H4895 temperature sensitive?

[Austend95]

New to the forum but I've been reloading since I was little. Ran into something weird as I loaded my 308 with 40.5g of h4895 and was getting great accuracy out of it in 90 degree weather. Haven't shot in a couple months and now it's 60 and my groups went to crap! Only variable I can think of that has changed is temp. Loaded up to 40.9 and like magic I'm getting 1 hole groups again. Anyone care to explain? Same powder lot

[Hammerhead]

According to Hodgdon, H4895 is one of their 'extreme' series rifle powders that "was developed to give shooters consistent performance, load after load, in even the most extreme heat and cold."

[jmr40]

Most powder will see a change in velocity of between 1-2 fps for each degree temperature changes. The "extreme" powders will still be effected by changes in temps, just much less so. About 1/2 fps for each degree.

With only a 30 degree change you would see 30-60 fps difference with most powders and about 15 fps change with a powder designed to be less sensitive.

I've never heard of it changing accuracy. You really have to see a lot greater change in temperature and start shooting at ranges greater than 200 yards to see any real difference. A load developed at 90 degrees and shot at -10 could be 200 fps slower. At longer ranges it'll be hitting enough lower to miss.

Another worry is that a load approaching max developed at 40 degrees could be over pressure if fired at 90-100 degrees. The speed and pressure changes work both ways.

[F. Guffey]

Anyone care to explain?

Not me; I would call Hodgdon, around here it would depend on which can because I have old cans and new cans of powder, most of my 4895 is IMR, IMR was temperature sensitive.

And then there are those TEXANS that develop loads in the summer and hunt in Colorado in the Winter, or Wyoming. I always suggest they place their hunting loads in the freezer. And then place their cold loads in a cooler then take the cooler full of ammo to the range and test fire. I also suggest they take their hunting loads to the range without refrigeration and test for a difference in pressure and accuracy.

And then? I can not remember seeing ammo on a shelf anywhere that read; developed for cold climate or developed for hot climate.

At the range, I have shot with some very disciplined shooters; to avoid heating the chamber up they will not allow anyone to fire a round and leave it in the chamber while they score the shot, they insist on removing the case from the chamber immediately and they recommend leaving the bolt open. All of these things are automatic to them.

When heat effect the round in the chamber the longer it takes to take to aim and pull the trigger the more the heat effects the powder. So, there is the first shot, are you shooting at the same thing all day long or do you have one chance to get it right? I have a 30/30, I am concerned only with the placement of the first shot.

F. Guffey

[Jimro]

I loaded my 308 with 40.5g of h4895 and was getting great accuracy out of it in 90 degree weather. Haven't shot in a couple months and now it's 60 and my groups went to crap! Only variable I can think of that has changed is temp. Loaded up to 40.9 and like magic I'm getting 1 hole groups again. Anyone care to explain? Same powder lot

First, you need to explain what "crap" is shooting like.

If you say "one hole groups" are easily done with H4895 in your rifle with 40.5gr in 90 degree heat, a drop in 30 degrees F might open them some, but whether that is 1 moa or 2 moa we can't help much.

The other thing is that you probably did one of two things; cleaned your rifle bore REALLY good before you put it away, OR you didn't clean it at all, and your barrel took more than a few shots to get to the same state that it was in when you were shooting "one hole groups" in the summer. You might find that 40.5gr from a fouled bore in 90 degree heat is equal in velocity and accuracy to a 40.9gr load from a clean bore in 60 degree weather.

Jimro

[Austend95]

By crap I mean 1moa+. But when i have been consistently shooting .25 and .5moa groups it thoroughly confused me. And when it first started I thought maybe it was dirty so I did a quick clean and shot a few fouling rounds and it didn't change anything still 1+ at 100.
And I will include a pic since Jimro seems a bit leary about my "one hole groups" lol

[RC20]

I too have had some odd things happen temp wise.

Usually its the other way around, I get some good loads going in cooler winter months and come summer they go to hell.

No good explanation, none of them are pushed.

We don't get hot and its mor3e like 45 degrees is a crossing line,

Check the action screws, check scope screw and mounts, is the barrel contacting the stock now (free floating before)

Your powder should be as immune as it gets and I do feel the pain

A lot of times its trigger and how you hold the gun.

One theory I have is winter time I have more cloths on and the hold is different.

Good luck.

[Jimro]

By crap I mean 1moa+. But when i have been consistently shooting .25 and .5moa groups it thoroughly confused me. And when it first started I thought maybe it was dirty so I did a quick clean and shot a few fouling rounds and it didn't change anything still 1+ at 100.
And I will include a pic since Jimro seems a bit leary about my "one hole groups" lol

Try for five shots

But, there are two likely scenario, either your load changed "just enough" with a 30 degree drop in temperature that the barrel harmonics changed from a "still" node to a "scatter" node, or the H4895 powder inside your brass had started to "clump" and change its burn characteristics that way. You might pull a few apart and see if you have clumps of powder that stick together. If you do, it means there was probably some bullet lube that ended up inside the case.

I've had plenty of powder "clump" on me, and my experience is that it will cause flyers.

Jimro

[T. O'Heir]

What kind of stock, wood or synthetic? Wood can expand when the relative humidity changes. Kind of suspect the humidity will change a bunch from 90 F to 60 F.
Wouldn't worry too much though. Your 40.5 is only .5 above minimum for a 180 grain bullet. Way under minimum for lighter bullets.

[Austend95]

All screws were tight but I loosened and retourqued them just to make sure. Rifle is rem 700 still in factory sps-v stock so its not free floated

[Jimro]

One more question,

Were you going from virgin brass with 40.5 gr to once fired brass that opened up until you pushed it to 40.9 gr?

Jimro

[Austend95]

Oddly enough it's 40.5 behind a 168 match king. Ppu brass which averages like 179g I think. Winchester primers and a 26 inch barrel

[Austend95]

It's all once fired in my chamber. I'm starting to lean towards a free float stock of some sort but I hate to spend the money if it doesn't help any because I am AMAZED at the accuracy of this gun in factory form. Only upgrade was a timney trigger and that was to take my error out of the equation. Could the stock be part of the issue?

[Jimro]

Did you remove the barreled action from the stock between shooting sessions? If yes, then it can take a few rounds to seat the barreled action back into the stock properly and get your groups to "settle in." If not, odds are temp or something else...

Jimro

[Austend95]

Idk I'll have to do some more loading and experimenting when I get some time. But if 40.9g stays consistent I guess my problem is solved.

[F. Guffey]

I also suggest they take their hunting loads to the range without refrigeration

Strictly optional; and then there is climate control and relative humidity. Humidity in the case will freeze, I would think loading on warm/hot/dry days would be better than loading on hot/humid days when loading on hot days and shooting on cold days.

It would be like the southern fishermen that go north to ice fish. A lot of them paid good money to be successful; like the old gentleman on the Johnny Carson said; "You got keep your worms warn".

http://www.fishfinder-store.com/fish...s-stories.html

F. Guffey

[brasscollector]

Could the stock be part of the issue?

If your stock is in contact with your barrel (or if you can flex the stock to touch) at the forward end of the stock then the answer is yes. Then all it takes to change how your gun groups is to change the amount of pressure on the fore end. Factory plastic Remington stocks will flex as bad as the rest. There are some alternatives to spending $300+ on an aftermarket stock. What it comes down to is the depth of your wallet or your ability to stiffen the current stock.

[Unclenick]

The Remington stock contact bumps usually do well on accuracy, but you do want your load tuned to them. I would go through loads to find both a lower and upper limit before accuracy deteriorates, then use the middle of that range.

Denton Bramwell showed that barrel temperature has more effect than the ambient temperature range that the powder burn rate is stabilized for. That stability helps a hunter taking a shot from a cold gun, but if you shoot enough to let the gun warm up, all bets are off. In 60 degrees the barrel will cool faster between shots than at 90 and that may be the cause of the problem.