Author Topic: Q's about the .30 Herrett vs the .30-30 (Read 847 times)

Bug · « **on:** January 31, 2005, 02:15:22 AM »

I was poking through my manuals and came about what I think is a discrepancy. Or at least a case (bad pun intended) of comparing apples to oranges.
In my Hornady handbook, the loads for the .30-30 are held to lower velocity than those for a .30 Herrett. Sometimes to a lower pressure, too. Both test guns are Contender 10" barrels, with a 1-14" twist. The loads are held to a lower velocity with the .30-30, either through a slightly reduced powder weight, or with the same approximate powder charge (coupled with increased case capacity) to produce a reduced velocity. Has to be reduced pressure, too. Doesn't it?
It isn't a big difference, but this doesn't make sense to me. At least at first glance. Given the same barrel length, same twist, and same parent brass, shouldn't the .30-30 be slightly faster than the Herrett? Albeit with a larger powder charge? Does the short barrel create a variable I'm not considering? Seems to me, that a larger capacity case should outstrip, or at least equal the smaller, given the same length barrel, twist, and pressure ceiling? What am I not considering?

fyrepowrx · « **Reply #1 on:** January 31, 2005, 12:47:32 PM »

Years ago i remember reading something JD Jones wrote about this very subject, although i dont rember all the details he gave.

I am assuming the reduced case taper on the herrett transmits less backthrust to the frame than the long , skinny 30/30 win case does; so it can be loaded to higher chamber pressure.

vol89 · « **Reply #2 on:** February 01, 2005, 08:45:55 AM »

Bug, may I ask what Hornady manual you are using? Is it the latest volume? Thanks, vol89

Bug · « **Reply #3 on:** February 01, 2005, 09:08:54 AM »

vol89,
Good question. No, it isn't the latest. It is the third edition, I was referring to.
A quick look at the latest Annual Manual shows the Herrett no longer listed. And the bullet/powder selections to be radically different, too. So, no help with the explanation, there.
fyrepowrx does bring up a valid point. A straighter case will have proportionately less backthrust than one with more taper.

karbo · « **Reply #4 on:** February 01, 2005, 11:38:43 AM »

It might also be that they are trying to hold the 30-30 to SAAMI specs, so they keep the pressure lower.

Lone Star · « **Reply #5 on:** February 01, 2005, 04:39:16 PM »

Hodgdon/IMR data shows that the .30-30 is held to slightly over the SAAMI pressure at 40,000 cup, while the .30 Herrett is held to 45,000 cup. This would explain most of the velocity difference. The rest would be easily explained by the normal variation from barrel to barrel.

Remember too that the Hornady data is not absolute - few if any of their maximum loads were ecer actaully fired in any barrel - the max data was developed graphically. The difference between the true maximum loads of the two cartridges could be much less than 100-200 fps shown in the #6 manual.

Bug · « **Reply #6 on:** February 02, 2005, 01:18:24 AM »

Lone Star,
I was surprised to hear that the SAAMI pressure standards were different, between the two cartridges. That would explain a lot. Do you have a website that lists the pressure standards for cartridges? I thought I had one bookmarked, but I don't seem to find one.

Lone Star · « **Reply #7 on:** February 02, 2005, 02:28:55 AM »

There is no SAMMI standard for the .30 Herrett because it was never loaded by members of SAAMI. T/C has stated that the Contender is safe in this chambering at ca. 45,000 cup, so many manuals use that as a reference. Accurate Arms lists their data in psi, not cup, but the "true" pressure is the same: http://www.accuratepowder.com/data/PerCaliber2Guide/Handgun/Standarddata/30Cal(7.62mm)/30%20Herret%20Page%2075.pdf

However, not all manual data is actually pressure tested. Older Speer data for example used the traditional "signs" of high pressure like stiff opening, case expansion, primer appearance, etc. rather than pressure testing equipment. Speer was, IIRC, the first manual to publish data for the .30 Herrett, but they have not published data for this cartridge in years. Manual Number Ten is the last Speer book to carry .30 Herrett data.

The IMP/Hodgdon site lists the pressures they actually used for their maximum loads. They apparently feel that 45,000 cup is safe:
http://www.imrpowder.com/data/index.php

karbo · « **Reply #8 on:** February 02, 2005, 05:00:44 AM »

I think the 30 Herrett data in my Sierra reloading software mustn't be pressure tested because the loads are way hotter than anything I've seen elsewhere. Their starting loads are hotter that others max loads. They show 2250 fps with 125 grain out of a 10" bbl.

Racepres · « **Reply #9 on:** February 02, 2005, 11:32:06 AM »

It is amazing ... the difference between reloading manuals .... Compare 30 Herrett data from Lyman to Sierra to get a clue!!!! For me the Fifth printing (1992) of Handloading (the NRA publication) has been invaluable in sorting out some of this apparent discrepancy ... I highly recommend it... Marty
BTW There seems to be any number of differences in barrels including freebore and therefor overall case length, as well as apparently large deviations in case capacity. Be Safe