Optimal Bbl Length for 20 VarTarg?

[-Yo-]

I'm slowly putting the pieces together for a 20 VarTarg project. (I almost quit on it after learning Lapua wouldn't be making the brass--but it still seems ideal for California ground squirrels).

Barrel choice has me stumped.

I've been running QuickLOAD projections. I'm pretty handy with this program and can usually get it within 15-20 fps of the real world. My first instinct, based on 30BR experience, is that 21-22" would be fine, that you wouldn't get much velocity increase after 23" or so.

However, QuickLOAD is projecting a significant velocity difference for 27" vs. 22", with the 32gr V-Max. (Projection for VV N120.)

22" prediction = 3684 fps
27" prediction = 3830 fps

I've seen 27" and even 30" bbls shoot in the ones, so I'm not too worried about losing accuracy in a long tube. (I also figure a longer bbl will be quieter and won't heat up so fast).

So you 20 VT guys--what's the real deal? Will a long bbl really give you another 150 fps or so more than a a 22"?

Will a long barrel be quieter or cooler?

What length barrel would you recommend in the 20 Vartarg?

[Gary in Illinois]

I can't help with the ideal barrel length for this cartridge but I can provide some information about real world velocities in a 24" barrel. The VarTarg can reach 3850 FPS safely using 32 grain VMax bullets and VV N120 powder but at the expense of short primer pocket life. Velocities higher than 3850 FPS result in case head scrapes and are too hot (imo).
I decided on a load with the above components generating 3650 FPS for prairie dog shooting. I figured this would allow for some pressure increases due to higher temperatures in the prairie dog fields with a margin of safety.
I doubt that you would pick up significant velocity after 22 - 24" barrel length. Check out the test of velocity vs. barrel length in the .204 Ruger at: http://www.bullberry.com/204Rugerdata.html
Good luck in your quest and let us know how it turns out.


Gary

[Dan C]

I have no doubt that you would get higher velocity with a 27" barrel, your QuickLoad projection sounds plausible to me. The question is if the added length and weight is worth the slight increase in speed. It usually is to me.

If it's a heavy bench gun I wouldn't hesitate to go with 26 or 27", there are no real drawbacks that I can think of as long as it's proportional to the stock being used. Some rifles such as the CZ Kevlar Varmint have pretty short forends and don't balance real well on the bags with too long/heavy a barrel.

As for Bullberry's test, that's not conclusive to me. He's an outspoken proponent of short barrels and I have to wonder why he didn't start with about 28", and use a chronograph setup that was a little more reliable?? I had a Tactical 20 built by Greg Tannel at the same time he did one for himself. Same barrel brand/type and same reamer. Mine was 24" and his was 26 1/2", and his was considerably faster than mine. I realize there are many other variables that come into play here but I am sure that barrel length played a major part.

Those are my thoughts. I like to get as much speed as I can at reasonable pressure, and barrel length is an obvious way to do it, even with the little cases.

[Alex]

... that I don't see a lot of difference in the performance of my Model 21Cooper Classic (22 inch barrel) and my Model 38 Varminter (24 inch). I've been fiddling with the loads for both, but haven't really done any A/B velocity comparisons.

What I have found is that such a comparison is often not valid when done with two different rifles. The chamber volume and other factors play just as an important role as the barrel length. Fred (Bullberry) has the stuff to make the comparison by cutting back the length of the barrel, but somehow, that's not an option on my Coopers.

I'm not sure a hotter cartridge like the 204R is proper to compare with the 20 VT.

22 inches handles a lot better than 24. Lots of trade-offs.

Alex

[Gary in Illinois]

Another comparison of barrel length vs. velocity was conducted by Lilja using a 338-378 Weatherby cartridge reducing the length of the same barrel from 46" to 24" in 2" steps. It would seem that a cartridge with this capacity should benefit considerably from increased barrel length. The velocity increase from 24" to 30" was 111 FPS (2888 vs. 2999).

http://www.riflebarrels.com/articles...l_velocity.htm

There is also a test reported on the Accurate Reloading forum using the same .223 Rem barrel shortening it in 1" increments from 22" to 10". The change from 22" to 18" using the fastest load tested was 121 FPS (3177 vs 3056). It is unfortunate that they did not start with a 30" barrel but from looking at the data I tend to believe that the marginal increase in velocity per inch of barrel length would be declining with each additional inch of barrel length.

http://www.accuratereloading.com/223sb.html

I believe that many factors influence the difference in velocities of two "identical" barrels from the same maker with the same length and twist. Some barrels just seem to be "faster" than others for reason beyond my understanding. No doubt there is some free velocity to be gained with increased barrel length but there is also a price to be paid in terms of handling qualities as Alex mentions above.

Good luck,
Gary

[-Yo-]

Gary, Dan and Alex--

Each one of the responses so far has been really helpful. I looked at the .204 Ruger Cut-down tests from Bullberry. It looks like there they did pick up 50 fps or so above going from 21" (3991 fps) to 24" (4049 fps). But it appears most of the gain came in the jump from 21" (3991) to 22" (4034")

The .20 VarTarg likes very fast powders, and burns less powder than a Ruger .204 so maybe it responds in the same way. But I can't see any real disadvantage to starting with 26". This gun will always be shot from bags or a bipod.

Better to start long I think. As Stan Ware, my gunsmith says... "You can always cut a barrel, but you can't make it grow back".

FYI, last year Jackie Schmidt did a cut-down test for me with N140 in a 6mmBR loaded with 107s. We cut it from 33" to 28" in 1" increments. To our surprise, we only lost 40 fps, and it was pretty much a linear 8 fps per inch.

But that's not to say you wouldn't get a much bigger change in the 5" from 22" to 27", even with the small VT case.

That Accurate Reloading test with the .223 was VERY Interesting becuase they used three different powders. All of the powders experience big velocity increases (50 fps) per inch going from 17" to 18". But, H4198 gained more than N135 going from 21" to 22".

It was also interesting that the best Average Group Size was at 15"--and it was significantly better than at 22".

22" Group Average = 0.623"
15" Group Average = 0.420"

[kenbro]

All very interesting stuff.
After all the powder is burned, does the bullet start to slow down if it's still in the barrel?
Regards,Ken.

PS. Does barrel length effect accuracy in any way?
PPS. Sorry for hyjack.

[tdoyka]

i bought a 20 vartarg t/c encore, with a 16 1/4" MGM barrel. while waiting for my dies, i read somewhere(i can't remember) that 21" barrels were best. i don't know if it is true or not, but it is interesting!!!!

[william t. oviatt]

If you get a quality 20 cal barrel, you will not see much difference in fps to amount to anything beyond 22 inch length for a Fireball powder capacity cartridge. There are MANY considerations in choosing barrel length, taper and twist rates.
Go with what your "Best Feelings" are and a quality barrel and you will not be disappointed. My mantra is: "If it ain't accurate, all else matters not!". Much of the "all else" is a "mental satisfaction" which to me, is pretty important. Get what you want....

Also, the main issue for me in 17s is the "muzzle blast". 17s pierce the air with a deafening crack that the same case with a larger caliber will not produce!!! 20 calibers are much more forgiving! A 20 VT with a 22-24 inch barrel will give the best the caliber can do (ina quality made barrel)! If you want more fps get a bigger capacity cartridge.

Let us know what you pursue and how it performs....

Bill

[RareBear]

A longer barrel also means the muzzle blast is further from your eardrum.