Whoops! Posted September 3, 2019 Share Posted September 3, 2019 I see a lot of people thinking 9 major is cracking more slides than 38 super because of chamber pressure. Why? Chamber pressure is exerted mostly on the barrel (the chamber, ironically). Slower powders exert more total pressure even though the pressure peak is higher with faster powders. So, slower powders may wear out barrel and slide lugs faster and still not do what people are intending - preserve the slide. The main difference that I believe people are looking for is that slower powders tend to exert more pressure on the comp, potentially slowing down the timing of the slide and forcing it to move slower in open guns. 38 super exerts even more pressure on the comp, slowing down the slide further. What we should really be looking for as a culprit for slide cracking in 9 major is slide speed. So, what are some things we could do to counter act slide cracking/speed in 9 major? Not mill so much off the slide, obviously, but this is less practical since we still want optimal performace. Or even better: Use a larger comp (It doesn’t have to be heavier, just have more surface area - remember, 9 major exerts less pressure on the comp, so the gun unlocks sooner and the slide moves faster - as a result of the lower comp pressure, we could use less material thickness in order to keep the comp the same weight and trade off some long term comp durability for some long term slide durability, a fair trade for many people with cracked slides) If I were a gunsmith, I would offer a 9 major comp specifically with larger expansion chambers than 38 super. Link to comment Share on other sites More sharing options...
Joe4d Posted September 3, 2019 Share Posted September 3, 2019 less gas in 9mm. you wouldnt get any pressure in the larger comp. Lookk at 9 minor open guns, smaller comps than 9 open Link to comment Share on other sites More sharing options...
jim vaughan Posted September 3, 2019 Share Posted September 3, 2019 If you want your open handgun to last consider the following combination: Round profile slide with no metal removed between 10mm in front of the barrel locking lugs and 10mm behind the breachface. Remove metal from the swoop above the firing pin to obtain a slide weight of approx 310 grams. Use 157 round nose lead bullets sized to .357" in a full length case such as 9x23 or 38 supercomp. OAL 31.7mm in a 9x23. Slight amount of additional throating. Use a bullet such as the Lee 6 cavity RN bullet which has a bevel base. I use Hitek coating. Use a relatively slow powder such as 3N38. Do not use fast powders. Have a compensator with relatively large ports and quite long. I use 3 v ports with a large square port in the front. Do not use any Popple holes. Set up the handgun for a 7lb recoil spring, 17lb mainspring. Remove your steel grip and use a plastic grip. You might just be amazed by how good this combination is - light, accurate, reasonably fast, soft, low pressure, predictable dot lift, fantastic dot return, ejection distance quite close, etc Back to back tests show that this compares very well with open handguns shooting minor factor loads in terms of feel and recoil but is major factor. Jim Link to comment Share on other sites More sharing options...
gianmarko Posted September 3, 2019 Share Posted September 3, 2019 i have never seen cracked slides even in 300k+ rounds guns. is it really such common problem? Link to comment Share on other sites More sharing options...
Sarge Posted September 3, 2019 Share Posted September 3, 2019 Sometimes you just get bad slides. A few years back STI made some defective slides. Matt used one on my build and it cracked. STI replaced it. Link to comment Share on other sites More sharing options...
Hi-Power Jack Posted September 3, 2019 Share Posted September 3, 2019 I may be wrong,but I believe it was ZZT (here on BEF) that said a few months ago that cuts on slides to lighten the slide should be placed more carefully - where you can afford to lighten the slide. Not where most of us make the cuts - out on the end near the muzzle - ??? Link to comment Share on other sites More sharing options...
GetAwayDriva Posted September 3, 2019 Share Posted September 3, 2019 I’ve cracked two slides in less than a year. First crack was at the ejection port, second one on the replaced slide was at the extractor tunnel. Link to comment Share on other sites More sharing options...
zzt Posted September 3, 2019 Share Posted September 3, 2019 I did post a comment and picture stating if you remove no metal where it counts, your slide will not crack. I have three slides like the picture below. I don't keep track of how many rounds I actually shoot. However, the oldest has seen many, many years of service. The newest (below) has 6000+ rounds through it this season. I know becuase I buy fully processed brass in 6000 round lots and I'm well into the second lot. Here is the oldest. Link to comment Share on other sites More sharing options...
gianmarko Posted September 3, 2019 Share Posted September 3, 2019 i know slides will eventually crack, usually in the ejection port area, but i would think an open gun slide is not that stressed. the compensator removes most of the recoil impulse and thats why in open guns is common to run very low weight springs. perhaps sometimes too low? a friend was getting springs from Eric Grauffel at the EEO, he wanted a VERY low recoil spring, and Eric said "do you want to change spring, or to change gun?" Link to comment Share on other sites More sharing options...
ChuckS Posted September 3, 2019 Share Posted September 3, 2019 I discussed this with my gunsmith after my 9 open slide cracked at the factory ejection port. He pointed out that the highest energy event in the firing cycle is when the round first fires and the base of the case slams into the bolt face at thousands of pounds of pressure. The slide is locked so this rearward force just stretches the slide. The likely weak point is the ejection port. Recoil, springs and buffers come into play later in the cycle. Makes sense to me... YMMV Link to comment Share on other sites More sharing options...
MikeBurgess Posted September 3, 2019 Share Posted September 3, 2019 9 hours ago, Whoops! said: I see a lot of people thinking 9 major is cracking more slides than 38 super because of chamber pressure. Why? Chamber pressure is exerted mostly on the barrel (the chamber, ironically). Slower powders exert more total pressure even though the pressure peak is higher with faster powders. So, slower powders may wear out barrel and slide lugs faster and still not do what people are intending - preserve the slide. Unfortunately this is not correct. chamber pressure pushes in ALL directions, including front to back, as i in trying to push the barrel forward from the breach face, this force is held by the locking lugs between the slide and barrel, most slide cracks I see are in the ejection port area most often on the right hand side where there is less material to hold this front to back force. Link to comment Share on other sites More sharing options...
ChuckS Posted September 3, 2019 Share Posted September 3, 2019 2 minutes ago, MikeBurgess said: Unfortunately this is not correct. chamber pressure pushes in ALL directions, including front to back, as i in trying to push the barrel forward from the breach face, this force is held by the locking lugs between the slide and barrel, most slide cracks I see are in the ejection port area most often on the right hand side where there is less material to hold this front to back force. He didn't say that it was all the force, but the rearward vector was more energetic than when the slide finally stops its reward motion after dumping energy into the recoil spring. Link to comment Share on other sites More sharing options...
MikeBurgess Posted September 3, 2019 Share Posted September 3, 2019 11 minutes ago, ChuckS said: He didn't say that it was all the force, but the rearward vector was more energetic than when the slide finally stops its reward motion after dumping energy into the recoil spring. I agree I was referring to the OP saying chamber pressure affected mostly the barrel Link to comment Share on other sites More sharing options...
yigal Posted September 3, 2019 Share Posted September 3, 2019 24 minutes ago, ChuckS said: I discussed this with my gunsmith after my 9 open slide cracked at the factory ejection port. He pointed out that the highest energy event in the firing cycle is when the round first fires and the base of the case slams into the bolt face at thousands of pounds of pressure. The slide is locked so this rearward force just stretches the slide. The likely weak point is the ejection port. Recoil, springs and buffers come into play later in the cycle. Makes sense to me... YMMV u pull trigger to hard. Link to comment Share on other sites More sharing options...
theWacoKid Posted September 3, 2019 Share Posted September 3, 2019 5 hours ago, MikeBurgess said: Unfortunately this is not correct. chamber pressure pushes in ALL directions, including front to back, as i in trying to push the barrel forward from the breach face, this force is held by the locking lugs between the slide and barrel, most slide cracks I see are in the ejection port area most often on the right hand side where there is less material to hold this front to back force. The issue here is the barrel is not a static pressure vessel so while the pressure acts in all directions, it does not stress all components equally. The fore/aft force vector stressing the barrel in tension through the lock up is not equal to the pressure times the area, it is only equal to the resistance of the bullet going down the barrel (which is basically the same for 9mm vs 38 Super). The rest of the imbalance of pressure acting at the base of the case accelerates the slide/barrel/gun rearward. Link to comment Share on other sites More sharing options...
Whoops! Posted September 3, 2019 Author Share Posted September 3, 2019 (edited) 6 hours ago, MikeBurgess said: Unfortunately this is not correct. chamber pressure pushes in ALL directions, including front to back, as i in trying to push the barrel forward from the breach face, this force is held by the locking lugs between the slide and barrel, most slide cracks I see are in the ejection port area most often on the right hand side where there is less material to hold this front to back force. As stated - the majority of the chamber pressure is exerted on the barrel. Breech face wear occurs long before slide cracks in most open guns. The breech face wear is the evidence of the pressure applied against the slide when the round is initially fired. That initial force against the breech is not what is causing slides to crack in 9 major guns vs 38 super. If it were, manufacturers would put in lighter recoil springs to make slides last longer by allowing them to start moving and dissipating that initial force quicker. This one is pretty straightforward. The slide will move and dissipate that force as it is exerted and there is much less of the overall pressure exerted on the breech to begin with because of the surface area of high pressure brass exposed to the slide versus the barrel. Not only that, the slower powders will exert more force on the breech than the faster powders while the slide is locked up. It’s going to get very complicated if we look at fatigue points of the slide with a greater pressure for a shorter period of time than a lesser pressure for a longer period of time. But, I believe that once the calculations are done, you will see very little change in breech or slide fatigue from that initial force with fast versus slow powders operating at the same energy levels. The barrel will not move in the direction of the force vectors applied to it and it takes the majority of the pressure by encasing the ammo’s expansion chamber to begin with. The slide also has the benefit of the back of the case which will essentially act as a brass recoil buffer. So, when does the slide want to crack? When it impacts the rear of the frame. Edited September 3, 2019 by Whoops! Link to comment Share on other sites More sharing options...
MikeBurgess Posted September 3, 2019 Share Posted September 3, 2019 32 minutes ago, theWacoKid said: The issue here is the barrel is not a static pressure vessel so while the pressure acts in all directions, it does not stress all components equally. The fore/aft force vector stressing the barrel in tension through the lock up is not equal to the pressure times the area, it is only equal to the resistance of the bullet going down the barrel (which is basically the same for 9mm vs 38 Super). The rest of the imbalance of pressure acting at the base of the case accelerates the slide/barrel/gun rearward. False while the bullet resisting travel through acceleration, deformation and friction does cause the build up of pressure it does not change how that pressure acts. If a load has a peak pressure of 65 KSI it will try to push the breach face away from he barrel with about 7,800 lbs of force. Different loads with different case capacities and burn rates may create different peak pressures as well as different pressure curves that will have a impact on how much load is applied to the slide and how that load is applied both of witch can have an affect on how the slide will react to it. Link to comment Share on other sites More sharing options...
MikeBurgess Posted September 3, 2019 Share Posted September 3, 2019 I would be willing to bet if someone actually built a fixed test barrel and started doing Pezio pressure readings on 9mm Major loads a lot of people would be very very surprised at the readings. I would not be at all surprised to find that many 9mm Major loads are running north of 75,000 psi also for reference in this discussion a 40sw loaded to 40 KSI (5,00 over max) is only exerting 5500 pounds on the slide about 30% less than a likely best case 9mm major oddly they don't seem to break as often. Link to comment Share on other sites More sharing options...
zzt Posted September 3, 2019 Share Posted September 3, 2019 (edited) 15 minutes ago, MikeBurgess said: I would not be at all surprised to find that many 9mm Major loads are running north of 75,000 psi I would be astonished. I'd be very surprised if my 168PF major load was much over 40,000 psi. Edited September 3, 2019 by zzt Link to comment Share on other sites More sharing options...
Whitefish Posted September 3, 2019 Share Posted September 3, 2019 38 minutes ago, MikeBurgess said: I would not be at all surprised to find that many 9mm Major loads are running north of 75,000 psi I recall back in the good old days my 38 Supercomp loads with 125 grain JHP's (and available 9x23 commeercial ammo) were running in the mid to high 40,000 psi range. That was based on the available testing info from the commercial 9x23 ammo. That is why most of us ran small rifle primers with the harder cups to prevent cratering and flattening. I am able to run small pistol primers with my current 9 Major ammo with the same 125 gr bullets (different powder) and no popple holes. All of that is predicated on powder and bullet selection (and popple holes), but I would be surprised if my 9 Major ammo is much, if any, over 45,000 psi, a long way from 75,000 psi. 75,000 is well beyond most rifle rounds and would almost certainly destroy a pistol in short order. Link to comment Share on other sites More sharing options...
Aircooled6racer Posted September 3, 2019 Share Posted September 3, 2019 Hello: From the dozen or so slides that I have seen that have either cracked or broke a piece off where made from very granular steel. I think the problem is bad steel more than a 9mm problem. I am guessing here but I think alot of these slides are coming from the same source and then machined and called there own. Another factor maybe that more people are shooting open 9mm than ever before so there are more open pistols out there. Thanks, Eric Link to comment Share on other sites More sharing options...
theWacoKid Posted September 4, 2019 Share Posted September 4, 2019 5 hours ago, MikeBurgess said: False while the bullet resisting travel through acceleration, deformation and friction does cause the build up of pressure it does not change how that pressure acts. If a load has a peak pressure of 65 KSI it will try to push the breach face away from he barrel with about 7,800 lbs of force. Different loads with different case capacities and burn rates may create different peak pressures as well as different pressure curves that will have a impact on how much load is applied to the slide and how that load is applied both of witch can have an affect on how the slide will react to it. It actually does change how the load is applied to the slide. A FBD diagram will explain how the accelerating bullet reduces the tensile load in the slide/barrel assembly as compared to treating it as a static pressure vessel. The extreme thought experiment is how firing a 9mm in a 40 barrel works. Link to comment Share on other sites More sharing options...
caspian guy Posted September 4, 2019 Share Posted September 4, 2019 5 hours ago, Aircooled6racer said: Hello: From the dozen or so slides that I have seen that have either cracked or broke a piece off where made from very granular steel. I think the problem is bad steel more than a 9mm problem. I am guessing here but I think alot of these slides are coming from the same source and then machined and called there own. Another factor maybe that more people are shooting open 9mm than ever before so there are more open pistols out there. Thanks, Eric I think you are on to something Eric. Link to comment Share on other sites More sharing options...
CHA-LEE Posted September 4, 2019 Share Posted September 4, 2019 How about this.... There are a lot of cool looking Open gun slides with all kinds of crazy cuts and or design patterns. When you put the importance on fashion instead of function, structural integrity is usually circumvented. I have seen way more “cool looking” Open gun slides crack than plain Jane slides with sufficient meat in the right places. You want it to look cool or work reliably? Link to comment Share on other sites More sharing options...
gianmarko Posted September 4, 2019 Share Posted September 4, 2019 13 hours ago, Whoops! said: If it were, manufacturers would put in lighter recoil springs to make slides last longer by allowing them to start moving and dissipating that initial force quicker. for what i have seen so far, the slide starts moving long after the bullet has left the barrel so recoil spring imho is completely irrelevant re the breech/barrel forces that tend to separate the two when the firing occurs. i use Vectan SP2 and the cases are in better condition than the cases in my minor loads using N320 so id say the pressure of my major loads is not higher than most loads. but i have to say that i have seen badly maimed cases picked up at the range when other open shooters were training. perhaps not everybody uses slow powders in the correct quantities. and not everybody has properly calibrated scales, and chrono regularly.... as my shooting buddy realized when he almost blew up his gun shooting ammo that caused the gun to spit the mag and blow up the case. i suspect these events will shorten the life of components, in a way or another. i have seen production guns with a cracked slide, they had hundreds of thousands of rounds on them, i think it all boils down to the normal lifespan of a gun, and the occasional material defect causing premature failure. everything will break, eventually. Link to comment Share on other sites More sharing options...
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