I think it was the end of last week I finally got around to checking that strain gage. After removing the protective tape it was indeed loose and had lost its bond. No wonder, I don't understand why I chose that damn gun to begin with, it had engraving under the gage and bond, and was sure to loose bond at some point....... Oh well.....
I chose another gun, I have 4 of these things laying around currently anyway. I added the strain gage, let it sit for 24 hours, then taped over it to protect it and it sit for probably another 3-4 days curing. I decided today was the day to revisit this, my curiosity peaked..... But first, we had to check the strain gage connection to make sure it was good, and on top of that we had to check a known load to see how it compared with past tests.
This will be the third Marlin set up with strain gage and tested.
The old standby Load is 405 Remington with 40/IMR 4198.
From my data I see I tested this load on 12/21/2005 and at that time it gave 1615 fps at 32600 PSI.
Another gun, tested on 8/22/2014 it gave1540 fps at 28600 PSI. Both Velocity and Pressure lower than the 2005 test, but still within 4000 PSI, which is acceptable, especially considering velocity matches the lower pressure given.
Now, today, yet a different gun and new strain gage the same load gives 1621 fps at 30100 PSI. Well within spec.
This is 3 different guns, span of 15 plus years, different brass, primers, powder..... yeah, I would say well within reason and spec. I feel more than confident we are getting good readings.
Now, on to the question at hand, that peaked my curiosity...............
Can 45-70 be loaded with Red Dot or Unique?
I tried a 405 Remington with 15/Unique a couple of weeks ago. Very light load, showed no real pressures, and tested at 1109 fps in the other gun.
Today, in the different rifle, now connected with a proper gage we get 1122 fps and 25600 PSI average. While the velocity gave a very low ES (Extreme Spread) the ES for pressures was not good at 3700 PSI. This is not acceptable to me.
I went up to 405 Remington with 17/Unique for 1230 fps at 31200 PSI. ES was stupid good with velocity, and a little better with 2800 PSI on pressures.
Rules of Pressure...... #1 Rule WEIGHT EQUAL PRESSURE
I dropped the bullet weight down and tested a 300 Remington HP
Using 17/Unique with the 300 Rem HP we get 1335 fps at 21700 PSI ES was 2200 PSI
Moving up to 20/Unique 300 Rem HP we get 1517 fps at 28600 PSI ES 2600 PSI.
I will accept the larger ES for PSI for these light loads, normally when they top over 2000 PSI ES I start looking at them harder... but for these type of loads not really sure it makes much difference. What is crazy is the ES for velocity is stupid low on all of them........ They would appear to be great loads if that is all you looked at.......... I suppose they are plenty good enough, if they meet your Pressure parameters......
I believe some thing was mentioned about pressures for TrapDoor guns? I really do not know what the upper end is for those weaker guns, since I never dealt with any personally....... Just a quick search as I type this I see 21000 PSI mentioned on one search, and 28000 PSI mentioned for modern replicas........ Before you shoot yours, make sure you know...........Knowing this, I would probably stay with the lighter bullets......... especially with Unique.
I am going to dive into this a little further on the Pressure Works thread I started before this..... Here, I am just addressing the Unique question. Over there, I suppose I am going to do some Paste/Copy and you will see nearly the same thing, but I have some other loads to list..........