[Ericc]

Hi guys,

Another forum member asked me to share some data I've been posting over at CMP's forum. It's easy enough to cut/paste so I'll repost it here for those that might be interested and have not seen it yet. A little background. For the past several months I've been measuring the actual pressures seen in the gas cylinder for as many different loads, setups etc that I can put to together. Below is just a summary of my latest outing.

[Let me know if those images are too huge for people, if so I'll scale them]

I had a semi successful day today at the range. I went to the range to test many new combination of bullet weights / Powders / Vented plugs etc. I manage to get about half way through the testing before my transducer surrendered. So posted below is just a quick summary of the data.

What I managed to get tested before the sensor failure was: Cylinder pressure data for HXP-65 (again), LC-66 (New), HXP using a smith enterprises muzzle brake, and data using HXP in a schuster vented plug on both sides of (Failure to cycle, and Cycle).

Graph #1 :

1. HXP-65 and LC-66 both show almost the same peak pressures. 2056psi for the HXP and 2048 for the Lake City.

2. The most surprising result was the Smith Enterprises brake... I had a hunch it would increase cylinder pressure but I was not prepared for how much it did. Using the muzzle brake with HXP-65 resulted in the equivalent peak pressure as the "hot" walmart 155gr ammo but it also had a significantly LONGER pressure period. Using the brake increased the impulse on the op-rod and did so for a longer time. I dont want to think what the pressure would be if you started with a hot round like the walmart Winchester stuff and used a brake. I'll probably only use the brake again with a vented plug. On the same note I've run probably 600+ rounds through a different M1 that always has a brake on it for F&F that want to try a garand. I haven't had any op-rod issues with it ever. After I replace my transducer I'll gather several more round of data on the brake.

Graphs #2:

1. This data set is dealing with the Schuster adjustable gas plug. The graph consists of two cylinder pressure traces. The Lower pressure graph ejected the round but failed to load. The higher pressure graph cycled normally. (In both cases I used a full enbloc so the forces on the bolt/system would be the same.) HXP-65 was used for both shots.

2. The pressure differences on the graph represent 1/4 turn of the gas plug. The minimum cycle pressure lays somewhere between the two. If I had to guess I'd say closer to the top graph. Perhaps ~1700 psi. The op-rod spring is new for these tests and the receiver is greased appropriately.

3. What I didn't get to test was about 8 different reloads, most are listed as max loads for the 30-06. All are outside of any Garand safe published loads that I've seen. Since my transducer gave up, I only shot one of each of these loads to capture a velocity on the Chronograph. I'll have to do the cylinder pressure on those next time out. I did a quick field strip and the op-rod looks good and still passes the tilt test.

As I parse more data I'll try and update the thread.

- Link to Previous thread with additional data: CMP Discussion Forum - Updated Garand Cylinder Pressure Graphs

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Peak pressure Comparisons:




Total Impulse Comparisons:

Eric

[texnmidwest]

Great info!!! Thanks for posting this!

[gunnerdave]

Thanks Eric, The pics do seem a bit large to me, but i'm having a bit of trouble with my browser/display. It appears that my confuser seems to think I'm visually handicapped. Working on it.

Dave

PS Got it fixed, but the pics are still just a tiny bit large, but no big deal.

Great stuff. Thanks!!