Author Topic: 7" KKM barrel, would you?  (Read 2444 times)

Ridgerunner665

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7" KKM barrel, would you?
« on: April 28, 2017, 05:46:47 AM »
I'm fighting the urge to buy one for my Glock 40 MOS.

The ONLY reason I'm interested is a little extra power/speed.... I have no interest in longer case life because I don't reuse the brass (not worth the risk as all my loads are pretty warm).

I have a good safe load that propels a 200 grain XTP at an average of 1,216 fps when the factory barrel, accurate too. It uses 12.6 grains of #9...

I was wondering if anybody know the velocity gains per inch of barrel with Accurate #9 powder?

I know what the "Ballistics By the Inch" website says... But I really don't think that info comes from a large enough sample to mean much, and those factory loads all use faster burning powders.

So, would you get the 7" barrel and how much velocity would you expect it to gain over factory?

AT SAFE LOAD LEVELS.... That is, loads that are within 1/2 grain of respectable load data (I prefer powder manufacturer data)...I will not go much over book data, been there, done that.... All I got from it was a flinch, wondering when the gun was gonna let go.

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sqlbullet

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Re: 7" KKM barrel, would you?
« Reply #1 on: April 28, 2017, 07:03:22 AM »
Rule of thumb is 25 fps per inch.  That seems pretty well confirmed in the limited data on the BBTI site.  And, while I agree that data is limited, it might be the best option you get.

If you had a Glock 20 and were looking to add a 6" or 7" barrel, I think the gains would probably be worth it.  But since you already have a G40/6" barrel, I don't think you will gain enough to really matter.

Lets assume you picked up a full 50 fps from the extra 1".  This is a very best case scenario.  Buys you and extra 55 lb-ft at the barrel, 0.7" less drop at 100 yards, 3.2" at 200 yards and 7.2" at 300 yards.

A more realistic 25 fps only gets about half the gain.

The_Shadow

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Re: 7" KKM barrel, would you?
« Reply #2 on: April 28, 2017, 07:19:03 AM »
Ridgerunner665, various barrels will gain some velocity to a point.  Many factors go into this equation first is actual chamber to cartridge fit, bore to bullet fit, to seal in the gasses as they drive the bullet down the opening.  Then there is the frictional surfaces of a given bore vs. the gilding metal used in the projectile.  Temperatures will also play into all aspects with small changes in physical sizes.

With all that being said, a KKM 7" barrel for one inch over the stock 6" you will likely see any wheres from 75 to 150 fps.
My best reasonable questament would be your 12.6 grain AA#9 load will be 1335 fps for the 7" KKM.

I will also say the pressure curve will also change due to the better chamber support and quicker chamber seal for the expanding gases to work to push the bullet more efficiently.

There could be more or less velocity gains and or losses using other powders.
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The_Shadow

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Re: 7" KKM barrel, would you?
« Reply #3 on: April 28, 2017, 07:44:30 AM »
Here is a test I did between different pistols and barrel lengths;

Smith &Wesson 1006 5” Barrel
Hornady 200 Grain XTP  10.5 grains Blue Dot (Max Load) 1181 fps Average

Smith &Wesson 1076 4.25” Barrel
Hornady 200 Grain XTP  10.5 grains Blue Dot (Max Load) 1109 fps Average

Glock 29 3.78” Barrel factory BBL
Hornady 200 Grain XTP  10.5 grains Blue Dot (Max Load) 1090 fps Average
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sqlbullet

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Re: 7" KKM barrel, would you?
« Reply #4 on: April 28, 2017, 12:28:26 PM »

I will also say the pressure curve will also change due to the better chamber support and quicker chamber seal for the expanding gases to work to push the bullet more efficiently.


Was coming back to comment on this so I will add onto Shadow's spot on point.

Glock factory barrels are typically about .401-.402" "groove" diameter.  Groove in quotes as a poly barrel doesn't have traditional lands and grooves.

The KMM barrel will likely slug out to about .399"-.400".  That tighter bore will allow a good bit less gas blow by, resulting not only in higher peak pressure, but a higher overall pressure curve.  More pressure = more velocity.  You might see a 50-100 fps gain over the Glock factory barrel with a 6" aftermarket barrel just because of the tighter bore.  Add to that another 1" of travel, and 150 fps gain isn't out of the question.

This would be significant.  2" less drop at 100 yards and 90 lb-ft more energy.  9" at 200 and 20" at 300 yards.  For longer ranges the flatter trajectories will extend your point blank range.  A 200 grain WFN at 1350 fps has a 10" point blank range of about 165 yards with a 125 yard zero.  That is 30 more yards of point blank range compared to a 1200 fps muzzle velocity.

Ridgerunner665

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Re: 7" KKM barrel, would you?
« Reply #5 on: April 28, 2017, 01:19:17 PM »
I ordered the barrel.

I called KKM with a few questions, still on the fence about the barrel... The customer service experience tipped me over the edge.

I got it with the black nitride finish so it'll be about 6 weeks or so.

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sqlbullet

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Re: 7" KKM barrel, would you?
« Reply #6 on: April 28, 2017, 02:05:48 PM »
Be sure to let us know what the velocity increase is.

Ridgerunner665

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Re: 7" KKM barrel, would you?
« Reply #7 on: April 28, 2017, 02:34:11 PM »
Will do.

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Ridgerunner665

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Re: 7" KKM barrel, would you?
« Reply #8 on: April 29, 2017, 08:43:00 AM »
My reasons:
The longer barrel will slightly delay the unlocking, it needed that with the full toot loads.

In a hunting pistol, every bit of power your can get is good.

I can now shoot pretty much any lead bullet I want, probably never will, but I can if I want.

I actually think the extended barrel will look cool, I know thats of no real use for anything that matters... KKM will make a barrel to any length you want (no extra charge), I considered 7.5" because that is a popular length for revolvers but I think the 1" extension is enough without protruding too far out of the holster.

Possibly more accurate, but I sorta doubt it.

And I've always had a need for speed.


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« Last Edit: April 29, 2017, 09:41:10 AM by Ridgerunner665 »

Ridgerunner665

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Re: 7" KKM barrel, would you?
« Reply #9 on: May 05, 2017, 03:07:06 PM »
I just confirmed that my G40 is unlocking a little early with warm loads.

Measuring the chamber and the smiled brass leaves no doubt that the slide moved ~.050" before the brass swelled on those warm loads.

This begins at about 7.8 grains of Longshot and 12.8 grains of AA #9 under a 200 XTP ... In my pistol, yours may be different.

I was pretty sure of it before I did the measuring, now I'd bet a weeks pay on it...

The 7" barrel I have on the way should slow the unlocking down a bit. The length of it will add some barrel time and the extra weight of the longer barrel will hold things in place a little longer as well.

Then there's the ounce that I've added to the slide weight too (Deltapoint Pro).... I'm still using the stock spring, with the added length and weight, I believe the stock spring will be fine.

Ridgerunner665

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Re: 7" KKM barrel, would you?
« Reply #10 on: May 11, 2017, 05:49:12 PM »
Got the optic mounted today...just waiting on the barrel now.


Ridgerunner665

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Re: 7" KKM barrel, would you?
« Reply #11 on: May 15, 2017, 08:09:32 PM »
I gave in and ordered a new chrono just now...I've had I think 3 ProChrono Digitals in a row now, maybe 4, if you use them, you will eventually shoot them, especially getting long range readings...that is firing through the chrono from 600-1,000 yards.

This last one has been hit 4 times but it has managed to keep working after some reconstructive surgery...at least until a couple of weeks ago when it started misbehaving. It was time to put it out of its misery.

I decided to try something different, but didn't want to spend the $$$ on a LabRadar...OK, I did want to...my wife, however, did not.

I ended up ordering a Caldwell G2 Ballistic Prescison chrono, funny thing...I thought of that inverted design about 20 years ago.

I figured I'd better get one that works before I get the new barrel and blow my fingers off! So far I still have all 10, I'd like to keep it that way.

Ridgerunner665

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Re: 7" KKM barrel, would you?
« Reply #12 on: May 23, 2017, 08:56:37 AM »
I just got a shipping notification from KKM...

Looks like my barrel is on its way.

Ridgerunner665

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Re: 7" KKM barrel, would you?
« Reply #13 on: May 26, 2017, 04:23:55 PM »
From the 7" barrel...

12.6 grains of AA9 under a 200 grain XTP, seated at 1.26" oal...

6 rounds....

1,293
1,296
1,293
1,295
1,294
1,296

For an average of 1,295 fps at 15 feet from the muzzle...

True muzzle velocity at the muzzle....

1,305 fps!

And the brass says I could go more...
« Last Edit: May 26, 2017, 04:27:51 PM by Ridgerunner665 »

Ridgerunner665

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Re: 7" KKM barrel, would you?
« Reply #14 on: May 26, 2017, 04:48:39 PM »