Signs of too much pressure

[brickeyee]

Do you have a chronograph? One way to check for high pressure is to check velocity. If the bullet is moving faster than the max loads in the manual, you can be sure you pressure is over max.

A chronograph can only tell you what the average pressure that drove the bullet down the barrel was.

It does not tell you what the peak pressure was.

Average pressure determines velocity, peak pressures blow things up.

[mehavey]

As before, a chronograph will tell you whether you are in excess of published performance for a given powder. It will not give you specific pressures in the lower/mid regimes (though they can be extrapolated if the published data lists MIN/MAX pressures/velocities. Change in velocities for different barrel lengths from the published loads will also have to be estimated, but has also been discussed extensively in Forums such as this one.

A chronograph alone will not give precise pressure even when married up with the manuals (and manuals are maddenly different for many cartridges). But accurate velocity info can oft-times be a literal lifesaver.

Now if the shooter marries up his chrono data with a professional internal ballistics program, he's got the next best thing down from lab pressure data. Again, not "exact" since it takes at least two velocity/powder weight data points to more precisely model/calibrate the effective powder burn rates in the particular rifle -- but a whole lot better than just hope. (And hope is not a plan unless you're in the federal gov't these days.)

[Unclenick]

One has to be careful about what a chronograph tells you about chamber pressure. A short throat followed by a loose bore could give you higher peak pressure relative to final velocity than another gun did. Also, some folks don't seem to realize different barrel lengths mean different average velocities, and will try to get their 18" rifle to match the velocity of 24" rifle data and wonder why their bolts are getting hard to open.

For a given firearm using a particular bullet and a particular powder, the average % velocity change for a given average % change in powder charge is fairly consistent over the normal load range. Typically the ratio of the percentages is about 1:1. You can look through load manuals to get a sense of the range you might expect, but you do best to look at such data for the combination you are using and expect to get the ratio the manual authors got. Thus, if you've been seeing about 1% increase in velocity for 1% increase in powder charge, but on the next 1% increase in powder charge you get something other than a 1% velocity increase, you may have a problem. The velocity needs to be averaged over several rounds to get a valid reading, so it is the average for each load you pay attention to.

Too little velocity increase or no velocity increase or even a loss in velocity means something in the gun is stretching and increasing the powder burn space. It may be the chamber and it may be the brass, but something is changing. The least troublesome possibility would be uneven bolt lug contact correcting. The most troublesome would be lugs stretching back or a chamber diameter expanding (which also usually cause sticky extraction).

An unexpected jump in velocity, on the other hand, would indicate you experienced a pressure spike and should back the load down. Trail Boss, can do that in response to being compressed. Other powders, like Blue Dot have also been found to peak unexpectedly under some circumstances and for unknown reasons. The bottom line is, figure out your expected velocity increases based on what you see with your lowest starting load increments. Back off if the velocity suddenly diverges from that expectation significantly.

[mehavey]

"...some folks don't seem to realize different barrel lengths mean different average velocities..."

Agreed. A little knowledge is a dangerous thing.

Too little velocity increase or no velocity increase or even a loss in velocity means something in the gun is stretching . . .

I'm going to have to post a graph of some M1A/H380 data here later today. I'm finding (what appears to be) significant changes in that powder's performance over different days/different loads/different temps** -- Some where the velocity has in fact gone down w/ increased charges (low-mid range) with what might be differential cold-soak of 5-round test groups when loaded in the warm but adjusting to range line temps while sitting in the cartridge box.
~~~~~~~~~~

**The internet buzz seems to indicate temp sensitivity for this powder. Has anyone else experienced it?

[Unclenick]

Interesting to hear. H380 is canister grade WC852, originally intended for M2 Ball in the .30-06. I've never run it in a .308. I will say I've seen trouble getting my M1A to perform consistently with another spherical propellant. One season in the mid-90's I ran Accurate 2520 in it and could not get a tight grouping load until I started deburring case flash holes. Apparently that improved ignition enough to matter to it. It never made any difference to stick powder loads in that gun, but the 2520 appreciated it to the tune of 40% tighter groups. No small difference.

I was running Federal 210M's in the gun back then. Today I'd load #34's. The added case pressure from the magnum primers might have made the same kind of difference deburring the flash holes did.

What are you lighting the H380 with?

[mehavey]

I stay w/ either CCI BR-2's for the stick powders, and CCI250/LRMagnums for ball propellants in both the Garand & M1A. (Ditto BR4 in AR)

I'll try and get the H380 data graph up later this evening. Group-wise it's a been a bit temperamental (no run intended), running 5-shot groups from 7/8" inch out to 1-1/2"+ for the same load on the same day (fired 30 minutes apart/alternated with another load.) It's attraction to me is the absolute uniformity when thrown out of a Harrells (almost no variation at all.)

[Kayser]

How reliable is the flattened primer thing? I reload .45, .357 and .44 mag. Right in the middle range all the time - no funny business.

I've noticed that I absolutely never see flattening on my .45 or .44 mag reloads.

But I -always- see flattening on the .357 (fired through a Python). Like, 100% every round, ever. I've checked, rechecked and checked again. I'm 100% sure my loads a fine. Yet I always get the flattening.

What gives here?

[mehavey]

Per discussion, here's the graphical data for H380/Lot XX-2094 in my 308Win/M1A.
- 175SMK seated to 2.800"
- WW brass (55.6cc), 3rd firing, smallbase sized 1.630" (Hornady Gauges)
- CCI250 primers.
- Giraud trimmed each time to 2.005"
- Powder thrown (Harrells) checked against RBCS ChargeMaster +/-0.5gr (really)
- Scale left on all the time, but check-weighted before each loading session
- Chrono is an Oehler35 at 10 feet.



DataSet#1 (12 Feb - 45DegrF) is the one that made me wonder if I was seeing things. Velocity went down going from 44.0 to 44.5gr. I pulled the last bullet in the 5-rnd series and confirmed it was in fact 44.5gr.

I also just grouped/graphed ALL data together over the 10 days -- one set with everything and one set w/ the anomalous 12 Feb/44.5gr group eliminated.


The results showed a more consistent predictability (R2 = .84) but still with a lot of variability that only a day-by-day accounting tends to show.

[Brian Pfleuger]

Originally Posted by Kayser

How reliable is the flattened primer thing? I reload .45, .357 and .44 mag. Right in the middle range all the time - no funny business.

I've noticed that I absolutely never see flattening on my .45 or .44 mag reloads.

But I -always- see flattening on the .357 (fired through a Python). Like, 100% every round, ever. I've checked, rechecked and checked again. I'm 100% sure my loads a fine. Yet I always get the flattening.

What gives here?

It might be somewhat reliable in isolated, insulated situations.... I have Federal SP Match primers that I used in 357sig. They will flatten and mushroom at ANY and ALL load levels from sub-9mm to 357sig "+P", I have CCI SP primers that show little or no deformation at ANY load level.

End result: Not reliable across cartridge, powder, case or primer brands.

[Unclenick]

Mehavy,

On another forum chronograph reliability in cold weather came up. One fellow, years ago, actually sent his 35P back to Oehler when getting low or erratic readings at temperatures down around 40°F. Came back checked out and with a clean bill of health, except Oehler had changed the battery to an industrial grade. These days, the Lithium 9V is the way to go. Good down to -40° (the battery, that is, not the chronograph).

[Kayser]

It might be somewhat reliable in isolated, insulated situations.... I have Federal SP Match primers that I used in 357sig. They will flatten and mushroom at ANY and ALL load levels from sub-9mm to 357sig "+P", I have CCI SP primers that show little or no deformation at ANY load level.

Ok, that's kind of what I assumed. I am absolutely meticulous about my loads - emphasis is on cheapitude so I keep it right in the middle of the range with just the tiniest of tweaks.

Fwiw, I don't seem to get cratering, mushrooming, pocket enlargement or backing out of the primers. They just flatten up a bit, and it's exclusive to .357 (using WSP) through my Python. I've done thousands and thousands of .45 acp with nothing of the sort.

[Wag]

Originally Posted by XD-Guy

another is your slide sticking out of your forehead

How do you get beer out of your keyboard? LMAO!

Dude, you owe me a new keyboard.

--Wag--

[mehavey]

...chronograph reliability in cold weather ...low or erratic readings at temperatures down around 40°F....Oehler had changed the battery to an industrial grade... Lithium 9V is the way to go. Good down to -40°....

Fresh (alkaline) battery at start of 12 Feb series, UncleNick, but you raise a point that I'll check out this weekend running a string w/ the current bat, then shifting to a new Lithium for second string of same load.

`Will report.... (`sposed to be 43° here in Fairfax)

[Unclenick]

Thanks. Be interested to hear if it does anything.

There's not usually a false triggering problem with .308 at 10 feet, but I've gone to 15 feet from the check screen just because that's what the manual testers, ammo makers and magazine writers use. You could try it to see if you get more than a few fps difference. The added distance is just added insurance against false triggering. Also, take a tape measure and make sure the screens really settle at the same spot on that EMT pipe each time and that there's no wiggling into the pipe indentation that's needed.

Another trick with the Oehler that came up on the other board is to go to Radio Shack and buy a 9V Battery snap connector and wire it in parallel (red to red, black to black) with the original to have a second connected battery in the spare battery space. That makes for extreme long battery life with the Lithium batteries and halves the battery impedance of any kind of battery you use (don't mix types or age if you do this).

If you go by Radio Shack, see if they still sell De-Oxit use that on the battery snaps just to insure a good connection.

Also, you might want to number the shots (Oehler printer order) for each load level and enter them in Excel or Calc or your own graphing program and plot velocity vs. shot number and do a regression to see if there's a significant correlation? I'm thinking ascending order would indicate how much influence there is from the chamber getting warmer. If that influence is noticeable, starting from a lower temperature will get you get a bigger spread. Powder takes awhile to pick up chamber heat, but the primers are part of the metal-to-metal thermal circuit and don't have much thermal mass, so they heat up pretty fast. Their temperature sensitivity could be the culprit. You could try Federal's 215M's to compare. They're pretty hot.

One last thought is to check for a screen sensitivity issue. I long ago numbered the plugs on my 35P, so the same sky screen is always in the same position on the pole, but if swapping the check screen for either the start or stop screen changes the ratio of the check screen velocities to start and stop screen velocities, that would indicate a problem with one of the screens.

[mehavey]

The 3 sensors are "permanently" attached to the spacer bar, and the whole assembly (including the disassembled orange screens/arms/CPU/Bogen tripod) goes into one of those ($$$) metal guncases with foam inserts. I can set it up/tear it down in only a few minutes that way, and the "important" parts are always fixed in the same place. I'll run it out another five feet from the muzzle [but wouldn't the 3-screen comparison software subroutine negate (or at least indicate/flash) the effects of false triggering?] I guess I'll find out.

I'll start doing shot-sequence analysis as you suggest. I'd be surprised if chamber temp affects that analysis more than fouling-condition changes, but I can run the data on several 10-shot strings of late to look for dependencies. When running group sequences, I generally single-load into a magazine already in the receiver, let the bolt go home, and fire within 30 seconds as my eyes settle down. Then there are usually 2-3 minutes between shots as I record the data/draw the numbered impact point into the log book's bullseye grid/image. (So I can watch/analyze impact point drift as well.)

This takes longer to write than to do as it's all second nature now.

I did get data-capture anomalies when shooting in the mid-20s temps. (Doggone thing just quit working altogether in some instances) So the Double/Lithium retro-fix might be an eye-opener for me. I've always used dielectric grease on all my (very British) motorcycle leads, but might start using it on the battery leads as well.

I'd normally not even consider using Federal primers with a bolt having a free-floating fin-pin on a Garand-derivative design. (That dimple on the primer always impresses me.) Are the Federal 215M--which I use on the 500S&W--significantly harder?

[Unclenick]

Roger the concern on the primers. I used 210M's in both the Garand and M1A without problems for many years, not knowing any better at the time. These days I use the CCI#34's just so as not to tempt fate. But if you seat the Federals deeply and push firmly after the primer touches down on the bottom of the primer pocket to get them well below flush with the casehead, the probability of a slamfire is not likely large so long as your gun is in spec. I'm not suggesting a long term change, but just trying 100 to see if the primer is the culprit.

Federal uses (or, at least, used to) heavier cups on their small rifle magnum primers than on their standard primers. I don't know if they are doing that with the 215's over the 210's or not. Unfortunately, I don't have any 215's on hand to check against 210's.

You could also go in the opposite direction and get something milder, like the Tula or Wolf 7.62 military primers, and get a comparison there. Remington 9 1/2's are another possibility and may be easier to get in a small test quantity. I'm just trying to think of a way to see if switching primers makes the scatter better or worse?

One more thought: How are you seating the primers? One of the writers in the Precision Shooting Reloading Guide commented that he had gone to seating primers really hard. He found that if he did so he was able to get most rifles to shoot to 10 fps MV ES, but could not do so with just the usual primer pocket bottom touchdown. So, you might try just seating the primers you have harder.