Maximum loads for a .30-06, based on bullet?

[orpington]

I recently reloaded rounds for a .30-06. One load used a 173 grain lead bullet, No 311041, and I used 13 grains of SR-4756 powder, which yielded a velocity of somewhat over 1406 fps and a pressure somewhat in excess of 22,800 psi. I then loaded rounds using a 220 grain Jacketed RN bullet, using IMR-4350 powder, using 50 grains powder. Velocity is in excess of 2309 fps and pressure is in excess of 40,700. It says the maximum load for this would be 53.0 + grains, with a velocity and pressure of 2500 and 49,200 Copper Units of Pressure (what is that, by the way, as opposed to psi?). The maximum load using the 173 grain bullet and SR-4756 yields a velocity of 1653 and a pressure of 36,400. Why is the maximum load using the cast bullet so much lower than that of the jacketed bullet? I assume it has to do with leading, but are there other reasons? Also, why would the starting load using the 220 grain bullet be so much greater than that using the 173 grain bullet? There was a noticeable difference in recoil between the two loads.

 

[tightgroup tiger]

Why is the maximum load using the cast bullet so much lower than that of the jacketed bullet?

The jacket on the jacketed bullet offers a lot more resistance traveling down the barrel then a lead bullet will. The lead is somewhat self lubricating to begin with, then has lubrication put on it to help stop the leading.

Jacketed bullets have no lubrication and the jacket material is much harder then the lead is. That make more resistance so it takes more powder to get it up to velocity.

Also, why would the starting load using the 220 grain bullet be so much greater than that using the 173 grain bullet?

Same reason as stated above. It simply doesn't take as much pressure to drive lead as it does for jacketed bullets

Copper Units of Pressure (what is that, by the way, as opposed to psi?).

PSI is measured by a Piazo transducer and is more accurate than the older copper crush method.

With the Copper Crush method a pure copper pellet was put in a hole in the barrel with small piston below it, then sealed up. When the firearm was fired the pressure of the charge would drive the piston up and crush the copper pellet. The pellet would then be measured for thickness and a determination of the pressure would be derive from the amount of thickness the pellet lost from being crushed.

 

[ArchAngelCD]

WARNING, SR-4756 is NOT a powder that should be used in rifle cartridges. The powder you should be using is SR-4759. That is the correct powder for reduced rifle loads and lead bullets.

 

[orpington]

The load I used using SR-4756 was straight out of the Lyman reloading manual, both for my .30 WCF (.30-30) AND my .30-06.

 

[gamestalker]

In short, lead bullets operate within a completely different powder family than jacketed bullets do, particularly when it concerns bottle neck cartridges. This alone will explain the reason for the major variation in pressures, and the powders that your inquiring about. These questions should have been addressed in your reloading books.

GS

 

[ArchAngelCD]

The load I used using SR-4756 was straight out of the Lyman reloading manual, both for my .30 WCF (.30-30) AND my .30-06.

Well well, yes it is... My mistake. Ignore the man behind the curtain.

 

[41 Mag]

WHile a lot of the information on this site LASC Article Indexis about handguns, in this link from that main pagte you will probably find a good explanation of just what your asking about, Indes Brennan

Don't be afraid to browse around there either. There is a TON of information, and precisly what your after might be spread out in another section. ALso look under the articles of Glen Frexell as well.