Barrel time effect

[RichinKansas]

Ok, some of you math geniuses help me out here. I've hear often enough from a number of shooters that a shorter barrel time (shorter barrel) gives noticeable better results on barrel movement. I been trying to quantify that and am not able to. Here's my thinking:
Using a 17 inch barrel vs a 29 inch barrel (just happens to be one foot :) I do use a 29 inch barrel by the way.
By 17 inches the bullet should be near maxed out around 1080 fps for average standard velocity target ammo. It will loose a bit to the muzzle of the 29 inch barrel, but lets just say its 1080 fps also for sake of argument. Should be close. That means the additional barrel time is about .0009 seconds. Not a whole heck of a lot. I think trigger time is more than that! Anyhow if the muzzle of the 29 inch barrel is moving 12 inches per second, the additional movement of a 29 inch barrel over a 17 inch barrel. .0009/12 = .000075 inches. That translates to .005 on target at 50 yards. Where have I gone wrong? Perhaps I am assuming the muzzle is moving to slow. Yea, I just grabbed that 12 inches per second out of the air thinking the real number would be less and that I was figuring worse case. Rich

 

[RichinKansas]

On rereading my post it does not make clear that I believe those folks that say it makes a difference, I'm just trying to get a feel for how much. I know the movement is a intangible that it is hard to identify. Personally in offhand I know there are two kinds of movement for me. normal movement that varies day to day. I cannot control. And that caused by a muscle flinch. The second causes a much faster movement and much worse shot. I guess to identify just how much benefit to a shorter barrel may not be realistic.

 

[KevinThomas]

Rich,
not sure we're getting exactly what you're going for here, but yes, it makes a significant difference. One of the reasons that airguns make better training rifles than rimfires, and rimfires make better trainers than centerfires. Barrel time and follow through is the difference. Screw up a little in centerfires and you'll hang a nine. Do the same thing with a rimfire and you've just shot a six. With an airgun, you're lucky to stay in the same zipcode. That's what makes them so valuable for such things; they force you into a consistently good follow thorough.

A shortere barrel will reduce the barrel time of any of these, but I don't think that's the primary reason I'd chose a barrel length for a particular discipline. I'm building up a 40-X rimfire as a Hunter Rifle (Silhouette) right now, so this is a topic near and dear to my heart.

Kevin Thomas
Lapua USA

 

[mongochicago]

As I understand it, you were concerned about barrel movement affecting the bullet, and the longer the barrel the more movement. That's another benefit of heavy barrels. I love em, the thicker the better.

 

[Bamban]

I'm building up a 40-X rimfire as a Hunter Rifle (Silhouette) right now, so this is a topic near and dear to my heart.

Kevin Thomas
Lapua USA

Kevin,

I am going through the same exercise right now, building a silhouette rifle based on the 40x. Just curiosity, based on your experience what length would you spec the barrel on your project?

 

[msprairiedog]

Rich, You might post this question on benchrest central and address it to varmint Al. He has had several posts on barrel whip or movemant related to tuners or lack of a tuner and might give a better answer than most of us. Him being a retired engineer dealing in questions like yours. I am sure barrel profile would make a difference. Max

 

[RichinKansas]

No, I'm not talking about barrel vibration, but the movement of the barrel caused by the shooter movement. The longer the barrel the longer the bullet is in the barrel. If the shooter moves after they pull the trigger but before the bullet has left the barrel, how much off target will they be with a longer barrel. I have heard for years that a shorter barrel is better. The bullet is out of the barrel quicker. But my calculations are that a 17 inch vs 29 inch barrel is only about .0009 seconds difference. In competition where a point may be the difference between winning an losing the shorter barrel may be better for some competitions. But I'm not sure an individual could detect this difference. There are many more important reasons I believe for a long or short barrel.

 

[msnations]

I'd like to sidestep the question and point out that among the best 3P and prone smallbore shooters there still seems to be a majority of long barrels. The fact is that longer barrels are heavier, which is beneficial. So,its really a trade off that each shooter must resolve for themselves. We're not shooting off benches here...

-Mark

 

[GerryM]

Here's alink that might help' Of course you do need to know some Math.
It explains in detail barrel time velocity etc.
The graphs are very good
www.TheLongfamily.com

 

[camoman]

I followed you on the .0009 seconds part, but for muzzle movement I got .011" after multiplying 12"/sec times .0009 seconds.
D=V*T

 

[blawton]

The point to a short barrel is not that you cant jerk the shoot off less. The main reason why people stick to shorter barrels is the have way less harmonics then a long one. If your not worried about MV then the shorter the better (up to a point).

 

[moorepower]

On a rimfire, I think part of the reason for the longer barrel is to make sure the bullet remains sub sonic when it exits the muzzle.

 

[fivering]

The primary reason for the long barrels in small bore shooting is the longer sighting radius.
This is also the reason for the extension (bloop) tubes used by some Long Range High Power shooters. The advantage of the bloop tube would be the longer sight radius without the extra barrel time.

 

[TAJ45]

FiveRing has hit it square in the X ring. Was reading thru to make sure the sight radius had not been addressed but FR had it covered.

The ammo the serious shooters use are subsonic per the mfrs loading. The really good stuff has the velocity printed on the box. EG 1068, 1056, 1072 as most competive shooters have a good idea what their rig likes fps wise.

It does seem like the Biathalon ammo is 5-10% hotter and my GUESS is a different powder to offset the ambient temps.........of course looking for ignition consistency.

Yes, there are different harmonics in each and every bbl, thus tuners needing proper tuning to redux the effects and thus the search for the grail/specific lot numbers of ammo that work best in your action/bbl combo.

The bloop tube is here to stay and has been for a long time. One notable is that most Olympic rifle 10 meter airgun offerings have in the neighborhood of 16" of actual bbl length. The rest is shroud and of course the front sight is mounted at the end of same. They KNOW about bbl time.

Consider my IZH 46M Oly 10 meter pistol, the best cheap intro you can get for practicing for that event.............It has nearly twice the bbl length of my S&W model 41, muzzle vel is just at half that of a sub .22 40gr. So 2x bbl length is 2x the bbl time and add to that twice as slow moving thru it..........you get 4x the time needed to clear the crown of the muzzle.............if that don't make you follow thru, nuttin' will.

Most folks at the range don't like it one bit, even with the trigger in the ounces. You just can't play with the shot.

This is just a "Hmmmm, I wonder" opinion, but curious about the idea of a fat 18 - 22" bbl with a bloop tube. It seems like Varmint Al and some others have plotted the max velocity of the 17HMR and prolly .22 rf an inch at a time as they cut the bbls and chronied same.

I'm sure you get into what really feels right for a position shooter as far as balance etc which my experience is basically limited to college and a bit of High Power some 35 yrs previous, so can't really comment about the plusses of the 29" bbls for position.

I enjoy these discussions and "how about this idea" musings.

Tom
NRA Life '76

 

[KevinThomas]

Bamban,

Sorry for the loss of thread here, but I guess I got sidetracked here. My apologies for that. I'm going with a 22" barrel, but as a silhouette rifle this really has more to do with the balance I was looking for than any ballistic reasons. Can't tell you quite how this will work out just yet, and that's a long tail of woe. When I wrote my original post, I'd just sent my CMP 40X action, a new bolt and a Hart barrel off to my gunsmith. A week or so later he emailed me that he hadn't seen it yet, and I went back to UPS for some questioning. They informed me that the package had been damaged in shipment, and they were returning it; and they did. An empty, damaged package, no 40X action, no bolt and no barrel. I'd over insured it, so I'm not really out anything, but here we are nearly six months later and I still haven't gotten my replacement action from Remington. They were actually pretty good about this, and it should be here shortly, from what the guys in the custom shop have said. The barrel's already been replaced and my gunsmith has it waiting on his bench. Patience may be a virtue, but I'm gettin' tired of being virtuous. I wanna shoot this thing a bit before I take it to the nationals!

Kevin Thomas
Lapua USA

 

[RichinKansas]

A couple of things. The velocity on Eley packages doesn't seem to match up with any gun that has been tested from post I've read on benchrest.com. However if a particular speed produced on a give machine works good, then another lot of the same labeled speed and machine has a good chance of also being good with that gun.
Lapua doesn't label the speed of their ammo. But back in the late 90's I would find about every lot shot about the same speed. I might have to test this great lot of Center-x I am shooting now.

Airguns are entirely different internal ballistics. Their barrel length has entirely different length requirement.

Looking forward to an ARA benchrest match this Sunday. I'll be shooting a 24 3/4 inch Lilja 1 in 17, 6 groove and my Granddaughter the same except 24 1/2 inches. With benchrest barrel length/time is entirely different from 3p or silhouette. With them sight radius and balance are important. With benchrest balance somewhat less although it needs to ride the bags well. We shoot one piece rest with delron balls that the stock rides on, free recoil, only touching the trigger. I am convinced the bullet leaves the muzzle before the gun has recoiled 1/16th inch.

Slight variation in the topic (but I started it), but why aren't 16 inch barrels popular in unlimited benchrest? I see very few short barrelled guns and none by top shooters. Would seem a shorter stiff barrel would be better. I don't think anyone has concrete proof, but a longer skinny barrel can be tuned easier with a tuner to be more accurate than the short stiff barrel. And be lighter weight. Also lower velocity in the longer barrel for less wind drift. And the one most difficult to prove is that longer barrels give a lower Standard Deviation, thus better accuracy. So many things to consider with selecting a barrel length.