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Old November 12, 2012, 12:39 PM   #1
Saltydog235
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Barrel Length

OK, last year I bought a 7mm08 SPS Varmint with a 26" barrel. I changed out almost every part on the gun to make it what I wanted and shot it. Originally I had intended to have the barrel taken down to 20" in order to make it more maneuverable in the deer stand. After I shot it, I decided not to, it was way too accurate and I didn't want to mess up a good thing.

I've kept my eyes open and bought another SPS Varmint in 7mm08 to experiment with. I will "build" this one the same way with the same components as the last one but I'm taking the barrel down on this one. However I have a dilemma, do I take it to 20" or can I go as far as 18" without too much velocity degradation. Most of my deer stand shots for this gun will be 200yds and under.

My load is a 150grn Nosler BT over 45.5grns of H4350 and a Win LR primer. Out of the 26" barrel I get 2700fps in the 700 and 2675 or so out of the same load in a Sako 75 with a 22 3/8" barrel that I own. I know all rifles are different but this is an exercise to find out if anyone has any similar experiences. It is flat out devastating on whitetails and accurate in the two that I already own. Hopefully it will be in the new one as well but who knows.

Why would I want to cut down a heavy barreled gun? I have a Savage 10 PC in .308 with a 20" barrel that shoots lights out, I just prefer the 7mm08 as a cartridge. I like to be different. I also like a heavy barrel over a light one if for nothing else but personal choice. Also I may have it threaded so that one day I can add a can were the option available.

What say the masses?
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Old November 12, 2012, 01:59 PM   #2
loademwell
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I have no idea!!! Maybe you should ask this question in the SMITHY part of the forums...
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Old November 12, 2012, 03:59 PM   #3
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10-4. Kind of a cross sectional question I guess.
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Old November 12, 2012, 08:39 PM   #4
davery25
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sounds like a good plan. What's the actual question though?

20 inches is more then enough i'd say, id be dubious about 18 inches because of the slower burning H4350 powder but even that could be fine.

Cut it down to 20 and do a full test, then cut back to 19 and 18 while retesting.

Worst case is that the 7-08 doesnt perform to its full potential but you have 2 other rifles to do that with, and now you'll have a fast handling, lightweight rifle thats probably still going to be very accurate.

Do you buy 7-08 brass or just buy 308 and neck down?
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Old November 12, 2012, 08:52 PM   #5
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I typically buy 7mm08 brass. I also load .308 and .243 its just easier to have the proper head-stamps to avoid any confusion. I also have quite a few people that I know who shoot the cartridge and save their brass for me.
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Old November 12, 2012, 09:04 PM   #6
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Actual question is should I go 18 or 20"?
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Old November 12, 2012, 09:23 PM   #7
Brian Pfleuger
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QuickLoad thinks your load should be a little faster than you're getting, 2,798 from a 26" barrel. It says the 22.375" barrel would be 2,712. Obviously not an exact match for your conditions but it gives you numbers to compare. It thinks a 20" barrel would be 2,645 and an 18" 2,579. So, you're probably looking at a difference of about 65fps.

Personally, I see no difference in maneuverability between barrel lengths. I honestly don't understand it. I've used barrels from a 15" handgun to 30" shotgun. Never a problem. Carrying around a heavy gun is one thing but sitting in a stand isn't an issue and the difference between 20 and 18 is irrelevant from a weight standpoint.

On the other hand, no animal would know the difference between 2,700, 2,600 and 2,500 either, so it's all a matter of what you like.
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Old November 12, 2012, 10:31 PM   #8
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Some of our stands are tight with sides and shooting ports on them, maneuvering a longer barrel carefully takes time in order to make sure you don't bump anything, that 6" is a bigger deal than you would think.

Interesting on that shooting data. I've never seen 2750 out of that load. I'm basically at sea level with normally 70+ temps and 80-90%RH.

I marked the barrel and I think 20" will be the benchmark. I can always cut it shorter were I to decide to.
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Old November 12, 2012, 11:11 PM   #9
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You may also want to read the Houston Warehouse experiments before finalizing a length. Different barrels and case capacities can cause two barrels to differ by 100 fps with the same load, so I wouldn't worry about the QL prediction difference. If I tweak QuickLOAD a little to give me your 2700 fps result from a 26" barrel, it says a 22.375" barrel should give you 2609 fps. That you actually get 2675 fps in your 22.375" Sako barrel tells me it likely has a tighter chamber or bore or both, so it's a fundamentally faster barrel. It's normal to have these differences.

For your bullet and load, figure to loose about but that if you cut the 26" barrel you have right now down to match that length, it's velocity would be closer to QuickLOAD's prediction. You should loose in the range of 0.9% to 1% per inch from 26" down to 18", landing on about 2470 fps at 18" if you cut down your 26" barrel and 2565 fps if you cut down your 23.375" barrel to 18". If you get yet another 26" gun and cut it to 18", you probably land in that range somewhere.
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Old November 13, 2012, 07:24 PM   #10
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The "Warehouse" link was an interresting read. Thanks for linking that, Unclenick. It would be sooooo nice to have a convenient inexpensive indoor 100 yard range to really figure out a rifle. Where we live the wind can blow darn near daily and sometimes it gust and swirls, and generally makes fine tuning a pain in the butt.

One thing for sure--some people carry accuracy to a technical level that is baffling.

I also enjoyed the remark during the interview about "cheeking" the gun. I have found if shooting from a bench, not doing the famed "cheek weld" I can overcome flinching almost instantly. Getting even a light punch from the comb of the stock in the old cheek bone over and over eventually will make me flinchy. And shooting trap will make the flinch even worse.

Thanks again!
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Old November 13, 2012, 07:44 PM   #11
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For me 20" is as short as I'll tolerate and 24" is as long as I'll tolerate. It has more to do with balance and muzzle blast than bullet speed. There is simply no way to predict exactly how much speed you'll lose with a shorter barrel,from another gun. But I've looked at a lot of data. With almost any chambering there is very little difference between 20-24". Going shorter than about 20" often results in large velocity drops, going longer than 24" usually results in almost no gains.

I you were to use one of your existing barrels and cut it shorter it would be easier to predict. Somewhere between 15 fps up to 25 fps for each inch you go shorter would be in line with what others have gotten when they cut a barrel.

But starting with a new barrel is just a wild guess. I've seen 2 different guns, with equal barrel lengths shoot ammo from the same box 130 fps differently. I've seen a 20" barrel shoot faster than another gun with a 22" barrel with ammo from the same box.

Quote:
id be dubious about 18 inches because of the slower burning H4350 powder
This is a common misconception. If the powder you are using is getting the best speeds with with a long barrel, that is the powder you will get the best speeds with from a shorter barrel. Using a faster powder for shorter barrels is a myth.
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Old November 13, 2012, 11:36 PM   #12
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Once you are at 20, 18 makes so little difference as not to matter.

And as you are at under 200 yards, you really are fine

So if you think the 18 will suit your needs better, do it (and let us know of course!
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Old November 14, 2012, 12:10 AM   #13
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Quote:
This is a common misconception. If the powder you are using is getting the best speeds with with a long barrel, that is the powder you will get the best speeds with from a shorter barrel. Using a faster powder for shorter barrels is a myth
I didn't mean it as in the shortened barrel length means everythings different and he'll have to find another load, rather my concern is that if the barrel is too short for a powder and that powder doesnt finish burning and hence muzzle flash is produced then that load doesnt do what he intends for it to do as the pressure levels never get quite high enough.

of course the load might still shoot well, but its a concern.

or am i still off on that train of thought?
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Old November 14, 2012, 11:15 AM   #14
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Quote:
Originally Posted by davery25
I didn't mean it as in the shortened barrel length means everythings different and he'll have to find another load, rather my concern is that if the barrel is too short for a powder and that powder doesnt finish burning and hence muzzle flash is produced then that load doesnt do what he intends for it to do as the pressure levels never get quite high enough.

of course the load might still shoot well, but its a concern.

or am i still off on that train of thought?
Your train is partially on track and partially off.

Muzzle flash and inefficient use of the powder because of incomplete burn is all true.

"Pressure levels never quite get high enough" is off track. The pressure levels peak in the very early part of bullet travel, so unless you're talking about a barrel that barely extends beyond the end of the chambered round, you're going to get peak pressure.

The idea that the powder that produces best velocity in a long barrel will also do it in a short barrel is generally true up to a point. It's generally true if you go from 24 to 22 or 20, for instance, but it might start to change if you get down to 15" or 12" for example, such as in an Encore handgun that shoots rifle cartridges.

On the other end, it's also usually true that the powder that produces the best speed in a short barrel will also do it in a longer barrel, such as going from 3" to 6". At some longer barrel length, that rule breaks down too and if you think about it, those two points converge at some approximate barrel length where they are each no longer true and the other becomes true, depending which direction you're going.

Clear as mud, right?
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Old November 14, 2012, 11:51 AM   #15
Saltydog235
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I'm going with 20" after looking at it. That will offer the maneuverability that I am looking for in the gun. Now, I just have to get time to make it all come together, plus the funds. Hopefully my stocking is full of Visa Gift Cards this Christmas.
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Old November 14, 2012, 12:53 PM   #16
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Saltydog,

The reason I put the Warehouse link in is they came to the conclusion, for reasons they did not understand, that 21.75" was a magic barrel length that tended to produce best accuracy in many chamberings. I thought it might be something you'd want to try before cutting all the way down, just to see how it feels and shoots.


Colorado Redneck,

Yeah, a 300 yard indoor range is benchrester's dream come true.

It sounds to me like you may need a custom stock. When I was in my middle teens a number of standard commercial shotguns and rifle stocks would bruise my cheek, but I actually grew out of it. So it had something to do with my body proportions at the time. I don't know if it was arm length or neck length or shoulder position or what, but the fact it happened to me at any time in my life means it could happen to someone else, regardless of age.

It should be possible for recoil to tend to pull the stock away from the cheek rather than driving into it if the comb is properly shaped for the shooter. In your shoes I would probably start by putting an adjustable target type butt plate on one of the guns causing me trouble and see if either raising or lowering it above or below the original butt plate position would tend to correct the cheek impact issue. A custom stock maker who has a try-stock for shotguns should be able to find the right proportions for you, but those aren't so common these days.
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Old November 14, 2012, 01:03 PM   #17
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20" will be fine

The 308 cartidge family, 243, 260, 7-08, and 308, have excellent expansion ratios (bore versus capacity). My experience is anything past 22" gains very little with them.
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Old November 14, 2012, 06:58 PM   #18
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The Remington Model 7s use to be 18.5 now they only make 20s.
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Old November 14, 2012, 08:58 PM   #19
davery25
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The houston warehouse experiments read was an interesting read.

It really puts into perspective how little difference case prep would make to the average rifle.

When they talk about barrel length are they refering to tube length including chamber or length of the barrel that is taken up by rifling? Wasn't quite sure from reading it
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Old November 14, 2012, 09:19 PM   #20
Bart B.
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GeauxTide:
Quote:
The 308 cartidge family, 243, 260, 7-08, and 308, have excellent expansion ratios (bore versus capacity). My experience is anything past 22" gains very little with them.
Then why do Palma rifles need 30 inch barrels to get 3000 fps with 155 grain bullets from a .308?
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Old November 16, 2012, 02:21 PM   #21
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Gee, let me think......

I chrono 2920 from my 22" 788 in 308. What does 80fps give me? The OP was talking about hunting rifles. Who wants to lug a 30" barrel bolt gun hunting?
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Old November 16, 2012, 04:56 PM   #22
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Exactly. I like a shorter gun in the stand but I'm picky about the cartridge that I shoot. I hunt the bays, bogs and woods of coastal SC 90% of the time so I'm not looking for a 500yd shot out of the gun, mainly a 200yd poke. If I were going to send one over a bean field or powerline, I'd opt for one of my other rifles. Plus I'm a gun nut and like to experiment with these "assemblies" to see what I can get. The heavier barrel option is just something that I personally like.
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Old November 16, 2012, 06:27 PM   #23
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Please answer this question.

GeauxTide doesn't answer my question about longer barrels getting higher muzzle velocities, but instead states:
Quote:
I chrono 2920 from my 22" 788 in 308. What does 80fps give me? The OP was talking about hunting rifles. Who wants to lug a 30" barrel bolt gun hunting?
I'll assume you're using 155-gr. bullets as that's what I referred to in 30 inch bullets. I think the peak pressure it gets to push a 155 out at 2920 fps is way, way over safe limits. So. . .

What load does your 788 use that gets 2920 fps with a 150 or 155 grain bullet?

Meanwhile, answers to your questions. . .

An extra 80 fps gets you 3000 fps. Enough to keep those light weight bullets supersonic through 1000 yards with excellent accuracy. Someone hunting with a .308 Win. and 150-gr. bullets wanting 3000 fps muzzle velocity, safe peak pressure and excellent long range accuracy will use a longer barrel.

Last edited by Bart B.; November 17, 2012 at 06:41 AM.
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