Longer or shorter OAL for major .40 N320 load

[acekc]

I recently purchased an EAA Witness Elite Limited in .40 and have been working on a load for it. After lots of research on the forum N320 seems to be the overwhelming favorite for major .40 loads so I purchased some along with some MG 180gr bullets and started load development.

While it seems a lot of people with S_I guns load very long with their N320 loads, there are also a contingent of people who load at or near max SAAMI length (1.130-1.135") because they're using Glocks. Initially I went down the path of shorter OAL because I liked the idea of something I could at least shoot in my other .40 guns (not concerned about making major in anything but the Witness). I was also under the impression that the Witness mags liked a shorter OAL.

One thing I noticed is that the Witness needs more powder to get to major than a lot of the Glock loads I've seen posted, presumably because of a 4.75" barrel vs. the G35's 5.32" barrel. I've settled on 4.9 grains of N320 at 1.3" OAL and with normal seating depth variances on my progressive I get an average PF of 168 over 20 rounds. At this point the primers (CCI SP) look slightly more flattened than lower power loads, but nothing I would consider scary-looking. I'm using a U-die and setback doesn't seem to be an issue (I cycled the same dummy round through the gun ten times and the bullet had moved around 0.003" when I was done).

After getting some 21 rounds mags from Henning's shop for Christmas and watching the videos on his site, he references a 1.175" OAL for the magazines. I just saw the video last night so I haven't checked to make sure that 1.175" will clear the lands, but even if I have to go a little shorter this gives me a bigger playground than I thought I had before.

Based on my data working up the load above, it seems likely that if I increase the OAL significantly I would also have to increase the charge further, and of course a longer OAL means that I wouldn't be shooting this load in my G23 with Storm Lake barrel or my Sig P229. My question is whether it would be advantageous to blow the OAL out to the max even if it means further increasing the charge, or whether I should just stick with what I have. Criteria would include pressure/safety of course as well as whether the short/less charge or long/more charge load would give me more of the "push" recoil that people look for in their 180gr major .40 loads.

Clearly nothing is stopping me from loading a bunch of longer rounds and experimenting further, but I'm hoping to hear from someone who's already done similar experiments to help me determine whether it's a worthwhile exercise. Between work and difficulty getting to the range for chrono testing I've already spent several weeks getting to this point and I'd just like to know if the longer OAL path will get me anything.

[a matt]

If your loads run( no FTF or ejecting issues) and make the PF use them. Watch for over pressure signs and choot em. My 2 cents

[glefos]

If these are the new Mecgar K40 mags, the max you can load to is 1.145 according to a few recent posts. With the old 10mm or 40 with spacers removed, folks here load out to 1.225.

Search in the Tanfo sub-forum. you'll see a post from casman explaining it. Very good info.

[acekc]

Thanks for the pointer, glefos. If the max is 1.145" (and Casman seemed to think that 1.14" would be better) then I'm not going to bother testing a longer length. This actually makes a lot of sense - this morning I was looking at the clearance of 1.135" rounds in the K40-based mags I recently purchased and thinking "I don't see how 1.175 would fit." I guess that's because it won't!

[Maksim]

This year at nationals I ran the new k40 mags. 1.145 ran all day long, but seemed it was about tops for it.

180 grain PD fmj, 5.1 gr of N320 made 170 pf.

[deerassassin22]

Here is some N320 Data for CMJ's and TG as well. I switched to lead so I threw that in their shot all this today.

[SirLoin]

My cousin and I have done around hundreds of rounds of load development over the past couple of months on .40 S&W using N320 and have tested a number of OALs and grains (from 3.1 to 4.7), as well as barrels (Glock OEM, KKM for Glock; Para match barrel, etc.). You do have to use more powder the longer your OAL is, and from what we've seen, each additional .01 of OAL leads to a measurable impact.

We decided to stick with as near SAAMI specs as possible, so for major, we load to 1.135 OAL, and for Minor, we stick with 1.125: they fed great, and the Majors on 1.135 didn't show overpressure.

One thing we found interesting: you also need to factor in how much space the bullet takes up inside the brass. You might load different 180 grain bullet designs (e.g., round nose vs flat points) to the same OAL, but the volume they take up inside the brass will not be the same, and less space leads to higher power factor. A Berrys 180 round nose flat-point - ROUND-SHOULDER, for example, will take up .017 less space inside the brass than a Berrys 180 flat point - STRAIGHT SHOULDER. The PF difference was significant -- around 8-15 PF change. And the ONLY difference there is the design of the shoulder. Bullets with even more differences should have varying degrees of differences with regard to space inside the brass and power factor.

Edited January 18, 2012 by SirLoin

[waktasz]

Good to know!

[SirLoin]

Clarification: A Berrys 180 round nose flat-point - ROUND-SHOULDER, for example, will take up .017 less space inside the brass than a Berrys 180 flat point - STRAIGHT SHOULDER. The PF difference was significant -- around 8-15 PF change. And the ONLY difference there is the design of the shoulder. Bullets with even more differences should have varying degrees of differences with regard to space inside the brass and power factor.