Mitdr774 Wrote:If my memory is correct, the bullet starts a gradual taper right at the cannelure. It might be a little in front of it though. Either way, it is enough of a taper to allow the use of such a long RN bullet without having to stuff it all the way into the case. From what I recall it seats about as far into the case in my 6.5 Grendel as it does in my 6.5x55 and the Swede has the original throating for the 156gr RN military ammunition.
Thanks for that, that does help. Im still about .100 less/shorter col on average in 3 bolt guns with the 140 HotCor. Which I thought, just eyeballing it, had a lot more taper. But then again, maybe it doesnt?
I'm guessing that if you used a bullet comparator you would find that the point of contact on the ogive would be drastically different between the two at the same overall length. If I have time tonight I can try and get some measurements on some 160 RN bullets.
05-04-2020, 04:02 PM (This post was last modified: 05-04-2020, 04:26 PM by iNheRchOnieS.)
Mitdr774 Wrote:I'm guessing that if you used a bullet comparator you would find that the point of contact on the ogive would be drastically different between the two at the same overall length. If I have time tonight I can try and get some measurements on some 160 RN bullets.
These are rough numbers using a generic resized Hornady case with a split neck and Speer 140 HotCor.
bigblock Wrote:I usually record my gas port diameters but I forgot on this barrel. I can say that the rifle cycled fine with a non-adjustable gas block with the brass coming out at 3 o'clock which is where I time most of gas rifles. The only timing mitigation was the carbine lower this was fired from has an H buffer. Im also not seeing any extractor strain on the case head or extr/ej swiping, which is usually the case with with latent pressure (and/or overpressure). Here is the predicted gas curve via QL. Im thinking its pretty close based on the previous.
As someone else noted, QL is predictive model that isn't failsafe, but the actual evidence I've seen so far hasn't tripped any wires for me yet.
I agree with you.
I looked at your quick load graph you gave and it looks like the velocity increase becomes constant, straight line, after 9.5 - 9.75 inches. No major acceleration of velocity because extra energy of burning powder. So if your gas port is after that point you should be OK. That would explain why you not having any problems with tubes breaking.
Mitdr774 Wrote:I'm guessing that if you used a bullet comparator you would find that the point of contact on the ogive would be drastically different between the two at the same overall length. If I have time tonight I can try and get some measurements on some 160 RN bullets.
You are correct the ogive is way above the cannelure.
![[Image: pressure-curve-160gr-HRN-16in.png]](https://i.postimg.cc/mzN3YYCW/pressure-curve-160gr-HRN-16in.png)