Hot barrel inaccuracy...

[molonlabetn]

It is fairly common knowledge that most firearms experience a reduction in accuracy when the barrel is excessively hot. But something that I was thinking about after the last trip to the range, with a friend who was shooting his recently acquired (used) pistol for the first time. None of the pistols which I have owned ever exhibited any significant loss of accuracy when fired extensively in a short period of time. I don't ever intentionally get my own handguns super hot, simply because I like to take my time shooting, instead of just blasting away. However, this past weekend while shooting an S&W SW40VE Sigma, I noticed that between each 100rd which was put through the gun, my own groups would open up noticeably. I had been somewhat impressed with it, at first, since it would hold a nice 2" group at 15yd offhand during the first 2 magazines which I fired through it (14 rounders loaded with 10 each). Then my friend (the owner of the pistol) proceeded to blast away with the rest of the first box (100rd WWB .40s&w)... When I got to shoot the gun again, immediately after that, I couldn't get it to hold any better than slightly less than a 3" group out of 4, 5-shot strings. The Sigma has a horrible trigger, it felt like 15lb, but thought it was still acceptable and had no trouble working around it using a consistent squeeze; the heavy trigger was not the cause of the inaccuracy... Again, my friend proceeded to blast away with his gun while I shot my P239 in another lane... When he was done, and handed it back to me (blazing hot), I tried again with just the 10 remaining rounds; both groups which I tried to print were just barely in the 10-ring. So, through just 200rd (in a short amount of time, due to my friend's desire to fire rapidly), the gun lost considerable accuracy (went from 2" at 15yd, to roughly 6")... a phenomenon which I have never witnessed in a pistol to this extent simply because of getting the barrel extremely hot.

Has anyone here noted any particular models of pistols or barrels to be more prone to this? I know that my Sigs, XDs, Berettas, and 1911 have never done this (but, like I said, I don't just blast away for the heck of it, causing them to get insanely hot). Are the barrels of S&W pistols made of a softer steel? Or could it perhaps be a wide tolerance between the slide/barrel lockup which is accentuated by heat? Sigmas aren't known for high quality, but the inconsistency I saw makes me wonder if there's a particular reason for it to be especially susceptible to heat. It is certainly something which I would like to avoid, when considering other makes/models of pistols to buy... I didn't before, and certainly wouldn't now, ever consider purchasing a S&W Sigma.

After this revelation, and given some time for the pistol to cool, I took my friend aside with a new box of ammo and coached him on how to handle and shoot his pistol for accuracy (as opposed to the noise-making he was so fond of), since his groups had been all over the silhouette. But I didn't get to shoot the pistol again after it had cooled down...

BTW, the gun jammed 1 time out of 250rd that day, while I was shooting my last 5rd string. It was a FTE, the spent casing remained completely in the chamber, and the slide attempted to double-feed another round. The extractor did not deform the case-rim. The case came out easily when I cleared it (tap, rack, "crap", strip-mag, rack, rack, rack, inspect, insert mag, rack, bang...).

Thoughts?

[Marswolf]

Sight radius on a pistol is so short that the problem of barrel heating probably isn't significant compared to other factors like shooter fatigue. You'd probably have to use a Ransom Rest or equivalent to really tell.

You're more likely to see the problem on accuracy rifles like Remington 700s or target rifles although I've never noticed a problem with my .308 WIN 700VS. Probably because of the heavy barrel and the special hand loads I use.

[shaftbass]

Those Sigma's are cheap, bottom of the line semi-auto guns. I'd rank them right up there with Llama.

I've ran 100 rounds straight through my Beretta 92FS I used to own, Glock 36, and my Springfield XD-45 and haven't seen any loss of accuracy beacuse of it.

[Guest Fuel]

The Sigma has a horrible trigger, it felt like 15lb,

I have a S&W SW40C. The trigger pull on these pistols is unbelieveable. I ran across a mod a while back that involved removing a spring (as I recall) that would significantly lighten the trigger pull. I never tried it as monkeying with the trigger assembly gives me the heebie jeebies.

Those Sigma's are cheap, bottom of the line semi-auto guns. I'd rank them right up there with Llama.

I'm afraid you're right. I wish I hadn't bought it now. I got it years ago before I realized what I was purchasing. I need to sell it and upgrade.

[molonlabetn]

Sight radius on a pistol is so short that the problem of barrel heating probably isn't significant compared to other factors like shooter fatigue. You'd probably have to use a Ransom Rest or equivalent to really tell.

You're more likely to see the problem on accuracy rifles like Remington 700s or target rifles although I've never noticed a problem with my .308 WIN 700VS. Probably because of the heavy barrel and the special hand loads I use.

I would have chalked it up to my shooting hand becoming fatigued, but my groups with my P239 were completely consistent during that same session. Besides that, I know that I tend to push a bit left when my trigger finger gets noticeably fatigued, but all groups stayed centered... I didn't fire the Sigma nearly enough for the heavy trigger to affect me like that.

That's why I'm surprised, I don't know what to attribute this to... But, something was obviously loosening up as the gun got hot, or the barrel was expanding un-evenly. The rifling was not fouled, I checked that later when I was showing him how to disassemble it... besides, we were firing FMJ.

[shaftbass]

I'm afraid you're right. I wish I hadn't bought it now. I got it years ago before I realized what I was purchasing. I need to sell it and upgrade.

http://www.springfield-armory.com/

You know what you must do

[Marswolf]

But, something was obviously loosening up as the gun got hot, or the barrel was expanding un-evenly.

Well that is a mystery. Can you see the group expansion is evenly distributed around the X or is it primarily top to bottom or right to left? Top to bottom might be an indication that the barrel isn't seating in exactly the same way after it heats up. Might just need a little more barrel fitting.

[molonlabetn]

Well that is a mystery. Can you see the group expansion is evenly distributed around the X or is it primarily top to bottom or right to left? Top to bottom might be an indication that the barrel isn't seating in exactly the same way after it heats up. Might just need a little more barrel fitting.

Now I wish I'd thought to take pictures of the targets, my groups were all well centered. The POI was low, compared to the POA, but I am pretty sure that it was a minor sight elevation issue since it stayed consistent. The shots were evenly distributed, and progressed from an approx 2" tall x 1 1/2" wide 10-shot group (after the first magazine), to a couple of 2" - 2 1/2" tall x 3" wide 5-shot groups, and then finally was barely holding a 6" circle during the last 10 rd after the gun was very, very hot. I fired each shot very slowly and methodically, every few seconds, concentrating on smooth and even trigger-pressure, and sight alignment. Normally when I do this, my groups get better with a gun I have never fired before, as I get used to it. I've fired pistols with heavy triggers before, such as a G17 with a NY2 trigger, etc... There was certainly something going on with the Sigma as it got hotter. I could visibly see the bullets striking the target well off of the point-of-aim.

I wouldn't think that a Sigma would be worth the effort of putting any work into the barrel lockup, especially considering that the owner of the gun was also really turned off by the trigger, and wanted to get rid of it for something else after we were through shooting it. He liked the grip angle, which was reminiscent of a Glock, though shaped more ergonomically... Next time he comes with me I am going to suggest renting a Glock and a S&W M&P for him, he already took a liking to my Sig, but only for its trigger-pull.

It was weird... No big deal though, my only concern is if this is common for Sigmas, or any particular barrel material/type/brand, so that I can avoid it!