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**Hateca** · 12-14-2009, 9:09 PM

**Gnzrme** · 12-14-2009, 10:00 PM

are there that much differences in factory vs custom....Can you abuse a factory more than a custom? or do they just over engineer it....

**buffybuster** · 12-14-2009, 10:24 PM

Originally posted by Gnzrme

are there that much differences in factory vs custom....Can you abuse a factory more than a custom? or do they just over engineer it....

The difference between a factory and custom chamber is not that the factory is over engineered. The factory chamber will always be larger than the custom chamber. Match chambers are almost always cut to the minimum specification while factory chambers are cut large to maximize tool life and reduce pressures. The larger factory chamber will allow the case to expand, lowering the pressures. A custom, minimum spec chamber will not allow the case to expand and the pressure will build faster and given the same charge to a higher peak pressure. As a result, usually custom chambers will provide higher velocities than factory chambers, since more of the combustion gases are used to drive the bullet than expanding the case.

**Hateca** · 12-14-2009, 11:16 PM

+1 and not to mention bore diameter in a custom barrel can be tight as opposed to a factory barrel being loose as a goose.

Read these based on two rifles I built using match chambers with tight bore barrels. I was pushing faster speeds with factory ammo then you are with overpressure loads using lighter bullets, with one of the builds using am 18" barrel. There can be a big difference in custom barrels over factory.

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**freonr22** · 12-15-2009, 12:11 AM

HAH, I just started reading you post Randy and Now i get you username. i was reading ha teca not hate ca. very nice build, and have heard great things about you guys. sorry op didnt mean to thread crap

**Gnzrme** · 12-15-2009, 11:09 AM

Randy,

What was the powder that you used in those 155's....I know Wes keeps questioning the velocity that I am getting with my chrono, but I have nobody else around me with a chrono, so I am stuck...I am shooting a Rock bbl that was bought as part of a group buy on the Hide. I know its a 1-11.25 twist, but not sure how tight it is...Wow...that was about the velocity I was getting with 46.0 gr out of the 20" and you were getting it out of a 18"...Now it was only about 50 degrees yesterday, so that will have some effect on velocity and pressure was low...26.47 and you were above 29, so air was thicker....

**Gnzrme** · 12-15-2009, 11:19 AM

Never mind Randy, just found your load data in the 2nd thread....Anyway, interesting how much difference a bbl makes.....

**Gnzrme** · 12-15-2009, 6:54 PM

Ok, see what happens when you post in 2 different subforums...I cannot find my other post but Randall you asked for the h20 capacity of a fire case, so I went to the range and viola:

Randall

ok, better late than never....sampled 15 cases...water weight filled was from 57.2-57.6grs with an average of 57.4 Average OAL is 2.009 with a high of 2011 and a low of 2.005...I should be trimming these cases to 2.005. I noticed today that I didn't even break 2700...average velocity was around 2670 something...was cold and windy at the range and I assume with the higher pressure and humidity, that accounted for the rounds going slower....Thicker air = more drag = lower velocity....correct? Hope so....I am really supprised how tempeture sensitive RE15 is....I wish I could find Varget, thats supposed to be resistant to temp change....any other powder suggestions....thanks in advance for the data.....

**buffybuster** · 12-15-2009, 7:03 PM

Originally posted by Gnzrme

Ok, see what happens when you post in 2 different subforums...I cannot find my other post but Randall you asked for the h20 capacity of a fire case, so I went to the range and viola:

Randall

ok, better late than never....sampled 15 cases...water weight filled was from 57.2-57.6grs with an average of 57.4 Average OAL is 2.009 with a high of 2011 and a low of 2.005...I should be trimming these cases to 2.005. I noticed today that I didn't even break 2700...average velocity was around 2670 something...was cold and windy at the range and I assume with the higher pressure and humidity, that accounted for the rounds going slower....Thicker air = more drag = lower velocity....correct? Hope so....I am really supprised how tempeture sensitive RE15 is....I wish I could find Varget, thats supposed to be resistant to temp change....any other powder suggestions....thanks in advance for the data.....

There's not going to be enough additional "drag" in the first 10ft to make that kind of difference. Sure sounds like something's not right with your chronograph.

**Gnzrme** · 12-15-2009, 7:32 PM

Originally posted by buffybuster

There's not going to be enough additional "drag" in the first 10ft to make that kind of difference. Sure sounds like something's not right with your chronograph.

I am going to argue....weather (pun intended) its 10mm, 10" or 10 miles...the air pressure is constant and needs to be overcome...I think it will affect velocity and apparently RE15 is known to be temp sensitive and being 42 degree's out when I was shooting with 78% humidity, this makes the air thicker....hence forth, things move slower.....And, the questionalble velocities were measured with the same chronograph, so it should be off by the same amount if it is off....

I really need somebody else with a chronograph so I can check my numbers...I will be at cuyama this Satuday and Sunday....do you want to join me?

**ar15barrels** · 12-16-2009, 1:09 AM

The air density differences within 10ft of bullet travel won't make a measurable difference in velocity.

This is NOT load data.
It's a computer simulation.

I have found that while the powder charges shown in QL might not generate the exact velocity that QL predicts, this is often due to case volume differences between the computer model the and actual case or due to temperature variation.
So, disregard the powder charge data below and instead focus on the correlation of velocity to pressure.
Work up your own loads and watch the velocity and pressure signs.

Code:

Cartridge          : .308 Win.
Bullet             : .308, 155, Sierra HPBT Palma MK 2156
Cartridge O.A.L. L6: 2.800 inch or 71.12 mm
Barrel Length      : 20.0 inch or 508.0 mm
Powder             : ? Alliant Reloder-15 ?, [B]Temperature: 50 �F[/B]

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.417% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step    Fill. Charge   Vel.  Energy   Pmax   Pmuz  Prop.Burnt B_Time
 %       %    Grains   fps   ft.lbs    psi    psi      %        ms

-04.2   99    46.00   2662    2439   50670   9599     95.3    1.060
-03.8  100    46.20   2674    2460   51363   9640     95.5    1.054  ! Near Maximum !
-03.3  100    46.40   2686    2482   52066   9681     95.7    1.047  ! Near Maximum !
-02.9  101    46.60   2697    2504   52780   9722     95.9    1.041  ! Near Maximum !
-02.5  101    46.80   2709    2526   53504   9761     96.0    1.034  ! Near Maximum !
-02.1  102    47.00   2721    2548   54238   9801     96.2    1.028  ! Near Maximum !
-01.7  102    47.20   2733    2570   54982   9840     96.3    1.022  ! Near Maximum !
-01.3  102    47.40   2745    2592   55738   9878     96.5    1.016  ! Near Maximum !
-00.8  103    47.60   2756    2615   56504   9916     96.6    1.009  ! Near Maximum !
-00.4  103    47.80   2768    2637   57282   9953     96.8    1.003  ! Near Maximum !
+00.0  104    48.00   2780    2660   58071   9990     96.9    0.997  ! Near Maximum !
+00.4  104    48.20   2792    2682   58871  10026     97.1    0.991  ! Near Maximum !
+00.8  105    48.40   2803    2705   59683  10061     97.2    0.985  !DANGEROUS LOAD-DO NOT USE!
+01.3  105    48.60   2815    2728   60508  10096     97.4    0.979  !DANGEROUS LOAD-DO NOT USE!
+01.7  105    48.80   2827    2751   61344  10131     97.5    0.973  !DANGEROUS LOAD-DO NOT USE!
+02.1  106    49.00   2839    2774   62193  10164     97.6    0.967  !DANGEROUS LOAD-DO NOT USE!

Results caused by � 3% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 3% relative to nominal value:
+Ba    104    48.00   2825    2747   61482  10016     98.2    0.973  !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 3% relative to nominal value:
-Ba    104    48.00   2731    2566   54700   9920     95.3    1.023  ! Near Maximum!

Code:

Cartridge          : .308 Win.
Bullet             : .308, 155, Sierra HPBT Palma MK 2156
Cartridge O.A.L. L6: 2.800 inch or 71.12 mm
Barrel Length      : 20.0 inch or 508.0 mm
Powder             : ? Alliant Reloder-15 ?, [B]Temperature: 80 �F[/B]

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.417% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step    Fill. Charge   Vel.  Energy   Pmax   Pmuz  Prop.Burnt B_Time
 %       %    Grains   fps   ft.lbs    psi    psi      %        ms

-04.2   99    46.00   2707    2523   53588   9665     96.9    1.035  ! Near Maximum !
-03.8  100    46.20   2719    2545   54322   9703     97.0    1.028  ! Near Maximum !
-03.3  100    46.40   2731    2567   55066   9740     97.2    1.022  ! Near Maximum !
-02.9  101    46.60   2743    2589   55820   9777     97.3    1.016  ! Near Maximum !
-02.5  101    46.80   2754    2611   56585   9812     97.4    1.010  ! Near Maximum !
-02.1  102    47.00   2766    2633   57361   9848     97.6    1.003  ! Near Maximum !
-01.7  102    47.20   2778    2655   58149   9882     97.7    0.997  ! Near Maximum !
-01.3  102    47.40   2789    2678   58947   9917     97.8    0.991  ! Near Maximum !
-00.8  103    47.60   2801    2700   59757   9950     98.0    0.985  !DANGEROUS LOAD-DO NOT USE!
-00.4  103    47.80   2813    2723   60579   9983     98.1    0.979  !DANGEROUS LOAD-DO NOT USE!
+00.0  104    48.00   2824    2745   61413  10015     98.2    0.973  !DANGEROUS LOAD-DO NOT USE!
+00.4  104    48.20   2836    2768   62259  10047     98.3    0.967  !DANGEROUS LOAD-DO NOT USE!
+00.8  105    48.40   2848    2791   63117  10078     98.4    0.961  !DANGEROUS LOAD-DO NOT USE!
+01.3  105    48.60   2859    2814   63988  10109     98.5    0.956  !DANGEROUS LOAD-DO NOT USE!
+01.7  105    48.80   2871    2837   64871  10138     98.6    0.950  !DANGEROUS LOAD-DO NOT USE!
+02.1  106    49.00   2883    2860   65768  10168     98.7    0.944  !DANGEROUS LOAD-DO NOT USE!

Results caused by � 3% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 3% relative to nominal value:
+Ba    104    48.00   2867    2829   64959   9999     99.1    0.950  !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 3% relative to nominal value:
-Ba    104    48.00   2778    2655   57903   9987     96.9    0.998  ! Near Maximum !

Code:

Cartridge          : .308 Win.
Bullet             : .308, 155, Sierra HPBT Palma MK 2156
Cartridge O.A.L. L6: 2.800 inch or 71.12 mm
Barrel Length      : 20.0 inch or 508.0 mm
Powder             : ? Alliant Reloder-15 ?, [B]Temperature: 110 �F[/B]

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.417% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step    Fill. Charge   Vel.  Energy   Pmax   Pmuz  Prop.Burnt B_Time
 %       %    Grains   fps   ft.lbs    psi    psi      %        ms

-04.2   99    46.00   2749    2600   56461   9694     98.1    1.012  ! Near Maximum !
-03.8  100    46.20   2760    2622   57233   9727     98.2    1.005  ! Near Maximum !
-03.3  100    46.40   2772    2644   58016   9760     98.3    0.999  ! Near Maximum !
-02.9  101    46.60   2783    2666   58811   9793     98.4    0.993  ! Near Maximum !
-02.5  101    46.80   2795    2688   59616   9824     98.5    0.987  !DANGEROUS LOAD-DO NOT USE!
-02.1  102    47.00   2806    2711   60433   9855     98.6    0.981  !DANGEROUS LOAD-DO NOT USE!
-01.7  102    47.20   2818    2733   61262   9886     98.7    0.975  !DANGEROUS LOAD-DO NOT USE!
-01.3  102    47.40   2830    2756   62102   9916     98.8    0.969  !DANGEROUS LOAD-DO NOT USE!
-00.8  103    47.60   2841    2778   62955   9945     98.9    0.963  !DANGEROUS LOAD-DO NOT USE!
-00.4  103    47.80   2853    2801   63820   9974     99.0    0.958  !DANGEROUS LOAD-DO NOT USE!
+00.0  104    48.00   2864    2823   64697  10001     99.1    0.952  !DANGEROUS LOAD-DO NOT USE!
+00.4  104    48.20   2876    2846   65587  10029     99.2    0.946  !DANGEROUS LOAD-DO NOT USE!
+00.8  105    48.40   2887    2869   66490  10055     99.2    0.940  !DANGEROUS LOAD-DO NOT USE!
+01.3  105    48.60   2899    2892   67406  10081     99.3    0.935  !DANGEROUS LOAD-DO NOT USE!
+01.7  105    48.80   2910    2915   68335  10106     99.4    0.929  !DANGEROUS LOAD-DO NOT USE!
+02.1  106    49.00   2922    2938   69278  10131     99.4    0.924  !DANGEROUS LOAD-DO NOT USE!

Results caused by � 3% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 3% relative to nominal value:
+Ba    104    48.00   2904    2903   68368   9943     99.7    0.930  !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 3% relative to nominal value:
-Ba    104    48.00   2820    2737   61055  10015     98.1    0.976  !DANGEROUS LOAD-DO NOT USE!

**Gnzrme** · 12-16-2009, 9:30 AM

Thats exactly what I am getting for velocity for the 50 degree table....Thanks Randall...Ok, now I just have to get a freezer/oven that plugs into a cigarrette lighter and heat/cool my ammo accordingly!!!! LOL

**ar15barrels** · 12-16-2009, 10:22 AM

Originally posted by Gnzrme

Thats exactly what I am getting for velocity for the 50 degree table....Thanks Randall...Ok, now I just have to get a freezer/oven that plugs into a cigarrette lighter and heat/cool my ammo accordingly!!!! LOL

When QL predictions closely match the powder charge to measured velocity, it's safe to assume that the predicted pressure is also probably accurate.
It's one of those deals where if you know 2 variables in a 3 variable equation, you can probably find the unknown variable.

Start working your load up and see if velocity tracks with the predictions above.
If the velocity tracks, the pressure is probably tracking too.

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