanks again and I'll see what happens this weekend.

quote:

I was probably using a lead sled originally, and have gone to a front and rear benchrest type of rest, so that could affect POI.

Hey db, I'd guess that was the POI shift too. And since you even mention Lead Sled, then what Ol' Joe had to say about a split stock has increased greatly. I've seen 4-5 posts about stock splits due to Lead Sleds on various Boards here at AR. You may not have one, but then again you might.

Anything different in a Cartridge can effect the performance. The dried Lube could be a factor, but I really do not know.

If you are determined to use the chronograph, shoot enough shots that the data becomes significant, Normally 3-5 shots is OK when Developing the Load. Then once you have the Final Load selected, 15-18 makes the data Statistically Significant enough that it can't be argued with - unless the chronograph acts goofey.

quote:

Originally posted by Hot Core:

quote:

I was probably using a lead sled originally, and have gone to a front and rear benchrest type of rest, so that could affect POI.

No surprise, Hotcore nailed it! I'd bet the farm that is the 3" to 3.5" POI difference.

Although I'd say the point is moot. What counts is where you hit when shooting your 375 H&H off sticks, like you'll be doing in Mozambique. If you'll be hunting in 90 degree weather, develop your loads in 90 degree weather.