4831SC Temp Sensitive?

[Bacarrat]

As I understand it, 4831SC and the whole line of Hodgdon Extreme line of rifle powders are not temp sensitive. Is there a lower and upper limit on what temps they are not sensitive to?

I was shooting the 7WSM at the 600 yard line the other morning. Nothing out of the normal, little to no wind, typical hot and sunny Summer day in Houston, but as the day went on, the shots started hitting high. I was shooting at a 10" square piece of steel and was getting consistant hits, but after sitting out in the baking sun for about 2 hours, all my shots started going about 1.5-2 MOA high at 600 yards. Looked at the brass, you could start seeing some pressure signs on some of the brass but nothing major. Has anyone experienced this with the Hodgdon Extreme line of powders? What else could be done other then put a towel or close the ammo box to cool down the ammo other then putting it in a cooler.... I don't want to go to that extent.

 

[Rafael]

Re: 4831SC Temp Sensitive?

The Hodgdon Etreme line is "less sensitive" than most but not immune. They all have some sensitivity to temp swings.
I have not used 4831SC but I can say that I have observed less differential with the Extreme line than with other powders.

 

[Bacarrat]

Re: 4831SC Temp Sensitive?

Thanks Raf. I have used mostly Hodgdon powders in the past for the reason that it wasn't sensitive to temps, but this is the first time I have seen this much swing in POI. Then again, I don't think I usually leave the ammo sitting out baking in the sun for this long too often either.

Also got to shoot a friends .308 loaded up with Win 748. It also was sitting out as long as mine was. Last shot of the day, we were just shooting to get rid of some old loads sitting in the box. Needless to say, I do not know where the primer went.

 

[FCS]

Re: 4831SC Temp Sensitive?

1.5 to 2.0 MOA difference as day warms up, humidity increases isn't all that abnormal. Air temp increase and humidity increase is going to "thin" the air so impact point at distance is going to move up.

Keep ammo in a solid color plastic box, not the see thru plastic box and keep ammo/ammo box out of direct sunlight as much as is reasonably possible.

I would submit you had two variables that created your 1.5 to 2.0 MOA shift in impact. Ammo getting heated by sun and thinner atmosphere for bullet to traverse. I saw very similar effect at 2004 Nationals but my ammo was kept in shade/under towel w/no pressure signs. Cool morning turned into pretty warm & humid day. I had to come down 2.5 MOA from what was needed first string in morning to last string fired about noon. YMMV.

H4831sc has been pretty temp insensitive for me in my 300 WSM. However, no powder is completely temp insensitive.

 

[ChadTRG42]

Re: 4831SC Temp Sensitive?

Correct. It has more to do with the enviromental condidtions than the powder. Though the powder may be a small factor. Definitly record these findings, because you might need to know this during a match when you have the same conditions.
At the Tac Pro sniper match earlier this year, about 5 shooters, including myself, re-zeroed our rifles at 100 at the end of the first day. It was in the 90's that afternoon. On the cold bore shot at 300 yards the next morning (in the 70's), everyone that re-zeroed was 2 MOA low. You could have put a level straight across on our shots they were that level.

 

[Bacarrat]

Re: 4831SC Temp Sensitive?

It's been noted. Another odd thing is that I shoot at 2 different ranges and the dope at 600 is about 2 MOA different at both ranges with about the same atmospheric conditions for the most part. At first I thought it could have been a one off deal. But it has happen on every occasion when I switch ranges. My normal range has elevated berms for us to shoot at and the targets are a little higher up, then the place I shot at this past weekend, where it was flat all the way to the target. I am not sure if that has anything to do with it or not, but I found it odd that I would have 2 different dopes for 2 different ranges.

 

[ChadTRG42]

Re: 4831SC Temp Sensitive?

Yes! I have different dope than normal at a few ranges, also.

 

[Grump]

Re: 4831SC Temp Sensitive?

If you're shooting through boiling mirage on a flatter range, as compared to berm-to-berm, you can actually be shooting 1-1.5 MOA higher at the flat one because of the mirage optically displacing your target image UP. Shots hit high there, so you click up there, and then you're high without the same mirage.

The thickness of the mirage zone being fired through can have an effect.