The video posted after mine?
http://glocktalk.com/forums/showthread.php?p=20688651#post20688651
The impulse is torquing his one handed hold on the gun, sort of like limp wristing. But it is the higher impulse of the Underwood Ammo, is such that the recoil is not straight back in his web of his hand.
At the furthest rearward travel of the slide it is causing his grip to flip up, when the cartridge is in free travel being pushed by the slide to the forward position the cartridge is bounced around slightly, its nose sometimes not guided to the chamber entrance but stuck to the left.
The video also showed him using the 45ACP from the same slide and a barrel swap, this would indicated that the breech is cut or worn to where the 45 ejection rim is fitting the breech area. If there is that much slop in that fitting, then the rear of the 10mm cartridges can shift around as they are sliding up the breech and under the extractor.
The first thing I would consider tuning is: The extractor in this scenario. Is it the correct 10mm extractor? Is it the 45 extractor?
The extractor's fitting is another thing of interest as it is fine for the 45's thinner extractor rim, but maybe too tight for the thicker 10mm extractor rim. The spring tension may be off or the extractor needs a little polishing to allow the casings to slide in under it.
Gotta get them extra power mag springs too.
I think the malfunctions were caused by the longer 15 round mags being pushed forward by the bottom of his hand.
If you noticed, the gun worked perfectly with the standard length G29 mags, and even with the G30 mag.
This is a common problem with compact Glocks being fired with the full length magazines. They actually make a sleeve for this purpose, to prevent the mag from being pushed forward out of alignment.
Perfect title for what's going in my Glocks. I have a had a few range trips where they shot it all fine. Keep in mind "a few". This latest trip had all kinds of misfeeds where the round was kind of sideways or just not pushed all the way back in. I was using my six inch ported stormlake barrel, an arredondo mag extension, and a 24lb stainless steel competition captive recoil spring from Glock store. I tried different barrels and different combinations with no success in reliability. Hell, I even went entirely stock and can't get it to work. My next bet is to try PBR ammo and hope it runs smoother. I already returned my barrel to stormlake once because the chamber was too tight for UW but not other manufacturers. They loosened it some and it runs them smoother but still not 100%.
What kind of brass measurements you getting?
I really don't know in either barrel. I need to check if I'm going to nail this down. All I can say from slight bulges there are no huge bulges and no blown out primers.
Try the 24 pound spring while keeping everything else stock, if you didn't already.
I'll look into another spring for it. I have a 23 lb spring in my G29 that actually feels like 23 lb. This supposedly 24 lb in my G20 doesn't feel too unlike the stock one.
So I managed to put a stouter spring on the rsa that I've had for awhile. The other one I think really lied about its supposed weight. I couldn't get complete success with the arredondo extension or the 6 inch stormlake barrel. In a more stock like setup I did have complete reliability out of two full 15 rd mags. I was out of 10mm for that range visit. Much cheaper to shoot 50 10mm and 150 9mm then all 200 10mm:) Would like to try some PBR on the stormlake barrel at some point. I've had complete success with it on all loads besides underwood so far.