Last weekend I got the first chance to use the PressureTrace system to measure some handloads in my .30-06 M70 rifle (see http://www.shootingsoftware.com/pressure.htm). It was an eye opener.

We were on an army range and had to cease shooting at noon. The weather was poor: heavy rain driven by
strong winds. At 11:45 we got a window. It was a case of quickly connecting the PressureTrace to the rifle and the laptop ASAP, and bang off a few rounds to see if the kit works and capture some data - nothing serious.

The three loads I tested were similar:

1. Speer 150gn RN, Fed 210, N140 52.0gn, Lapua case
2. Sierra 150gn Spitzer, Fed 210, N140 52.0gn, Lapua case
3. Hornady 150gn FMJBT, Fed 210, N140 52.0gn, Norma case

The Speer RN has a long bearing surface and produced the 'smoothest' and most consistent traces; the Sierra Spitzer has less bearing surface and was slightly less consistent; the Hornady FMJBT has the least bearing surface and was fairly consistent - but produced excessive pressures.

I have not yet calibrated the instrument to any known load so the pressures I mention are indicative not absolute. That said, the Vihtavuori manual suggests a pressure of 49.3K PSI for their maximum load (53.2gn) and I was 2.3gn below that and obtaining around 45K PSI which looks sensible.

All three loads rose to a pressure peak of 43-44K PSI in about 0.5ms, but all three loads also exhibited secondary pressure peaks lasting about 0.25ms just before the bullet exited the muzzle at 1.25ms. Obviously this isn't desirable and, I'm told, means my powder isn't fast enough. I was surprised: N140 is no slouch.

Loads 1 and 2 produced secondary peaks that rose from about 12K PSI to 22K PSI i.e. an increase of about 10K PSI. But load 3 was horrendous: the secondary peak equalled the primary peaks in pressure (i.e. rose to 45K PSI) but one shot reached 63.5K PSI.

I've prepared some more cartridges loaded with the same bullets but using N135 (faster burning) and N160 (slower burning). I've also prepared the same loads but 'buffered' the powder with a 1/4 sheet of tissue paper (2.1gn) under the bullet to hold the powder in place. I may get a chance to test these tomorrow morning.

Has anyone used magnum primers and the .30-06? In this case the components are Federal 215M with 150gn bullets and N135, N140, N160?

Welcome to the club! There are now quite a few people using the PressureTrace, and, as you say, it is quite an eye-opener.

I have used magnum primers in the 7.62x54R, which is quite similar in case capacity to the 30-06. I have not detected any increase in pressure when using them. In fact, with 4831, there was a real decline in pressure with magum primers.

At least one strain gage system manufacturer prior to PressureTrace found the secondary bumps, and simply suppressed them. Fortunately, PressureTrace left them there for us to see and to figure out, if we can.

I think there are two secondary bumps.

One starts out as flat spot in the pressure decay, before the bullet exits. As you increase the load, it gradually grows to a damped, single cycle sine wave.

The other happens after the bullet exits, and has a very fast risetime. When powder gasses exit the barrel, they have no oxygen, but are hot enough to glow. They are also rich in hydrogen. One fairly popular theory is that when the hot gasses hit the air, they re-ignite, and cause the secondary spike. This seems to happen more with light bullets, and long barrels.

As to your calibration, your PressureTrace "knows" the hoop strain equation, so if you do a proper job of attaching the gage, and can get the required dimensions to about three digits, your results are as accurate as your inputs. The reference ammo is just to be double sure you didn't get an air bubble under your gage, and that you entered your data correctly.

The Federal High Energy 180 grain stuff is about 58.5 KPSI in my rifle, and it seems to be a good "limit sample". The batch of 180 grain Super X I tried came in at about 52 KPSI.

There is enough batch to batch variation in powder that published PSI levels for handloads aren't a good reference. I think commercial loaders test each batch of powder, and slightly adjust their loads to get constant pressure and MV.

Suggestion: When doing a new load, make up four pairs of cartridges, about half a grain apart. When you shoot them, record peak pressure and MV. Then you can do graphs of pressure vs. powder, MV vs. powder, and MV vs. pressure. They are quite revealing. Be sure to keep your barrel at pretty constant temperature when you do this.

Denton,

Is there any provision in the "Pressure Trace" software for to calculate pressure versus bullet displacement? This would tell you immediately if the secondary spikes were occurring while the bullet was still in the barrel or if it was a result of the bullet's recent exiting of the barrel.

ASS_CLOWN

here is an interesting link on the matter. Charlie Sisk is a custom rifle builder who is also doing some studies on the secondary pressure spike you guys are talking about.

http://www.24hourcampfire.com/ubbthreads/showflat.php?Cat=&Number=309519&page=2&view=collapsed&sb=5&o=14&fpart=1

dhs

AC...

PressureTrace does calculate and mark the exit point of the bullet. The horizontal axis is time, so other than that one point, you don't know displacement.

dhs...

Good link. Thanks.

Let me get this straight . You guys are saying your little gizmo is telling you there is a sharp rise in CHAMBER PRESSURE AFTER the bullet leaves the barrel ?

I think my logic/BS detecter goes into overtime with that notion.....