Temp and Velocity

[metallica]

How does temp. affect ft/sec??? does waremer or colder weather make a bullet move faster??

 

[FOTIS]

Metallica:

Go here http://noslerreloading.com/phpbb2/viewtopic.php?t=2459
and plug in different numbers and see how trajectory is effected.

 

[metallica]

Thanks for the link but I am unable to download those things on this computer.......... Im not looking for exact #s im just wondering cause this is the first time i have used a chrony and it was -12C out when I was shooting. Im just wondering if my ft/sec will be faster or slower when it gets warmer out durring the summer cause then I know I have to cut back on my loads cause i am shooting a 180grn AccuBond out of my 300wby at 3500ft/sec

(IMR 7828 84grn, 26" barrel)

It seems to be a little fasdt for my liking but i was thinking maybe it was faster cause it was cold out....??????


thanks

 

[metallica]

I am also wondering what is average range in ft/sec for a 5 shot group??? Between 5 shots there was 7 ft/sec difference...... is this high or low??? thanks again guys

 

[wildbio_13]

theoretically, everything being held constant but temperature, the bullet should travel faster as temp. increases. Think of a hot air balloon: the air in the balloon is heated, the air molecules exhibit greater movement with resultant greater intermolecular space and lower air density (in the balloon). Because the air density in the balloon is less than the outside atmospheric air....the balloon rises. Lower air density (warmer air) means less air molecules in a given space and less resistance to the bullets travel. The same is also true of differences in air density with differences in altitude (elevation above sea level). The higher the elevation, the lower the air density) due to gravity....with higher bullet speed at higher elevations. Of course temperature also affects pressure in the cartridge...increase the temp. of the cartridge results in greater pressure generated with increased velocity resulting. I have no idea how much any of this is a factor for a hunting load....the ballistics calculators show the biggest influences the further from the muzzle you get.
One result: a .308 dia, 180gr muzzle velocity of 3500fps
temperature: 70 degrees f (21C), 4000 ft elevation = 3054fps at 200 yards, 2848fps @300yards, 2650fps @ 400yards and 2462fps @500yds
temperature: 10 degrees f (-12C), 4000 ft elevation = the numbers stay the same When using the calculator altitude had a much greater influence on velocity whereas temperature had no effect (at a range of -29C to 27C)

*3500fps for a 180 grain makes me think something is amiss. factory loads max out at 3200fps

 

[Ol` Joe]

According to E.H. Harrison in the NRA "Fact Book" both velocity and pressures rise with the temprature. The figure he came up with in 1930 useing national match ammo loaded with berdan primers and IMR powder was 1.7 fps for every 1 deg F change in temp. He claimed the line had trouble with the ammo, and blamed it on it being left in the sun. He didn`t give pressure variations found, but noted factory ammo was loaded conservatively to prevent danger from being left in the sun where it could easily reach temps of 130 deg F or better quickly.
I always try to work up my hunting loads in the summer when temps are high. This allows me to ASSUME my loads will be safe during hunting season. I do have to recheck my zero when season rolls around but it normally is off and if it is I see no more then 0.5" -0.75" chance in impact. Most of that is likely because of difference in clothing and how much coffee I`ve been drinking.... :grin:

 

[Guy Miner]

Metallica, 3500 fps with a 180 is Smokin' Hot. What's the max load according to the loading manual you're using?

Check to see if your chronograph is set up far enough from the muzzle to escape the muzzle blast which can throw off the readings.

Check the chronograph against a known velocity, preferably with another chronograph handy.

Higher temps will cause both pressure and velocity to increase. Some powders are more affected by this than others.

If all your shots are within 7 fps of each other - that's very good. Single digits are good! :grin:

 

[Guy Miner]

Okay - I just checked Hodgdon's web site, which now has loads for IMR powders as well.

Max load for a .300 Wby mag and a 180 grain bullet on their site is 80.5 grains of IMR 7828 for 3064 fps and 53,400 CUP.

I'd say your 84 grain load just might be a little on the warmish side... :grin:

 

[FOTIS]

Thanks for the link but I am unable to download those things on this computer.......... Im not looking for exact #s im just wondering cause this is the first time i have used a chrony and it was -12C out when I was shooting. Im just wondering if my ft/sec will be faster or slower when it gets warmer out durring the summer cause then I know I have to cut back on my loads cause i am shooting a 180grn AccuBond out of my 300wby at 3500ft/sec

(IMR 7828 84grn, 26" barrel)

It seems to be a little fasdt for my liking but i was thinking maybe it was faster cause it was cold out....??????


thanks

OK:

You do not download all of them. You just plug the numbers in while online.

180 AB's at 3500 fps? Unless you are shooting a 30-378 WBY-- at max pressures no less-- you're toying with disaster buddy. :shock:

 

[Guy Miner]

Okay - now I checked another manual, and 84.5 seems okay with it... Sheesh... Guess every rifle is different. That's quite a spread, and I do wonder, at 3500 fps, if you're playing with excess pressure?

Beats me - but at that velocity, I'd tread carefully and check for case head expansion & for all the other pressure signs.

Regards, Guy

 

[metallica]

Thanks guys, i thought it was a little fast. The nosler reloading book shows a max of 84.5 grn for IMR 7828......... And there was anouther guy at t5he range with anouther chroney that i shot through and it was the same just under 3500........ and both chronies were about 20' away from the bench........ I know its a little hot well really hot for my 300bee thats why i wanted to know if it was the Temp. and if your saying it will only get faster as it warms up then yeah i have to figure stuff out.......




I shot 4 diff loads of 7828 that day (and have one sore shoulder) and they were....



80grn 3100ft/sec
82grn 3250ft/sec
83grn 3400ft/sec
84grn 3500ft/sec




now im starting to think that maybe its the wrong powder in the container........??????


time to buy a new batch of powder and work my way up from 75grn and see what kind of speed i get....... Or any other thoughts..?????


thanks

 

[metallica]

And the cases check out ok, so far, they only grew .004" after being fired and the head space checks out ok..... I do have to say I do like this new Nosler brass......

 

[Guest]

If you're new virgin brass is expanding .004", I think that may be a lot. I was under the impression that unfired brass shouldn't expand more than about .0001" and once fired brass should expand less than that by a factor of just over half, for a limit of .0004-.0005". If you're getting .004, you're going to lose an eye or worse at some point soon. I hope it was a mistype on your part and you meant .0004".

And here's a question, folks:

How much casehead expansion is considered too much with higher pressure magnum rounds? I know the above information is touted to very closely approximate 50,000CUP or 60,000PSI, but what about Weatherby rounds where 65-68Kpsi is the expected norm? How much is too much?

 

[metallica]

I didnt think that a case lenght increase of .004" (before re-sizing) wasnt too bad..??? All the material Ive read says that you may trim a case up to 4 times and up to .060" Is what im reading wrong?? please let me know, thanks


my nosler brass came from the factory at 2.810" well away from the max case lenght of 2.825" so i figured that a .004" before re-sizing increase wasnt too bad??? there in the tumbler right now but ill post what they come out as after re-sizing..........

 

[kraky]

Being that 300 wby is one of my favorite calibers and I own two guns and reload for others I'm finding that velocity unreal.
Are you shooting out of a weatherby rifle with freebore or a different gun without it?
If you are really doing that velocity I can't believe there aren't blown primers and that the bolt would even open.
I also wonder what kind of capacity the nosler brass has.....is it reduced by quite a bit compared to wby?
I'd like to keep this thread alive till the answers are found out. Either we have 2 bad chrono's......nosler brass is made of titanium or some high tech alloy never before heard of....the powder in the can isn't 7828....or unknown gremlins are at work.

 

[Guy Miner]

On the other hand... If Metallica is really getting 3500 fps, and the load is safe in his rifle... He may have found something we'd all like to find...

That is just a whole lot of velocity - high enough that the figure raises all sorts of "caution" flags in my mind.

So how'd it shoot at more normal velocity, say 3000 - 3200 fps? :grin:

 

[Guest]

I didnt think that a case lenght increase of .004" (before re-sizing) wasnt too bad..??? All the material Ive read says that you may trim a case up to 4 times and up to .060" Is what im reading wrong?? please let me know, thanks


my nosler brass came from the factory at 2.810" well away from the max case lenght of 2.825" so i figured that a .004" before re-sizing increase wasnt too bad??? there in the tumbler right now but ill post what they come out as after re-sizing..........

Alright, you're ok on length there, metallica. I was talking about case head expansion, which is the area (on belted mags) just above the belt becoming larger diameter, and it must be measured with a blade mic. We were talking about two different things. Sorry for the confusion.

I still think you need to evaluate these loads very carefully, as they seem to be surprising all of the other 300Wby shooters on here. What do the spent primers look like? Are they flat around the edges, or are they still rounded where the 'bottom' of the primer turns up to the side? Also, do you have any trouble opening the bolt on the gun after firing? What about if you tried to rechamber a piece of brass without re-sizing it? Does it go easily, or is it hard to get the bolt closed? (You can do this with any piece of spent brass and see if it is really tight in the chamber. Just drop it in through the bolt opening and then close the bolt on it, but don't do this in a mauser action.) Also, is there a little shiny spot on the case head where the stamp shows the caliber, a place that is noticeable shinier than the rest of the case head?

I think you're experiencing some excess pressure, just based on what I read about the 300'bee, but I could be wrong.

 

[Ol` Joe]

Thanks guys, i thought it was a little fast. The nosler reloading book shows a max of 84.5 grn for IMR 7828......... And there was anouther guy at t5he range with anouther chroney that i shot through and it was the same just under 3500........ and both chronies were about 20' away from the bench........ I know its a little hot

Pressure and velocity are related, you can`t have one and not the other! 60K psi can only do so much work, no more. If you see a large jump in velocity you can strongly assume pressures are hopping too.
Nosler does list 84.5 gr of 7828 but they only show 3185 fps as their velocity. I would suspect and load that gives over that velocity with the components shown. Speer stops at just over 3100 fps in their manual. both use a 26" bbl. Both likely load to the same pressure levels. The difference in charge weight between the two books is probably caused by the change in bullet bearing surface, jacket and core hardness and the primers used. The Speer book also used a rifle as a test bed where Nosler uses a universal reciever with a SAAMI spec pressure barrel in theirs. I haven`t checked other sources but the fact you are over 300 fps faster then these manuals report and according to other posters likely the same over other books would make me very shy of the load. I`d back it back down to the point of equal velocity with the book useing the same components and call it max. Eyes, fingers, ect are not free and I would hate read of someone loseing any.

 

[wildbio_13]

If you're new virgin brass is expanding .004", I think that may be a lot. I was under the impression that unfired brass shouldn't expand more than about .0001" and once fired brass should expand less than that by a factor of just over half, for a limit of .0004-.0005". If you're getting .004, you're going to lose an eye or worse at some point soon. I hope it was a mistype on your part and you meant .0004".

Dubyam, Hodgdon's 2004 manual talks about 2 methods of measuring expansion: 1. at the expansion ring (just ahead of the belt on belted mag's) and 2. at the "web"(just ahead of the extractor groove as outlined in Hornady Handbook of Cartridge Reloading). Both methods compare expansion of new unfired brass with fired brass just measuring at different locations. I used the expansion ring method for some 7mm rem mag loads using Nosler brass and came up with about 0.0043" avg. expansion (factory load was 0.0055 for comparison). Using the web method, one would expect much smaller expansion figures (and requires a blade micrometer to fit into the area measured). For that method, Hornady found that for low-pressure cartridges (e.g., 30-30) expansion should be 0.0003 to 0.0004, mid-pressure cartridges (e.g., .22-250 or 30.06) should be 0.0005 to 0.0006, and belted mags should not expand more than 0.0006 to 0.0007"
data is expected to differ slightly with different brands of brass due to variations in thickness, hardness, and composition.
As expected expansion is much less using the second method due to measuring expansion at a much stronger part of the case.
I used the first method to make sure I wasn't exceeding pressures of factory loads....made a nice chart plotting grains vs expansion (and grains vs velocity)....I also examined primers to check for pressure signs....from what I've read folks should be looking at all of these pressure indicators.

 

[Guest]

wildbio, I have read the Hornady #4 & 7, as well as the Speer #12, and while I am not sitting right with them right now, I remember that measurements were listed as right above the extractor groove on unbelted, right above the belt on belted, and right above the rim on rimmed cartridges, respectively. If I am remembering wrong, pardon me. It is possible. But to your point, casehead expansion should run somewhere in the ten-thousands of an inch, not thousandths of an inch, when measured this way. I have always read to measure once fired brass, and then measure again after firing, and use the difference as a gauge. I also read that up to three firings could be done with accurate measurements, but then I have read contradictory statements about that, too, stating the safest way to do it is with once-fired brass. To that end, I did a little checking, and Barnes lists their procedure as not more than .0005" with once-fired brass, and not more than .0010" with virgin brass. I am about to start measuring caseheads for one of my rifles, so I will try to post a little something on what I find. First, I have to wait for my blade mic to arrive. Those little buggers are hard to find at a decent price!