Home Forums Hunting & Shooting Ask The Gunwriters Question about velocity/pressure

Interesting how we wallow in the ballistic minutia. Much more fun to shoot & hunt.

i wonder if anyone ever posted those kinds of results ?

The Mole ratio stays the same

Yes that's true, but its the interest of the topics being discussed that has developed the rule of thumb reloading methods, gun manufacturing etc.. that has allowed a larger participation in the fun side.

Explanations for the non technical reader often require some simplifications.

I haven’t looked deeply into the specific “burn” rates, but the deflagration process involves varying time dependence of the phase change of molecules from solid to gas.

So I ran an unintentional experiment this morning with my 338 WM. Wanting to test some velocity starting points with new brass and bullets I decided to make 5 blow off rounds to shoot through a squeaky clean bore to begin with. For those five cases I used SIG 7MM RM fired brass, decapped them and ran them through a FL sizing die only. I did not run them over a mandrel to size the necks (neck tension was skookum) nor did I anneal the cases as I normally do before sizing. I did nothing else to the case. I added a primer, 71gr of IMR 4451 and a 225gr SST seated to the cannelure.

Here are the results. I wouldn’t call this velocity finding stability.

Have you ever noticed how handloaders, me included, chase the last foot second from our loads that don't compromise accuracy?

Have you ever noticed that factory loads commonly don't reach factory specs leaving 1-200fps gaps between factory and your handload?

Have you noticed when you hunt with fcatory ammo than animals fall over with well placed shots?

We never learn do we.............

Rookie stuff..

First question I would ask is "how are you quantifying pressure?"

Assuming peak pressures are the same, some powders are apparently showing a slower tail off in pressure basically increasing the "push" down the length of the barrel (versus just kicking it in the ass out the case). In other terms some powders increase the "Area Under the Curve" or AUC in the Time/pressure curve. That's kinda been the holy grail for powder manufacturers with people experimenting with duplex powder loads (layered charges of different burn rate powders) and other strategies. Some manufacturers have apparently cracked the code on that (or so says "Johnny's Reloading Bench YouTube Channel").

That phenomenon is well known by older highpower shooters. The M1 Garand 30-06 loadings were limited on powder selection because of the requirements of the gas system. Slower burning powders that we today accept as providing optimal loading density (like 4350) can't be used in Garands without risking damaging the gas system. Powders in the acceptible burn range like 4064 and 4895 didn't fill the case and left alot of opportunity for variation in positioning in the powder charge. An old highpower trick was to tip the barrel upward to settle the powder against the primer.
The introduction of the 308/7.62 NATO chambering (and the M14) brought an immediate increase in scores. 7.62 chambered Garands saw similar improvements. It wasn't that the 308 chambering was more accurate...but rather the powder constraints placed on the Garand handicapped the accuracy.

I've not experienced pressure increases that can be attributed to twist rate, alone. Conclusion is based primarily on MV of same loads shot thru different twist rate barrels. Fastest twist tested was 1:1 (looked "threaded" more than "rifled").

On the "secondary explosion", I've never seen that documented via the piezo pressure measurement technique. If anyone has one, please post it as it would be fascinating to review.

I am quantifying pressure by the Hodgdon 2024 Reloading Manual. I seriously they would print bogus data of that nature.
40 Gr SPR SP 13 GR LilGun 2826 FPS 28,400 CUP
40 Gr SPR SP 11.2 GR H110 2795 FPS 41,800 CUP
What I don't have a clue how you get 31 FPS difference with 13,400 CUP difference, with the slightly faster charge getting that much lower CUP. LilGun is magical beyond my expertise. Thats what I was hoping one of the many smarter fellows than I could explain why and how.

Those numbers don't tell you the entirety of the pressure curves.

Nor are they all that precise compared to piezo pressure measurements.

All "science" measurement devices have limitations. Understanding these and building models, math or otherwise, to fill in the gaps is part of the methodology. There are many "Black Swan" events in a single cartridge firing.

Measurement uncertainty is ever-present, and the precision limitation of the device is only part of it. For those interested, the GUM (Google it) will tell you all you want to know and more. Fair warning- it takes some effort to get undergrad physics students to understand the nuances, as it’s not a light read.

Another good tool box is Matlabs Neural Network toolbox

Ristow's pressure graphs are available on the wayback machine. He used Strain though, not piezo. I'll see if I can link some stuff in here.
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