Chamber questions

[bigboremaico]

I'm asking this question here because to me, it's relevent to reloading as much as anything else.

Can any one give me a defintion of "unsupported Chamber" or barrel.

I have seen a drawing of a supported and unsupported barrel in a book I have. So I THOUGHT I knew what it was. I pose this becasue I have a Glock .40 and there is much squealing about the unsupported chamber. Upon looking at a 9mm and .45 Glock, and a PT 945 Taurus, they all have exactly the same barrel configuration. So what gives? Why the Glock .40's taking all the heat?

Thanks in advance.

bbm

[Brass Nazi]

The 45 operates at a lower pressure and does not pose as much of a problem. The 9mm operates at a high pressure as does the .40. Most people feel that the 40 is less supported than the 9 for most glock examples. I do not personally know if this is true.

One problem with the 40 is that if the bullet experiences "setback" the increase in pressure is usually higher than if the same amount of setback happened with another cartridge. This is due to the 40's low internal case volume and thick web.

If the ammunition is assembled properly and also meets mechanical and pressure specifications you should never have a problem.

[BigSlick]

It's all in the dimensions.

What many consider to be a Glock problem in reality isn't just a Glock issue. Many guns have poor support in the 6 o'clock position in the chamber.

Glocks were made notorious/famous by gun rag writers.

If you look at a piece of brass, you will notice the web, near the case head, is thicker than the case mouth.

Semi auto handgun chambers are ramp fed. The barrel ramp has to be cut into the chamber mouth to allow the loaded round to feed properly.

Some manufacturers cut more off the chamber mouth than others in forming this ramp. Early Glocks were fitted with barrels with a liberal ramp cut in the chamber mouth to assure correct feeding under almost all circumstances. Other manufacturers have less or as much (some maybe more) of a ramp cut than even the early (Gen 1 and Gen 2) Glocks.

This area removed in forming the ramp is the same area providing support for the web of a chambered piece of brass. With good brass, and medium or low powered loads this isn't (usually) a problem. This certainly can be a problem with hot loads, many times loaded or defective brass.

The portion of the brass that rides right over the ramp cut in the chamber mouth, of course is 'unsupported' by design. High pressure generated by a load being fired will sometimes (many ?) cause the brass to 'flow' to fire form to the dimensions of the ramp cut in the chamber mouth. This can (and has) caused brass to stretch to the point of failure, affectionately known as a kB!

Glock 9x19 and 45 ACP don't seem to suffer the same history or reputation as early Gen Glocks in .40 cal. The 45 ACP is a MUCH lower pressure round, and 9x19 brass is (usually) designed with the thick part of the web much higher up the brass than .40.

3rd Gen Glocks have MUCH improved ramp support, and to my knowledge there have been no reported kB!'s with a 3rd Gen gun with known good brass and any sane load.

What needs to be mentioned here is Glock is by no means the only mfr to experience the same issue. Beretta, Colt, Smith and others all have similar dimensions in some of their offerings.

I have a 1911 in 10mm that had a barrel (from the factory) that had worse ramp support than the first Glock that rolled off the line. I replaced the barrel and it's great now.

A lot of us run aftermarket barrels in Glocks to get around the poly rifling vs lead issue, and/or gain additional chamber support. I use an aftermarket for brass support, as the chamber dimensions are tight and fired brass lasts a good long time. I can take a fired brass out of the Storm Lake barrel and it will pass a case gauge.

3rd Gen Glock factory barrel dimensions are somewhere between an aftermarket barrel and older Gen factory barrels. You can still see some case expansion on a fired brass, but not near as much as older gen guns.

Loads using fast powders and heavy bullets are most known for causing kB's as the pressure builds all at once rather than more slowly as with load recipes using a slower burn rate powder.

That's one reason a lot of folks (including me) stay away from fast powders and heavy bullet combinations. Yes, you can load heavy bullets with fast powders, but the margin for error is small, and there are other load recipes that will get a bullet downrange with less potential for error.

There are ramped barrels out there. These have ramps built into the barrel, with little or no ramp in the frame of the pistol. These generally provide outstanding brass support, but, may require your pistol frame to be cut to allow for the ramped portion of the barrel to fit your gun. These are predominantly found in 1911's and variants and not available for Glocks (that I know of).

[Ledhore]

I just bought a new Lone Wolf barrel for my Glock 35 and was shocked to see that the stock Glock barrel had more chamber support at the feed ramp than the Lone Wolf barrel. The Lone Wolf chamber is tighter overall, but the feed ramp was cut deeper into the chamber. Kind of bummed me out.

[BigSlick]

Wow, I would never have expected that either.

I know Storm Lake barrels are still tight as a banker

[CZ93X62]

What Slick said, in both posts. Well-presented, sir.

There is a definite difference in resizing feel between 40 S&W brass fired in my OEM Glock 23 (G3) chamber and its Storm Lake barrel. The OEM-fired brass isn't obviously distended, but does mic a bit larger and takes a bit more OOMPH to run through the T/C sizer. For this reason, 95% of the G-23's range time gets done with the aftermarket barrel. I change out my carry ammo every 3-4 months, and that gets fired through the OEM tube--with whatever jacketed handloads might be easy to grab in the ammo cabinet. That way, the OEM/street carry configuration gets a periodic test drive.

My authorized rounds are good ones--WW 180 SXT Ranger, and the jacketed reloads duplicate its ballistics with Hornady XTPs of the same weight. Most of the time though, it's Lee 175 TC castings through the SL tube. These are also loaded to dupe the carry load, with Herco getting the nod for the reasons given by Slick earlier.