Temperature Sensitivity

[elmbow]

Hey all, I'm in southern Utah where we warm up a mite in the summer months. Typically I don't do much load development or shooting in the summer because it's just too hot. When I do go out, it is first light, and temps are usually mid 80s. Not too bad for an hour on the range.
I drew my Utah once in a lifetime Henry Mountain bison tag and I am going to load up some 250 Partitions in my Whelen AI for the December hunt. I have always used Remmy ammo to fireform my cases. This morning I used new Hornady 35 Whelen brass, and some old Hornady 180 SSSP bullets over 52.5 grains of 4895. This should have given ~2400-2500 fps in my 24 inch barrel. They clocked 2800 fps!!!
Absolutely no pressure signs, easy extraction, etc. So I decided to chrony one of my elk loads, 225 Partitions driven by 59 grains RE15. This combo ALWAYS produces 2825-2840 fps in this rifle. Today, temp at 85 deg F. Produced 2900 fps on the. Chrony.
So two questions:
1. In 40 years of reloading I have never seen seen such a difference between book speeds and chrony speeds, 300 fps on the 180s. This can't be caused by 85 deg temps??
2. My 225 Parts going 70 fps faster than normal? Is RE15 this temp sensitive?
Seriously, the 52 grains of 4895 is the Hornady manual starting load

 

[g.willikers]

So who are you going to trust.
What you see with your own eyes, with your own equipment.
Or what is published in a book by someone who probably is using completely different equipment?

 

[elmbow]

Well I mostly trust my Chrony Beta, but it isn't one of those fancy Oehlers and I have seen Chronys do some weird shyte over the years. Still, those 180s clocking 2800 instead of 2450+- is pretty unusual. I will admit that my custom AI barrel has always been fast but this is kinda scary fast. I will chalk up the 225 Partitions extra 60 or so fps to the summer temps, but can not attribute the extra 300 fps on the 180s to temps. Common sense tells me that I should be using ~48 grains of 4895 to push those 180s 2400 fps, not the manual's starting load of 52.5 grains.
I am just using these 180s for fire forming my cases. I have several hundred of them left over from my old 35 Remmy T/C Contender days. I have used them in the Whelen for small game loads, 1700 fps with 25 grains of RE7. I'm surprised they didn't blow up @2800 fps given they were designed for single shot pistols 1700-2400 fps velocities

 

[F. Guffey]

I shoot with some disciplined reloaders, when shooting with them I do not have to worry about temperature sensitivity; the next round to be fired is not in the chamber long enough to get hot. And then? After I pulled the trigger I do not have time to scope out the target, they want the last fired case out of the chamber and the bolt left open. One of them was complaining about developing winter loads for in the summer I suggested they keep their winter loads in the freezer and take the ammo to the range in a cooler.

F. Guffey

 

[brasscollector]

For 180gr speer bullet (FWIW) the online Hodgdon manual has a starting load of H4895 (not IMR 4895) at 56.0gr which resulted in 2640fps. Max load was 60.0gr at almost 2800fps. Not sure what difference the AI would have with starting loads, likely the barrel makes more of a difference than the extra chamber volume at that point.

 

[F. Guffey]

I built a wildcat and then made the mistake of posting my procedures on the Internet, one kind response suggested I was into some risky stuff. I did not agree so I called Hodgdon, It was not necessary for Hodgdon to agree with me, it was import to me they understood what I was doing and why.

Hodgdon instructed me not to use my fire forming loads after the cases were fire formed.

F. Guffey

 

[Slamfire]

I carefully align my Chrony's and fire a "standard load" over the screens for a reality check. If bullet does not go straight over the sensors I have received erroneous readings. Off axis sensors usually lead to erroneous high readings. Also, muzzle blast residue will cause high velocity readings. I have to move the Chrony out when I am shooting long barreled guns, and I had to move the thing way out with black powder. I put it so far out that I had to look at the display with my spotting scope, must have been 15 yards out to get readings with a 58 caliber Musket.

For rifle shooting I often take a 22 lr and shoot some rim fire rounds as a velocity check. I have a large data base for Remington Target SV, but only a couple of bricks left. I shot a lot of these rounds over the screens to verify that the readings are ball park.

 

[jmr40]

I don't have load data for 35 Whelen AI. But standard 35 Whelen data shows your 180 gr load well below starting data. The point of the AI version is safely get more powder in the case. With the right powder you should be able to get 3000 fps with 180's. Why would you even be loading them at 2400 fps. You can get near 2900 fps with 180's in a 30-06.

The numbers for the 225's and RL15 are right where my data says they should be, and yes an extra 50-100 fps in hot temps is perfectly normal.

The extra 300 fps from the 180's is theoretically possible, but doubtful. I think something else is going on with this load. According to my data you are well below starting loads, and that can at times create excess pressure.

Most powders will change velocity 1-3 fps for each degree temperature changes. Assuming you developed those loads at around 45 degrees you'd have a 40 degree temp change shooting them at 85. I'd expect around 50-120 fps faster speeds with most powder.

Some powders are designed to be very stable in a wide range of temps. But even they will change about 1/2 fps for every degree temps change. And they will be quite stable in some cartridges and not others. RL-15 was designed to be very stable in 308, and it is. It will be less stable in other cartridges. Without knowing what the temps were when you initially chronographed the 225's it is impossible to say. But a difference in 70 fps could actually be pretty good.

 

[kraigwy]

The Army Marksmanship manual using the M14/308 says for ever 10-15 degrees in temp, adjust your elevation 1 MOA. In my 40 years of shooting HP with a 308 I found that to be pretty close.

But there are problems people don't take into account. How do they store their ammo when shooting. I've seen people leave it in the sun. Some shade it.

Worse yet, how long does it stay in the chamber before you fire, and how hot is that chamber. Some when shooting a string will close the bolt, then pause waiting for a wind change. Others keep the bolt back until the instant they shoot.

The chamber of a semi normally gets hotter then that of a single shot.

If you take one of those laser temp gadgets you can get at your auto parts store you can get an idea.

The trick, like any other aspect of shooting is consistency. The more consistent the more accurate your zero.

 

[elmbow]

jmr40, to answer your question, the 180sssp is a discontinued bullet that Hornady designed for use in the original Thomson Contender pistol with the 35 Remington. It was designed for velocities from 1600-2400 fps. They have been taking up space on my shelf for twenty years. I have used them in my Whelens and 358 Wins at 1600-1700 fps for small game getters when out on rambles and now instead of screwing with corn meal and malt o meal for fire forming some new brass, I am using these 180 ssps at moderate velocities. I understand why eastern whitetail hunters would use 180-200 grain bullets in their pumps and autos but out here in the Great Basin and rockies, I hunt deer with long barreled flat stepping cartridges like the 270 Win and 270 WSM. My Whelen has one job and that is to put the hurt on 400+ lb. elk at ranges up to 450 yards. It is the ultimate elk rifle in my opinion and my bullet weights start at 225 and go up from there. A 180 bullet in a 35 Whelen is a non starter for me and that is why I am not trying to push these fire forming loads to 3000 fps.??????