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6.5-.284 Barrel Lengths, Short and Stiff? Powder burn efficiency?

 
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  #1  
Old 03-31-2012, 11:04 AM
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Location: Lewiston, Id
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6.5-.284 Barrel Lengths, Short and Stiff? Powder burn efficiency?

looking at rebarreling my 6.5-.284 with a shorter barrel this time with a couple things in mind. also thinking of this same concept with a .22-250 ackley. what is your opinion going off these main points listed below.

1st- accuracy- short, stiff barrels tend to be easier to "tune in" because of having less harmonics, vibration, and/or whip. therefore leading to good accuracy (don't get me wrong, longer barrels create great accuracy too).

2nd- weight- a little bit of weight is saved, not too big a deal

3rd- cartridge powder burn efficiency- dan lilja did a barrel length vs. velocity test and it is a good article to read if you can. there is a point when smaller cartridges like the .308, .223, .243, 6.5-284 do not need a 28"+ pool cue length barrel to obtain their powder burning efficiency. Now with an overbore like the 7mm mag, ultra mags, and big monster killing cartridges coming out these days i can see all the need for having that barrel length to get all the powder burnt efficiently and create optimum velocity.

4th- velocity- some say that velocity is going to drop tremendously with the shorter barrel but i beg to differ (as long as we are talking about smaller, similar cartridges like the few listed earlier). the .308 obtains good velocities (for a .308) out of 20" and 22" barrels all day long but there is no great gains in velocities with longer barrels and then you start getting into problem with the 1st point listed, barrel harmonics. Here again larger cartridges will mostly benefit better from the longer barrel because of the 3rd point made above; there in turn creating more HP or velocity as we more commonly say. i have a .300 wsm with a 23" pencil thin barrel that could probably use a little more barrel but i got a load with 190 gr bergers shooting at 2980 fps and putting 3 shots in .242 groups (barrel heats up too much after 3). this load would probably jump over 3000 fps easily with a longer barrel.

What is your opinion on barrel length and the 4 factors above..... preferably just looking at the smaller cartridges. .22-250 ackley and 6.5-.284 are the two guns i want to get to rebarreling so share your thoughts
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Old 04-01-2012, 03:48 PM
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Re: 6.5-.284 Barrel Lengths, Short and Stiff? Powder burn efficiency?

where's some input from everyone
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  #3  
Old 04-01-2012, 04:52 PM
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Re: 6.5-.284 Barrel Lengths, Short and Stiff? Powder burn efficiency?

I would have offered some advise yesterday here but I don't share the same view as alot of shooters regarding barrel length benefits. Since you asked again for it, I will just hit you between the eyes.

Many 'tests' used to compare velocity for given barrel lengths are used with the same barrel and the same powder. The same barrel part I agree with. The same powder I do not. It is not an apples to apples comparison. Powders need to be matched to a given barrel length for optimum performance.

Yes it is true that a 20" 308 barrel will offer OK velocities with powder X. When you chop 2 inches off of the barrel the loss may not be that great. However, when using a longer barrel and a powder that will be able to take advantage of the added length, the gains can be very large. Try running VV N-540 in a 20" barrel and then a 26" barrel. The gains are great. With the shorter barrel it takes a faster powder to lower the muzzle blast. Higher muzzle blasts are not as condusive to accuracy than lower muzzle blasts. Running short barrels and slower powders offers horrible accuracy unless you cut back on the charge quite a bit lowering the velocity a ton. So to offset this, faster powders are used. Using a faster powder does little in a longer barrel. Hence the reason many believe that longer barrels for 308's and 6.5x284's are not of much benefit.

You can get awsome accuracy AND velocity from a longer barrel using the right powder.

With that in mind, try running RETUMBO in a 6.5x284 with a 22" barrel versus a 26-28 or even 30" barrel. In this case, longer is better. Unburned powder from a barrel is never a good thing which is what you will have in a 20-22" barrel in a 6.5x284

Long barrels can be tuned just as well as short ones. Yes they are stiffer. Yes they still have harmonics. Tuning is tuning.

If you want a short stiff barrel, there are better choices than the 6.5x284 such as the 260 Remington. It will take less than 50-53 grains in a 6.5x284 in a short barrel to make it worth using. If you are going to go with 45-50 grains, go with a 50 grain capacity case.

Hope that helps,

M
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Old 04-01-2012, 09:01 PM
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Re: 6.5-.284 Barrel Lengths, Short and Stiff? Powder burn efficiency?

1st- accuracy- The question is simply whether a reasonable load workup is atainable with either one and the answer is.. yes. Both can be accurate. Perhaps one has an advantage from a bench or rail setup? But, not likely under hunting conditions.

2nd- weight- all else being equal shorter is lighter and easier to handle. This can sometimes be a problem with a shotgun or carbine as too short can cause one to over-swing. Conversely, extra sight radius is an advantage with iron sights as in Palma. Weight can be your friend when your heart is pounding and you get ready to squeeze the trigger on a long range precision shot.

3rd- cartridge powder burn efficiency- I'm not going to debate something Dan Lilja studied. Especially without seeing the study. I think the data is all present in Quick Load to do a pretty thorough study.

4th- velocity- Someone asked a while back about 6.5x284 barrel length and another person indicated from their Quick Load calculations that while shorter is possible, 6.5x284 responds well to longer barrels as is often the case in F-class competition. Their conclusion from Quick Load was that if you desired a shorter barrel, you would do well to go with yet an even smaller case.

My 25" Kreiger Palma 6.5x284 hunting rifle pretty much shoots the same velocity as my Savage 12F with a 30" barrel and with slightly less H4831sc powder. Is it the barrel length? Or, the barrel itself? Or, the chamber, etc? Is it optimal or sub-optimal? I don't know or much care. It simply shows that a 25" 6.5x284 can easily get 2900+ fps without pressure. Perhaps 260 Rem or 6.5x47 could do just as well with an even shorter barrel and longer barrel life? Either way, I'm happy with my setup and was able to use dies, brass, etc that I already had on hand.

So, how did I end up at 25"? Well, it wasn't scientific for sure. It needed a setback after 800+ rounds. And, I wanted to cut off the end of the barrel where it had been tapped for palma sights.

Would I recommend shorter? Probably not.

-- richard
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Old 04-01-2012, 09:07 PM
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Re: 6.5-.284 Barrel Lengths, Short and Stiff? Powder burn efficiency?

...and, to Michael's point. I've never attempted to get to 3000 or 3100+ fps with the 142's in my 12F as is the case with many competitors.

I'm pretty sure it would stand a better chance than my 25" M70.

But, I'm more about consistency than flat out velocity with those 2 rifles.

-- richard
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  #6  
Old 04-01-2012, 10:01 PM
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Re: 6.5-.284 Barrel Lengths, Short and Stiff? Powder burn efficiency?

My bench buddy has been not totally happy,with a barrel. He cut 2+'' OFF it ,24'' about now and shot a 100 5x @1000. With his same loads. He is going to tweak his loads some more. Likes to run at 3000-3050 out of a 6mmdasher.
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