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Discussion Starter · #1 ·
What I'm wondering is at what length has the 17 M2 cartridge burned all available powder? I don't want a barrel that is too long so that it starts to slow the bullet. On the other hand I don't want one too short so that it exits the barrel w/ a bunch of unused powder. Has anyone chrony'ed different barrel links to find what the ideal is or which length achieves the highest velocity? TIA.
 

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Don't have a chrony

My "messings around" tell me that the HM2 has reached its peak about 14.5" up the barrel, and so I ported the barrel just immediately prior to that point, knowing that at some 2,000+ FPS, the bullet would be out the barrel by the time the gas pressure began to see a drop. I think getting down as close to 16" as you can, is the way to go with HM2, and I use BLAZER037's VQ barrel to support my theory, as his 16.25" Carbon barrel shoots exceptionally well. Both barrels are able to function/cycle without bolt weight, after extensive testing, and sharing thoughts and ideas. Longer barrels aren't able to do this, at least any that I have messed with won't, they all need weight of some sort.
My theory is: ANY barrel length beyond terminal velocity is wasting the projectiles' energy, and you cannot give it more, you can only lose less. :t
But, even if this barrel length didn't show the highest velocity, its accuracy is such that I wouldn't trade for more velocity at the expense of accuracy, that'd be going backwards. A chrony isn't necessarily a way to find the best answer, consistent groups is more important overall speed, but I am not saying that my bullets are moving slower, I just don't know for sure how fast they are going.
 

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Discussion Starter · #3 ·
Skeeter27red: I was just poking around to try and get the most out of the cartridge. But you raise an interesting point. Accuracy is best. Have you found that different barrel lengths shoot more accurate than others? The main reason I am asking is that I am a fan of longer barrels (purely for asthetics). But I value function over form and will give up looks for an awsome tac driver.
 

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SubSonicSnipper:

It is a misconception that short barrels don't allow all the powder to burn. In most cartridges the pressure peaks (most all the powder is burned) and is going down after the bullet has traveled only a few inches. The longer barrel give the gas more time to push the bullet down the barrel. But the bullet is a tight fit in the barrel and the friction between the two is pretty high (faster twists of the rifling increase that friction). If the barrel length is too long the exit velocity of the bullet may be less than if a shorter barrel was used, as the friction overtakes the remaining pressure. 22LR barrels of much more than 18 inches are a waste as far as exit velocity is concerned. The 17HM2 is a different animal than 22LR and testing would have to be done to find the optimized length, but the testing would depend on the exact barrel to be used. As we have seen in the 17HM2 there are tight and loose barrels in this caliber so each would have to be tested to be sure.

LDBennett
 

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A coupla things:

First, I use Moly Fusion, which removes most all of ANY friction that would otherwise be created in the barrel.
So, I'd have to get ahold of a chrony to be able to answer my muzzle velocity question once and for all, I honestly don't know, but have been told it should be UP by about 100FPS over an untreated barrel.
The "Champagne bottle pop" sound my rifle makes when fired, is telling me the timing that the event would like to see, is right there. :t
Second, The barrel shoots great at 50 yards, but I still have a ways to go at 100 (It's in the .7-1.00" range most of the time), and am re-lining a barrel in 1:10 twist, just to see what it does. With different twist rates, and a barrel tuner, I hope to hone in on what's going on, because it is not just wind.
If I was going to buy a HM2 barrel, it would be that VQ THM 16.25" Carbon fiber barrel, not even questionable. Its not as light as a "Pure" CF barrel, it still has a metal barrel that is just a little smaller, then the CF tube, is put under tension from end to end, and in this instance, I'd have to say the darn thing works great!
Beyond that, it has an excellent balance to the rifle, and is ravishingly gorgeous to boot.
 

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:yeahthat:

OK, some observations about things related to the 17M2 question.

1. The 2100 FPS velocity is measured using a 24" barrel. This info is taken from a Shooting Times article.

17 HM2 Shooting Times article

2. Fred Smith of Bullberry profiled the velocity vs barrel length characteristics of the 17 HMR and published it on his web site. Fred found that the 17 HMR attained it's maximum velocity with a 19" barrel.

Bullberry 17 HMR velocity study

3. If you examine the Bullberry test you will find that the 10" HMR test resulted in a velocity of 2276 fps.

Conclusions: (actually SWAGs)

1. The HM2 velocities taken from a 24" barrel had been dropping for 7" to 10" before exiting the barrel.

2. The maximum velocity for the 17 HM2 will be found at a barel length between 14" and 17".

3. I'll be scratching my remaining hair out if my velocity measurements this coming weekend, with my brand new 14" 17HM2 barrel, don't support conclusions 1 & 2. :Flush:

A17Shooter

:snipersmi
 

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Yeah, that too!

Being as my barrels' first set of ports is at about 13.500" from the leading edge of their holes back to the first part of the bullet to reach full diameter, and the overall length is 16.375" from breech to muzzle, I guess I'd have to tend to agree with you about those guesses. Just know that it will take more than a coupla hundred rounds to "Bring it in". :t
 

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Question.. If say,15" would be optimum and since you need a barrel 16" (plus a bit) to satisfy the ATF can you do the same thing that is done on the AR's to meet this requirement? Make a 15" barrel and permanently attach an extention tube to make up the 16" inches. This would give you the utlimate barrel length with rifling and the legal barrel length for total length. Heck if you had a way to crown the barrel you could just backbore a 16.5" barrel 1.5 to 2 inches...

Any thoughts?

DonT :cool:
 

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You are right on target.

I have had thoughts about back boring and re-crowning to the desired length.
One thing that has stopped me, is that the barrel has very little friction to begin with with the Moly Fusion treatments, and another, is that the porting also accomplishes the pressure relief at the right time.
I have a " Maternal Twin" to this barrel, but 20" long, and unported, and I had thoughts of possibly back boring that barrel, but, I'm kinda off on a coupla other tangents, like a 1:10 twist lined barrel, and then I have some tuning stuff in the works that may take the accuracy I am looking for out to 100 yards (I have this deal in my head, that under a half at 100 should be possible, and groups should be consistantly smaller than they are now).
I don't think back boring would be a bad idea, I think it would work well. :t
 

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Doesn't Randy at CPC backbore the stock 22lr T barrel a couple of inches and re-crown it for accuracy, seems like he could do that to a 17HM2, 2-4 inches, whatever it takes to hit the right length. got one of the Boyd specials with a helical ER Shaw barrel, coming. and I'm already having thoughts about having Randy backbore it to the optimal length, when ya'll get it figured out, and I haven't even got it yet, much less shot it...."too much knowledge, is an expensive thing" :D
 

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Getting my curiosity up.........

My 14" TC barrel seems to perform equally in the field with both my Marlin and Savage rifles. Hold over and thumping power seem the same but I will definitely have to get the Chrony out and let you know the results. Most of my ground squirrel shooting with the M2 is under 125 yards which may be the reason I don't see an obvious difference in performance between short and long barrels. MV with the 14" HMR barrel is 2,380 fps.
 

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Ideal Barrel Length???

Well, Midway and the Brown Truck people did an excellent job of delivering my 14" Contender barrel chambered in 17 HM2 early last week. After getting it in my grubby hands I proceeded to strip the iron sights off and after scrounging around in the gun closet, came up with a Weaver 92A base, some high rings and that old Simmons 6-18 X scope. After installing the barrel on my pistol frame, boresighting and cleaning I declared it ready to go. All I had to do was wait for the weekend. (Bummer)

Finally got to the range about 9:45 Sunday morn. Setup the chrono, rest, rear bag, etc. on the 50 yd line and proceeded to sight in. The first two shots impacted with a .16" separation. Good omen there. Oh yeah, perhaps some of you would like to know what kind of velocity you get from a 14" 17 HM2 barrel.

I fired 75 shots, of Hornady ammo, at the range and got chrono readings that included 60 of them split into nine groups. The firings started about 9:30 and I finished with the HM2 about 12:30. Velocity list:

2037
2049
2043
2077
2109
2076
2096
2093
2124.

Not too bad for a 14" barrel. Almost the same velocity as Hornady claims for their ammo from a standard rifle barrel. I am attributing the velocity increase during the firings to the morning temperature increase. The temp went from 70 degrees to 94 degrees during the time I was working with the HM2 barrel.

Now, if among the vast legions of 17 HM2 shooters we could get postings of velocity from different barrel lengths perhaps we could get closer to determining what is the ideal barrel length for a 17 HM2.

If you are interested my 50 yd groups averaged 0.5". Not spectacular but, not bad. :)

A17Shooter

:snipersmi
 

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Thanks for sharing A17Shooter.......

Don't know if you saw my post but I averaged 1,928 fps with the Hornady ammo in my 14" TC barrel.......goes to show that not all barrels are created equal. My results were from only 5 shots fired. Even though my barrel shoots the CCI and Eley quite a bit faster than the Hornady ammo, it shoots them all very accurately and very close to the same POI at 50 yards. Sure hope we get a lot more folks posting velocity results from various barrel lengths.
 

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Guns Magazine had a review of a Kimber, a Savage, and a VQ a few months ago. Here are the velocities:

Kimber (20")
CCI 2064
Hornady 2022
Rem 2051

Savage (21")
CCI 2051
Hornady 1993
Rem 2018

VQ (18.5")
CCI 2080
Hornady 2034
Rem 2068
 

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Check out this thread:

http://www.rimfirecentral.com/forums/showthread.php?t=104875

Compares 21" Savage Barrel against 14" with several brands of ammo and it again supports best length of something just a bit over 14". I'm guessing it is going to vary between 14 and 16 inches depending on brand of ammo. My "Space Gun" project has a 24" and I'm seriously thinking of trimming back to 19" which would match my 22lr barrel for the same gun. I think it may also be more accurate. I can't complain about 1/2"groups at 50 yds from a 4.5 lb gun but I'm thinking it needs a trim!
 

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One step closer

I fashioned a "Special tool" (As per TFranks' help/instructions) today, one step closer to "Runnin' the liner in" on my 1:10 barrel project.
I have to do some machining, and when I go to set the crown, you can bet that it will be as close to the 16" minumum as I can get, I don't even question where the ideal barrel length is, I feel great about the barrel I already built, and feel that a 14.5" (from breech face) is about perfect, but I gotta be 16", so there you have it.
Believe it, or not.
I'll try it from there, knowing that the port configuration I already have, works great, wouldn't change a thing.
I'm more interested in the difference in twist rate, and 100 yard accuracy, and a long barrel "Ain't where it's at". :t
 
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