Non issue or a concern? Bullets not listed in data

[300WSM]

I've always been concerned and avoided using a particular bullet/powder charge combination when the exact two items used in combination aren't printed in any data.

More specifically mfg "A" lists a particular powder using a 180 gr bullet(or any weight) made by let's say..... Speer....
But I want to use a nosler..( or any mfg not used exactly in the printed data) of the same weight and can't find the exact combo printed anywhere...

If the two...
specific powder and specific bullet...
aren't listed I just avoid using the combo until I can find said combo.

My thinking is although the two bullets are of the same weight the geometry of the two bullets will be different. Length, Boat tail or flat base etc
Which would change the pressure...
If I had both bullets I could measure certain areas but without a VERY EXPENSIVE comparator it would only be close...
I doubt I could find exact blue prints of the two bullets and compare that way

So.....

My ultimate question is am I too worried about this and as long as the weight is same the geometry has a negligible effect on pressure?

Maybe this is nothing and I'm being overly cautious ( i know one can never be cautious enough with loading ammo)

Thx in advance for any and all opinions on this

 

[RL338]

If you want to add case capacity to the mix also. Some of the newer players in brass manufacturing are making their cases thicker to last longer but reduce internal capacity.

 

[KinleyWater]

Meh. You only live once. Of course, you may continue to live with a disfigured face and fewer fingers...

Really, I've substituted bullets before, and the typical precaution I take is to:
a) measure the bullet OAL to see if it's getting seated deeper at the same COAL
b) reduce my powder to a starting load (or, sometimes only back off halfway, if I'm feeling confident)
c) think about the firearm I'm going to shoot it from. Let's face it, some are just built better than others.

That said, the bullet manufacturer is really the best source to look to for load data.

 

[Lazy Bushman]

Not an issue. If your exact bullet isn't listed then go with another of similar kind eg if your 180gn is a cup and core, then select another 180gn, preferably cup and core, and just work up from minimum. If the other in my example wasn't a cup and core but bonded then I would still do the same as they are still materially much the same. More margin of error would be built in if I was going from a lead jacketed bullet to a mono-metal

 

[TexasLife]

Have you tried carbon paper? WHAT, you ask? An easy way to blueprint a bullet! Tail to tip and measure! More accurate!

 

[TackDriver284]

I have only used cup and core bullets, regardless of bullet brand, I always start low and .010" off the lands and work my way up to max pressure. If using a certain bullet weight, I research powder charge weights for that bullet weight. I use different manuals to determine starting and final charge weights, for some rifles, sometimes I go past maximum powder charge if velocity is not reached as long as I read pressure correctly. Most importantly, always start low, watch your case trim length, and do not jam bullets. Bullets being seated long in long throated rifles may give a lower velocity due to extra case volume, its reason I go past maximum powder charge to achieve the desired velocity I want.