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Gen 5 barrels slow?


deerslayer
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I am working on a Precision Delta 124 HP load for my Gen 5 17 MOS for CO.  Started at 4.0 grains of Titegroup at 1.120, which was slow and was not a big surprise.  Went to 4.1 and 4.2.  Need 1009 to make minor and I want 1050-1060 (130-131 pf).  4.2 averaged 1022 (126,728).  I had hoped the 4.2 charge would get me where I wanted to be.  Have any of you thought your gen 5 was slower than previous Glocks?  4.1 went 1060 in my gen 3 34.  Yes it has poly rifling and an additional 7/8" barrel, but others have said that 4.0 makes 130 pf or so all day out of a 17.  I've seen no pressure signs, so should I shut up and add powder or shut up and get a 34 MOS?  4.3 or 4.4 seems high.  

Edited by deerslayer
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I use 125gr Blue Bullets with 3.7 gr TG at 1.12 OAL. In my 34 this gets 133PF and the 17 is 128 PF. I don't think there is much difference in PF between the generations, but its possible to have a slow barrel. When I shot Tanfo my practice gun was almost 5 PF less than the match gun when they were both new. 

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16 hours ago, deerslayer said:

I am working on a Precision Delta 124 HP load for my Gen 5 17 MOS for CO.  Started at 4.0 grains of Titegroup at 1.120, which was slow and was not a big surprise.  Went to 4.1 and 4.2.  Need 1009 to make minor and I want 1050-1060 (130-131 pf).  4.2 averaged 1022 (126,728).  I had hoped the 4.2 charge would get me where I wanted to be.  Have any of you thought your gen 5 was slower than previous Glocks?  4.1 went 1060 in my gen 3 34.  Yes it has poly rifling and an additional 7/8" barrel, but others have said that 4.0 makes 130 pf or so all day out of a 17.  I've seen no pressure signs, so should I shut up and add powder or shut up and get a 34 MOS?  4.3 or 4.4 seems high.  

I think my gen 5’s were a little slower than previous gens. 

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4 minutes ago, dg370 said:

Confused. By definition the speed should be greater with polygonal rifling.
http:// https://en.m.wikipedia.org/wiki/Polygonal_rifling


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You’re correct and that’s what the OP is saying I believe, that the gen 3 34 has it but the gen 5 doesn’t, well it kind of does but it’s supposed to be more accurate
 

To the OP, the gen 5’s have different rifling so I could see it making a difference. 

obviously the barrel length in your 34 will make some difference as well. 
 

Are temps the same as when you chronod the 34? 
 

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We have 4 Glocks 34's in the stable.  Two are Gen 3 guns and the other two are Gen 5 guns.  I recorded a 25 FPS  decrease in velocity with the Gen 5 gun, almost exactly shooting the same as a Gen 3 gun with .1 grains less propellant.  The Gen 5 gun was new at the time and the Gen 3 gun had many thousand of rounds down the barrel.  I have not checked it in a year or two.  I just went up a .1 grains and shot the gun.

 

I have said it a lot in other threads but I will add it hear as well.  I can tell the Gen 5 guns are more accurate.  

Edited by 12glocks
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  • 3 months later...

Gen 5s that I have tested are a bit slower. I believe the difference is in fact the rifling. The polygonal rifling used before was meant as a way to increase barrel life but it doesn't bite into the jacket as hard. The rifling in the new barrels are. The flip side is there is a slight increase in the the new design barrels though not appreciable for most. I tested this at 25 yards off of a rest. I took gen 4 and gen 5 17s, same load, triggers, sights and found that the groups averaged 0.15" - 0.25" ( ten round groups) better in the gen 5 barrels. I've seen the same results for a 34 as well. Both 147 grain loads I shot in the 17s performed noticeably better in the gen 5 barrels than they did in the gen 4 barrels, being 0.25" improvement, ten shot groups, extreme spread.

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