LOADING 357SIG FOR LARGE FRAME GLOCKS: LL357Sig
Around 2003 I proposed on the 357Sig Forum that in an aftermarket barrel in a G29 or G20 a “Long loaded 357Sig” (I labeled LL357Sig) could be loaded to the approximate pressure and performance of 9x25 Dillon. Spongeman made significant contributions with his knowledge and software, and Grendelbane added his experience with development on the 1911 platform.
I use to be able to Google “LL357Sig” to find my GlockTalk info, but the original thread is gone now. My hard copies elude me as well. I am in the ridicules situation now of having to rely on my old pity-full memory and engage in new research to reinvent this wheel.
Still don’t need any additional pricey dies or additional inventory of brass, but things have changed slightly and deserve a few words of reflection and refinement.
It is great that Spongeman references results of the LL357Sig project thread occasionally. It is of concern to me that load data for LL357Sig is presented sometimes as equal charge loads as the 9x25 Dillon. Spongeman does a wonderful job in his reports accurately providing ample warning with his data to monitor for high pressure signs.
I have also seen other contributors offer load data not significantly beyond standard 1.140” COAL 357Sig recipes. The LL357Sig will perform like and kick like the 9x25Dillon and 10mm with similar weight bullets.
I would like to reflect upon the then-and-now, learn from other persons experience in the interim and start reloading LL357Sig again myself.
I was using small rifle primers in LL357Sig back in ‘04. Same fire as Magnum Pistol primers but handle pressure better. Don’t think that was or is now necessary. Nice experiment however. If someone is having problems with primers, give small rifle primers a try.
You only need to load 95% of the 800x or Longshot powder charge as listed for the 9x25 Dillon to approximate the same pressure and performance from the LL357Sig, because that is the ratio of case volumes loaded with identical bullets to the same 1.26” COAL. I reported in the original thread I was able and inclined to load longer than 1.28” COAL in my old magazines for maximum case volume. 1.272” is my new specification because my newer G20 magazines are not internally as long as the old ones!
Back then I only had a 3.8” import G29 357Sig barrel. The 95% rule worked well. I never saw any pressure signs, ever.
I read now that persons are noting pressure signs with aftermarket Glock 6” barrels. I now own several 6” 357Sig aftermarket barrels.
357Sig barrels for Glocks are tight and fully supported. 100% 9x25 powder charges in LL357Sig are not likely to KABOOM Glocks. (Unlike other unsupported pistol barrels and shorter internal length (1.26” COAL Max.) such as in some 1911s.) I don’t see the point of loading to the edge of disaster. Rule of Averages. Murphy's Law: Anything that can go wrong eventually will go wrong.
Two observations here: 800x does not meter well, and, in 10mm volume cases 800x continues to INCREASE pressure as it burns inside barrels even beyond 14” in length!
So, what happens when I use the 100% of 9x25 load data, throw an occasional heavier-than-average 800x charge from my powder measure and let fly from a 6” or longer barrel? I think the occasional pressure signs I read about are explained and inevitable. Darn that Murphy!
I load Longshot in my standard 1.140” COAL 357Sig pistols. Longshot meters well and has as much horsepower as 800x in 1.140” COAL cartridges. I never developed Longshot loads for the LL357Sig because 800x has more horsepower in +1.260” COAL loads.
I never have forced 9x25 Dillon powder charges into LL357Sig. I will weight check each 800x charge per my old 95% rule. If pressure signs are observed, I will subsequently LOWER the 95% rule. I don’t rule out better metering powders for better consistency and safety. Always willing to learn.
I originally envisioned the LL357Sig as a longer distance hunting or target cartridge compared to the 10mm. I favor the heavier more solid and streamlined bullet designs for distance work. What ever is the target, it won’t matter whether the identical bullet comes from the 9x25 Dillon or LL357Sig.
I have been known to wear a protective glove when testing loads. I single load and remove the magazine to provide a low pressure exit of hot gasses in case of case failure when testing.
Clearly, I am getting old. I value and need to preserve my middle finger(s) for future conversations.
Enjoy your reloading and shooting. Save a few bucks, try to make improvements, don’t forget the science and statistics. Take precautions. Don’t push the project to the ragged edge of safety. Murphy's Law still rules!
Reference: #11 10mm reloading Forum https://www.glocktalk.com/threads/imr-powder-data.179348/
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WHAT I WAS LOADING THEN: I have reconstructed my “Proof of Concept” LL357Sig loads:
1. 3.8” Federal (Dasan Korean import) barrel in G29, 357Sig brass, small rifle primer, 125gr Roze Distributor Zero jacketed soft point bullet, 1.285” COAL, 11.5gr 800x. Estimated 1700+f/s. No pressure signs at all.
2. 3.8” FederalArms barrel in G29, 357Sig brass, small rifle primer, 147gr Roze Distributor Zero jacketed hollow point bullet 1.285” COAL, 10.5gr 800x. Estimated 1400+f/s. No pressure signs at all.
Other persons safely shot these from 6” barrels without problems or pressure signs. It is important to find out near maximum loads safely. Keep tight tolerances on your loading procedures.
Too long and powerful for 1911 conversion barrels, or other unsupported chambers.
More often the 10mm cartridge with similar bullet weight served my interests better than LL357Sig or 9x25Dillon. I did not develop the project further with a broader array of bullets.
Choose bullets that can handle the velocity. Many popular bullets will shatter at these velocities.
Never seen a 357Sig conversion barrel for large frame Glock without sufficient lead prior to rifling to long load LL357Sig. I suppose they could exist. Storm Lake, KKM, Jarvis, Bar-Sto, EFKFiredragon, Dasan under any number of labels, etc. My barrels from several manufacturers are more than a decade old. Email the manufacturer for current specs.
WHAT I AM LOADING NOW:
1. For barrels up to 6” length, 125gr as above, any small pistol primer, 1.272” COAL, 11.2gr 800x.
2. For barrels up to 6” length, 147gr as above, any small pistol primer, 1.272” COAL, 10.2gr 800x.
I provide load data for two bullets with max and more conservative loads. The max load approximates McNetts 9x25Dillon published old data (but not DoubleTaps production loads). The newer data should still be more lively than Underwood Ammos 9x25Dillon production loads. All are good products for their intended purpose.
It is prudent to start low and safely work up to the load your firearm/barrel chambers, feeds and fires safely. It would be a rare indeed that the fastest most powerful loading is always the best loading for your purposes.
