Powder less than max... Velocity Over Max.... Help !!!

[LouD]

OK, now I'm befuddled....  I'm working up loads for my 270 Win using 140gr Sierra HPBT's with IMR 4350.   @ 53 gr I chrony'd between 3030 and 3080 last Sunday.   Today I backed off the load to 52.5, 52.7, and 52.9 (groups of 3 each) which chrony'd at approx 3100, 3150 and 3200 fps respectively.   The cases show no signs of excess pressure.  My original objective was to get the load to about 3000 (max in the sierra manual although the powder max is 53.5) but I'm wondering if I should just go with the 53 gr. load as it is most accurate, even if the velocity is approx 200 fps over the manual.  For what it's worth, our range is at an altitude of approx 5500 feet, so perhaps my velocities are OK   Is it typical to see such variations in velocity from day to day ?  Brass and primers were the same.    I would appreciate some experienced input on this one please.   By the way, I'll be hunting even higher, between 6000 and 8000 feet.

Cheers !!!
Lou

[Catfish]

Lou,
   You had me thinking there till you said your range was at 5,500 ft., that will give you more velosity with the same gun and load than you will get closer to sea level. Longer barrels also give you more velosity than shorter ones, with most loads and to a point. Pushing the bullet 200 fps over max. recomanded is not enough to destroy the bullet as you have seen, but it will expand faster at closer ranges. If your hunting heavy skinned game this could be a problem causeing lack of penitration, or with deer size game you may lose alittle more me due to the rapid expantion, but I doubt you will be able to any difference. I once pushed the Serria 50 gn. Blitz bullet to alittle over 4,000 fps. and their recomanded max. was 3,700 fps. Didn`t get to play with them much because I sold the gun, but the guy I sold it to was very pleased with the loads and what they were doing to groundhog.

[stimpylu32]

Another thing to look at , how was the weather on both days , temp , humidty ect. and is your barrel longer or shorter than the one that they used for testing .

I agree , i do not see a problem with the extra 200 fps if pressure is staying were it should be .

[Val]

The muzzle velocity called out in the reloading manuals is that achieved by the particular test gun used by Sierra under the conditions in their test facility. Your results will indeed vary as a function of your environmental conditions, the tolerances of your chamber and barrel as well as barrel length. Chronometer readings might also vary under different lighting conditions and how they are set up from day to day. 200 fps is a pretty small percentage variation. The key is that you checked the cases for signs of pressure. I don't believe you have a problem.

[Mac11700]

Today I backed off the load to 52.5, 52.7, and 52.9 (groups of 3 each) which chrony'd at approx 3100, 3150 and 3200 fps respectively

Some of the problem may come from trying to varify your velocity with such a short shot string.Whenever I am working up loads...I use a minimum of 10 shots now..It will give you a better idea of your velocityspread. Other than that...check the calibration on your scale..and verify your charge weights..As to getting more velocity than what the book shows for any one rifle...there are so many different variances possible..getting an extra 100 or so fps isn't nothing major to worry about...especially with the 270...I've had a couple of them that always gave higher velocity...just as I have had 1 that always gave lower than normal...Like what was said...if your not getting any pressure signs..I wouldn't worry too much...

Mac

[drdougrx]

Hi,

Sounds like a scale issue.  Do you use a digi and do you calibrate it every time you begin loading?  Do you let the barrel cool at all between shots?  A hot barrel will give a higher velocity.  IMHO...just us the 53gr load if it's accurate and be done with it.

Good shooting!

[beemanbeme]

The load books are excellent guides but are not writ in stone.  They are guides.  I find the increase in velocity with the lesser loadings strange however.  Have you tried to duplicate the test??  100fps increase with just .4grs powder is a bit much for a case the size of a 270.
I wouldn't worry too much about the 200fps extra in itself if you haven't any signs of pressure. 

[The Sodbuster]

If I may offer another bit of wisdom:  check another reloading manual.  You may find another manufacturer publishes a higher velocity for the same amount of powder than the Sierra manual.  I've seen published velocities vary quite a bit for the same powder and bullet type between manuals.

[PaulS]

At your altitude you might get a lot more velocity over the tests done at sea level. A loose barrel will add to the difference and a long freebore will give yet more velocity. Some bullets will give higher velocities and lower pressures than others. I never concern myself with velocity until after I find the load that provides the best accuracy over the widest range of conditions.
The only reason to check the velocity is to predict the trajectory of the round at various ranges and altitudes. So find your most consistently accurate load and then check the velocity so that you can use your favorite ballistics program to predict trajectory.