I started working up a load for my 257 today and made a bit of a mistake.
I didn't think it through and loaded standard pressure loads in some +P brass. What I got was the first signs of over pressure. Heavy bolt lift and marked primer flattening. Nothing real severe but when I got back home and compared the +P loads and the regular pressure loads I found out that due to the smaller capacity of the heavier +P brass the loads are actually 3 grains lighter than the standard loads in regular brass. So my starting load of 48 grains of H414 with an 87 grain bullet was already 1 grain above the max load for a +P case.

I am going to have to make up different loads for the two types of cases that I have. I am hoping that I have more standard cases than +P cases.

I don't normally make mistakes like this and it is a good reminder for me to double check the sources when it comes to +P for the 257 Bob. That is what I get for assuming ...

The only cost was the 30 rounds that gave me no usable data and my pride. Onward and upward!

you still have your teeth Mate so chalk it up to experience and thank the good Lord you still in one piece.

Nope! lost most of my teeth years ago - but I was the last in my family to lose them.. some kind of genetic flaw. I should have been born with shark genes.

Yeah, I was lucky this time so I wanted to pass on the notice to others. The +P cartridges are a lot smaller than the standard. I will have to lat the +P cases aside and work up my loads with other cases. Oh darn! I have to load and shoot more ammo. How very disappointing...

Wait! I love it!
See you all later.

Glad you didn't run more than some flat primers. I've always found that brass makes a significant difference and I never could develop a load in one manufacturer's brass and assume it would work in another. Though I've never run into a situation with a 3 grain difference like you did here.

I had to look it up...I'll be damned. Still learning I guess. Never ran across a rifle cartridge that was marked "+P".

So far, I think the 257 Bob is the only one. What I don't understand is why they use a case with less capacity to build the +P loads. Did somebody tell them that the brass was too light to use a 50000 PSI load? Did they forget that the chamber supports the brass and pressures?
I am going to do as much work with the standard brass as I can. As I collect more brass I will be sure it is not the +P brass.

The case web, just forward of the extractor groove and case head is not supported by the chamber wall. To beef the case web up, the brass must be thicken with resultant capacity loss. this is the situation with the 6.5 Grendel, it has a 52,000 psi limit because of a thin bolt and case web. 6.8mm SPC II has stronger brass and has a 58,000 psi limit.

I measure case web expansion on new brass all the time as one of my indicators of chamber pressure.

It is being used in a Browning A bolt so the case head is pretty well surrounded by steel. The cases used were once fired in my rifle and partially neck sized when reloaded. The accuracy of these overloads was surprising at 1.12" to 2" at 100 yards. Nothing that I found acceptable but when I realized that my starting load was 1 full grain over maximum and the ending load was 3.5 grains over maximum listed loads for the +P case it is easier to accept. I have a mess of brass in the tumbler and I will sort it to separate them by make and watch for any +P cases. The next time I shoot test loads I will be in better shape with ammo that is not over the maximum loads.

so load up the
+p cases with something along the lines of a heavy partition at good speed for accuracy and keep them for your bush /closer range loads

then use all the rest for all the rest with something along the lines of ballistic tips/SSTs so no way you will mix them up.
just a thoguht...

Elvis wrote:

so load up the +p cases with something along the lines of a heavy partition at good speed for accuracy and keep them for your bush /closer range loads

Always the practical one that Elvis. Agreed, use the +P brass for one load where you don't need the case capacity then the other brass for another one of your favorite bullets.

I will see what I need this fall. I live in the middle of wheat country so tight brush shots may not be the popular hunting method. I have a couple of places that are open to the public and a piece of land that is privately owned but the owner is an acquaintance who may be open to letting my daughter-in-law and me hunt. We will make a great couple while hunting. She is a gorgeous young lady and will be shooting her 243 and I'm an old man with a 257 Roberts. I figure I'll have time to shoot while the young bucks are looking her over.

I would be interested in knowing what your velocities were. Maybe the case capacity increases pressure as well as velocity making the lower charge weights acceptable. I notice you are using H414, which according to a Handloader article is the same powder as AA2700 and W760. My lot of AA2700 produces near maximum velocities at nearly 2 grains less than the listed data in my .243 Winchester.

I did know that W760 and H414 are the same powders but I didn't know that AA2700 was part of that club.

Since I have quite a lot of AA2700, I was pretty happy to find that out. Makes load data a little easier to find for some cartridges with normal care in development. The jugs in my lot are at least 17 years old and the formulation at that point is a bit too warm to rely on today's data, but it is still a good place to start.