I have known for some time that a new lot of powder can have a different burning rate from an older lot of the same brand and type but this was driven home this weekend when shooting my 416 Rigby. With the old lot of R22 100grs behind a 400gr A frame gave an average vel of 2416. The same load (brass and primers are of the same lot as before) now pushes the 400gr A frame at an average of 2560. My shoulder concured with the screens. I should have known something was up when the powder measure which had been throwing wihtin a few 10ths with the old lot was coming up short with the new lot requiring the addition of a fairly significant amount of powder to weigh the same. In other words I was increasing the volume to reach the same weight. This is the first time I have seen this kind of extreme just by changing powder lots. Anyone else seen anything similar? I believe I will have to drop to 96-97grs to get back to my spec of 2400fps.
Mike - I almost always shoot across my chrono at the range. While I have noticed some deviation between powder lots, I have never witness such a dramatic change. I do not shoot R22 much so I cannot provide any insight into this occurrence as a norm for R22. However, a 144fps increase is significant. Did you see any signs of excessive pressure? (other than a sore shoulder?)
Z
Posts: 10780 | Location: Test Tube | Registered: 27 February 2001
Z, no, I did not see any pressure signs although I would not expect to with a Rigby until I was bumping the 2700 mark. The case is so large that pressure remains very low. The 2560 would be OK but I don't need the velocity nor want the recoil. I'll see what a drop of 3grs does to the load. Thanks for your response.
Mike, I just had someone locally ask me about my experiences with RL-22. Seems he changed bottles and pierced a primer in his 220 Swift. Seems like caution is advised. There are a few posts on benchrest.com with similar warnings. FWIW, Dutch.
------------------ For evil to prosper, good men must do nothing. (Burke)
Posts: 4564 | Location: Idaho Falls, ID, USA | Registered: 21 September 2000
Your difference in weight may have been due to moisture. The benchresters that shoot large cased rounds keep telling me that they throw charges by volume, not weight, because powder is hygroscopic (absorbs moisture from the air) and this moisture will affect the weight of a given volume of powder. If the older lot had les volume per charge weight, this could have been part of the problem. This small amount of moisture does not affect the performance (we're not talking soggy wet) other than making it LOOK like there are more weight grains of powder being used when in actuality if the same weight of perfectly dry powder were measured out it would result in a high pressure load.
There's an ongoing discussion over at http://benchrest.com/wwwboard/ concerning this particular powder and this particular behaviour. I've taken to using it in the 6.5x55 with great results, but apparently there are two or more lots out there with problems.
