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Old April 11, 2012, 07:29 PM   #1
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.222 Barrel length plus Twist Effect MV

Question 1: Does Barrel length and rate of twist effect MV?
Question 2: What data do I use to achieve 3000 MV in a Ruger Mini 14, 18.5 Barrel, 1-10 twist and Why?
This is in .223
All bullets have SD .157 and BC .255
Here is the data
Speer #11 manual
Rifle Ruger Mini 14 18.5 barrel", twist 1-10, cases W-W. Primers CCI 450
55 gr Spitzer SD .157 BC ..255

Powder H335.
25.0 gn. 2948 MV
26.0 gn. 3067 MV
27.0 Gn 31.93

Speer # 13 manual
Rifle Ruger 77 Mk11, Barrel 22", Twist 1-12 Primers CCI 450, case IMI
55 gr spitz-SP, SD.157, BC .255

Powder H335
24.0gr. 2805 MV
26.0gr. 3092 MV

Speer #8 Manual
Rem 700, barrel 24", Twist 1-14, Case Rem, Primer Rem 7 1/2
55 Gr Vmax SD.157, BC .255

Powder H335
21.7 gr 2700 MV
22.5 gr 2800 MV
23.3 gr 2900 MV
24.1gr 3000 MV
24.9 gr 3100 MV
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Old April 11, 2012, 10:20 PM   #2
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1.) yes, the longer the barrel the higher velocity you can achieve
2.) best way to is to pick a powder and bullet and while working up your load, measure your velocity. All guns are going to shoot differently, a 3000 fps load in my gun may not have the same velocity in your with the same barrel length. But keep in mind, your highest velocity load may not be the most accurate.
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Old April 11, 2012, 10:52 PM   #3
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I don't know if you will ever be able to get 3000 fps out of a 18.5" barrel.
Twist rate has no affect on MV.

Most loading manual data is developed using a 24" barrel. As a ball park figure you can use 40 fps loss for every inch of barrel length. The only way you will ever know is to use a chronograph.

Most loading manuals are conservative with regards to max loads. If you are looking for the highest velocity with acceptable accuracy you can load above max but only in .3 grain steps watching very carefully for over pressure signs (primer crating, ejector pin marks on the case head) if you see any of these signs back off.

The rounds you load over book max need to be marked (with a red Sharpie) in some manner that you will know those rounds are over book max. (I color the necks)

I also use a red sharpie to write the powder weight on every case.

Here are some photos of 223 Rem load development I just completed. This group is at 100 yards and is .5 gr over book max.

Last edited by Will Lee; April 11, 2012 at 11:12 PM.
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Old April 12, 2012, 10:23 AM   #4
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Why the differance

Why the differance in powder weight in the 3 manuals?
max load
Speer #11 H335 27.0gn 3126 MV
Hornaday #8 H335 23.2gn 3100 MV
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Old April 12, 2012, 04:28 PM   #5
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The bullet manufactures each have there own different test variables so the data they produce is based on their barrels, powder, primer and case etc. they use. That's why it's a good idea to have a few manuals to use for reference when developing your loads. Their max load may not be the max load in your gun. A general rule is start at least 10% below published max and work your way up.
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Old April 13, 2012, 11:06 AM   #6
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As noted above, each manufacturer has their own equipment for measurement of pressure and velocity. Variables in this equipment and its calibration can all cause slightly different reading from lab to lab.

No two rifles shoot the same it seems and variables in just the rifle barrel and components can and do make a difference in the results, even in the tightly controled test barrels of ballistic labs.

A few variables:

Barrel length
Chamber dimmensions
Throat or leade dimmensions (I.e. 5.56mm v. .223 Rem)
Rifleing (polygonal or conventional)
Actual bore dimmensions down to the 10,000 of an inch
Powder lot
Primer lot and manufacture
Brass manufacture and lot (a heavy for calibre case will have less internal volume than a lighter case of the same diameter or length)
Bullet design for a given weight. A 180 grain VLD (low drag) bullet will have less bearing surface than a 180 grain round nose bullet.

Given all these variables of reporting pressures and velocities, you can easly see why it is advised to start low and work up to your weapon's maximum load.

The pictures of the primers posted by Will Lee show primers that exhibit what looks to be a safe pressure. While primers are not an exact measure of pressure, the fact that they have a rounded radius around the face and that there is no cratering (flow of metal into the firing pin hole) indicate that his load is within a safe operating pressure even though he states that it is slightly over the book maximum load.

Of course primer manufacture can and does change these indicators. A hard primer (those for semi or full auto weapons) will usually show pressure signs later than a primer made of softer metal.

All good loading manuals will state the make of primer and case used in their loading data as they are an important part of the pressure measurement.
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Last edited by Scharfschuetzer; April 13, 2012 at 11:12 AM.
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Old April 13, 2012, 02:18 PM   #7
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The last listed load uses a Remington 7½ primer, a known blowtorch that can increase velocity. You didn't list bullet lengths and COL's and that can affect pressure, to, by changing the amount of space the powder has to burn in.

The manuals you list are all Speer and are of different ages. If the pressures were measured in copper crushers for the old manuals rather than in modern conformal piezo transducer equipment, that alone can move the data around a good bit. The Powder lots used for the tests will be different, and powder burn rate variation these days is held to ±3% by Hodgdon, but I don't know what it was when #8 was published. In general, old load manual data is obsolete unless you can prove otherwise.

Increase in rifling twist rate will rob a little energy from the powder. We are usually talking only half a percent or so of the muzzle energy, though so it's not normally enough to matter.

Velocity loss with barrel length is greater as the barrel gets shorter. It looks overall like with your choice of bullet and powder, though it varies with how warm the load is, you lose around 2% of velocity going from 24" to 22", and around 4% from 22" to 18.5", or around 6% going from 24" to 18.5".
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Old April 13, 2012, 02:24 PM   #8
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Twist rate has no affect on MV.
Actually, it does. Greater twist imparts greater friction as the bullet travels down the barrel. The effect may be small, but it is measurable.
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Old April 13, 2012, 07:23 PM   #9
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Correction on last manual

The manual should be Hornady #8
Sorry for miss information
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