1911Forum banner

1 - 6 of 6 Posts

·
Registered
Joined
·
50 Posts
Discussion Starter #1
maybe I'm just to paronoid but why take a chance right ? Here's my problem.

I have some lead 200 gn .45 acp SWC and lead rnfp colts, Now reading my reloading manual I can find recipes for brand name bullets, only lead or jacketed, nothing in the book shows a differnce for swc, rn, fp's ect, What I'm wondering is...
Some of the differnt bullets have differnt lentgh's from the bottom of the bullet to the shoulder or where it would stop just above the brass when installed, so two differnt bullets will have a different length seated into the case, that would make the volume of the case smaller which if using the smae amount of powder could cause higher pressures (correct?), I can't seem to find any data explaining how much powder difference I should use say with a bullet that will seat further into the case, I have a diffence on these rnds about .102 of seat depth, just for giggles in case I'm not explaining this good, I posted a pic to my web site. http://www.bikershut.com/gun/bullets.jpg

Thanks
tom

[This message has been edited by tmg (edited 11-25-2001).]
 

·
Registered
Joined
·
21,720 Posts
Vihtavouri is the only source of information that I know of, and that not much. I have an old leaflet of theirs and a reprint in Modern Reloading by Richard Lee. They show some examples in terms of OAL but give the relationships based on case volume. You will have to do the work to convert seating depth or OAL to available case volume. The usual recommendation is a bullet seated in an unprimed case and a hypodermic to fill the case with water. Then weigh and get the case volume in grains of water, convertible to cc's if you wish. A 10% change in case volume will lead to a 13% change in chamber pressure - an inverse relationship, of course; smaller case volume, same powder charge, more pressure. Not much difference in velocity, though. Vihtavouri says +10% case volume = -13% chamber pressure = -3% muzzle velocity. And vice versa -10% volume = +13% pressure = +3% velocity. By their figures that 13% change in pressure is equivalent to a 6.5% change in powder charge. So don't be bashful about cutting the load for a deeper seated bullet nor worry about a loss of power going to a shallower seat.

Jacketed bullets add another dimension. The friction of a copper jacket in a steel barrel is a lot greater than for greasy lead. A jacketed bullet will generally produce more pressure than cast over the same load. So load data should be converted only one way at the high end.
 

·
Registered
Joined
·
366 Posts
For semi-wadcutters the OAL is generally 1.245 to 1.255, some guns as low as 1.230. 1.255 is considered the maximum. The key to reliable feeding is to have enough of the straight part of the base of the SWC over the end of the case to allow for proper feeding. Keeping in mind the OAL, if the bullet immediately begins to curve inward at the case, then reliability will be a problem as it is too short. If I had a few left overs I would measure this case-to-curve distance for you.
 

·
Registered
Joined
·
50 Posts
Discussion Starter #5
Originally posted by Car Knocker:
tmg,

If I read your post correctly, you only have one manual and that is published by a bullet manufacturer. I suggest you either procure a manual put out by a powder company (they generally have a better mix of generic bullets) or peruse their websites.
I have the reloading book by Richard Lee and a .45acp book from Midway, My problem is the difference in seated depth, I got a couple different style bullets that have a diofference in height, but it is the part that gets put into the case that is different I was worried about getting to high or too low of pressure due to more or less volume with say 4.0 gns powder, it seems to me that more or less spce in the cartrige would produce differnt pressures,
 

·
Registered
Joined
·
3,686 Posts
You're right about the seating depth affecting pressure, that's why they specify a Minimum OAL. But I've never heard of compensating for seating depth by adjusting the powder charge. Most adjust the powder to get the speed/power they want, and seat the bullet to not mess it up. That is to say, the seating depth has to be within the bounds of safety, but it's sort of determined by the fact that the round has to feed in your pistol reliably or else what's the point. So the seating depth may be adjusted, within the Minimum and Maximum lengths, in order for them to feed in your gun. Once you find the good length, adjust the powder charge to get the velocity/power you want.

I share your frustration with the manuals, I have the Lee, and the LoadMap from Midway (the best book) as well as Hodgdon's, and an old Speer (for .45 ACP it's still current.)

I usually don't get the brand name bullets. The Midway pictures are useful here, if it matches, use it, at least for OAL. The "Midway" bullets from the LoadMap are what I use for generic bullets.

The SWC referred to as H&G #68 has a shoulder, then tapers off to the flattish top. These, most recommend to seat the bullet so that the shoulder is just sticking out of the case, about 1/32 to 3/64ths of an inch. As long as the little bit of shoulder is showing, the OAL should be safe (with a listed load.) Note what you wind up with for OAL, so that you can adjust it later, slightly, if function/feed doesn't go smooth.

The Flat Point bullet is trickier, once you put the bullet in the case, it's hard to tell exactly where the cylinder starts tapering into the flat topped cone. I also can't find clear advice, but it looks like you want about the same, just a little less, as SWC, but substitute "cylinder" for "shoulder". The taper should start just above or at the case edge. But make the OAL close to what the Midway book shows, and you should be close enough.

For example, I have my 200gr LSWC set for an OAL of 1.240, and my plated Flat Point 185gr are at 1.190. But these seating depths will stay the same, even if I increase or decrease the powder to get the velocity/power I want.

These factors are among the reasons everybody recommends starting with the lighter loads, and then working up. The difference in pressure isn't nearly as likely to be a problem on the low end of the scale.

Stay safe!

[This message has been edited by ranger (edited 11-28-2001).]
 
1 - 6 of 6 Posts
Top