Some thoughts on barrel length for F-TR

[Down South]

Calgary Canada, I'm not running Varget with 200s @ 2685 ftps, that speed is with H4895 and my fired Lapua brass was 57 gr water capacity (Palma). I do have a Varget load with 200s that is just as accurate as the H4895 load but Varget seems to shoot best about 2665 ftps. The 200s are seated above the neck/shoulder junction in this chamber/barrel but not near as high up in the neck as the 215s in my other barrel.

As for the 215s I'm playing with, I'm using Varget with Palma brass also but can't remember the OAL at the moment but they are seated super long. The very bottom of the bullet is at the neck/shoulder junction. Less than 1/2 the shank of the bullet is being held in the neck (only about 1/4 is being held). It wasn't my intention to set it up quite this long but it happened. I've tested it in 95 degree weather with zero issues, easy bolt lift, brass looks good with no ejector marks, etc.

Both of these barrels are 32 inch not 30 inch.

 

[Scott Harris]

I use 32" barrels and shoot the 200 hybrids at 2670, 185 Juggs at 2760fps currently. Previously ran the juggs at 2800-2820 with great accuracy. These speeds don't seem to match the OBT nodes highlighted earlier. I'd love to try the OBT concept out, but with spreads of 150-200 fps between nodes, it seems a little impractical. What am I missing?

 

[Down South]

I use 32" barrels and shoot the 200 hybrids at 2670, 185 Juggs at 2760fps currently. Previously ran the juggs at 2800-2820 with great accuracy. These speeds don't seem to match the OBT nodes highlighted earlier. I'd love to try the OBT concept out, but with spreads of 150-200 fps between nodes, it seems a little impractical. What am I missing?

Scott, after shooting with you several times now i can honestly say you aren't "missing" anything as you consistently shoot very well no matter what quick load says........lol

I saw Devon burned it up in the 600 yard match last week, that kid is something else. When i saw him make that wind call last year at nationals after waiting it out in that rough stuff i was VERY impressed. Your whole family shoots great!

 

[savagedasher]

I use 32" barrels and shoot the 200 hybrids at 2670, 185 Juggs at 2760fps currently. Previously ran the juggs at 2800-2820 with great accuracy. These speeds don't seem to match the OBT nodes highlighted earlier. I'd love to try the OBT concept out, but with spreads of 150-200 fps between nodes, it seems a little impractical. What am I missing?

Why worry if it shoots if you have speed and accuracy why change Larry

 

[Scott Harris]

Scott, after shooting with you several times now i can honestly say you aren't "missing" anything as you consistently shoot very well no matter what quick load says........lol

I saw Devon burned it up in the 600 yard match last week, that kid is something else. When i saw him make that wind call last year at nationals after waiting it out in that rough stuff i was VERY impressed. Your whole family shoots great!

Thanks Jade! Devon is a trigger slapper....sometimes he does phenomenal and other times he stinks it up.....pulling my hair out trying to get him to squeeze the trigger...lol

 

[calgarycanada]

Why worry if it shoots if you have speed and accuracy why change Larry

This is exactly what we all need to do and forget about OBTs.

 

[calgarycanada]

You can do that. I'll be happy to let others do as they wish while I continue using OBT as a reloading approach, saving significant time, effort, and components.

Good for you brother but I guess that limits your bullet choices, that's all.

 

[Dos XX]

Can someone with Quick Load run a hypothetical .308 Win load with a 32" barrel and the same load with a 30" barrel and tell us what the pressure difference is? Let's say .168 or .170 free bore, common F/TR reamer, and say 43.5 gr Varget. Let's use Down South's 57 gr water capacity with Palma brass.

Or really, a better question might be, what pressure does it take to get 2650 with a 30" barrel and what pressure does it take to get 2650 with a 32" barrel

 

[calgarycanada]

Can someone with Quick Load run a hypothetical .308 Win load with a 32" barrel and the same load with a 30" barrel and tell us what the pressure difference is? Let's say .168 or .170 free bore, common F/TR reamer, and say 43.5 gr Varget. Let's use Down South's 57 gr water capacity with Palma brass.

Or really, a better question might be, what pressure does it take to get 2650 with a 30" barrel and what pressure does it take to get 2650 with a 32" barrel

What bullet & OAL? I don't know what OAL length will be from freebore. The way I come up with OAL is by having .150" bullet shank seating depth in case neck, that keeps bullet base out of donut area. If you like I can do that, just tell me what bullet.

 

[Dos XX]

What bullet & OAL? I don't know what OAL length will be from freebore. The way I come up with OAL is by having .150" bullet shank seating depth in case neck, that keeps bullet base out of donut area. If you like I can do that, just tell me what bullet.

3.05" OAL. 200 Hybrid. I run that reamer and that is my OAL.

 

[calgarycanada]

Assuming we are talking about 200 hybrids. 3.050" OAL
30" barrel 43.5gr 2621 fps 58937 psi
30" barrel 44.1gr 2651 fps 61397 psi
32" barrel 43.5gr 2649 fps 58937 psi

All numbers are based on my lot of varget, different lots can give considerably different pressures, so work your load up

 

[Dos XX]

Interesting. So there is 2460 psi or roughly 4% less pressure with a 32" barrel than a 30" barrel at 2650 fps. Max SAAMI pressure on .308 Win is 62,000 psi, I think?

Is that significant? Will it get you another loading or two before primer pockets get too loose?

You are right on about lots of Varget. I am running the 200's at 2660 ish in 2 different barrels and am using less Varget than your numbers show. My last lot of Varget was almost .5 gr different.

 

[calgarycanada]

Interesting. So there is 2460 psi or roughly 4% less pressure with a 32" barrel than a 30" barrel at 2650 fps. Max SAAMI pressure on .308 Win is 62,000 psi, I think?

Is that significant? Will it get you another loading or two before primer pockets get too loose?

You are right on about lots of Varget. I am running the 200's at 2660 ish in 2 different barrels and am using less Varget than your numbers show. My last lot of Varget was almost .5 gr different.

Yes max pressure is 62000 psi but my experience is anything over 58000 psi reduces brass life considerably. I lost primer pockets on one set of lapua brass in 5 firings. Of course it's calculated pressure from QL based on my inputs, I don't have strain gauge so actual pressure is unknown. I had no pressure signs at all, just lost 20% primer pockets after 5 reloadings .
Loaded under 58k has one set of brass going good after 11 firings.
This brass is large primer, no experience with Palma brass

 

[Dos XX]

I just started running Palma brass last year, so I can't comment on how many loadings I will get yet.

If you travel to shoot larger matches, like the Berger SWN, or FCN's, you need to be able to take almost 400 rounds to a match. I am running 450 pieces of brass on each of 2 barrels right now. I would estimate 3000 is rounds is about max on a 308 barrel for match accuracy, so if I can get 7 loadings that would be 3150 rounds or enough to retire a barrel. It will be interesting to see.

 

[whatwind?]

I have .340 nk, .199 fb on a 31" 10.25 rot bartlein with lapua lrg primer brass, 44.75 gr varget, fed 210m, 200 gr hybrid pointed, 2.345 bto, getting 2734 fps average today in 73f, 29.99 bp, 1100ft da (Louisiana)

1-2 pieces of brass out 20 show pressure signs, none have heavy bolt lift, bbl has 500 rounds on it

 

[XTR]

I think you guys are missing the point of my original post.

No matter what QL says, loading my identical loads in a 30 and a 32, the MV difference using a magnetospeed was within the extreme spread of the two loads. The average MV difference between the two was on the order of 10FPS.

I know how people on this site get into the minutia. I wish I had the time to whack the barrel with 4700 rounds on it down to 30 and 28 to compare the same load in the same barrel, but as posted, with 4 barrels, the MV with the same loads nearly identical.

 

[Dos XX]

I get it. That would be a cool experiment. I would be curious to know if as the barrel gets shorter does the pressure increase even if the velocity stays the same?

I have a 31" and a 32" chambered with the same reamer. They also run almost the same velocity. Again, I wonder if the pressure is the same? I may can judge by brass life.

 

[XTR]

My possibly flawed understanding would be that the max pressure would be the same, but the pressure impulse would be a few milliseconds longer until the bullet exited the tube.

Over on a board I frequent for smokless muzzle loaders there are some guys who have the sensing equipment and have posted probably hundreds of pressure curves with various weights of bullets with a variety of powders and charges. All put up online for the general knowledge base. (There are very few "book" loads for smokeless MLs) The shape of curves is kind of interesting, but in all cases peak pressure is achieved long before the bullet leaves the barrel. I think it's usually in the first 1/3. The pressure curves are in milliseconds on the horizontal axis, and I've seen some posted up with predicted OBT nodes marked.

One note that is completely off topic, QL has an awful time trying to figure out what is happening in straight walled cartridges like the 45-70 and in MLs. At least it did a yr or two ago.

 

[memilanuk]

Interesting thread; wish I'd seen it earlier!

So here's my $0.02 worth...

I used to use OCW/OBT extensively, along with QL. Somewhere along the line, when Varget became unobtainium in 2008-2009, I switched to N150. The burn data in QL for N150 is considerably different from reality (in all fairness, pretty much every burn rate chart shows it closer to H4350 than Varget, which is where it falls in my experience), and I eventually let my license expire.

Last year I was having fits trying to get my 200gn load to work the way I thought it should. Since I was again using Varget (185s) and H4895 (200s) I renewed my license for QL and fired it up. I plugged in the data for my 185gn load (30" Krieger barrel 1-12" tw with a very long throat) and it fell right smack on top of an OBT node. Couldn't have hit it any better. Made sense, as that was a pretty accurate combination in that gun. Then I plugged in the data from my 200gn load - and had to do a double take. The load I have runs the 200s @ ~2650-2660 fps from a 30" Krieger 1-10 tw barrel using H4895. According to QL, there should be a node @ 2530fps, and another @ 2715-ish. I tried - there is indeed a nice tight accuracy node @ 2715-2720... but I blew the primers right out of virgin Lapua Palma cases doing so. Pass...

Interestingly enough, it looks as if - in theory - a 32" barrel should be just enough to hit that upper node, while keeping the pressure within reason. My next barrel getting chambered is a 32", so we'll see how that goes.

The 30" 1-12 tw barrel for my 185s is about done... it shoots great, but the throat is out to the point that if I seated out to the lands, the bullet would probably fall out of the neck. Thinking about having it set back and seeing if I can get some more useful life out of it on a back-up gun.

 

[Dos XX]

Monte,
What is your free bore for the 200's?

Seems like several people on this thread, myself included, are running the 200's at 2650 to 2675. Seems something is going on around that area, too.