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Posted: 4/2/2012 1:29:34 PM EDT
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This subject has often caused me to wonder.
Saami specs say 1.169 OAL for 9MM. Yet most people (including manuals) use/specify shorter, usually anywhere from 1.09 to 1.12 Now understandably, powder charges vary as wildly... shorter, less powder. I've seen specs for 115g & 125g bullets range from 1.080" all the way to 1.155" Looking at 2 pistols: Ruger P85 & Tanfolio Witness Match... both chambers appear (as best as I can measure) to be around 1.18 before a 115g Rainier touches the rifling. Loading with this bullet to 1.165" the cartridges will drop right out of the chamber. (even if pushed in hard to be sure) Some examples: Lyman 49th: Hornady XTP 115gr COL: 1.090" w/ 231 from 3.5g to 4.9g pressure: 20.7K to 32.1K Vel(f/s): 959 to 1253 (4" .355 BBL) (doesn't even list a 115g FMJ... seems odd) Hodgdon: Speer GDHP 115gr COL 1.125" w/ 231 from 4.7g to 5.1g pressure: 25.3K to 28.1K Vel(f/s): 1075 to 1167 (4" BBL) Speer 11: Speer 115gr (HP or FMJ) COL: not specified** w/ 231 from 5.2g to 5.7g No pressure given Vel(f/s): 1125 to 1191 (4.9" BBL Beretta 92) **COL from Speer 11 in intro to 9mm has warnings about setting deeper, says Saami spec 1.169", but then says best function for 100g is 1.080" & 125gr is 1.100" (of course this manual is old, and most consider some loads to be pretty hot) ++Interesting HP38 same weights, they get Vel: 1155 to 1218 I realize the bullets are not EXACTLY the same, but they aren't as different as the COL variations either. Why so much variation from Saami spec? Wouldn't it be like with rifles, closer to the lands, is usually better for accuracy? Why wouldn't so much variation cause feed issues? I have not noticed (maybe there is) that much variation in other calibers for the same type bullet. Personally, I've usually used a factory round (in this case 115g WWB) and used it to set-up the seating die as a start point. Once I have a load, I make a "dummy round" & use it to reset the seater if I use different bullets in a caliber. For example, I have "dummies" in .223 for 7 different bullets from 52g to 77g. ETA: Barrel test length |
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SAAMI spec reflects maximum allowances.
It in no way reflects feed ability. I think we've had this discussion before with rifle. Cartridge over all length in generic sense has nothing to do with seating depth. Seating depth varies from one make of bullet to another. Pistol bullets require different oals for one main reason, feed ability. Generic manuals such as Lee and instances with Lyman as well list an oal but don't reflect type bullet used. This is a problem. For instance, in 45acp. lbnswc vs lswc. Interpreted, lead button nosed semi wadcutter vs lead semi wad cutter. I know when seeing a recommended oal of 1.115 it's for lbnswc. When seeing an oal of 1.240, it's most likely for tall truncated, lswc. When seeing an oal of 1.260, it's likely for 230 grain ball. The trap is seeing recommended oal of 1.115 and trying to seat 230 grain ball at that height. Ogive or curvature of bullet will be seated below case mouth. Try seating lbnswc at 1.260 and seating depth might not be enough for case mouth to even grip bullet's base. As a rule we seat pistol no deeper than 1/32" from case mouth to ogive. see this OP.http://www.ar15.com/forums/t_6_42/322671_.html&page=1? |
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Well... OK...
Saami is MAX length. Take a bullet, 9mm, either 115gr or 125g, or 147g. (it doesn't matter, they're just the most popular) Different manuals, and different people will load the the same bullet to different COL. The powder charge will vary with depth, understandably. They all feed at the different COLs. What is the advantage (if any) of loading shorter or longer? Assuming you are a safe distance (let's say .005) from the lands, wouldn't the longer seating (generally) be expected to be most likely to be the most accurate? 1911Smith, as far as your example and the thread you linked, certain types (style, profile, whatever) in .45 ACP, generally need a tighter range of COL to feed reliably. NOT SO in 9mm. I am talking about the same bullet, let's say MG 124gr. Different sources will load THAT EXACT BULLET to anywhere from 1.080" to 1.155", the powder charge will vary, but that's it. WHY?? What is the advantage of what appears to be an extreme COL spread? I know "all guns are different" but that spread seems excessive. I'm trying to understand what 1.080" might offer over 1.155" (and vise versa) when loaded to the same velocity. |
| COAL controls the seating depth for a particular bullet. The same length with a 115 gr bullet would have a lot more of the case filled with a 147 gr bullet. This changes the internal volume of the case, which changes the pressure for a given load. Different sources will use different COALs to control the case inside volume. In many cases, there is a lot of flexiibility, but always start with a listed load and adjust carefully. And only if you have a good reason to. |
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Quoted:
I understand that, to me anyway, that is obvious.
COAL controls the seating depth for a particular bullet. The same length with a 115 gr bullet would have a lot more of the case filled with a 147 gr bullet. This changes the internal volume of the case, which changes the pressure for a given load. Quoted:
Different sources will use different COALs to control the case inside volume. In many cases, there is a lot of flexiibility, but always start with a listed load and adjust carefully. And only if you have a good reason to. This is the part I'm trying to figure out... same bullet, but different seating depths with corresponding powder adjustment. Why vary the length? What is the benefit of the different lengths (all else... end velocity being equal) I've heard it can have an influence on the completeness and efficiency of the powder burn. Less powder in a smaller space, providing more efficient and cleaner burn than more powder in a larger space... (even though the net velocity and pressure end up being the same). Seems to make sense on some level... |
| As above, that is the MAX length––using 147 gr. bullets. You would NOT want to load the heavy bullets any shorter, as pressures in a "high intensity" caliber like 9MM will rise greatly––even as much as double for as little as .010" extra seating depth. Not good that, when it already runs as high as 32,000 PSI. |
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Quoted:
Well... OK... Saami is MAX length. Take a bullet, 9mm, either 115gr or 125g, or 147g. (it doesn't matter, they're just the most popular) Different manuals, and different people will load the the same bullet to different COL. The powder charge will vary with depth, understandably. They all feed at the different COLs. What is the advantage (if any) of loading shorter or longer? Assuming you are a safe distance (let's say .005) from the lands, wouldn't the longer seating (generally) be expected to be most likely to be the most accurate? 1911Smith, as far as your example and the thread you linked, certain types (style, profile, whatever) in .45 ACP, generally need a tighter range of COL to feed reliably. NOT SO in 9mm. I am talking about the same bullet, let's say MG 124gr. Different sources will load THAT EXACT BULLET to anywhere from 1.080" to 1.155", the powder charge will vary, but that's it. WHY?? What is the advantage of what appears to be an extreme COL spread? I know "all guns are different" but that spread seems excessive. I'm trying to understand what 1.080" might offer over 1.155" (and vise versa) when loaded to the same velocity. If you could give me specifics i could better help you. For instance give me source and page number to look at in manuals. |
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Quoted:
Many loading books will list that COAL as "minimum cartridge length". I think this is a great clue to what they're getting at. They list a dimension that you should not go less than, so you don't cause excessive pressures.
Quoted:
I understand that, to me anyway, that is obvious.
COAL controls the seating depth for a particular bullet. The same length with a 115 gr bullet would have a lot more of the case filled with a 147 gr bullet. This changes the internal volume of the case, which changes the pressure for a given load. Quoted:
Different sources will use different COALs to control the case inside volume. In many cases, there is a lot of flexiibility, but always start with a listed load and adjust carefully. And only if you have a good reason to. This is the part I'm trying to figure out... same bullet, but different seating depths with corresponding powder adjustment. Why vary the length? What is the benefit of the different lengths (all else... end velocity being equal) I've heard it can have an influence on the completeness and efficiency of the powder burn. Less powder in a smaller space, providing more efficient and cleaner burn than more powder in a larger space... (even though the net velocity and pressure end up being the same). Seems to make sense on some level... Most of the time, I go with a pretty consistent OAL whatever the specific bullet or powder, but I always make sure that this is within the max and min OAL numbers. |
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