SmallCaliberCentral

OK I am wondering what I am missing here? Typically when the bullet weight goes down the charge rate can go up correct?

Looking through the Sierra Edition V at some 22-250 loads I find a couple of powders that show greater max loads with a 55 gr bullet than say a 50.

Examples:

N135 powder 50gr bullets show 33.7 max and 55gr bullets show 34.7 max

H380 50gr Varget max 36.0 and 55gr max 36.1

748 50gr max 36.6 and 55gr max 36.8

I know the std YMMV applies and start 10% low and work up etc. but this just seems wrong.

TDM: Once you take the actual burning rate of each powder into consideration, THEN the charge weights will make much more sense. You can't assume more powder of any kind in a given caliber just because bullet weight is decreased.....just don't happen that way.

Good thing for us that each bullet maker has their own ballistics lab, eh?

Could the higher max charge with the heavier bullet indicate the 2 bullets are designed differently? Maybe a shorter bearing surface, or HP vs FMJ? Maybe the 55 is heavier, but it somehow creates less pressure?

It would be easier to comprehend if the other powders folowed the same bass ackwards trend. More powder behind a heavier projectile just does not compute.

Common sense says the smaller bullet can take more powder and the rule seems to apply to other powders listed. The 40gr does then the 50 drops off hard then increases for the 55.

One additional question/thought. Are powders generally similar in BTU's, just different burn rates?

In other words would 34.7 grains of N135 produce less heat than say 38.0 grains of H380?

TDM: They have similar, but different burn temps. If you really want to find out about all this, log onto Varmint Al's website, as he's got answers for virtually everything related to the technical side of the hobby.

http://varmintal.com/

A virtual goldmine of info and entertainment. Al is a retired engineer and lifetime varmint shooter that lives in the north Bay Area of SF and really enjoys the small calibers. His website would take a week to fully navigate and is one you'll want to bookmark. Check it out.

Mentioned by another...but some bullets have a different design - longer body in contact with the bore. Can and usually does make a difference when building loads.

The Sierra 50's must be quite different. They group all 7 of their 55gr bullets together with same load data.

It's the same way with the .22 Hornet, according to Dick Lee's data, anyway. He's got heavier loads listed for the 40gr. jacketed bullets than the 35 gr. V-Max, with 1680 powder as an example. 14.0 Max for a 40, while only going 13.5gr. Max with a 35.
Yep, it seems counter-intuitive, but I'm not willing to risk a rifle finding out if he's full of beans.