Adjusting 9mm COL

[rico68]

Hi, guys. I need some advice on overall length for 9mm.

I'm going to be setting up loads with WSF powder under a 115gr FMJ bullet. The Hodgdon/Winchester load data has min charge of 4.9gr (24,200 psi) and max charge at 5.7 (31,900 psi). No problems there. But they list COL at 1.169. That's right at max COL for the 9mm and doesn't leave any room for variance. (Have you ever seen COL spec'd at max like that?)

I have factory ammo that runs fine in my guns that come in at 1.158. so I know I'm good up to that. I'll run a drop test at 1.169 just to be sure I can go full length.

I'm thinking about cutting back on the COL just a bit to allow for a bit of variance in seating without exceeding max. I know decreasing COL will increase pressure, but how sensitive is it? If I cut my COL back to 1.160, does that 9/1000 send pressures crazy? I'm not interested in hot loads. I'll start at min and probably run in the 4.9 - 5.3 range. Is a .009 decrease pretty safe when I'll be in the low to mid range?

Thanks for any insight on this. I'm new to reloading the 9mm and I keep hearing how sensitive the 9 is.

Rick

 

[ZeSpectre]

It really depends on the bullets you are using because they can have very different shapes.

For example, Hornady XTP is listed as having something like a 1.08" COAL in the Hornady book (sorry, book is out in workshop, not going to go out there to check the actual number).

 

[Blue68f100]

OAL is gun specific so you need to find what works in your gun with the bullet your going to use. Then work up the load. Jumping to max is a very bad habit unless your looking to KaBoom.....

 

[gamestalker]

When your using the same bullet as in the data the pressures they are showing was from a different barrel or firearm. For me, I consider .010" the limit without re-working the powder charge from start. 9mm is indeed a high pressure cartridge, and is also pressure sensitive to decreased seating depth variances. In my Speer #10, Speer seated a bullet .030" deeper than in a previously tested cartridge that was producing a nominal 28,000 cup. Pressures went to 62,000 cup as a result.

I generally seat some where between touching the lands and the published OAL. If I don't have data that is specific to the bullet I'm using, I will just find another bullet with similar characteristics, and start near the minimum charge data, at an OAL that clears the lands and fits the magazine. Just remember that there is no issue with seating longer than what is published and clears the lands, it's when you reduce that OAL that a sensible work up must be used.

GS

 

[1SOW]

I use one method that works for me. I would't do this using a really fast powder like maybe Titegroup, because the load range is sooo small and the powder is a lot more sensitive to very small changes in the load.

If it's with the same weight and bullet type/shape, I use a proportion to determine a starting load for min load at another oal.

4.9grs/1.169 = "S" grs/1.135....... 5.562 = "S" x 1.169....... S = 5.562/1.169 ........"S" (starting load at 1.135")=4.7grains of 231.

So I would load 4.6 or 4.7 grs, make sure it goes bang, works the action and actually hits the paper; and then work up from there.

 

[holdencm9]

I think if I was varying more than a couple hundredths of an inch, I would take an even more conservative approach than 1SOW. I am still pretty new and very cautious, but I think it would be smart to proportion the charge to internal volume rather than COAL, still ensuring the powder is not compressed.

For instance, (I am just throwing these numbers out there since I haven't measured for 9mm).

Case length = 0.75"
Case base thickness = 0.08"
Bullet is seated into case 0.15" to achieve 1.169" COAL
Internal case length = 0.75" - 0.08" - 0.15" = 0.52"

If you seat a bullet 0.05" farther into the case, to achieve 1.119" COAL, the new case length will be 0.47" which is a 10% decrease in internal case volume, or 10% increase in pressure.

Compared to evaluation using COAL, where the same change would lead you to a 4% increase in pressure assumption. But of course using a starting load you should be fine either way.

 

[LiveLife]

WSF powder under a 115gr FMJ bullet ... I have factory ammo that runs fine in my guns that come in at 1.158. so I know I'm good up to that.

Not quite. Even though same weight 115 gr FMJ bullets from different brand manufacturers can have different nose shapes (ogive) that will allow the bearing surface of the bullet to engage the rifling at different OALs.

For this reason, you should always conduct the barrel drop test to determine the Max OAL and feed/chamber from the magazine to determine the working OAL.

BTW, Hodgdon load data lists same start/max charges for both FMJ/JHP bullets but if you look at the chamber pressures, they are different. So the same OAL with different bullet types (FMJ vs JHP) results in deeper seated bullet base for JHP and increases chamber pressure (31,000 PSI for FMJ vs 32,100 PSI for JHP). So if you are using shorter OAL (say 1.135", slight reduction of max charge may be a good consideration - but you should always conduct a full powder work up from start charge).

115 gr FMJ WSF OAL 1.169" Start 4.9 gr (1060 fps) 24,200 PSI - Max 5.7 gr (1195 fps) 31,900 PSI

115 gr JHP WSF OAL 1.169" Start 5.2 gr (1095 fps) 28,700 PSI - Max 5.7 gr (1165 fps) 32,100 PSI

Another consideration is neck tension. With 124/125 gr bullets with longer bullet base, I have plenty of bullet based seated inside the case neck and reduction of OAL (bullet set back) after feeding from the magazine is less of an issue. But with shorter 115 gr bullet (especially jacketed), if I load longer than the typical 1.125"-1.135" OAL, I start to have issues with neck tension and increased reduction in OAL.

For 115 gr application, if you want/need to load to longer OAL (better for match shooting application), Berry's MFG has an interesting solution of hollow base RN with thicker plated bullet (HBRN-TP). The hollow base extends the bullet base and allows more bullet base to be seated inside the case neck and offer greater stabilization of bullet while the longer bearing surface engages the rifling. With Berry's TP bullets, I have used jacketed load data with good results.

I hope this helped.

 

[rico68]

Thanks, guys.

I won't even be adjusting a hundredth. What you're telling me is what I suspected and was hoping for. I may back off my initial charge .1 gr but that's about it.

Thanks.

 

[ZeSpectre]

BDS...love the diagram!

 

[david_r]

I would look at older data. I would also look at the numerous people running this reload and what their COL is.

FYI, Rainier 115 g round nose -- going from 1.169 to 1.040 reduces available capacity 7% and reduces free space with 4.9 grains by 19%. Going to 1.150 the numbers are 4.6% and 12%. What does it mean? Well, at max COL, start load has 0.244 cc free volume and max load has 0.177 CC free volume. At 1.140 the start load has 0.199 CC free volume or 12% more free volume than the max load at 1.169. Somewhere in there is some safety margin. I would feel safe with my own gun running greater free space than the max load has by reducing OAL and running a lower charge weight.

Maybe someone with QuickLOAD will come along and run some numbers on this combination.

 

[rico68]

Wow, bds. We must have been posting at the same time. Your post wasn't up when I started writing. That's a lot of good info. Thanks so much.