Underwood 220gr Hardcast (New Load)

[Intercooler]

  I think you are seeing things correctly. The 8 good ones have a faint line on them, but don't think they have been "smiled".

[mt10mm]

It might be that the picture is tricking me, but the primers on the bad rounds appear flatter than the eight.  That would be interesting.  I might also be wrong, but I also think I see a smile line in the far right case of the 8 standing. 

The load is too hot.  If the glock is unlocking early, its doing it VERY consistently, as the cases seem to show the smile in the exact same location, case after case. 

The primers popped out when he was shooting a tighter chamber (Lone Wolf), but stayed in with the factory barrel.  Its just a pressure thing, too much of it for the gun.  The Glock barrel might keep the primer in the case, but might cause a head separation earlier because of stretching the brass more. 

Handloading solution would be simple.  Just back down a half grain and keep alert for pressure signs.  Credit Underwood for trying to stay at max performance, and also credit him for backing this one down just a bit.  I'm just glad you didn't fire these on a 95 degree day when the rounds were in the sun for awhile before hand.

Greg

ya, me too. I didnt even notice the blown primers till I was searching for my brass. It was a learning lesson for me to be more careful in the future.

[Intercooler]

Were all of them shot from the same barrel/setup?

[mt10mm]

Yes , all that I sent you were from lw barrel with factory rsa

[Intercooler]

  Very odd stuff. Those 8 look fairly normal except the flattened primer and ever so slight ramp protusion. To date I have never lost a primer which is shocking but that might possibly be a reflection of a loose area back there allowing too much expansion of the brass. If I took a measurement of the primer pocket I bet it would be oversize compared to one of the pieces with an intact primer. I think the spring for sure didn't help matters and might have prevented a few of those which are real bad. I run nothing but 22lb springs in my 10's except the Hunter which seems to do fine with a 20lb. If a 24lb spring or higher was offered for the 4.75" pistols I would for sure try it! In a Glock where you only have the spring of the striker (correct me if I'm wrong) it would only make sense to run the heaviest functional spring you can.

[Intercooler]

  I have a Glock question since I don't know. Can the striker spring be increased to help with slide velocity/lock-up?

[Intercooler]

 Stock is 5.5lb and Wolff makes a 6lb which doesn't seem like much of an increase. They do list a 24lb recoil spring assembly though.

[4949shooter]

  I have a Glock question since I don't know. Can the striker spring be increased to help with slide velocity/lock-up?

That's a good question. Wolff Gunsprings usually makes their standard weight springs slightly more high powered. They run great in my Colt Commanders!

I don't know if the striker spring would help with what you speak of though. The heavy weight RSA's might be a different story.

An excellent guy to ask would be Freakshow10mm from Glocktalk. He built his own Commander with a light weight aluminum frame in 10mm, and from what I understand he has fired tens of thousands of rounds through it. I don't know if he has any experience with Glocks, but he still might know the answer theoretically speaking.

[Intercooler]

 One of the Glock owners with access to a high speed video camera should run a test making these changes as it relates to slide movement/lock-up. Everyone has probably viewed the STI recoil spring video that shows some valid hammer fired information.

[mt10mm]

Just returned from a small shoot. I shot 2 different types of ammo with complete stock set up glock 20 4th gen. 25 rds of DT 200gr cast & 40rds of UW 200gr TMJ. I had no blown primers and only a few very slight smiles with the UW 200tmj. I had 1 FTF with each but feel it was me with limp wrist. Didn't try the heavier RSA and didn't get a chance to shoot as much as I would have liked to. It's raining and very windy here today.

[Intercooler]

  Do you have a 22lb+ spring setup on order?

[mt10mm]

 I bought the heavy spring about a week ago and did bring it but I didnt get a chance to try it due to the weather today

[The_Shadow]

Some issues may not just be recoil spring related with the Glock setups...have a look at this post; http://greenandbrass.blogspot.com/2011/10/oh-no-broke-glock-sorta.html

The MGSL may not be the answer but info contained in the article may show areas of concern as it relates to Lock Up!

There have been some people that had the Locking blocks break...picture of locking blocks.

Having a close look to see if these items are damaged or not making the correct geometry for positive lock up are things that would be of concern.

[Intercooler]

  That looks to be a cast piece. I wonder what the XD uses?

[The_Shadow]

That piece may actually be MIM (metal injection molding)...