Velocity differences

[bowfishn]

Bowfishn:
The oal of the jhp .620 the cast TC .595. Coal of the jhp 1.589 the coal of the TC 1.585


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It would appear that is not enough to make the velocity difference according to QL . Both should be close to 1800 fps with a 20" barrel.
As the others have said you need to run a string with each to tell the actual velocity.

Also the less friction on a bullet or in the barrel equals less pressure which equals less velocity. (exception would be long barrel and low powder volume where barrel length begins to slow down bullet. In that case less friction can equal more velocity. Example 22LR with long 24" barrel, some friction proofing products have seen increase in velocity)
I run HBN on all my jacketed rifle bullets and when I switched from non coated to HBN coated I lost velocity with 2 different 30-06 rifles, 2 different 6.5 CM rifles, a 308 win and a 243 win. The lower friction allows adding a bit more powder and in the end gaining velocity. (with the 6.5 CM using RL26 it was .5 grains to equal velocity loss)

[Bkingnsmth]

Had I gone to do chrono work I would have taken more ammo, as it was I only went with enough to check my sights.


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[Jim22]

I find it sad that some want to make light of Bkingnsmth's report. We all know that a string of one shot across a chronograph is not very representative but he reported it any way. I thank him for the information.

[Larry Gibson]

Whom is "making light of it"?

Seems a good discussion to me.

[Goofy]

Well, I’ll jump into the deep end just for grins. I’ve not attempted to investigate the issue but have some observations that support the OP in general terms. 170 gr jacketed bullets from my Mod 94 Trapper use more powder and are slower than 180 gr gas checked cast. It’s not a big difference in velocity, around 50-75 FPS, but I think the surprise comes in seeing this with 3-5 grains less powder. Why? Haven’t a clue, but it’s chronograph data, not my imagination. I normally shoot 5 shot groups. I have seen similar results with a Marlin 94 shooting the .25-20 Win, but in this case the J-bullet is 75 gr and the cast is 85.

It is what it is and I couldn’t care less. YMMV

[44MAG#1]

I have posted data and it was quite rapidly started to be picked apart.
I hesitate now to post any data on anything that I have obtained.

[dtknowles]

When I post data. Data is data. People can try and pick it apart but that does not change the data. Ask questions that is fine but don't insinuate that I am not posting the facts. Exceptions are made for groups sizes. I don't believe any group sizes that don't have corroborating witnesses with multiple repetitions. One group is meaningless. Averages or aggregates are what matters.

Tim

[Larry Gibson]

I have posted data and it was quite rapidly started to be picked apart.
I hesitate now to post any data on anything that I have obtained.

Yup, happens all the time to most all of us.....look at what happened to the data I posted in the recent thread about using SR primers in the 9mm. As with dtknowles, I certainly don't mind anyone asking questions or analyzing the data. I'm more than happy to answer questions where I can. I also don't think anyone should object to a analysis that might differ from theirs but should discuss it intelligently because we all may just learn something in the end. In the case here, the OP has posted velocity from only a one shot test using one bullet and comparing it to the velocity of another using a different bullet, both with the same load. Based on my own extensive experience chronographing thousands of different loads since '73 it is my opinion attempting to draw any meaningful comparison as why the discrepancy between the two velocities is not really meaningful.

No criticism of anyone who is trying. because as I stated earlier it is unknown what the ES of each of those loads actually is. Additionally, I have done considerable velocity/pressure testing of different cartridges attempting to answer the question as to whether, with a given load and similar weight bullets, using jacketed bullets results in more pressure and less velocity than cast bullet or visa versa or any combination of pressure and/or velocity. So far my testing has shown there is no rule of thumb to answer that question. Sometimes there is more pressure and more velocity with either bullet, sometimes more pressure and less velocity and sometimes there is less pressure and more velocity. Just too many variables to get a concrete answer.....

The data I post is factual based on velocity and/or pressure testing I've done myself. I have a MagnetoSpeed, 2 different Oehler chronographs and the Oehler M43 PBL which measures velocity pressure and a myrid of other internal and external ballistics. Problem is, while the data speaks for itself, many misinterpret the data or take offense because it goes against their preconceived ideas based on the writings in gun magazines/books. Sometimes the discussion can seem heated but if personal attacks are left out I don't mind. As my daughter used to say; "no sense getting a wedgie over it".....

[44MAG#1]

And so it goes in the world of firearms, ammunition and reloading/handloading.
And the world of Confimation Bias among us.

[Goofy]

Kinda like flying a chopper inverted. First time doesn’t tell you much other than it’s fun and you want to do it again. Question that puzzled me, is that flying or controlled falling. Anyone know?