nitroexpress
Member
- Joined
- Sep 4, 2011
- Messages
- 28
My latest handloading quest began rather innocently, my son asked for some "squib"or "mousefart" loads for his 7mm Mauser. Not wanting to reinvent the wheel if I didn't have to, I googled up some information. That's when I happened on this little tidbit, don't forget to enlarge the flash hole, which helps limit the amount of shoulder setback.
Shoulder setback: I've experienced this many times, usually with mousefart loads, sometimes with "normal" reduced loads, and fairly often (if I don't pay attention) with the 35 Remington, with it's diminutive shoulder.
A few more searches, and unfortunately not much authoritative information. Some specific references to a # so-and-so bit or a some fractional drill bit, but nothing too scientific. The one constant in all the searches, was to be very careful not to use these cases with drilled out flash holes for full power loads, because of the elevated pressure they would generate.
So out came the 30 cal. buckshot and after running them thru a 284 swagging die I had a dozen or so 50 gr projectiles. I examined the flash holes in my cases, which ran app. 0.080". I loaded up 5 with a scoop full of powder, (LEE 0.3cc, app 2.5 gr of Universal), a Fed 215 and did some test firing. Actually my son did the shooting. Fairly accurate, shoot real low, was the evaluation I got.
But I was more interested in the shoulder setback, yes, app 0.004" on all 5. And in each case the primer had backed out. The article I'd read explained it thus, the pressure created by the primer igniting pushes the case forward, and without the opposing pressure that a normal charge of powder would provide, succeeds in setting back the shoulder.
My observations would tend to support that theory. My next test would be to enlarge the flash hole and repeat the test. The only puzzler was, too what size should I enlarge it? The primers pressure is regulated by the size of the flash hole, so if I were to increase the area of the flash hole by 50% the pressure would be reduced, probably not by 50%, but there should be a noticeable difference.
The test was repeated, same Fed 215, same scoop of powder, same projectile, same lot of brass only with significantly enlarged flash holes. You'll notice I referred to "it" as a projectile, not a bullet. What emerges from the sizer after you punch a 0.310" lead ball through a 0.284" sizer is not very pretty, but serves the purpose, until a suitable mold can be purchased.
The test results confirmed the hypothesis, none of the shoulders were set back, none of the primers were proud of the base.
What I needed was some scientific data, I'd like to know how much bigger I could safely go, and I wanted to know how much the pressures would be elevated if any of these cases were to inadvertently be loaded with normal loads.
Luckily I discovered a pdf on this exact subject, a scientific thesis written by an explosives engineer.
I skimmed the 256 page paper and gleamed the following scientific information. The author had tested normal commercial ammunition in 223 and 308 Win. Pressure tests were performed on 308 Win. ammunition with 5 different flash hole diameters, 1.4mm, 2.0mm, 2.4mm, 2.8mm and 3.0mm. 2.0mm (app 0.080) is the normal or control size for 308 Win. I'd enlarged mine to 0.100" (2.54mm) so the pressure increase created by the 2.8mm and the 3.0mm were of particular interest. BTW, 3.0mm is 0.118", or nearly the 1/8" mentioned in one of the posts I'd read.
I took a bit to understand the graphs, I just wasn't seeing a large elevated pressure spike. Pressure increase wasn't nearly as significant as I'd expected. Any variation in pressure was within +/- 4% of the control.
Bottom line, if any of my modified cases were inadvertently loaded with normal loads, there wouldn't be any dire consequences. My rifle wouldn't explode.
What I found interesting was that some of the larger flash holes had produced more accurate ammunition.
If you wish to read the document, a search for "The effects of physical flash hole deviations on
factory-grade rifle ammunition" should do the trick. It's free access but copyrighted.
Nitro
Shoulder setback: I've experienced this many times, usually with mousefart loads, sometimes with "normal" reduced loads, and fairly often (if I don't pay attention) with the 35 Remington, with it's diminutive shoulder.
A few more searches, and unfortunately not much authoritative information. Some specific references to a # so-and-so bit or a some fractional drill bit, but nothing too scientific. The one constant in all the searches, was to be very careful not to use these cases with drilled out flash holes for full power loads, because of the elevated pressure they would generate.
So out came the 30 cal. buckshot and after running them thru a 284 swagging die I had a dozen or so 50 gr projectiles. I examined the flash holes in my cases, which ran app. 0.080". I loaded up 5 with a scoop full of powder, (LEE 0.3cc, app 2.5 gr of Universal), a Fed 215 and did some test firing. Actually my son did the shooting. Fairly accurate, shoot real low, was the evaluation I got.
But I was more interested in the shoulder setback, yes, app 0.004" on all 5. And in each case the primer had backed out. The article I'd read explained it thus, the pressure created by the primer igniting pushes the case forward, and without the opposing pressure that a normal charge of powder would provide, succeeds in setting back the shoulder.
My observations would tend to support that theory. My next test would be to enlarge the flash hole and repeat the test. The only puzzler was, too what size should I enlarge it? The primers pressure is regulated by the size of the flash hole, so if I were to increase the area of the flash hole by 50% the pressure would be reduced, probably not by 50%, but there should be a noticeable difference.
The test was repeated, same Fed 215, same scoop of powder, same projectile, same lot of brass only with significantly enlarged flash holes. You'll notice I referred to "it" as a projectile, not a bullet. What emerges from the sizer after you punch a 0.310" lead ball through a 0.284" sizer is not very pretty, but serves the purpose, until a suitable mold can be purchased.
The test results confirmed the hypothesis, none of the shoulders were set back, none of the primers were proud of the base.
What I needed was some scientific data, I'd like to know how much bigger I could safely go, and I wanted to know how much the pressures would be elevated if any of these cases were to inadvertently be loaded with normal loads.
Luckily I discovered a pdf on this exact subject, a scientific thesis written by an explosives engineer.
I skimmed the 256 page paper and gleamed the following scientific information. The author had tested normal commercial ammunition in 223 and 308 Win. Pressure tests were performed on 308 Win. ammunition with 5 different flash hole diameters, 1.4mm, 2.0mm, 2.4mm, 2.8mm and 3.0mm. 2.0mm (app 0.080) is the normal or control size for 308 Win. I'd enlarged mine to 0.100" (2.54mm) so the pressure increase created by the 2.8mm and the 3.0mm were of particular interest. BTW, 3.0mm is 0.118", or nearly the 1/8" mentioned in one of the posts I'd read.
I took a bit to understand the graphs, I just wasn't seeing a large elevated pressure spike. Pressure increase wasn't nearly as significant as I'd expected. Any variation in pressure was within +/- 4% of the control.
Bottom line, if any of my modified cases were inadvertently loaded with normal loads, there wouldn't be any dire consequences. My rifle wouldn't explode.
What I found interesting was that some of the larger flash holes had produced more accurate ammunition.
If you wish to read the document, a search for "The effects of physical flash hole deviations on
factory-grade rifle ammunition" should do the trick. It's free access but copyrighted.
Nitro
