Sig Expansion Chamber - Gimmick or Feature

[Sensei]

So, my only experience with this slide modification is on the P365 X-Macro and I do not shoot the P320 or P365 platforms all that well. However, I was all over the place with that gun. After swapping the slide and barrel to a P365 XL, the groups tightened up a bit. I can’t say that there was a noticeable change in recoil or muzzle flip with the expansion chamber.

This modification is being brought over to other product lines such as P320 and P226 X-Five. Now, it may be that the expansion chamber’s performance is variable depending on a variety of factors ranging from barrel length to bullet velocity/pressure. That is to say, it’s very possible the expansion chambers performance is best in longer barreled guns.

Still, from a competitive perspective, I’m not seeing this as an advantage since the expansion chamber is considered to be a comp that moves the gun into open division. That begs the question is the expansion chamber beneficial for defensive use?

[AMC]

My experience with these, or any comps on 9mms, is somewhat limited. I have friends who extoll the virtues of the 'expansion chamber' like its a +5 magic sword in D&D. My personal experience was that I noticed no change in performance of the gun at all.....though I also wasn't shooting for groups at 25 yards, so wouldn't have noticed the accuracy issues others have remarked on.

On the other hand, I wasn't particularly impressed with 1 or 2 port PMM comps on 320s either. They sure did make the gun louder, and may have slightly....very slightly....reduced dot bounce. I did not find the experience convincing. Others mileage may vary.

[Artemas2]

drop a pound or 2 in recoil spring weight and get the same effect...

Comps and by extension "expansion ports" need gas to work, unless you are running +P or greater loads, the benefit is rarely worth the cost or complexity.

[1911Nut]

In my experience with the 320 (I have P320 Spectre Comp Blackout) I see no added value from the expansion chamber. I don't think I could tell the difference between a "comped" and an "noncomped" model, assuming ammo was the same.

I like my Spectre Comp for other reasons, but all the "comp" adds to the shooting experience is that it makes the pistol more difficult to clean.

[Sensei]

I ask because I’m very much on the fence with the P226 X-Five Legion. My two hang-ups being:
1) I’d prefer a stainless steel frame.
2) I’m not at all sold on the expansion chamber.

Personally, I wish the first “tactical” iteration of the American P226 X-Five just had a subdued finish (Nitron or Legion) and X-ray sights. Everything else would be similar to the X-Five STAS.

[HCM]

So, my only experience with this slide modification is on the P365 X-Macro and I do not shoot the P320 or P365 platforms all that well. However, I was all over the place with that gun. After swapping the slide and barrel to a P365 XL, the groups tightened up a bit. I can’t say that there was a noticeable change in recoil or muzzle flip with the expansion chamber.

This modification is being brought over to other product lines such as P320 and P226 X-Five. Now, it may be that the expansion chamber’s performance is variable depending on a variety of factors ranging from barrel length to bullet velocity/pressure. That is to say, it’s very possible the expansion chambers performance is best in longer barreled guns.

Still, from a competitive perspective, I’m not seeing this as an advantage since the expansion chamber is considered to be a comp that moves the gun into open division. That begs the question is the expansion chamber beneficial for defensive use?

In theory it’s beneficial for defensive use. Though it’s not as effective as a traditional comp.

In practice, like yourself and @GJM , I saw and experienced multiple SIG pistols (XL, Macro and 320) with the expansion chamber comps which exhibited noticeable and consistent accuracy problems.

The system has bugs SIG doesn’t seem interested in acknowledging or addressing.

I won’t buy / use any SIG with the expansion chamber comps.

[Sensei]

In theory it’s beneficial for defensive use. Though it’s not as effective as a traditional comp.

In practice, like yourself and @GJM , I saw and experienced multiple SIG pistols (XL, Macro and 320) with the expansion chamber comps which exhibited noticeable and consistent accuracy problems.

The system has bugs SIG doesn’t seem interested in acknowledging or addressing.

I won’t buy / use any SIG with the expansion chamber comps.

I’d love to see a side-by-side comparison of a few models with an expansion chamber vs the same gun with full length slide and barrel. In addition, the X-Five models come with a test target. I’d be sure to inspect it on any P226 X-Five Legion that I was considering.

[Clusterfrack]

I’d love to see a side-by-side comparison of a few models with an expansion chamber vs the same gun with full length slide and barrel. In addition, the X-Five models come with a test target. I’d be sure to inspect it on any P226 X-Five Legion that I was considering.

I have zero interest in guns that require tuned loads and spring to work right. I tried a comp on a P-07 and it reduced flip a bit. Not worth it to me.

[Sensei]

In my experience with the 320 (I have P320 Spectre Comp Blackout) I see no added value from the expansion chamber. I don't think I could tell the difference between a "comped" and an "noncomped" model, assuming ammo was the same.

I like my Spectre Comp for other reasons, but all the "comp" adds to the shooting experience is that it makes the pistol more difficult to clean.

I’m not sure your gun is an apples to apples comparison since yours has a true compensator attached to a threaded barrel rather than simply an expansion of the slide. I will grant you that I’d expect a compensator to reduce felt recoil more than an expansion chamber, but it’s the chamber’s effect on accuracy that gives me the most pause.

In theory it’s beneficial for defensive use. Though it’s not as effective as a traditional comp.

In practice, like yourself and @GJM , I saw and experienced multiple SIG pistols (XL, Macro and 320) with the expansion chamber comps which exhibited noticeable and consistent accuracy problems.

The system has bugs SIG doesn’t seem interested in acknowledging or addressing.

I won’t buy / use any SIG with the expansion chamber comps.

My only thought is that barrel length may be coming into play in a big way. The P365 X MACRO shares the same barrel as the standard P365 at 3.1”. Truth be told, all of my other 9mm sub-compacts have at least 1/3” more length. Part of me is wondering if 3.1” sits at the ragged edge of length needed to stabilize most 9mm pills. If so, an expansion chamber coupled with extremely short barrel length may be the problem. On the other hand, accuracy issues in models with longer barrel lengths would suggest an inherent accuracy problem with the platform as you suggest.

I have zero interest in guns that require tuned loads and spring to work right. I tried a comp on a P-07 and it reduced flip a bit. Not worth it to me.

Good question. I’m unsure of how an expansion chamber affects reliability.

[bofe954]

If I really wanted that pistol I'd just find out of anyone made a long enough barrel, so that I could eliminate the chamber.