primer pocket uniformer

[Jimro]

Solocam72, last I checked Weatherby brass was made by Norma. Never heard any complaints about Norma brass yet.

Jimro

[Unclenick]

Bart,

That probably a good guess. Using your barrel dimensions and based on tweaks to the IMR 4895 model I made to match velocity performance in Hodgdon's published data, QuickLOAD is landing on about 44,000 psi. SAAMI MAP is 62,000 psi, so that's about 29% below max. Your guess is 19% below max. Getting two guesses within 12% of one another is, as near as I can tell, about as good as the Piezo transducers measure. SAAMI's one set of reference ammo data by transducer from several test facilities came up with 11% difference in average peak pressure reported. So I figure that's about the limit of trustworthiness of the Hodgdon data I based the powder model tweaks on. It made sense to me the number would fall somewhere below SAAMI max just because Federal brass is famous for its primer pockets getting loose in fewer reloads than other brands, yet you got 47 cycles. Despite the moderate pressure, it's pretty impressive to see a piece withstand all that working.

I note your mention of a 0.045" drill, but suspect you meant a #45 drill (0.082"). Here's a reference chart, should anyone have occasion to need it. One would have to do actual shooting to tell, but this test seems to indicate flash hole size matters a lot less than one would suppose from gut feel.

[Bart B.]

Unclenick, my comment:

So my SWAG is it was about 50,000 cup for peak pressure as that barrel's specs for diameters are smaller than SAAMI. . .

for pressure is a bit over 96% of SAAMI average peak pressure of 52,000 cup and the same as MIL-SPEC pressure of 50,000 cup. My cup-psi conversion formula says 50,000 cup is the same as 57,898 psi, but that's only an approximation 'cause the two pressure measuring systems ain't converted exactly but it's just a scientifically based guess; close enough for reasonable comparisons. And 42 grains of IMR4895 is the starting point Lake City Arsenal used for a new lot of powder in their M118 match ammo. I've weighed the charge weight from several lots of both M852 with 168's or M118 with 172's and it's all averaged within about 1/2 grain of 42.0 to get their specs of 2550 +/- 30 fps at 78 feet with 50,000 cup in a 22 inch barrel.

What? Me mistakenly use a decimal number instead of a drill index number? Why, that's absurd. But I was weak in being right. I've been getting those two mixed up for decades. But it's interesting to use a bunch of letter, metric, number or fractional drills in the range of .070" to .090" as pin gauges to measure flash hole diameters. They are pretty darned uniform from just being punched in by a steel die.

Most interesting way to ignite powder in .308 Win. cases I know of was done a few decades ago by a few folks using flash tubes. Yes, just like those used in military artillery cases. A bass tube about 1.5 inches long with a .080" inside diameter was threaded 6-48 on one end and the case flash hole was drilled and tapped for the same thread size. Then the flash tubes were put in and tightened in place and their bottoms squared up with a primer pocket uniformer. Cases were charged the same way with powder but after firing, a 2 inch long decaping pin had to be carefully used to push out the primer. But the idea was to ignite the powder at the top of the charge right below the bullet, not at its bottom at the primer. After extensive tests at longer ranges, they were found to sometimes help with certain types of powder, slower ones as I remember, such as IMR4320 and IMR4350 with heavier bullets. But the extra work was not worth it in the long run.

[solocam72]

Unclenick and Bart B, you guys have lost me in technicalness! LOL, I sure enjoy reading your guys posts and always look forward to your replies! How many years have you guys put in at the loading bench?

[Unclenick]

Bart,

Sorry, I thought I looked twice to be sure you'd written psi instead of cup, but if I get tired enough, the blinders go on. So we have a discrepancy there, but only in pressure and not velocity. If I use the standard QuickLOAD IMR 4895 model and put 42 grains into a case with 57 grains fired water overflow capacity, use a 22" barrel and use the M1 Type bullet seated to 2.800", I get a muzzle velocity of 2596 fps, which drops to 2553 fps at 78 feet (this is based on that bullet having a G7 BC of 0.239, which I worked out from Hatcher's data on it). The peak pressure, however, shows up as only 48,924 psi (not CUP).

That also is still not a disagreement out of line with possibility. SAAMI's own standard document for rifle cartridges includes, as an example, the results of 9 different copper crushers in 9 different facilities measuring the same lot of .30 Carbine reference ammunition and getting over 23% difference in average peak pressure reading for 10 shots while the velocity result is only about 3% different. Could the military measurement have been off that far? Sure. Also, When I've gone through the measured velocities produced for different years by National Match ammo along with the powder charges that produced them, I've found an estimated variation of about ±8% in burn rate. The canister grade is kept to ±3%, so I suppose it's possible the military specs were arrived at with a fast lot.

This may interest you.