Technical question on slides, for a change

[JCN]

Not as much of a full explosion but sees enough pressure to be moved backwards and cycled in 0.05 sec. The ejection port side has, naturally, ejection port that will bleed off some pressure. I presuming (but not stating as a fact) that breech face and wall opposite the ejection port will see the most pressure load. We have certainly seen breech faces cracked.

So the question remains: why SIG makes their wall 0.17 thick while HK makes theirs 0.24, while taking an effort and cost to thin out that wall towards muzzle (P365 does that too but to a much lesser extent)?

So bizarre.

Slide walls aren’t to contain blasts.

That’s what barrel chambers are for.

The only pressure slam the slide sees is BREECH FACE backwards.

So if you were asking about breech face thickness, sure.

Or barrel chamber thickness, sure.

But slide walls?

Riddle me this.

If it took any side loading, don’t you think you’d see a lot of slide side abrasion?





So you’re asking about this area?



Your question would be valid if your barrel was made out of rubber, lol.

The pressure is contained in the barrel chamber.



The slide walls don’t see it.

Breech face does get hammered but not exploded.

Case base contains that.

If the slide walls saw pressure through the walls of the barrel chamber, you’d see marks on the slide walls from friction in a shot up gun.



I still feel like maybe I’m misunderstanding what you’re asking because it’s like asking why Dodge used a certain hood sheet metal thickness when the explosions are in the engine.

As another data point…

Have you ever shot a Glock with a thumb over the back plate to prevent the slide from cycling?

It actually doesn’t take much force to do so.

Even the breech face isn’t getting super slammed because the case is pressed against it at ignition by the recoil spring and locking lugs of the barrel.

Breech face is also reinforced laterally in the unsupported area (yellow).



The red area doesn’t see pressure.

That’s my best understanding of how a semiauto works, anyway.

I could be wrong.

If you took a revolver and extended the question, the cylinder chamber would be like the barrel chamber and there is no slide thickness at all! Just the frame below and above. To the rear where the case is, pressure on breech face but if you held the rear of cylinder when firing (if you avoided cylinder gap to barrel in the front), your fingers would be fine. No pressure.

[Oldherkpilot]

No. I have only two non-9s, both described as mature designs in a neighboring thread. Didn't think they would help in understanding how modern designs are made.

I thought the consensus was "vintage?"😁

[JohnO]

I'm going to go out on a limb and suggest that slide thickness in the area of the breach is strictly structural. We are talking about an area analogous to the non-existent roof on a convertible and the design considerations implemented to maintain structural integrity throughout the useful life of the product.

[JCN]

I'm going to go out on a limb and suggest that slide thickness in the area of the breach is strictly structural. We are talking about an area analogous to the non-existent roof on a convertible and the design considerations implemented to maintain structural integrity throughout the useful life of the product.

Well said!

[YVK]

I still feel like maybe I’m misunderstanding what you’re asking

I thought I clarified that. I found that slides on my full sized guns are considerably thicker than on my slim gun. I measured that specific area simply because it was easier to do for a right handed person. If it isn't related to any pressure, as you explained well, then to what? The suggestions so far have been "related to cycling" or "structural integrity", sounds fair. If the latter is the case, that would be particularly interesting to me because P365 is one of my carry guns. It'd be nice to know that its structural integrity not compromised by making its slide appreciably thinner.

[DMCutter]

This is what I think from an engineering standpoint. Bear in mind I'm a civil engineer, not a mechanical, so what I deal with is generally static loading. The barrel chamber contains the outward force of the blast, so the walls are under hoop stress, which doesn't make it to the walls of the slide. The bottom of the cartridge is sitting against the breech face and subjects the face to some compressive loading during ignition and as the slide begins to move to the rear. Since there shouldn't be significant space between the bottom of the casing and the breech face, the shouldn't be significant impact loading-a push vs a punch. I surmise there's a minimum thickness requirement for durability under thousands of cycles but it's probably pretty thin, and I think it would vary with the specific composition of the steel used for the slide. The elastic modulus of brass is about half that of steel so you would see more deformation of the base of the casing than the breech face, and if there was significant compression of the bottom of the casing you wouldn't be able to reload them numerous times before they mashed down and widened out enough to have to be trimmed.

[GearFondler]

I've heard of at least one RDS milling shop that had to change its design because the pockets and windows they were milling into the slides were starting to crack in places but that was a result of the battering the slide takes as it cycles. And no, I can't remember exactly who it was but they did readily admit it.

[hiro]

@PensFan

ETA, hmm, mention isn't working. Perhaps the #shitmods can ask his opinion?

[YVK]

I surmise there's a minimum thickness requirement for durability under thousands of cycles but it's probably pretty thin, and I think it would vary with the specific composition of the steel used for the slide.

Thnx.

I've zero understanding of anything engineering, and my only other thought was whether the situation is somewhat comparable to what's described in Laplace law. I.e. larger in internal diameter slide of a full sized gun has higher wall tension and therefore requires to be thicker to withstand that. Needless to say, I don't really know what I'm talking about, just being curious.

[DMCutter]

Larger bore gives proportionally greater surface are (see "Associative Pet Peeve" in general discussion) but larger bore doesn't necessarily mean higher chamber pressure-SAAMI spec for .45 ACP is 21k psi vs 35k psi for 9mm or .40, so walls would need to be thicker in any 9mm vs a full size 1911.