Thought on longer barrels (34 inch) for both F-Class Open and FTR?

[SubVet]

Looking for thoughts on using longer F-Class barrels, specifically 34” FTR heavy Palma profile (223 and 308 calibers) and OPEN straight 1.25” (7mm SAUM caliber). I understand the weight limitations for both FTR and OPEN rifles have to be considered.

I came from an Engineering background and have done some initial action / barrel computer modeling, specifically regarding harmonic barrel vibrations. I am using the Finite Element Methods which break the subject (action / barrel) into many smaller sections for analysis. The modeling has the action (aluminum) non-movable and the (stainless steel) barrel free floating. I added action bolt slot and loading / ejection port to simulate a more refined action than just a cylinder.

The results are interesting, longer barrels model least impact of harmonics vibrations. Specifically in the vertical direction. Obviously, there are differences between the two caliber FTR and one OPEN barrel as the profiles are very different. The modeling shows these results. Anyway …..

Any thoughts?

 

[ogre1911]

Jim Borden addresses straight vs hv contour barrels in his latest Cortina interview. It's not so much about length but about the "tune ability" gain you get from a less stiff (not straight) barrel.

He has a great story about himself and Adamovich using hv or lv guns, I forget, in a heavy gun match and placing 1st and 3rd against much heavier guns.

Worth a watch.

 

[B Nettesheim]

I have more people asking for 30”-31” recently

 

[Ringostar]

I have more people asking for 30”-31” recently

We both know someone with initials BS, that has been using 30 1/2” for over 10 years now. It’s not really anything to do with an advantage though. They just fit better in his hard cases for travel. My newest 7 saum is 31 1/2”, just because the smith preferred to take a little more off the end. So far, it still shoots good.

 

[B Nettesheim]

We both know someone with initials BS, that has been using 30 1/2” for over 10 years now. It’s not really anything to do with an advantage though. They just fit better in his hard cases for travel. My newest 7 saum is 31 1/2”, just because the smith preferred to take a little more off the end. So far, it still shoots good.

It’s been more than a few people

 

[NZ_Fclass]

Hard to find a bag long enough though.

My FTR 308 is 31in Heavy Palma , 223 28in Heavy Palma, Dasher 30in 1.25 in parrallel. 6BR 29in Match Rifle - straight taper.

 

[big5ifty]

Looks like you're keen for an experiment.

The free floated traditional barrel length / velocity / contour / vibration discussion is old and toothless, there is no definitive accuracy answer to it.

Pick a barrel, length, profile and tune the load. Standard stuff.

Two things are worth trying and perfecting, IMO

1. a shorter length barrel for the cartridge, with a barrel block

-or-

2. a structured barrel

 

[CharlieNC]

Harmonics is your friend, optimize bullet exit time for tuning.

 

[gpoldblue]

I'd be more concerned about the number of bullet rotations{deformation) while under pressure inside the barrel. With an 8 twist barrel...that's almost 4 complete rotations before leaving....that's alot of stress on that bullet. Just a thought,but I don't shoot long range.....maybe it's necessary for LR shooting. In short range BR
our barrels typically rotate about 1.5 revolutions before exiting
Good luck and stay safe.

 

[Alex Wheeler]

When we tested contours in LR BR I came to the conclusion that if there was any difference we couldn't see it. I think the talk about contours is mostly theory. It should work in the way we think, but the best shooters I deal with could not prove it on target. At least with the heavier contours, Im not talking pencil barrels. Tune windows and raw accuracy were basically the same. Length on the other hand does seem to matter. Different cartridges do seem to have sweet spots when it comes to length. You need to look at trends over many barrels and shooters. Do not fall into the trap of coming to a conclusion based on a barrel or two. Talk to your smith who has seen 100's.

 

[SubVet]

Several good comments above. One goal in this effort was to actually see if the program modeled results for different profiles. Alex’s comments regarding actually seeing differences among profiles are well taken, fundamentally not seen on target.

Modelling gives me different and useful results for different barrels, where there may be advantages. As velocities may be increased which may open up new ‘nodes’ may be available. But, as usual, there are pros and cons, barrel life as an example.

In my actual rifle configurations, I have two barrels for each caliber (six total) and I have installed a tuner on one of the barrels of each caliber. Then I can measure actual ‘on target’ accuracies, comparing the tried and true powder loads and seating depths with adding tuning to see if accuracy can be improved. But, modeling barrel length has given me results I have seen on target and I have settled on 34” in all calibers. I believe the determining factor is increased velocities which will directly affect accuracy at distance.

At the end of the day, accuracy differences must be seen on target. Basically, if not move on ….. Thanks to those of you who commented, I appreciate your inputs and advice.

 

[davidjoe]

I think set backs are increasingly accepted now as legitimate in competition. The first life of a barrel at 34 or 35 inches will probably not be its best. A 35 inch barrel can have more than one set back.

Bullets get really hot at this original length. They can blow up. If they don’t they will still tend to deposit more copper the hotter they get.

I have some personal belief that an overheated bullet can lose accuracy potential even if it technically remains intact to the target.

The most obvious experience I observed was a 7 followed in a shot or two by a no pull. That barrel was indeed long, but more critically it was a tight bore.

As to non tight bore barrels that are 35 inches long I’m also of opinion that the group can just open up relative to a 30 inch or under barrel.

For example, while I have never blown up any bullet in a .284, certain very long barrels had mediocre accuracy performance at that length, though velocity was very high; I actually did or do look forward to setting them back, and that is not a good feeling as expensive they are.

The interesting thing is that it can work, and a few barrels have shot very good with 35’s, provided the bore is not tight, particularly chambered in Saum. Unfortunately when those barrels were identified, Saum brass could not be.

If you were not going to ever set back a barrel, I would not pay for the extra length.

 

[ebb]

Does the 34-35 length have any advantage other than setbacks? I assume with a 1000yd limit (as long as I've ever heard F class matches are) keeping the bullet supersonic is no issue but extra speed would have wind drift advantages also. I guess what I am asking is if not setbacks then why? I shot out a 300 Jarret chambered rifle when I first started shooting, It was fire cracked so far down the barrel a set back would have been too short to be legal. I am sure I should have looked earlier, but setbacks seem like they are too little too late to me.

 

[big5ifty]

At the end of the day, accuracy differences must be seen on target.

... and because there is no modelling software that can predict how a barrel / load /shooter will shoot on a given day.

 

[SubVet]

... and because there is no modelling software that can predict how a barrel / load /shooter will shoot on a given day.

Absolutely ….. Especially the shooter. Many variables at work, just need to work on those that help ‘on target’, given the ‘hunk of meat’ behind the stock. And, of course the wind …..