Some thoughts on barrel length for F-TR

[XTR]

I kind of got the idea for this seeing Bryan Litz's twist rate tests.

At this point I think I have six or seven barrels chambered for my F-TR rifles, and after I got a reliable chrono this month (magneto speed) I decided to do some experimenting with velocities in 30 and 32 inch tubes. (prior to this I used a Chrony)

Now a bit of history, 3 yrs ago I started the season with a 34" Keriger heavy palma, running identical loads shooting 185Juggs in two rifles cut with the same reamer I found that my 30" barrel was 30 to 40 FPS faster than my 34". Well, that didn't last long, and I had the 34 shortened to 32 either before or after it's first match. Didn't get back to do side by side testing on it though.

This week I had a new barrel chambered up, again a 32. This time, with lots of barrels to choose from and a pretty good load I decided to experiment, and here is what I found about 32 vs 30. The difference in average velocity between the two lengths is within the extreme spread for the load in these barrels (in this case about 10 or 15fps depending on the barrel on that days testing). I tested this in 4 different barrels, velocity spread for this load, between all 4, two 30s and two 32s is a total of ~ 23FPS. All are 1:10 barrels from Kreiger, Bartline or Brux.


Thoughts on buying barrels based on this info:

Until this last barrel every barrel I've gotten has been a heavy palma, which means when it's toast you are done, because on a non-custom Palma contour there isn't enough breach section to do a full set back and re-chamber.

My latest barrel is a 32 with a 5 inch breach section for this very reason. I've looked in my barrels with a scope, at 4700 rounds they are getting pretty chewed up in the first couple of inches. If I could lop off 2" and rechamber I'd bet they would run another 2000 to 3000 rounds. Not a bad idea when you have a local smith who will chamber for ~½ the cost of a new barrel delivered. With a 5" breach on a 32 you can cut off two inches, set it back, still have a 30 with virtually identical ballistics and I'll bet you can come close to doubling your barrel life. (and quite honestly I am dying to cut one of the 30s to 28 and see what I actually lose)

I think the reality is that the 308 just doesn't have the powder to keep pushing to the end of a 32, no matter what it calculates to in QL.

I know some folks have thought this one through. Scott Harris has a custom "Palma" style barrel he orders with a longer breach.

Just some thoughts and some findings for my testing.

I did do some testing in all three of my 32s with my load. With the same load, all three with round counts from less than 100 to just over 1000 to over 4500, the velocity with the same bullet with the same load was virtually identical. So much for the fast barrel theory (or maybe I just got slow ones).

I'm not really prepared to post up all of my data for evaluation, so take it for what it's worth.. What some guy on the WWW wrote it and didn't have any numbers, but quite frankly I don't want some new shooter trying to duplicate some of these loads and blowing something up.

If I had the time (which right now I don't) I'd really like to sit down and do this with some numbers I could post up, but as of now, my thoughts on 32s in a 308 are that they give you the possibility of getting a second lease on the same barrel, but they provide no advantage at the range.

 

[ShootDots]

If you are looking for barrels to produce MORE velocity, I would suggest another angle. I would stay with the 30" tubes and run either VV N540 with the 185 Juggs and VV N550 with 200+ grain bullets. You will, or is it better to say "should" produce at least 50f.p.s. faster, with the same or possibly less pressure. Additionally, if you are NOT already using it, try the Palma brass. It is almost indestructible!

 

[XTR]

Trust me, it's not indestructible if you put enough N550 behind a 215 you can break it in one shot...as in the primers fall out on the loading bench and it really doesn't show pressure signs getting there.... Three yrs ago I threw away 60 cases after a singe firing because they wouldn't hold a primer. I don't ever want to go back there again.

It may give a tad more velocity, but for competition shooting I would never suggest to anyone to use a double based powder (like N5** series or 2000MR or Rx15), the instability due to variations in temperature are just too great to deal with shooting in the summer in most of the US.

And for the record that is my personal experience with N550 and 2000MR. I about 10 pounds of N550 and 12 pounds of 2000 MR to support that opinion.

 

[Drop Port]

Your test using Kreiger, Bartlein or Brux is in 30" or 32" would be inconclusive if you incorporated them together. I would use the same barrel at 32 and cut it for the next reading if I wanted a true control. I know for a fact in the past two of the barrels you mentioned were vastly different in FPS when set up the same. That was discovered when chambering several hundred for pre-fit AI rifle set up for a specific military ammo. Two of the barrels you mentioned could not be interchanged, over 80 fps difference in the barrel runs at that time.

 

[XTR]

I said in the first post that this doesn't meet the controls of a true test; on the other hand. If you are building an F-TR rifle take it or leave it. I think it does make a pretty good case that in a 308 barrels longer than 30" do not provide any positive ballistic advantage. Beyond that I propose that a properly configured 32 can result in a more economical alternative.

My magneto speed numbers on a 32" Kreiger, a 32" Bartline, and a 32" Brux with identical loads chrono w/i 5FPS average for 10 shots.

One of the 30s is a Kreiger, I forget what the other one is, either a Kreiger or a Bartline.

The 32" Kreiger has I think 4700 rounds on it (over 4500 in any case) and it looks pretty much shot out at least for competition uses. If I had the time I'd get my smith to lop it back 2" at a time, but I'm kind of in the middle of a whole lot of stuff and don't have that luxury right now.

 

[Dusty Stevens]

Once you get to a certain point itll even start slowing down. Longer barrels whip more and if your bullet exits at different points in the vibration this can be significant. Instead of just following the crowd if you like to experiment get a stiffer barrel and start at 28". I think youll see improvements and ease of finding a load

 

[XTR]

Dusty I'd like to see what velocity one of these really shoots at 28".

I think based on some things I've read that you really do start to lose some velocity from 30" to 28". There used to be a thread on here that I have bookmarked, but with the new site software the link doesn't work any more, that went to some velocity testing done with 223s cutting the barrel back from 30". As I recall even the little 223 case did see some velocity drop from 30 to 28, though whether the loss is significant anywhere but on the internet or someones head is another argument.

 

[Dusty Stevens]

Velocity isnt everything. Just like with a dasher when you slow em down a bit off that ragged edge they agg better. Everybody seems scared to lose 150-200fps until they see what it does then they keep it to themselves!

 

[dkhunt14]

Once you get to a certain point itll even start slowing down. Longer barrels whip more and if your bullet exits at different points in the vibration this can be significant. Instead of just following the crowd if you like to experiment get a stiffer barrel and start at 28". I think youll see improvements and ease of finding a load

Velocity isnt everything. Just like with a dasher when you slow em down a bit off that ragged edge they agg better. Everybody seems scared to lose 150-200fps until they see what it does then they keep it to themselves!

Dusty, I have seen this in 1000 yard BR. Years ago when everybody was shooting a 308 Baer, they would start out using 32 to 36 inch barrels. I am talking the 1.450 diameter glued in a barrel bock. After a season of shooting they would get them rechambered and they would always shoot better aggregates after being made shorter.

I have also seen the same thing with a Dasher in the heavy and light guns. They just seem to do better shorter. I saw 2 different heavy Dashers that were shot for years and redone. In the end they were down to 21 inches and still winning. Both guys told me that their Chronograph reading was almost the same at 21 inches as it was at 30 when they started and the accuracy of the barrel was as good if not better. In our game we don't get the round count numbers that others get. Most barrels, if you don't rechamber at 500 to 800 rounds you lose your competitive edge. They just don't shoot good enough anymore to win. Matt

 

[Joe Wade]

Given that in F-class, it take 1/4 MOA groups to win the big matches, we should be talking about what length creates the best accuracy and not worry so much about velocity.

 

[M99]

My 308 F-TR barrel chrono's at 2775 using a 28" barrel with a 185 Jug and Varget. So I don't think you are getting much more out of a 30 or 32" barrel with the .308 cartridge.

 

[calgarycanada]

Lot of the successful shooters are not even close to OBT nodes, they run in between somewhere. Not saying it's not a thing but I don't think that's the only place you get accuracy required for disciplines like F class.
1/4 moa guns are great to brag about group sizes at 100-200 but when it comes to slow fire of F class a guy with 1/2 moa gun who knows how to read wind will beat me each & every time doesn't matter if I have 1/4 or even 0.1 moa gun/load because I suck at reading wind.

 

[Berger.Fan222]

Lot of the successful shooters are not even close to OBT nodes, they run in between somewhere. Not saying it's not a thing but I don't think that's the only place you get accuracy required for disciplines like F class.
1/4 moa guns are great to brag about group sizes at 100-200 but when it comes to slow fire of F class a guy with 1/2 moa gun who knows how to read wind will beat me each & every time doesn't matter if I have 1/4 or even 0.1 moa gun/load because I suck at reading wind.

It's nice to know I'm not the only one. But those tiny groups at 100 yards do help with placing the responsibility properly at 600 and 1000. I'm giving some thought the wisdom of trying out some hunting rifles out in 600 yard matches to learn their potential and limitations.

 

[calgarycanada]

"Lots of successful shooters" meaning whom, exactly? And how successful are they, really? And how do you know exactly where their loads are with respect to OBT nodes? I'd be willing to bet a significant number of top F-TR shooters in the country ARE close to an OBT node, whether or not they actually know it, or purposefully tried to be there. I have no doubt there are some that aren't, as you suggested, but I have no certain knowledge of what percentage of Top-20 (or so) shooters at big matches like the Berger SWN or FCNCs use OBT nodes, or some other loading approach.

Is it possible to find a good node that isn't an OBT node? Absolutely. My experience with ladder testing suggests that there are actually significantly more nodes corresponding to muzzle harmonic deflection maxima (high/low muzzle deflection) than there are OBT nodes. For that reason, I've recommended on several occasions very recently to friends that have barrel lengths where they simply can't hit an OBT node with reasonable velocity to do their testing exactly that way. Without a doubt other load development approaches will work, particularly if you don't have the option of hitting a higher OBT node due to barrel length. Whether the resulting load is as forgiving and precise as one that's on an OBT node is a question that can really only be answered by the individual. However, if you have a copy of Quickload and are either designing a new rifle or having one re-barreled, I can't really think of a good reason not to use it to your advantage. But as noted, that doesn't mean it's the only way.

Easy enough to know, anybody who's running 215 hybrids in 30" barrel, on any sane pressures is running them between OBTs. Slow node with any stable powders(Varget or H4350) is around 2450-2490 fps, higher node is not achievable unless they are using brass once and throw it out.
Bryan Litz posted his load here, he is running 2550ish fps. The general trend is these bullets shoot around 2550-2570 or 2630-2640fps.
I haven't run any numbers yet but I doubt we can run 200s or 210s on OBT at safe pressures.
That's just one example, I can give more accurate answers if I was sitting in front of Quickload. Quickload is not always 100% but it can't be that off either.

Again I'm not disagreeing that OBT exists, it's just that it is possible to NOT be at OBT and be accurate, atleast accurate enough to be able to hold waterline in a F class match.
I'm not arguing in case we are discussing benchrest here.

 

[Marksman63]

If shooting heavies is difficult to avoid double base powders for a proper ballistic gain compared to lighter bullets, considering OBT nodes for respective accuracy.

Before shooting 200 and 215 hybrid my to go bullet was the 185 jug, different barrel and throat, of course, same 32" lenght.
I shot the 185 jug at 2780fps for matches up to 800yds, and 2920 fps for 900/1000yds.

Currently shooting 200h at 2790 fps and 215h at 2700, with manageable pressures and keeping verticals within 1/3Moa. However here in Europe temperatures spreads are almost predictable, therefore weather forecasts and QL tuning allow very comfortable loads.

My 0.02

 

[XTR]

So just out of curiosity, where does QL think the node for the 215s is that is above 2550 in a 30 or a 32?

And where does it think it is for 200s in a 30 or 32? I believe that most are running those in the 2650± range. I'm pretty sure Jade shot a 200-13x in that general area with a 32" with 210JLKs.

 

[Down South]

So just out of curiosity, where does QL think the node for the 215s is that is above 2550 in a 30 or a 32?

And where does it think it is for 200s in a 30 or 32? I believe that most are running those in the 2650± range. I'm pretty sure Jade shot a 200-13x in that general area with a 32" with 210JLKs.

When I shot the 200-13X in FTR at Nationals I was running the 210 JLKs about 2640 ftps ish in a 32 inch 11 twist Bartlein that had 2200 rounds at the time.......I run the 200 hybrids in that same barrel about 2685 ftps ish......Both loads shoot extremely well at 600 & 1000.......I gave a friend of mine all the info at the time I was working up the loads and he said I was right where I needed to be according to quick load with the info I provided, the target I was testing on said the same thing.......

I'm testing the 215s in another faster twist barrel I have that is throated longggg and it looks like it really wants to shoot about 2620-2625 ish and its a 32 inch Bartlein as well. Haven't stretched it out yet, just playing around with it at 300 yards.

 

[calgarycanada]

So just out of curiosity, where does QL think the node for the 215s is that is above 2550 in a 30 or a 32?

And where does it think it is for 200s in a 30 or 32? I believe that most are running those in the 2650± range. I'm pretty sure Jade shot a 200-13x in that general area with a 32" with 210JLKs.

Nodes for 30" barrel are (ms).
[I numbered them just for this discussion I know there is one more faster node then #1 but not achievable in our case.]

1. 1.1087
2. 1.2728
3. 1.3684
4. 1.5320
5. 1.6281

Down South
For 200s running at 2685 fps using varget, out of 30" barrel, 3.191" OAL, 56.5 (lapua brass)grains of case capacity, barrel time is 1.401 ms, not a node.
At 2630 fps barrel time is 1.443 ms

Higher Node (#3)would be at 2725 fps(66k psi pressure, UNSAFE)

Lower node (#4)would be at 2523 fps

For 215s, using Varget, 3.255"(I doubt anyone is running them any longer than that)
Slower node (#4) would be at 2495fps

Next higher node (#3)would be at 2686 fps (VERY UNSAFE AT almost 72k psi)

User reported good points

2550 fps , barrel time 1.481 ms
2630 fps too much pressure with varget

215s using RL 17

Slower node (#4) 2580 fps
Faster node (#3) 2772 fps -UNSAFE- 67k psi

User reported
Slower velocity point 2550 fps- barrel time 1.559ms

Faster velocity point 2630 fps- barrel time 1.490 ms

Throat/OAL length change will affect numbers but barrel time and velocity numbers are not drastically different. If you guys want, I can run your OAL, powder and case capacity if you really like.

 

[calgarycanada]

185 jug. With Varget can be used at node #3 at 2767 fps.

 

[savagedasher]

I would make the barrel as long as you can .
You always can shorten it but you can't make it longer . Remember with a tunner There isn't a node . Larry