Max Pressure .30-06 vs 6.5-06/.270/.338-06

[chuckhammer]

Hi all.

First, some background:
The rifle in question is a Win M70 Supergrade in .30-06, one of the recent SC-built rifles. It has a 24" barrel. I've been experimenting with the 167 Lapua Scenar, the 175 and 190 SMK, and the 208 A-MAX. So far, I've tried H4350 and RL-22 but also have some IMR4350 to try at some point. A max COL of 3.395" allows it to feed 100% reliably from the mag. Combined with this rifle's fairly short throat, this mag length lets me seat all four of these bullets to within .010" of kissing the lands except the 208 for which I can get to within about .025". I'm using Lapua brass (now all once-fired) and Magtech primers. I recently picked up a chronograph (Shooting Chrony F1) but have yet to use it.

Now, the topic at hand:
In searching the various relaoding manuals and web forums for long range loads to develop in this rifle, I've noticed some folks use 65,000 psi as the max pressure for their handloads rather than the SAAMI max of 60,000 psi. This seems to be based on the fact that three direct descentents of the .30-06 (6.5-06, .270 Win, and .338-06) all use the same case head and web dimensions as their older relative but have a SAAMI max of 65,000 psi.

Since case strength (keeping the primer pockets tight) is the limiting factor in determining max chamber pressure for modern bolt action rifles, this appears to be a reasonable practice. Without a doubt, it will result in decreased case life and perhaps silghtly shorter barrel life (probably a nit) but it certainly doesn't seem dangerous.

What are your thoughts and/or experiences on this?

I have QuickLoad to use as a guide in staying below 65k psi but we all know it's not the same as actual data.

 

[BobinNC]

Re: Max Pressure .30-06 vs 6.5-06/.270/.338-06

From SAAMI with Love:

25-06 Remington - 63,000 PSI
6.5-06 A-Square - 65,000 PSI
270 Winchester - 65,000 PSI
280 Remington - 60,000 PSI
30-06 Springfield - 60,000 PSI
338-06 A-Square - 65,000 PSI

Since the brass for all the above is of identical construction, I can see no reason, in a modern strong, bolt action, to not use all the above to the 65K PSI Limit, if desired.

IMHO,

Bob

 

[Clark]

Re: Max Pressure .30-06 vs 6.5-06/.270/.338-06

I find that primer pocket looseness corresponds to 75 kpsi in Quickload in the above mentioned case head [1889 7.65x53mm Mauser built with a large Boxer primer pocket].

The best measurement I have found [for detecting primer pocket changes] is dial calipers on the extractor groove before and after firing.
The extractor bevel is aligned with the jaw bevel. That means the dial is pointed toward the case mouth.
The force of the jaws on the extractor groove is kept constant, and the case is rotated.
A min and a max are noted.
The cartridge is fired and the measurement is repeated.
If any change in the brass is detected, that is the end of the work up and the powder charge is reduced from there by a safety margin for useful loads.

If a powder charge reduction safety margin from brass change is chosen at 6%, ala Vernon Speer 1956, you may find you have 62 ~ 64 kpsi in Quickload.

I run more than 6% safety margin in .223 ammo loaded by the thousands while watching TV, and intended for rodents. .223 brass changes at 86kpsi, and I run it at 35kpsi.

I run less than 6% safety margin in a few precision built rounds of .243 for long range. 243 brass changes at 75kpsi and I run it at 65 kpsi.

 

[Greg Langelius *]

Re: Max Pressure .30-06 vs 6.5-06/.270/.338-06

After spending a lifetime in the computer business, I still don't have quickload, and typically use Pejsa mainly as a ballistic ballpark estimate for dope to get on paper at a given nominal distance. I got nothing against any of it, I just find that what computes is not always the same as what shoots.

I especially like the above monologue about measuring extractor grooves and intend to inocprporate it in my future testing. I figure pre-firing values can be Sharpied right onto the case wall.

I work in terms of post-firing case pressure indicators, CUP/PSI numbers are beyond my means.

Where pressures and velocities are concerned, I am less interested in getting maximum pressures, safe or otherwise, than I am in issues like arriving at and not especially greater than, transsonic minimum ontarget.

I envision a 1300fps arrival at 1Kyd as adequate, and more than that, as extravagant.

Usinging an '06 case capacity, I like the idea of a nice, big case, running along at cruise speed, and delivering my projos at an adequately sedate speed. More than this is neither necessary, nor compatible with my minimalist, 'Save the Bores' philosophy. For this, I like the .280. Better BC's for lob weight, recoil more to my liking, very tolerant of slower powders which can fill the case better for a higher load density percentage while still keeping the velocities in a more cruise missile-like range.

A higher pressure/velocity will get there with less drop and deflection?

Well, of course it will.

But whatever the values are, yours and mine, we are faced with the same issue, getting it right when we make our corrections.

One of us is gonna be better at it, and honestly, what velocity we're shooting isn't going to be the deciding factor; our doping skill is. My point is, I'd like to get the best bore life while I'm doing it.

Greg

 

[buffybuster]

Re: Max Pressure .30-06 vs 6.5-06/.270/.338-06

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BobinNC</div><div class="ubbcode-body">From SAAMI with Love:

25-06 Remington - 63,000 PSI
6.5-06 A-Square - 65,000 PSI
270 Winchester - 65,000 PSI
280 Remington - 60,000 PSI
30-06 Springfield - 60,000 PSI
338-06 A-Square - 65,000 PSI

Since the brass for all the above is of identical construction, I can see no reason, in a modern strong, bolt action, to not use all the above to the 65K PSI Limit, if desired.

IMHO,

Bob
</div></div>

The reason why the 30/06 is set at 60Kpsi is there are still many Springfields, Enfields and Garands around that need to be accounted for.

The reason why the .280Rem is set at 60Kpsi is the original rifle that it was chambered in (Remington M742) worked more reliabily at that lower peak pressure.

In a MODERN bolt action, there is no reason why you couldn't run either of these cartridges to 65Kpsi, like everything else.

BTW the .270Win has a 65Kpsi limit because it was introduced in the Win. M54 bolt action in 1934 with improved high nickel steel.

 

[chuckhammer]

Re: Max Pressure .30-06 vs 6.5-06/.270/.338-06

Thanks for your very insightful replies, gentlemen. I posted this question on three different sites and this one has offered the most directly related experience and knowledge on the subject.

The other sites were longrangehunting.com and thehighroad.us.