Looks like all of the Underwood ammo is being moved through Able Ammo.

Stainless, captive.

From Glock Store via Amazon: http://www.amazon.com/Stainless-Competition-Recoil-Spring-Glocks/dp/B00A6YEJ2A

Burned thru 45 rounds of Underwood's 180gr GDHP without issue using my G20SF. Case diameter prior to firing is .421 and after is .434.

No case smiles. Accurate. Perfect functioning.

Stock barrel w/20lb RSA.

I tried a few different rounds at the range yesterday.

First setup was G20SF with stock barrel and 20lb RSA at 10 yards.

Federal 180gr FMJ (didn't measure initial diameter):
- No reliability issues in 30 rounds
- I was all over the target. 3" to the right shooting LH and 3" to the left shooting RH.
- .433 dia

PPU 180gr HP (.422 initial dia):
- No reliability issues in 20 rounds
- Accuracy improving ...
- .430 - .431 dia

UW 200gr TMJ (.4215 initial dia):
- 1 FTF out of 25 rounds. Nose high, almost chambered. Was last round in a new mag in 3rd string of 5.
- On target now.
- .434 - .435 dia


Switched to KKM 6" barrel.

UW 220gr HC (.4215 initial dia):
- 1 FTF out of 15 rounds. Nose high and left. 3rd round of 5 in mag.
- Nice 2" groups. Very smokey!
- .430 - .431 dia


Switched back to stock barrel.

Armscor 180 FMJ (.421 initial dia)
- No reliability issues out of 10 rounds
- Good groups
- .435 dia

I got some fresh UW 220gr HC and tried some at the range today. They're a bit smokey, but I was getting nice 2" groups of 5 at 10 yards. No popped primers, no smiles, had one FTF though (nose up & left). It was the 3rd round of 5 in the mag.

I just measured the cases I managed to recover.

  9 @ .431
  3 @ .430

Unfired diameter is just under .422 (call it .4215) and COAL is 1.252.

I was using a G20SF with a 6" KKM barrel and 20lb RSA.

Not sure what to make of the FTF. Maybe I limp wristed. Mags are new. I'll need to do more testing.

I loaded this page last night to update the qty to 0. When I hit the "modify" link, it never came back. The database crashed and the site was essentially down.

More PPU cases @ SGAmmo. 6 5 4 3 left as of now.

http://www.sgammo.com/product/prvi-partizan/500-round-case-10mm-auto-180-grain-hollow-point-prvi-partizan-ammo

Not much to go on in the SwampFox video. Perhaps the biggest takeaway is that the equipment (chrono) is not as reliable or consistent as one may wish. I know nothing about chronos or their specifications. I also had no idea that they're affected by weather conditions. I've been considering getting a chrono someday.

I for one am learning with your help - thanks!

I am guessing that substantial efforts and premium equipment would be required to produce data identifying a strong correlation between RSA strength and projectile velocity. A large corporation like ATK or Olin/Winchester probably has the resources, but lacks the incentive. If such a company produced a report on this topic, I would review the data with high regard.

I am at the beginning of a journey of learning and will reach my conclusions carefully as knowledge is gained. I don't feel the need to settle on answers any time soon. I'll just sit back and study the data as it comes in.

Quote from: Intercooler on March 17 2014 05:25:16 AM MDT
TheOtherMike,


                      Did you view the video? What's your thoughts?

Yes, I just watched the video - thanks for bringing that to my attention. The data are interesting and I can see how they support the theories discussed in this thread. On the other hand, these are not controlled tests and the number of samples is rather low, yada yada yada. Here I go sounding like a jerk again, but I doubt the results are statistically significant and would hesitate to draw any conclusions.

For example, I can use the data to make a different argument. I'll refer to the 200gr UW trials. (Not trying to cherry pick. I didn't use the initial 155gr trials due to cold barrel and I didn't pay attention to the 40 or 357 data.)

Type	Weight	Average	Spread
Glock	17	1280	41
B.S.	22	1275	29
Tungsten	22	1277	36
Wolff	24	1292	17

I would expect a "loose" system (Glock RSA) to produce lower velocities. I expect a weaker spring that allows the slide to recoil too soon to produce a "mean shift" downward, meaning that the average velocity for such a system will be lower, due to a predicted drop in pressure before the projectile leaves the barrel.

Note that the Glock spring yielded the second highest average velocity, more than springs even 5 lbs heavier. The highest average velocity was realized with a spring only 2 lbs heavier than the spring yielding lowest average velocity.

Of all the unusual measurements of the springs made in the video (mass, rod diameter) the most significant factor (spring rate) wasn't addressed. How do we know what the actual spring rates are? What is the variability in a single manufacturer's products? I know some of you have made such measurements (Thanks!) and I have yet to look at your results.

The time between trials can be another factor as the barrel cools. Glock was always first, probably after a gear change. This may explain the higher spreads.

I could go on but I don't want to irritate anyone more than I probably already have. For me there still isn't sufficient information to support any conclusion, and I'm OK with that. I think a slow motion video of similar trials would be enlightening.

Quote from: DarnSkippy on March 16 2014 06:00:05 PM MDT

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.

I am also not sure what Intercooler means, and frankly disagree with such a statement.

Rationale: We've all seen slow motion video of a pistol firing. In every example, the projectile has left the barrel quite some time prior to the slide starting to react and moving to the rear. Conclusion: RSA is not a factor in projectile velocity.

Additionally, assuming a very weak RSA would allow the barrel to begin rearward travel too soon, thus presumably decreasing barrel pressure and hence projectile velocity, then the weaker, stock RSA would yield lower velocities rather than higher velocities as DarnSkippy measured. If RSA strength is a factor in projectile velocity, I would expect results that contradict what Intercooler is implying.

So to me, such a statement is illogical. However, I may not fully understand all of the factors involved and, if so, I would really like to learn what all this means.

ETA: Ah, good. I just read what was posted above while I was typing. However, I still don't see evidence that the RSA strength is a factor. With an avg = 1191, an sd=14 is neglible and partially (mostly?) due to other factors like measurement error, powder loading, etc.

I setup my G20SF specifically for this 220gr HC ammo with a 6" KKM and a 20lb. captured RSA with a stainless rod.

Everything else I have run through the G20SF was with stock setup.


Not clear to me what issue is being attributed to Glocks/polymer frames.

Also not clear what the RSA has to do with overpressure concerns.

Hope someone can explain.

Thanks!

Thanks guys.

For the record, the case diameter of the unfired Underwood 220gr HC rounds is .421.

I tried the 220gr HC today with a 6" KKM barrel.

Shot 10 rounds. First 5 were one round in the mag at a time. Everything looked OK to me as I collected each case after firing.

Then I loaded 5 in the mag. I had a failure to feed on the 2nd or 3rd round. Corrected and continued. I was only able to recover 2 more cases. 1 had no primer - probably the round leading to the FTF. I decided to stop there.

I measured the 7 recovered cases (of 10 fired):

  .431
  .432
  .432
  .431
  .431
  .432 *blown primer
  .432

I have 140 more of these rounds. Am I correct in assuming the experts here would recommend not to fire any more?

[ETA: These are the older, hotter 220gr rounds.]

Would it be possible to remove some of the powder and "reload"? (I have not started reloading so I have no idea.)

Would the stock Gen3 barrel be any better/safer? (Thinking that the looser chamber and shorter barrel may result in lower pressure.) Oops, forgot there's no jacket - my primary reason for getting the KKM.

Other options?

Interesting thread, but has some apparent derp here & there.

Regarding spring wear: Someone already correctly mentioned that cycling a spring is what wears is out, not static loading.

Regarding RSA (Gen4 I think) and handling all loads, weak to strong: Sounds highly suspicious. Hope it works for you.

Regarding frame flex with a stock/light RSA: The case is (should be) already extracted by the time the slide is all the way back. Thus any flex upon slide/frame impact cannot affect extraction.

Regarding stock/light RSA and smilies [I am speculating a bit here and would appreciate thoughtful feedback]: All slow motion video of a round being fired clearly shows the bullet exiting the barrel before the slide begins to move rearward. I suspect that once the bullet exits the barrel, the pressure within the barrel drops significantly. I propose that since the pressure drops, the only time a smilie is produced is while the pressure is high and the bullet is still in the barrel. And since the slide has not moved while the bullet is in the barrel, the RSA strength is not a factor in the occurrence of smilies.

For the record, I have a G20SF (almost 1 year old) and have fired most, if not all, of the ammo mentioned thus far in this thread without issue using the stock RSA. No smilies. No FTF. No FTE. I am not suggesting that nobody else is having issues, but I do suspect user mods have unforeseen consequences and mags/mag springs are often overlooked (also recently mentioned).

So, in summary: user mods and mags/mag springs are likely culprits.


And as a 10mm newbie, I am curious about the accepted practice of replacing the stock RSA. Is there some body of evidence and analysis that indicates it is necessary, or just speculation?

[I may sound a bit like a jerk, but I am seriously trying to learn.]

Thanks for the feedback.

I'll give it a go and if it seems like a workable setup, then I'll step up the RSA.