I have a 270 Win. Remington SPS. Really like the rifle, very accurate. I've been working on load development the past couple weeks, switching it over from Sierra GameKings to Nosler bullets. The rifle is 2 years old.

Our temperatures here have been in the 20-32 degree range. I've been using H4831 loads in the 59-61 grain range and using a Chrony F-1 chronograph....new Hornady brass, 130 grain Partitions, Ballistic Tips and Accubonds. The rifle is grouping nicely with several loads but my velocities seem to be very low....

My Nosler manual shows 3,124 fps using 59 gr H4831sc. Today I shot 3 shot groups with BTs, AB, and NPs using 60 grains of powder, chronograph readings were in the 2750-2830 range.

Do you think this is due to cold weather, bad chronograph or the rifle? I'm happy with the accuracy but not pleased with velocity I'm seeing on the chrony....thoughts?

Thanks in advance.

It is common for actual velocities to differ from loading manual velocities because of the many variables involved.

Shooting cold ammunition will result in lower velocities than shooting the same ammunition when it is hotter.

A simplified, rule of thumb, ammunition burn rate conversion table based on the velocity of the load at 70°F is* :

Ammo --- Velocity
Temp --- Conversion
in °F ---- Factor
================
00° --- -0.0323
10° --- -0.0302
20° --- -0.0275
30° --- -0.0241
40° --- -0.0199
50° --- -0.0147
60° --- -0.0082
70° ---- 0.0000
80° --- +0.0101
90° --- +0.0228
100°-- +0.0387

============================

So, for example, if you have a load that produces 2950fps @ 70°F and you are shooting it at 30°F then:

V30°F = 2950fps + (2950fps X -0.0241) = 2950fps - 71fps = 2879fps



Or, if you have a load that produces 2840fps @ 70°F and you are shooting it at 90°F then:

V90°F = 2840fps + (2840fps X 0.0228) = 2840fps + 65fps = 2905fps


==========

You can also use it to determine the velocity of a load shot at one temperature compared to shooting it at another temperature. The easiest way is to first, calculate the velocity @ 70°F and then use that for various temperatures at which you will be shooting.

For example, your .270 load averaged 2790fps at let's say 30°F.

First standardize to 70°F. We know that: V30° = V70° + (V70° X -0.0241)

We also know that V30° is 2790fps from the chronograph data.

So, 2790fps = V70° + (V70° X -0.0241) = (0.9759)V70°

Therefore, V70° = 2790/.9759 fps = 2859fps

Next, using your calculated velocity of 2859fps @ 70°F, create a velocity-temperature table specifically for that load.

It will look like this:

Ammo --- Calculated Velocity my .270
Temp ---- using Xgr of Y powder and
in °F ---- 130gr Nosler Partition bullet
=================================
00° ---- 2767 fps
10° ---- 2773 fps
20° ---- 2780 fps
30° ----2790 fps - measured
40° ---- 2802 fps
50° ---- 2817 fps
60° ---- 2836 fps
70° ----2859 fps - calculated and used as standard
80° ---- 2888 fps
90° ---- 2924 fps
100°--- 2970 fps

It is important to point out that we are talking about the temperature of the ammunition and not the temperature of the air.

These calculated velocities go into calculating trajectories and holdover. Do I do this sort of calculation for all my loads? No, almost never. The differences are not worth bothering about unless you are shooting at very long ranges and/or the temperature differences are great. I don't do the kind of long range shooting where small velocity differences matter. But the people who do run numbers like these all the time.


* Simplified from the Ammunition Burn Rate Conversion Chart in Hard Target Interdiction by Dean Michaelis.

.

Grenadier,
Very useful information. Thank you!

What altitude?

Altitude has an insignificant effect on muzzle velocity, meaningless in the practical world. But altitude does come into meaningful play when working up external ballistics.

Essy way to find out. Leave some rounds oytside so they fully reach the ambiany temp. Put several rounds in a baggy and pack them around in your armpit for a half hour or on the defroster of your truck. . Chronograph the warm ones first. Then the cold ones. If everything is the same, powder , primer , brass and bullets. Then that will be pretty definitive. As to the Chrony, if you have a low hanging sun, or sunny with snow on the ground. Or the bullets pass over the screens at different places. Or it it not plumb and level. It will give odd readings.
Lastly , H4831 is one of the Extreme Extruded powders. Like H4350. They dont fluctuate very much in the cold. iirc, I lost 15 fps from +60ºf thru -20ºf. With H4350 in my 6.5 Creedmoor. 140 gr bullets.

But, one of the main things I suspect is the book loads were shot with a barrel who's chamber was cut with close to a minimum Spec. reamer , . And perhaps your chamber was cut with a brand new , Max SAAMI spec reamer. Also, you may have a slightly slow barrel. Or the book barrel may be a fast barrel. There are lots of things that can cause 200 fps variation. But 20ºF is not one of them.

Thanks everyone.
The altitude is around 1,000 feet above sea level. My primary concern is that 60 gr of H4831 over a 130 grain bullet is a pretty classic load and most folks I know or read about are getting +3,000 fps out of it. I bought the powder because it isn't sensitive to temp...2700-2800 seems abnormally slow.

Has anyone had problems with their Chrony in temps below 32*f??

Variations from lot to lot of the same powder can make a big difference in velocities. Hodgdon claims that rifle powders in its Extreme line have small velocity variations with lot number. Those variations may be smaller with the Extreme line compared to other powders but the variations are NOT small. The USAFA conducted velocity tests with six different lots of Hodgdon Extreme H4831 in .25-06 and .300 Winchester Magnum cartridges and got lot-to-lot velocity variations over 100 fps in both cartridges. -- Read the report here: http://www.dtic.mil/dtic/tr/fulltext/u2/a572333.pdf

It's not uncommon to see those velocities with 60 gr H4831-130 gr in the 270. Some rifles will sho more velocity but it isn't uncommon to see velocities in the 2900 fps range from typical hunting rifles.

I shoot 61 gr in one rifle for 3100 fps which show how this stuff can vary rifle to rifle.

Thanks all.

Grenadier, that report was very informative.

I've used Shooters Chrony chronographs down around -45º F.
The problem is the battery ime. 9 volt. They drain very quickly in the cold.
I'm going to get a Magneto Speed next. They don't rely on light so I can chronograph at night. ;-) and , as it is attached to the barrel it is not level dependant. When I develop a load I use my woodshed full of firewood as a bullet trap . By chronographing as I work up from starting loads I save bullets and having to pull bullets.

Most 270 rifles don't reach the magical 3000 fps mark. They still kill well. Don't get hung up on numbers. Work up an accurate load and hunt it.

Dave

quote:

Originally posted by blacktailhunter:

Do you think this is due to cold weather, bad chronograph or the rifle? I'm happy with the accuracy but not pleased with velocity I'm seeing on the chrony....thoughts?

Thanks in advance.

Have you ever chronographed that rifle before? What is the bbl length?

I haven't chrono-ed it before, 24 inch barrel.

The best way to ruin a great, kill every thing rifle is to chronograph it.

quote:

Originally posted by p dog shooter:
The best way to ruin a great, kill every thing rifle is to chronograph it.

Amen to that...

quote:

Originally posted by blacktailhunter:
I haven't chrono-ed it before, 24 inch barrel.

Try chronographing some factory ammo.

quote:

Originally posted by Cold Trigger Finger:
Essy way to find out. Leave some rounds oytside so they fully reach the ambiany temp. Put several rounds in a baggy and pack them around in your armpit for a half hour or on the defroster of your truck. . Chronograph the warm ones first. Then the cold ones. If everything is the same, powder , primer , brass and bullets. Then that will be pretty definitive. As to the Chrony, if you have a low hanging sun, or sunny with snow on the ground. Or the bullets pass over the screens at different places. Or it it not plumb and level. It will give odd readings.
Lastly , H4831 is one of the Extreme Extruded powders. Like H4350. They dont fluctuate very much in the cold. iirc, I lost 15 fps from +60ºf thru -20ºf. With H4350 in my 6.5 Creedmoor. 140 gr bullets.

I did the same thing when I lived in MN; left soem outside and heated some on my dash with the heater blasting. Extreme powders faired quite well (Varget in particular was outstanding) but spherical powders gave huge velocity differences - more than 150 fps in some cases.

quote:

Originally posted by Cold Trigger Finger:
But, one of the main things I suspect is the book loads were shot with a barrel who's chamber was cut with close to a minimum Spec. reamer , . And perhaps your chamber was cut with a brand new , Max SAAMI spec reamer. Also, you may have a slightly slow barrel. Or the book barrel may be a fast barrel. There are lots of things that can cause 200 fps variation. But 20ºF is not one of them.

"Fast" and "slow" barrels are in reality "high" and "low" pressure barrels respectively IMO. This can be attributed to chamber size as well as small variances in bore.

quote:

"Fast" and "slow" barrels are in reality "high" and "low" pressure barrels respectively IMO. This can be attributed to chamber size as well as small variances in bore.

Well....not necessarily

I have seen barrels that hit a pressure "wall", but velocities were still sub standard for the cartridge.

And other barrels that gave normal velocities with cases that lasted a long time.

I think throat dimensions and internal groove diameter of the barrel have more of a bearing on this than chamber dimensions. I think it has to do with the nature and amount of resistance the bullet encounters traveling down the bore.

The previous posters pretty much defined all the possibilities. Personally, I would start with the chronograph. I've owned a bargain priced chronograph I can't recall the name of, the Pact PC2, still have a CED Millenium 2, owned a Magnetospeed and have finally settled on a LabRadar.

I've had as much as 100 fps variation from day to day based on different light conditions when using the Pact PC2. That's what prompted me to try the CED Millenium 2 and switch to the Magnetospeed and now to the LabRadar.

I would try another chronograph and if it reads the same, either live with the situation or switch components to see if a change in powder lot or different brand of cases would safely increase your velocity. If it shoots that good though, I'd not mess with it.

quote:

"Fast" and "slow" barrels are in reality "high" and "low" pressure barrels respectively IMO. This can be attributed to chamber size as well as small variances in bore.

Then if you really want fun chronograph revolvers and see the difference in chambers

quote:

Originally posted by nopride2:
Most 270 rifles don't reach the magical 3000 fps mark. They still kill well. Don't get hung up on numbers. Work up an accurate load and hunt it.

Dave

My BDL (22" barrel) reaches 3000 fps with 150g Partitions, with a 130g bullet 3000 fps should be no issue. Try backing off three grains, using Federal 215 primers and working your way back up. You should get there.

60 grs of H4831 has been killing game for ions both winter and summer in the .270 Win..Your velocities seem to be a flawed chronograph or something..Ive chronographed that load many time in hot Texas smmers and cold Idaho winters and usually got less than 50 to 75 FPS difference in my 22" mod. 70s, Rem 700s, Mausers and a couple of Rugers..You might need to check that out. I also notice your summer loads are definite max for that powder your using and real low in the winter for the same powder, unusual for sure.

I have a supply of old WW2 surplus 4831 and use Jack O'Connors pet load of 62 grs. and get awesome velocity with it..Todays powders wont
even come close/. With todays 4831 I doubt if you can get more than 60 grs. in a case, I have with some rifles, but it pushed bullets forward overnight about every time....

4831, historically has been the powder for a .270 in that it gets the highest velocity with the lowest pressure..My problem is that you should weigh every load, and I don't care to do that these days. so RL-22 is a good choice.

As was said here a number of factors are additive to get to where you are versus the Nosler manual. Its normal really. Cold temps plus powder and chamber and barrel differences.

Ive loaded 270s for a long time in various loads from 130s to 150s. These days Im using the Nolser 140 AB. In the warmer climate here in Texas I can get it to just about 2950 fps and that is with some loads that are a little over what the book might call for. Beings I have no issues with that load in terms of pressure or primers or cases, and its accurate, then I just stopped there.

The longer you shoot over a chrony you'll see that this is not unusual. Ive found various factory ammo loadings to be 100 and 200 fps low to the stated velocity. Some even more than that. I have seen the Weatherby factory ammo reach its published spec more than most others in my rifles and my buds for what that is worth.

Don't try to chase down their published velocities and just pick the the fast and accurate load. You will be happy.