Hoot wrote:Bmt85 wrote:Do you notice any signs that your over pressure? What was your CHG for 39gr of Lilgun?
The Lyman AR manual shows 39gr of Lilgun as a starting point with a velocity of 2328fps out of a 16" barrel. It's been said that current Lilgun is hotter than older Lilgun. So that could explain some of the increase, but your numbers for the 200 XPB still seems a bit high. With that said, I have a 16" Bushmaster upper, I run the 200 XPB with 43.5gr of Lilgun (current production) and a stab crimp. No pressure signs, and CHG is good (don't have the numbers in front of me at the moment). Don't have velocities, sorry.
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Wat Bmt85 said and I'll add one tidbit. I'm not sure about your recent weather, but we have had some withering hot days up here lately, which is to be expected in late July. All ball powders get hotter when the temperature gets hotter and 39gr is approaching the high end anyway. I usually wait out the hot time of the year, opting to doing 450b load work in the spring and fall. I usually hunt on the winter, so my loads are developed in cooler conditions. Pushing 200gr XPB's to 2600fps is not endangering your rifle, but is getting up there. I wouldn't be surprised if that same load velocity drop to 2400's under fall conditions. Some bores are tighter fits ad some are looser. You may have a tighter bore. That jacks up the resultant velocity also.
Hoot
Bmt85, what do you mean by CHG in your first sentence. I thought CHG = Charge and for that last load I was concerned about it was a Charge of 39gr of Lil'gun under that 200gr PBX. I suspect you mean something else. I couldn't imagine what 43.5 gr of Lil'gun would be like under that bullet. That has to be smoking.
The fact that I got the significantly higher velocity than I expected is why I am asking questions. Quickloads was predicting ~2418fps for my 20 inch barrel if I shorten the barrel to 16 inches the prediction lines up very close to what your Lyman manual states. When I got a touch over 2600fps I got concerned. Most of my other loads have been much closer (give or take 50-60fps or less) to other published data and/or Quickload predictions than this particular load.
I did not notice any pressure signs but I will look at the brass again tonight and take some measurements. I write the charge weight on the brass with a sharpie when working up new loads so I should be able to identify the cases.
Hoot, you may be onto something with the temperature. I did not think about that. It was mid afternoon and was easily 95 degree in Tennessee where I was shooting. The gun was hot too. That 39gr loads was fired right after the two five-shot test loads for the 275gr loads and the five-shot test of the 37.5 gr 200gr PBX load. Everything was hot.
Texas Sheepdawg wrote:Fine work there, mcb. These are the two bullets that are next up on my range testing. I already have them loaded and ready. I just need to find the time. My crimps will be different however and my OAL may differ greatly on the 275s as I loaded them to be shot out of my bolt action plus I'm using 1680 for the powder charge.
Please post your results with the 1680 powder when you get them. The local Cabelas carries that powder and I would be curious to see what results you get with it under that 275gr bullet.