Enviromentals?

[308win]

Developing a load for my son's 6.5 Swede and ran into a problem today...here's the setup

M38 Mauser 6.5x55 (22 13/16 inch barrel)
143 ELD-X
RL-26 (various charges)

Initially did a ladder test in search of pressure. Started load workup at 50.6gr of RL-26 at a velocity of 2737fps (Labradar). Worked up in tenth of a grain increments until max pressure was found at 51.5gr and 2799fps. First sign of pressure (as I know it) was at 51.3gr with a rough cratered primer. Decided based off of these results to do an OCW test starting at 50.8gr and work up to 51.2gr.

Per the OCW instructions the barrel was cleaned for any copper fowling. Started with 3 fowler shots at the first load of 50.8gr and immediately had pressure signs. First shot had a rough cratered primer. Thought this could have been from something left in the barrel after cleaning. Continued with 2nd shot and had heavy bolt lift. 3rd shot resulted in the same and discontinued test.

Both tests were conducted at 60 degrees. The ladder test was 34% humidity and the OCW test was done at 100% humidity in the fog. My question is, could this cause a pressure spike? My loads were exposed to the elements, meaning the cartridges were sitting with the bullet in the up position and had dew on them. On the day of the ladder test 50.8gr was resulting in 2733fps. This morning that same load was 2719fps with the same 60 OAT. Again, the only difference was the humitiy.

Any ideas?

 

[ShtrRdy]

What was the humidity like when you loaded the cartridges?

Some other questions:
- Is the brass, powder, bullets, primers all from the same respective lot?
- was the brass on the same loading/firing cycle?
- was the brass prepped the same way?

 

[308win]

All things done the same. The brass (Lapua) was annealed and neck sized only. This is the same method used every loading. All the same lot on the rest of the components.

 

[308win]

This was the 5th firing on the brass

 

[dok7mm]

Moisture on rounds is transferred to chamber and prevents your brass from gripping the chamber. My guess on the cratered primers and pressure signs.

 

[308win]

I have the next 3 rounds with the same charge ready to go, would you shoot them or pull them? Was thinking I would shoot them in dryer conditions and see if I got the same result? Don't want to hurt anything on that old gun.

 

[jasent]

Could be oil or solvent in the chamber causing preasure spike

 

[Texanjohn]

5 th fire for these cases? What's the case length? Could be your issue, find the cause before proceeding, last thing you need is to have a new web name, " statistic"

 

[ShtrRdy]

Back to your original question, ......, I've noticed different velocity for a different group of loads fired on different days. My theory is that the humidity, ( or something ), is different when I assemble the cartridges. Because when I fire them they have been up to 25 fps different. This is with all the same brass, powder, bullets, primers.

I've since learned that Relative Humidity probably isn't a good measure of how much moisture is in the air. Relative humidity is a function of the air temperature. Warmer air will hold more moisture for the same Relative Humidity number. At this time I'm using Dew Point. I'm not sure that is a better measure but it sounds like it might normalize temperature.

 

[308win]

Cases measured 2.156 before loading. 2.160 shows to be max. The 3 fired rounds are now measuring 2.16. As far as the conditions at loading, I'm not real sure? Can't remember? Am still a little nervous about firing the rest of them. Just not understanding why it would show pressure .7gr sooner all of a sudden?

 

[308win]

Does anybody else have any loads for a 6.5 Swede using RL-26 with the 143 ELD-X? Just wondering if I'm asking to much of the old rifle?

 

[Texanjohn]

Was your chamber cut to spec?, it's a custom chamber and anything can be the cause of your high pressure, was the powder all from the same lot or did you open a new can? Check everything! Something is different,and I personally don't think it's the humidity. good luck and keep us informed, we can all learn from each others experiences.

 

[tony d willIiams]

Developing a load for my son's 6.5 Swede and ran into a problem today...here's the setup

M38 Mauser 6.5x55 (22 13/16 inch barrel)
143 ELD-X
RL-26 (various charges)

Initially did a ladder test in search of pressure. Started load workup at 50.6gr of RL-26 at a velocity of 2737fps (Labradar). Worked up in tenth of a grain increments until max pressure was found at 51.5gr and 2799fps. First sign of pressure (as I know it) was at 51.3gr with a rough cratered primer. Decided based off of these results to do an OCW test starting at 50.8gr and work up to 51.2gr.

Per the OCW instructions the barrel was cleaned for any copper fowling. Started with 3 fowler shots at the first load of 50.8gr and immediately had pressure signs. First shot had a rough cratered primer. Thought this could have been from something left in the barrel after cleaning. Continued with 2nd shot and had heavy bolt lift. 3rd shot resulted in the same and discontinued test.

Both tests were conducted at 60 degrees. The ladder test was 34% humidity and the OCW test was done at 100% humidity in the fog. My question is, could this cause a pressure spike? My loads were exposed to the elements, meaning the cartridges were sitting with the bullet in the up position and had dew on them. On the day of the ladder test 50.8gr was resulting in 2733fps. This morning that same load was 2719fps with the same 60 OAT. Again, the only difference was the humitiy.

Any ideas?

The moisture on your cartridges will increase the OD, (Outer Diameter), of your brass. Water does not compress and will keep the brass from expanding in your chamber resulting in a smaller combustion chamber.
Not sure about the following though, but I will think about it more, it is here for you to consider if you wish.
I used water injection on gasoline engines and fuel engines. The reason was that water only expands so far and that is that. The compression pressure was greatly increased while the physical combustion chamber was not decreased in area. If there is water, condensation, in the gas area during the explosion the pressure would be increased.

 

[308win]

Best explanation yet.