New Storm Lake barrel test

[denclaste]

Just for fun I decided to compare the expansion ring on brass fired from the G 20 factory barrel and the Storm Lake replacement barrel I just received. Loaded up 60 rounds of new Win brass with 200gr XTP's and 7.8gr of Longshot. Fired 30 rounds thru each barrel and measured the expansion ring on each and got these averages:
Glock barrel: 0.433"
Storm Lake : 0.426"
The smiles were quite obvious on the Glock barrel brass. Had to look under 5x magnification to find the ones on the brass fired in the Storm Lake barrel. If you dont reload for your 10mm this isnt an issue. If you do reload now you have something to compare your brass against.
(Both barrels functioned perfectly: no difference there)
Dennis

[sqlbullet]

Good data.  Mirrors what I and many others have found when comparing brass fired from a Glock to brass from many other guns.  My Witness barrels tend to produce brass about .001"-.002" smaller at the head than brass with the same load fired from the Glock.  My Para conversion is about .003-.005" smaller.

[REDLINE]

Great information Dennis.  Thanks for sharing it.  It is always nice for others to post their insight for comparison to what others have suggested over time, and your data backs up the rest nicely.

Now what I can't understand is the extent to which I've seen chronograph data vary in similar conditions.  Sure, barrels can be a little different, and sometimes the differences make sense, but other times the data leaves me scratching my head.

What is the barrel length on your Storm Lake barrel?  I just got the Storm Lake 6.02" version for my G20 just a couple weeks ago or so.

[sqlbullet]

Since the relationship between pressure and velocity is geometric, small variations in the barrel can result in unexpectedly large changes in velocity.

[EdMc]

Since the relationship between pressure and velocity is geometric, small variations in the barrel can result in unexpectedly large changes in velocity.

Exactly, I've measured my Glock chamber with some pin gages......it tapers from 0.436 down to 0.425. The Lone Wolf 6.6 in threaded chamber tapers from 0.428 down to 0.424. As I think you found with the G29, my G20SF barrel slugged at 0.401. More volume to a Glock chamber with a larger bore.
Does make it feed most anything...

[sqlbullet]

Yes it does.

Those seemingly small variations can have a rather large impact on the peak pressure, and therefore the velocity.  That change in chamber size represents a 2% difference in volume of the chamber.  That would mean a 1,000 psi reduction in pressure for the exact same load.  A minimum spec rifled barrel at .399 compared to what my and your glock is at .401 is another 1% reduction.

It definitely adds up.

[Yondering]

Plus there's the throat dimensions, which dictate the amount of jump the bullet makes to engage the rifling. If this is tight, pressures go up.