Where'd the velocity go??

[ajjohns]

First off, I shouldn't even be doing this. It's not a huge deal to me, a target, or a deer. Last year with the help of you fine gents and a lot of reading, I was able to develop a perfect load for my 73 Winchester, 38 WCF. I loaded as follows,

Starline brass
cci large pistol primer
IMR 4227 powder at 17.2 grs
PSB at 6.3 grs.
BHN 16 180 gr boolit.

This load was made with psb (poly shot buffer) because my chamber has a big neck, anything else did not work out in accuracy and leading was bad. Run through my chrony, it averaged around 1350 fps and groups ran around 1.5" at 75 yds. I was so happy!
Well, those boolits dried up, I purchased some that are 12 bhn, 180 gr. and loaded the same recipe. Had to try the chrony again yesterday and here's where I scratch my head. I had two old rounds left, and two new ones. The "stand by" loads were at 1290-1305 fps and the new ones were 1315 or so. Chrony was the same distance away, the only other thing I can think of is it was 50 degrees out now instead of maybe 80ish. Is that enough to drop velocity 50 some feet? Don't get me wrong as my first statement, I'm not upset. This load still shoots as accurate as I can hold the sights for sure. Was just kind of surprised the speed was down. We are able to shoot either sex deer this year in my zone with one license, I'm looking forward for another hunt.

Any thoughts?

[kayala]

Ambient temperature might have played some role, humidity - dry air appears to be more dense (here's article explaining it). Denser air would provide more resistance to the bullet so I'd expect some loss of velocity.

[rking22]

Talking about 3 1/2 % difference. Ammo temp has an influence, air density, lots of possibilities. Your are right no not be concerned. Would take a designed experiment with much data to solve the question with certainty. Like you, I feel it dosent matter, so chalk it up to " somethings a lil different ".. others will find it intriguing to figure out. Both are " right"

[ajjohns]

Last year was hot and more humid. This year, awful dry and cooler. Haven't mowed the lawn for two months, not complaining there either. The load with the new pills shoots very well also, maybe better. I just thought the chrony was goofy but not so. Yesterday humidity was up, we finally got 2" of rain and can't tell either, the ground soaked it up fast. 50f was the temp. This load at whatever speed (though I like as close to old factory as possible) is a sure winner to me.

[17nut]

First off, I shouldn't even be doing this. It's not a huge deal to me, a target, or a deer. Last year with the help of you fine gents and a lot of reading, I was able to develop a perfect load for my 73 Winchester, 38 WCF. I loaded as follows,

Starline brass
cci large pistol primer
IMR 4227 powder at 17.2 grs
PSB at 6.3 grs.
BHN 16 180 gr boolit.

This load was made with psb (poly shot buffer) because my chamber has a big neck, anything else did not work out in accuracy and leading was bad. Run through my chrony, it averaged around 1350 fps and groups ran around 1.5" at 75 yds. I was so happy!
Well, those boolits dried up, I purchased some that are 12 bhn, 180 gr. and loaded the same recipe. Had to try the chrony again yesterday and here's where I scratch my head. I had two old rounds left, and two new ones. The "stand by" loads were at 1290-1305 fps and the new ones were 1315 or so. Chrony was the same distance away, the only other thing I can think of is it was 50 degrees out now instead of maybe 80ish. Is that enough to drop velocity 50 some feet? Don't get me wrong as my first statement, I'm not upset. This load still shoots as accurate as I can hold the sights for sure. Was just kind of surprised the speed was down. We are able to shoot either sex deer this year in my zone with one license, I'm looking forward for another hunt.

Any thoughts?

So the new ones are 10-25fps faster and that bothers you???
A difference in alloy would do that, what is the problem?

[buckshotshoey]

Camp Perry High Power Shooter tip......
You will see a lot of the more serious shooters cover their ammo so it is not in direct sunlight. Just the sun heating the brass and powder will significantly change velocity and point of impact. It does make a difference in sight settings. Maybe not so much at 100 yards, but BIG difference at 600 yards.

Slow fire stages are timed to 20 minutes and single loaded. Not allowed to load all 20 in a magazine. Your 20th shot will show a higher velocity then the 1st one. I always kept my rounds under my shooting mat so the sun couldn't heat them up over the 20 minute time period.

So not only the air temp/humidity of the air will make a difference, but the temp of the powder can make just as big of a difference in velocity.

Try this..... go out on a cold day and let you ammo get cold. Keep one round in your brest pocket to keep it warm. I'll bet your chronograph will show you what I'm talking about.

Again you won't notice a huge point of impact change at normal distances. So unless you go long range, I wouldn't even think about +/- 3 percent velocity.

[country gent]

The rule of thumb for the older powder in 308 ( these powders were temp sensitive in like sole of the newer powders) was for every 10* increase above or below your base temp was good for 1 min at 600 yds. I set my ammo in the shade under my stool for 600 yds. When shooting you wanted to break the shoot quickly after chambering it so chamber heat didn't have as much affect also. powder temps humidity age softening or hardening of the bullet hardening age hardening of the cases all could have an effect here.

Your chronograph may also have been affected by light angle, intensity, and small differences in the set up. I got in the habit of firing a few rounds from my RWS air rifle over the chronograph to check it before going to the test ammo. Some use a known lot number of 22 lr standard velocity and the same 22 rifle. Either of these gives a known "standard" to compare each times use with at the start.

[ajjohns]

17 Nut,
So the new ones are 10-25fps faster and that bothers you???
A difference in alloy would do that, what is the problem?

No problem, a little higher in the post I said last summer they were faster. This fall the same loads are a bit slower.

I can tell there's a lot more to this than I originally thought, thanks guys, great info to keep in mind from now on.
What I'm about to say is gonna hopefully not make me look too dumb, but I forgot one thing. The speed thing is still the same, down from last year on last years loads, but I have one variable that's different this year. It's not on all the loads but the once fired brass, I have only 3/4 sized the brass (basically just the neck) because of how big the neck gets when I fire them. So, some are new brass and some a partial sized. There's a difference in internal capacity for sure. I'm happy with where I'm at, they shoot just fine, better than a lot of rifles I have at home. I'll just keep pluggin away!

[Lloyd Smale]

if 44man was still here hed tell you how big of a difference temp is to 4227. He didn't like it because of that. Me, I like 4227 just fine but to get real consistant results with it I allways have had to use a mag primer. Especially in loads that might be used in deer season because it might be below freezing then compared to 70s-80s in the summer when I do most of my load development. Ive even put rounds in baggys and placed the on ice in a cooler when I went to the range to mimic winter conditions. H4227 allways seemed to be more sensitive then imr4227 but rumor goes its all h4227 now that hogdon and imr powders are the same. I like it because in some guns it just seems to outshoot anything but for the most part id rather load with aa9 or 110/296 if I want a slow powder. that said I use a mag primer with those powders too and don't even fool with anything but a cci 350 with 110/296 and 4227. With aa9 I can get consistant results with about any mag primer.

[ajjohns]

Lloyd, thanks for the response. I thought about that also. My summer results in testing last year were about a 30 fps gain using mag primer per powder charge, though they were Winchester primers. They say for standard or mag loads. With that, I just decided to use the standard primer. I was trying Hercules Unique and IMR 4227 because that's all I had on hand. I do have IMR 4198, but didn't go there, yet. I found out right away that I needed to use the psb so Unique went to the wayside, 4227 won out. Now, I carry this gun all year, with testing say a month from now when temps are consistently cooler, maybe a mag primer is in tune for rounds carried in the winter. That maybe the case and that's fine too.

[Griff]

H4227 allways seemed to be more sensitive then imr4227 but rumor goes its all h4227 now that hogdon and imr powders are the same.

Can I ask you to quote a source on this?