Bullet shape Question??

[GeoDudeFlorida]

Today I measured both the RMR JHP and the RMR FLAT POINTS, both 124 grain and they measured within .001". So why if they are the same length does it matter to reload them with the same COL? Casings are the same length, bullet length is the same, same amount of powder, is there a difference I don't get?

Maybe if your first post had been specifically about those two bullets, and included that information, you’d have gotten a different answer. And this thread would have been done-in-one.

 

[Walkalong]

All 124 Gr? All jacketed? Seating depth is the most critical, but assuming they are all seated to the same depth there will be very little difference.

A change in bullets at max/near /max, even with equal seating depth, would still warrant backing off and working back up, even though you may end up at the same place.

A plinker load well under max? If seating depth is different? Yes, I would still rework it. Seating depth the same? Not so much.

 

[lordpaxman]

Today I measured both the RMR JHP and the RMR FLAT POINTS, both 124 grain and they measured within .001". So why if they are the same length does it matter to reload them with the same COL?

My first step with any new bullet is to determine max and working COL for the cartridge. You may find your current working COL would be ok for either, but never assume it. If they are different, you can asses seating depth changes based on COL and bullet OAL differences. Then I look at load data and try to find charge data/COL and extrapolate for my combination.

In my 9’s, the RMR multi purpose and and match winners have the same working COL, they’re jacketed and I’m assuming similar construction, so I use the same load data.

 

[jmorris]

Today I measured both the RMR JHP and the RMR FLAT POINTS, both 124 grain and they measured within .001". So why if they are the same length does it matter to reload them with the same COL? Casings are the same length, bullet length is the same, same amount of powder, is there a difference I don't get?

That’s a different question than you asked in the OP. I was trying to show how this could be a potentially dangerously incorrect assumption.

I assume as long as they are all 124 gr that the shape of the bullet doesn't change the load data, am I right??

That said, I find it amazing two “different” bullets only differ .001”. I get more variation that that with the same bullet, just different ones in the box.

Like these SMK’s for example. Same bullet but an OAL difference of .005” isn’t unheard of, just grabbing a handful and measuring them.



Why, if I am trying to compare them I eliminate the tip, as a datum on ogive to base is always more consistent.



In any case, if your bullets are the same weight and only differ in length by .001” you should be good to go if they are the same diameter and coefficient of friction, assuming shape doesn’t cause some other problem, like shoving the bullet into the lands vs room to get a running start into the rifling.

What I was pointing out was how Speer had a safe load become dangerous with just a .030” base depth change and the difference between bullets of the same weight could be greater than that.

If you have already checked and are OK, you could have skipped that post. I wouldn’t even have posted it but the critical information was not in the OP and it is for certain all 124’s, ever made, shouldn’t use the same load data.

 

[GeoDudeFlorida]

A HIGHLY recommend both of these articles for anyone who has questions about COAL:
https://bergerbullets.com/effects-o...coal-and-cartridge-base-to-ogive-cbto-part-1/
https://bergerbullets.com/effects-o...coal-and-cartridge-base-to-ogive-cbto-part-2/
And because some people need a video: