Question(s) about high pressure signs
May 17, 2010 22:44:24 GMT -5
Post by artjr338wm on May 17, 2010 22:44:24 GMT -5
I would like some fact and experienced based information about the causes of high pressure signs as they might occur with the 10ML-II, especially if there are high pressure signs unique to the 10ML-II.
To be specific I went and shot my 10ML-II on Friday the 14th, and although the groups I shot were to the same level of accuracy I was expecting using loads I had long ago established as accurate and devoid of any high pressure signs. Except this time I experienced what I suspect were signs of high pressure.
The evidence I am suspecting was a sign of high pressure is based on the condition of my spent primers.
The primers in question are Federal 209As, which I have shot over 600 of in my 10ML-II and this is the first time I have ever observed or had spent primers in the fallowing condition:
Slightly compressed with a quite small but visible to the naked eye bulged out ring, uniform in size around the entire OD just below the flange. This "ring" varied in size from barely noticeable to definitely noticeable. And there was no consistency to which load would cause it or the size of the "ring", and it did not happen every time, only with the thightest fitting sabot/bullet combos. This only occurred when I used charges of RL10X at 75grns and 290/TMZs and H-4198 at 76grns and 245/Spit Fires and NOT when I used charges of IMR-4198 weighing 65 grains and 300/XTPs. My bolt might have been harder to open, but not so hard as I felt it was abnormally so.
First off let me say that I recovered over 90% of all my fired sabots and all wear recovered 100% intact with none showing any indication what so ever of abnormal wear or tear. And what I find truly bewildering is I have shot all these same exact loads dozens of times prior to this with no signs of high pressure what so ever and the Fed 209As all were in normal condition for a spent primer.
I will add three things I strongly suspect my have been the cause of my bulged 209As.
>#1-It only happend with sabots & bullets that loaded extremely tight, so tight in fact I needed both hands and all my strength to load them and even then I could not load the sabot/bullet combo in one motion and it required 2-3 separate pushes
>#2-I had not cleaned my 10ML-II barrel or breach plug from my last ranges session and the breach plug had close to 30 shots worth of fouling in it when I began this range session.
>#3-It only happend with charges consisting of 75grns of RL10X and 76grns of H-4198, but as I stated above, these loads of powder worked fine dozens of times in the past, and although the temp I was shooting in at the time was in the mid 50s, I had shot in warmer temps in the past with no pressure issues like the one I suspect I am having with my primers.
So what does anyone think? especially if you are certain in your cause. Keep in mind I still was still able to shoot four of my five 100yrd groups sub-MOA, to only one that was over MOA at 1.4", but oddly that was with a load that 99% of the time in the past shot MOA or smaller, but I tried using a sabot that caused a fit so tight I had to load it as i described above, and the same load using a slightly looser fitting but still quite tight sabot gave me a 1.0" group. All my recovered sabots looked exactly the same as all my ones saved form passed ranges sessions.
My vote for the cause is the extremely tight fitting sabots, but I basing this more on a guess than fact gained from experience.
I plan on going shooting again this week to try the same loads with CCIs and Fed 209s and with 2 grains less powder for both loads in question to see what happens. I have also cleaned both my 10ML-II barrel and BP as clean as I can get them. I will also invest in a portable battery powered digital scale for future range sessions as having one with me at last range session would have allowed me to reduce the powder charge weights and most likely answered my question and solved my dilemma then and there.
Thanks for your input on this,
Arthur.
To be specific I went and shot my 10ML-II on Friday the 14th, and although the groups I shot were to the same level of accuracy I was expecting using loads I had long ago established as accurate and devoid of any high pressure signs. Except this time I experienced what I suspect were signs of high pressure.
The evidence I am suspecting was a sign of high pressure is based on the condition of my spent primers.
The primers in question are Federal 209As, which I have shot over 600 of in my 10ML-II and this is the first time I have ever observed or had spent primers in the fallowing condition:
Slightly compressed with a quite small but visible to the naked eye bulged out ring, uniform in size around the entire OD just below the flange. This "ring" varied in size from barely noticeable to definitely noticeable. And there was no consistency to which load would cause it or the size of the "ring", and it did not happen every time, only with the thightest fitting sabot/bullet combos. This only occurred when I used charges of RL10X at 75grns and 290/TMZs and H-4198 at 76grns and 245/Spit Fires and NOT when I used charges of IMR-4198 weighing 65 grains and 300/XTPs. My bolt might have been harder to open, but not so hard as I felt it was abnormally so.
First off let me say that I recovered over 90% of all my fired sabots and all wear recovered 100% intact with none showing any indication what so ever of abnormal wear or tear. And what I find truly bewildering is I have shot all these same exact loads dozens of times prior to this with no signs of high pressure what so ever and the Fed 209As all were in normal condition for a spent primer.
I will add three things I strongly suspect my have been the cause of my bulged 209As.
>#1-It only happend with sabots & bullets that loaded extremely tight, so tight in fact I needed both hands and all my strength to load them and even then I could not load the sabot/bullet combo in one motion and it required 2-3 separate pushes
>#2-I had not cleaned my 10ML-II barrel or breach plug from my last ranges session and the breach plug had close to 30 shots worth of fouling in it when I began this range session.
>#3-It only happend with charges consisting of 75grns of RL10X and 76grns of H-4198, but as I stated above, these loads of powder worked fine dozens of times in the past, and although the temp I was shooting in at the time was in the mid 50s, I had shot in warmer temps in the past with no pressure issues like the one I suspect I am having with my primers.
So what does anyone think? especially if you are certain in your cause. Keep in mind I still was still able to shoot four of my five 100yrd groups sub-MOA, to only one that was over MOA at 1.4", but oddly that was with a load that 99% of the time in the past shot MOA or smaller, but I tried using a sabot that caused a fit so tight I had to load it as i described above, and the same load using a slightly looser fitting but still quite tight sabot gave me a 1.0" group. All my recovered sabots looked exactly the same as all my ones saved form passed ranges sessions.
My vote for the cause is the extremely tight fitting sabots, but I basing this more on a guess than fact gained from experience.
I plan on going shooting again this week to try the same loads with CCIs and Fed 209s and with 2 grains less powder for both loads in question to see what happens. I have also cleaned both my 10ML-II barrel and BP as clean as I can get them. I will also invest in a portable battery powered digital scale for future range sessions as having one with me at last range session would have allowed me to reduce the powder charge weights and most likely answered my question and solved my dilemma then and there.
Thanks for your input on this,
Arthur.
So new bees who might be reading this take heed and learn from my error and not only does it pay to take good range notes, but they only are useful/helpful if you remember to use them.
