reduce charge when changing bullets?

[snowman]

I've been loading .357s with a jacketed bullet for some time now. When I ran out of the brand I've been loading, I learned that they were no longer available, so I found one from another manufacturer of the same weight. I'm aware that a change in a component ordinarily requires reducing the charge and working up again to ensure that safe pressures aren't exceeded. I'm wondering in this case if this is necessary, given the following:

-the old bullet measures .357, the new one .3565(I measured a significant sample with a dial caliper to check this)

-the new bullet weighs, on average, around .1-.2 gr. less than the old one

-the cannelure on the new bullet is closer to the base, meaning that it won't be seated as deeply in the case


I'm thinking that logically, each of the above factors would point to the new bullet generating pressures lower than the old bullet rather than higher ones. Am I correct? If so, is there any reason that you folks know of to rework the load from reduced charges? The only other factor I'm aware of that would make a difference is the bearing surface of the bullet, and the two bullets appear to me to be identical in that department(though I have no means of measuring that with precision).

Thank you for your input.
Andy

 

[Gun 4 Fun]

It would seem that way, and given the fact that the seating depth will be less, you really shouldn't have any problems, but bullets can be a law unto themselves, so backing dow a few tenths of a grain and checking things out, then working back up is always prudent if you are uncertain.

As long as you aren't switching to a solid copper type bullet such as those made by Barnes, you should be OK though.

 

[Dragon88]

The safe thing to do is back off a little and work back up to desired velocity. However, if it were me, I wouldn't bother as long as it's not maxed out.

What I would be more concerned about is those undersized bullets. If they really are .3565, be sure to watch for reduced accuracy when you go out to test them.

 

[Titegroups]

The numbers you list would not be significant enough to cause much of a increase in pressure. If you felt uncomfortable you could always reduce a few down some, and try them before you load up a bunch. The safety factor margins designed into firearms are larger than what you might think.

 

[DonD]

The safe thing to do is back off a little and work back up to desired velocity. However, if it were me, I wouldn't bother as long as it's not maxed out.

What I would be more concerned about is those undersized bullets. If they really are .3565, be sure to watch for reduced accuracy when you go out to test them.

I agree, there is one thing that you don't know about the two bullets, the average thickness of the jacket or if it is in anyway alloyed. Suspect that as was said, pressures will be lower.

If you're in the middle of the charge range of a reputable loading manual and one where there is a wide range in pressure between bottom and top, I wouldn't worry at all.

Going from a max pressure load on a cast bullet to the same powder charge on a jacketed slug is an entirely different matter and a recipe for overpressure. Don

 

[snowman]

Thanks, guys.
Andy

 

[Ron H.]

Sir, given the differences in the bullet, you're probably going to have to re-develop the load for accuracy anyway, so I see no good reason not to start low and work up.

JMHO, FWIW.

Hope this helps, and Semper Fi.

Ron H.

 

[snowman]

A little additional information: probably 95% of these are used for defensive practice at 21 ft., so accuracy isn't an issue.

Andy

 

[OKFC05]

Where are you now with your load? Hotter than the hinges of Hades, or in the middle of the data? If you're low or in the middle now, I'd load and chrono. If you're hot now, I'd reduce if I changed anything.

 

[buck460XVR]

Where are you now with your load? Hotter than the hinges of Hades, or in the middle of the data? If you're low or in the middle now, I'd load and chrono. If you're hot now, I'd reduce if I changed anything.

My opinion also. Again, accuracy may change and the load may need to be tweeked to get the most outta it, but from my experience, changing to a different brand of bullet that weighs the same, has the same construction and has a similar profile, does not change velocity that much, unless seating depth is such, that case volume is changed considerably.

 

[Tell Sackett]

Shall we make it four?

My opinion also. Again, accuracy may change and the load may need to be tweeked to get the most outta it, but from my experience, changing to a different brand of bullet that weighs the same, has the same construction and has a similar profile, does not change velocity that much, unless seating depth is such, that case volume is changed considerably.

As these wise sages have stated, start over. It will give you more shooting time and make it a safe endeavor. If you don't go back to the starting load, I would understand. Say middle of the data to start. As OK noted, it would depend greatly on the load I was using to start with and the powder type. If it was H110/W296, I'm not reducing anything. If it was Clays or another fast powder with a steep pressure curve, I'm going to the basement on the data and working back up, PERIOD.

I don't think there is anyway for you to get enough of those slower powders in the case and have a pressure issue that would blow up the gun. Say you go to a 10% over charge of H110/W296 on a load that is already maximum, 16.7gr with a 158gr XTP. That would make an almost 2gr increase. I wonder if that would even fit in a 357Mag case and I'm not espousing that anyone try it. I'm just trying to point out that it would make a big difference in what I chose to do. Just me though. You do what you want, your the one responsible for your actions!

 

[snowman]

The end of the matter: I kept loading the same charge for the new bullet until the primer tray was empty. Went to the range today to check for pressure signs, put rounds with the new bullet in every other chamber. No signs of high pressure, maybe slightly less recoil out of the new ones, but barely perceptible if at all. No perceptible change in accuracy either.

I don't use any fast-burning powders, by the way. This is VV. N110, a relatively slow burner for handgun rounds. The charge takes up nearly all the space in the case.

Thanks again to everyone who took the time to reply.
Andy

 

[Tell Sackett]

The end of the matter: I kept loading the same charge for the new bullet until the primer tray was empty. Went to the range today to check for pressure signs, put rounds with the new bullet in every other chamber. No signs of high pressure, maybe slightly less recoil out of the new ones, but barely perceptible if at all. No perceptible change in accuracy either.

I don't use any fast-burning powders, by the way. This is VV. N110, a relatively slow burner for handgun rounds. The charge takes up nearly all the space in the case.

Thanks again to everyone who took the time to reply.
Andy

Do you mean that you ventured around the unknown, with new components and your don't have a chronograph? At least you didn't post any data for one. If you are going to fool around and handload, not reload, I suggest you get one. The life you save may be your own. Perception can be a foolhardy thing, friend!