It's not just you, Senor Gunz.  I have had primers fail to ignite on 10mm Underwood 180gr TMJ, 180gr XTP, and 220gr HC.  Sometimes a second strike lit them, sometimes not.  On one box of 50 Underwood 220gr HC I had 6 failures to fire.  I have had no failures at all with Hornady, Remington, Double Tap, or Precision One 10mm.

I want to love Underwood 10mm but I need to decide if a slower, more expensive round from Double Tap or Buffalo Bore is worth it to know that first round will go off when intended, under duress.  It's ironic because I've never had feeding issues with Underwood, just bad primers.  And I keep the firing pin channel scrupulously clean and dry on my G20.  Stock striker spring, too.

That vid by RedBull was one of the things that led me to say "why bother with a heavier spring, as long as reliability is good?".  IIRC on the 155gr UW, the stock spring had an extreme spread of 60 fps while the 22# Brass Stacker had a spread of 44 fps.  Just doesn't seem like enough difference to me to drop $25 on another part.  Again, though, this is only if the gun has good reliability.  I just checked my records and my G20 has had 0 malfunctions in firing 330 rounds.  This has been a mix of loads by UW, DT, and Precision One.  I can certainly see experimenting with different RSAs if a pistol has been malfunctioning.

I pulled one of those new 220g UW rounds (lot #B0901-003, same as Test #3):

powder: 7.9gr; I think a few flakes were left in the puller
bullet: 217.1gr

All: reading through my few posts here I think I am coming across as argumentative.  Not intended, I assure you.  I have been lurking here a long time learning up on the 10mm and I appreciate all the great info you guys put out there.  I have shot over 100,000 rounds through Glocks since 1998 but just last year got into 10mm.

Quote from: Intercooler on March 16 2014 05:15:07 PM MDT
In bold is your issue with the numbers.

Can you clarify?  Are you referring to the velocities themselves, the SD, both?

When putting together this G20, I read this forum and others regarding G20 recoil springs.  There just didn't seem to be a consensus.  Some insisted you need heavy aftermarket, some said stick with factory, others said it didn't matter.  Would love to get clarification if it yields improvement.

Forgot to mention, I've never had a malfunction of any type with UW ammo and the factory recoil spring, either with the OEM or KKM barrels.

Here is my experience with the UW 220gr HC 10mm load.

Pistol: gen3 Glock 20, factory recoil spring, KKM 5.3" barrel.  I chose this barrel length to line up with the end of the SureFire X300U light mounted on the gun, which gives more holstering options.

Test 1: UW 220gr Hard Cast, bought in October 2013, shot in mid December 2013; temp = 55 degF

1264
1244
1263
1256
1256

avg = 1257, sd = 7.14; can't recall if this brass showed overpressure signs

Test 2: UW 220gr Hard Cast, bought in October 2013, shot in mid January 2014; temp = 53 degF

1296
1271
1273
1272
1274

avg = 1277, sd = 9.45

Some of these rounds had mild smilies (even with the KKM barrel) and one blew out a primer.  I called Kevin about it in February 2014.  He replaced it all with ammo from newer batches, and sent me a shipping label to return the unfired rounds from what I had bought in October 2013.

Test 3: UW 220gr Hard Cast, lot #B0901-003 received in February 2014, shot on March 9, 2014; temp = 68 degF

1177
1215
1179
1189
1195

avg = 1191, sd = 13.68; brass looks good with no apparent signs of overpressure

So it looks like the UW 220gr HC load has certainly been toned down, especially since the higher velocities were recorded in weather that was 15 degF colder.  I put this gun together for use out West against large animals when I have no other option.  I'm now unsure if the load is powerful enough for that, though it's no good for the gun to blow up, of course.