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Old April 8, 2013, 01:50 AM   #1
Nate_Sandback
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Muzzle Velocity Slower than it should be

My Muzzle velocity is seeming to be much slower than it should be.
In search for a pet load for my Remington 700 SPS in .308Win
i did a fair share of load testing, and compared to all of the reloading manuals, everything I was delivering was significantly slower than multiple reloading manuals document. Case in point, my current load i settled with due to its Sub MOA performance is a 168gr Barnes TTSX with 43.5gr of Varget loaded at 2.830" COL in Nosler Competition Brass and CCI 200 Primers, and the velocities from the last test were:

2552
2509
2477
2512
2540

The Chrony was out about 10' from the bench, temperature was probably at about 20F, Altitude is around 700, humidity was around 50%

According to the Barnes Reloading Manual and Hodgdon my muzzle velocity should be around 2650, but those are indicated loads at 2.810"
I haven't tried loading at Saami specs because the TTSX as an all copper bullet its pretty long and the ogive is pretty far back and I want to get it as close to the lands as my internal magazine allows.

The only thing I have tried so far is to strip the barrel to ensure there's no fowling slowing things down, but i am coming up short with ideas.

Has anybody else ever had this problem or any ideas how to troubleshoot or fix this? Any help is greatly appreciated, thanks!
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Old April 8, 2013, 02:12 AM   #2
steveno
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that is the trouble when you buy a chronograph as it tells you the reality of what you are loading and shooting. shooting at 20 degree ain't doing your load any favors either. fouling probably won't have any affect on velocity but could affect accuracy
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Old April 8, 2013, 04:02 AM   #3
Mike / Tx
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What is your barrel length compared to what the load book list?

If yours is 20" verses theirs at 24", there is your missing 200fps.

The other thing as mentioned above, now you know your not getting what they did, instead of being happy your shooting sub MOA groups.

After you chase your tail trying to get what they got, then you will realize that the chrony while being a valuable tool in working up loads, can make your day less interesting if your simply looking for velocity which compares to factory or book listed loads.

I have two of them and I use them to look for shot to shot variations verses actual velocity when I am working up a load. About the only time I go by the actual velocity is when I am tuning up my bow. I know for a fact what it should shoot within 30fps, and with which arrows. With rifles or handguns, if I get in the ball park I am happy. If I am shooting sub MOA groups I am tickled to death.

Concentrate on the accuracy and once you have that, start shooting it out to 3-400yds, 5-800yds and so forth. Then you can figure your actual drops, and know for certain how well the load is actually shooting.
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Old April 8, 2013, 07:02 AM   #4
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I have tested many multiple times 'duplicate' guns.
Rarely do they shoot same-lot ammo at the same speed. I've even had 5" 1911s launch the same load same time with over 85fps variation.

You are simply observing the reality of "...in MY gun..."
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Old April 8, 2013, 07:26 AM   #5
Dave P
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"there's no fowling slowing things down"

That's a good thing - besides slowing down the bullet, all those feathers can be h**l on accuracy.
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Old April 8, 2013, 07:40 AM   #6
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I ran into the exact same thing as you did with my 300WSM.

You are lucky as I am usually seeing 250-350fps difference from advertised speeds and what my chrony tells me.

If you are shooting sub moa then start *SLOWLY* working your loads up a half grain or so at a time until your group begins to start opening up. Then you can find your optimal speed vs accuracy point.
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Old April 8, 2013, 07:47 AM   #7
cvc944
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Your actual average velocity is 2518. You're estimating a velocity of 2650. The difference is only 132 fps. That's about the speed a major league pitcher throws a basesball with only his hand. Don't get hung up on velocity numbers not matching what you were hoping for - focus on the accuracy that you're getting.
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Old April 8, 2013, 08:08 AM   #8
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Nate,

Welcome to the forum.

Your velocities are within reason for a 20" barrel. My M1A (22" barrel) always shoots in the 2550 fps range with typical match ammo. Figure the .308 loses about 20-30 fps per inch of barrel in that length range, though this varies with the charge weight.

The velocities you see published at Hodgdon's site (or for commercial ammo) are for the SAAMI standard length pressure/velocity test barrel. It is 24" ±0.010" long and has a chamber machined to within half a thousandth of an inch of minimum chamber diameters. That is done because a minimum chamber produces the highest pressures for a load, which is the worst case for the ammunition manufacturer. But with that highest pressure comes the highest velocities, and since most production rifles don't have the tight chamber or the exact same bore dimensions (also held to tight tolerance) they don't usually get as high a velocity even if they do have a 24" barrel.

At the Hodgdon site you will see a button that says "print". Only if you press that do you get a preview screen that includes the barrel length, case used, and primer used.

Most chronographs are made using consumer grade components. These are typically not rated below 0°C (32°F) so I would not be 100% sanguine about the validity of the measurements taken at 20°F unless the instrument instructions say specifically that it works OK that cold. Very often part of the problem is batteries that can't put out adequate current in the cold, either, so a lithium type is then best to use.

Also note that velocities measured to SAAMI standard have the midpoint between the screens at 15 feet from the muzzle. I usually use that distance for a comparison and also because, despite what the instructions say, you occasionally get muzzle blast effects from rifle loads that mess with readings at shorter distances. 10 feet works most of the time and is fine for handgun rounds, but with rifles I don't quite trust it. One fellow with a .338 Lapua Magnum reported having to go to 18 feet before his readings settled down.

One other thing about the chronograph, particularly one with short screen spacing (1 foot) is that it's easy to shoot a the bullet through it at an angle, which can lower the readings by giving the bullet a slightly longer path between the screens. I find the best way to handle this is with a laser bore sighter. When I set up the chronograph, I put a yellow plastic empty chamber indicator (ECI) flag in my chamber and then put the laser in the muzzle and prop the gun up on the bags so the sight stays on the target. I then go out 15 feet and fiddle with the chronograph stand until I see that laser light in the middle of each screen when I hold my palm there. This saves a lot of walking back and forth. When you return to the rifle you get to see exactly where the sights should be looking (above the center of the screens a little). And one more thing. The yellow ECI flag has the words "Remove Laser" on it in black Magic Marker. I remove the bore sighter first, then the flag, always in that order.
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Old April 8, 2013, 08:15 AM   #9
reloader28
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I never even bring out the chrono until I've settled on a load for the accuracy.
When it shoots around a 1/2" group at 100 yds, then your good to go. Bring it out if you want and check the speed.

My guns always shoot slower than their "test" guns. Every gun is different.
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Old April 8, 2013, 08:30 AM   #10
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You do occasionally see a gun with a "fast barrel"; one that's shooting faster than the published velocities or load data. This is a good thing to have a chronograph for, as these guns are experiencing more pressure than the test gun and should not be loaded to as high a maximum.
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Old April 8, 2013, 01:02 PM   #11
Nate_Sandback
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Thanks for all the feedback! Uncle Nick, I always enjoy reading your posts, very informative!

My only real motive with all of this is that the scope I just purchased (Redfield Battlezone 3-9x42) has a calibrated bdc dial for a 30 cal 168gr @2650fps. but I am going to see if they can make me a dial for my specific load. but it is not that much of a concern, as the load itself performs exceptionally well.

Thanks again everyone!
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Old April 8, 2013, 03:26 PM   #12
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Nate,

Your welcome to whatever help we can offer.

Check which 168 grain bullet they calibrated to. Most likely it's the Sierra MatchKing. The TTSX should come very close to a match for BC. If you use a trajectory calculator that accepts G7 ballistic coefficients instead of just the standard G1 coefficients, you get around having to mess with the number changing at different velocities for most boattails. The G7 BC's for the 168 SMK and TTSX are 0.218 and 0.222, on average, as measured by Bryan Litz on identical setups. There are free online calculators at the JBM ballistics site that will work with G7 BC's.

If you switch to a higher energy, slower burning powder than Varget, even with the missing powder space, you should, theoretically, be able to go a bit faster when you hit the same barrel time that your sweet spot is located at. Either Alliant Reloader 17 or Alliant ARComp powders appear capable of adding at least 50 fps at the same barrel time if not a bit more. You'll get more muzzle blast, too, but your ballistics will be closer to the sight knob. Use Winchester cases for maximum capacity (though I saw recently that some Hornady cases may also be in the same capacity range as Winchester; just haven't seen for myself yet).

If you can't change velocity, it appears to me, starting with a 100 yard zero, that you will have to use the sight knob come ups plus add an additional:

0.3 moa @ 200 yards
0.8 moa @ 300 yards
1.1 moa @ 400 yards
1.7 moa @ 500 yards
2.3 moa @ 600 yards
3.0 moa @ 700 yards
3.8 moa @ 800 yards
4.8 moa @ 900 yards
5.8 moa @1000 yards
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Old April 8, 2013, 03:56 PM   #13
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I've had the same thing happen to me with heavy-bullet loads for the .303 British, except in the opposite direction, and (I suspect) for the same reason as suggested above - the service SMLE barrel is LONGER than a standard pressure barrel. Bonus!

What are you hoping to shoot, and at what distance? Are those extra hundred-and-something fps and/or the energy they bring actually important at those ranges? Questions to ask yourself.
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Old April 8, 2013, 09:35 PM   #14
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Yeah great info Nick!

I sorta like to push the loads to where the accuracy and speed are both optimal. I have some more reserved loads that shoot 1/2" groups @100yrds but if I could get that same bullet traveling 300+fps faster with the same accuracy that would sure be awesome.

Using the above mentioned ideology I find myself constantly doing up a few batches to test for that never attainable "perfect bullet" Haha.
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Old April 8, 2013, 10:06 PM   #15
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Back in the day, most of the manuals had the test rifle listed. Even though most of them were pressure barrels, they still listed the twist rate and the length. Most of the manuals today tell nothing. I have no Idea if they used an 18" or 28" barrel. Most manuals today do not even tell what primer the data was developed with.
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Old April 10, 2013, 09:41 AM   #16
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Most reloading data that's published is from barrels other than SAAMI speck velocity and pressure test barrels. Such SAAMI spec barrels can cost about 2 times as much as top level match grade barrels 'cause they're made to exact dimensional specs and tolerances for chamber and bore/groove dimensions.

So, the data's gonna be different in factory or aftermarket rifle barrels in shoulder fired rifles compared to fixed mounted ones in standard test receivers.

To say nothing of the differences in firing pin impact, lot differences for powder and primers and how the barrel's held. SAAMI specs require a fixed mount of a standard universal receiver and test barrel; it does not move backwards in recoil like shoulder fired rifles do. It's easy to get a 100 fps difference in muzzle velocity from person A to person B shooting the same rifle and ammo; they don't hold the rifle with the same force and angle to their bodies which also are not in the same position behind the rifle. Example is shown below.

http://www.newlenoxordnance.com/univ...--barrels.html

http://wisemanballistics.com/product/
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Old April 10, 2013, 10:43 AM   #17
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I can't say I've ever had a problem finding barrel length. The only manual I have that you can't find a barrel lengths in is Lee's Modern Reloading, whose data is mostly compiled from other manuals, so all the data under one chambering isn't necessarily from the same length barrel.

You can usually tell pressure/velocity barrel data from the other data by whether or not pressure numbers are listed with the loads. If there are pressure numbers, it came from one of these test barrels. That includes all Hodgdon's data (click on the "Print" button to see barrel length, case brand, and primer used), Western's data (Accurate and Ramshot), and Alliant measures their loads and does contract pressure testing for other companies.

In Lyman's manual it is mixed. You'll find all the loads that list pressures turn out to have been fired in universal receivers (the kind the test barrels are mounted in), but where there are no pressure numbers they list a production firearm. They always give barrel lengths.

Speer is a funny case in that they develop most loads in production firearms, but Alliant then measures pressures for them for liability purposes, though they don't list that pressure data. They do list some loads developed in universal receivers, but without pressures being listed. They do list firearm and barrel length for every load.

Hornady and Sierra just develop loads in production guns, as near as I can tell, but they list the guns and barrel lengths.

Commercial ammunition is always developed in pressure barrels because they use bulk powders, for which burn rates vary too much to follow simple recipes. It's also the SAAMI standard, so I'm sure there are liability concerns. So you can find the barrel lengths used in SAAMI's standards, where they list the test barrel dimensions.

Handgun
Rifle
Rimfire
Shotgun
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Old April 10, 2013, 07:40 PM   #18
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I gave up on trying to match published velocities. I find factory ammo for my -06 is usually 200 fps+/- slower than published. I worry about accuracy and drop.
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