Tell me about Hodgdon Titegroup.

[Maxwell Haus]

Originally Posted by jetinteriorguy

So, have you actually used Titegroup and overloaded it beyond published data?

Sorry, not playing that game.

[Unclenick]

Originally Posted by 74A95

And yet they didn't seem to have that problem with 145 grain lead bullets where TG is loaded to 33,400 psi. Or with 135 grain lead, where it is loaded to 33,400 psi also.

Their 147 grain data looks anomalous. It also suggests that HS-6 is a poor choice for 147 grain bullets (27,900 CUP), though no issue with HS-6 and 145 grain bullets (33,100 psi).

Since the 147 XTP data with TG (and HS-6) is measured with CUP, I suspect there might be an issue with the CUP method, which has been rumored to be less reliable than using a piezoelectric transducer used for psi measurements.

No question that this applies only to one load component combination. But my choice of a prime candidate for the cause is not anomaly or measurement problems. It is the primer unseating the bullet during the one to three milliseconds it takes for the powder to get burning. This phenomenon is known to cause a lot of pressure and velocity variation because the bullet isn't consistent in how far out of the neck it is when the powder burn catches up. It is responsible for the observation that, in some combinations, a magnum primer produces lower pressure and velocity than a standard primer does. It is a chronic headache for 22 Hornet shooters who often have to resort to using pistol primers to get something mild enough not to give them large velocity variation and significant group expansion (which the Hornet's modest pressure levels allow them to do).

The clue primer unseating is happening with the 147-grain XTP Tightgroup load comes in comparing its charge weights to the 145-grain ACME RN coated bullet load in the Hodgdon data. The RN has a longer COL for more powder space and it is softer and more lubricated and is slightly lighter than the XTP, all of which suggests it should require more powder to achieve a given peak pressure. But the XTP maximum charge that reaches a lower percentage of MAP is heavier than the 145-grain bullet maximum charge. This suggests the 147-grain bullet moves forward and makes additional powder space before the powder burn gets seriously underway.

Unfortunately, without setting up a test barrel, we can't test and prove our speculations and are left to make the err-on-the-safe-side assumption that the variance in the 147-grain loads repeats.