Powder and velocity

[GhengisAhn175]

Hey fellas,

Currently in my load up, lapua brass, 44.0g of H4350 in my 26" barrel gives me 2940 fps on average. (Verified with oehler).

My question is I want to back it down to 2850-2900 ish fps and wondering if there's a well calculated rule of thumb for x grain = x +\- velocity ( since it doesn't scale at a linear level up to a certain point).

I so not have access to this oehler at my own will so need to know a calculated close # for the velocity to input into my ballistic app. Thanks fellas!


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[GhengisAhn175]

Also would like to add I did search and found several different answers ranging from .1 gr = 5-13fps but it seemed to vary depending on the entire bullet components


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[FCS]

Why not run 2940?

Powder charge difference between 2940 and 2850 is going to be 1.3 to 1.7 gr less. You'll need to find accuracy node, velocity will be what it is at next node down.

 

[GhengisAhn175]

Hey Andrew!

Well I feel like my groups can tighten up with a better load so I'm going to work down from 44.0 grains . When I happen to find the most accurate node I won't have te chrono available so just asking ahead. I guesstimated 2850 fps because I feel like I'll just go a few tenths grains lower.


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[FCS]

8 fps / 0.1 gr is ball park value for velocity change. You'll need to chronograph to have an exact or shoot at distance, back out a velocity from drop.

 

[GhengisAhn175]

Is 8 fps : .1 gr the standard rule or is there something that determines this ie: powder?


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[FCS]

Going to vary by burn rate of powder, your individual barrel, where you are on pressure curve, etc. Too many variables to give you an exact value.

 

[GhengisAhn175]

Roger this. Thank you sir


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[1SMALLJOHNSON]

Well, I looked up the definition of "Interpolate", and came up with the following. The description in the Wiki site is WAY too complicated. Here's the Cliff notes: Find two velocities, with two charge weights. From there, it's basically a cross-multiplication problem. If you understand algebra, you leave your resultant charge weight as the unknown, and plug in all other velocities and charge weights. If anybody's really interested in this simple formula, please PM me, and let me know of your interests. It is NOT perfect, but when dealing with non-linear algebra (ballistics), you CAN make assumptions and save yourself some time. Interpolation is a simple mathematic tool, and quite valuable in ballistics.

Interpolation - Wikipedia, the free encyclopedia

 

[Clark]

They taught us how to interpolate in 11th grade algebra for using log tables, before there were calculators.

Logs are not linear.

 

[No1]

cut an inch or two off the barrel.
.
.
seriously though, forget about the velocity and find the most accurate load. When you have 'the load' you are looking for then you can make a WAG at the velocity until such time you can shoot through the chrono again. I only chrono loads after I'm finished with load development.

 

[FCS]

I'd try going -.2, -.4, +.2, +.4 gr and test loads at 300 yards minimum.

 

[Pinecone]

If you have a range to shoot at multiple ranges, you can get close to the velocity by using a ballistics calculator and changing the MV until the calculator gives you the same come ups as you found by actually shooting.

 

[Twoboxer]

Hey fellas,

Currently in my load up, lapua brass, 44.0g of H4350 in my 26" barrel gives me 2940 fps on average. (Verified with oehler).

My question is I want to back it down to 2850-2900 ish fps and wondering if there's a well calculated rule of thumb for x grain = x +\- velocity ( since it doesn't scale at a linear level up to a certain point).

I so not have access to this oehler at my own will so need to know a calculated close # for the velocity to input into my ballistic app. Thanks fellas!


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While I don't think it will help much, verify what caliber and specify which bullet you are using with 44.0gr of H4350 to produce 2940 fps. Can then tell you what Quickload thinks that velocity should be, and then give you what powder reduction would reduce that by ~75fps.

But probably better to work up an accurate load and, as suggested above, actually compare its ballistics to your current load to guestimate it's velocity. Then use the app to extend the calculation to other distances.

 

[onethousandmeters]

8 fps / 0.1 gr is ball park value for velocity change. You'll need to chronograph to have an exact or shoot at distance, back out a velocity from drop.

Thanks! I reload for my .308 and weigh each charge to the 1/10th grain. This...drives...my...dad...nuts!!! LOL! He contends that if the thrown charge is 45.5, or 45.4, or 45.6, that I wouldn't be able to tell the difference in terms of accuracy / velocity. I agree that at 100 yards, I probably wouldn't see any change in POI whatsoever. MY fear is that when I shoot at 800, that load which is supposed to be exactly 45.5, and instead is 45.3, or 45.4, might cause a serious change in POI at the longer distances. Maj. Plaster's talks in both of his books about the difference 1 whole grain can make in velocities, and how much that can affect accuracy / POI at distance, but I'd never found any discussion on minute changes, as in 1/10th grain changes. I guess he was right to an extent, however, I get a certain peace of mind in knowing my rounds are loaded as precisely as I can make them. Thanks again for the info and this is a great thread!

 

[GhostFace]

Your dad is correct if you are in the accuracy node. Do some reading up on the OCW reloading method.

 

[onethousandmeters]

GhostFace,

Despite being 44, my dad still ceases to impress me! My .308 load is for the 175gr. I use 45.5 gr of CFE223 and it pushes the round right at 2609 in my rifle, using Federal brass. The FGMM 175gr chrono's right at 2611 in my same rifle, and both do 1/2" at 100 yards for me. I doubt I could get any more accurate (at least I doubt that I could be any more accurate). I'm happy with the load, and I guess I can give in when he's helping me reload about the .1 grain variance! LOL! The OCW method is pretty cool, and in the future, if I EVER get to own a Vintage Sniper Rifle, ie...1903a4 (even if it's a clone), I will certainly try that method of working up a load. Thanks!

 

[Houk8539]

Why not just go down .2 gr to 42 and see where the sweet spot is. Do this in 5 shot groups at 100 and rock on


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[Pinecone]

If you are in an accuracy node, small powder changes do not affect the POI/group size.

And if you are in an accuracy node, OCW predicts that a 3% change in powder weight (up OR down) will put you in another accuracy node.

Therefore, if you are in a node, and want to keep an accurate load, you need to go from 44.0 grains to 42.7 grains and accept the MV that you get. You can't just load to a given MV and necessarily have an accurate load.