Par for the course I guess...

All the best with these projects Paul.

Looks like some serious patience is required.

At least you have the freedom to pursue you interests freely.

They are going to be introducing a law here that if you make your own firearm at home you'll get 10 years. Now it's a good law for criminals but not sure how it will impact on LAFOs. But I'm off the topic.

I'm certain you'll resolve any issues you have with your firearms. Very interesting reading. Waiting for the next chapter.

Cheers

I've been doing A LOT of number crunching since the last range session trying to find something that works! What has become patently obvious is that "what is, is what is". In other words, there's only so much that can be done with the .308 Win case, and what I've got ballistically with the 8mm-08 is what I've got. Live with it, or move on.

I was (and, truth be told, still am) looking at the 8x284 Win. That case has sufficient capacity to drive the 220 Sierra at e speeds faster than I need to achieve 1500 ft-lbs at 300 yd with an impact velocity in excess of 1850 f/s. However, there is really no cartridge that 'ticks all the non-ballistic boxes' that I want ticked except the .308 Win/8mm-08.

Ballistically, 'things' were just enough marginal with the heavy ones that I kept looking. Generally speaking, when you go down in bullet weight you lose BC which means down-range impact energy and velocity suffer. Too often, too much loss in energy and impact velocity. As I moved down in weight from the 220 Sierra, I kept losing ballistic ground FAST. The reason is the .512 BC of the Sierra bullet. Combined with the 220-grain weight, that bullet beats every other bullet hands down when you start reaching 'out there' to 250 and beyond. All of the high-BC lighter weight bullets are boat-tails, and the extra length of teh boat-tail consumes too much case capacity. Lighter weight (than 220) flat-based bullets don't have the BC.

I was thinking about how I use the 130-grain HP in the .308 Win with great success for caribou, and figured I'd just keep going down and at least LOOK 'til I got to the 125s. Seems like a similar bullet SHOULD be able to be found for the 8mm. I looked at the Speer 150 spitzer (#2277). Hmm... that looked pretty good actually. Here are the paper-whipped numbers:

For a 23" barrel:


For a 28" barrel:


Good energies and impact velocities out to at least 275 even in the 23" barreled version. The combination of lighter weight AND flat base (for increased charge), allows the 150 to do a pretty good job while staying below the OAL limit of 2.810".

According to QuickLOAD (QL) I only gain about 140 f/s by lengthening the barrel by 5". Still, I might be inclined. I'd like to be well over 1000 ft-lbs at the maximum range I would use the rifle (300 yd). The 23" barrel barely gets there, while the 28" barrel has some 200 ft-lbs to spare.

Annoyed by pressure issues, I decided to get 'aynal' and instead of measuring the case capacity of several cases and taking an average, I am measuring ALL of them and tuning the charges to each case. Of course once 'the dust settles', I'll go back to practical, and use an average value. Also, I'm not comfortable using QL's bulk density values for the powders. So, once I have decided on a powder - and I have, CFE223 - I am determining case capacity using POWDER, not water. That ensures another level of precision that using water and then relating the bulk density of the powder to the water confuses if the bulk density value isn't 'perfect'.

So... I have loaded 5 rounds with charges predicted by QL based on each case's capacity of CFE223. (The above charts were created using the predicted MVs from those charges.) Each case was trimmed to a uniform length of 2.004". Each bullet was seated based on the 8mm (0.315") diameter point in the bullet's ogive, for an OAL of 2.775". (2.810" is the max that will fit in the magazine.)

It's been raining in biblical proportions for the last three days, so I haven't been able to get back to the range. It's supposed to clear up tomorrow, so maybe I'll get back to the range then. I might make 28" barrel from one of my milsurp take-offs tomorrow. I'm also thinking about milling a "single shot" follower for the AR-10 magazine. Were I to 'single load' the AR, I could use cartridges up to at least 3.25" long. That, coupled with a long barrel makes for a MUCH longer-range rifle. BUT... it would strictly be 'hand-fed', one at a time.

I still need to extract the case from the .358 Steyr chamber and shoot the Riedl to check on 'tumbling'.

Paul

By the way... Notice the difference in muzzle energy between the two barrel lengths and the difference in impact energy at 300 yd. At the muzzle, the longer barrel - due to increased velocity - has 280 foot-lbs more energy. One can certainly 'feel' 280 ft-lb.

However, at 300 yd, there is only 135 ft-lb of difference between the barrels. Pretty close to half the difference. That shows how muzzle velocity advantage is diminished due to the BC CHANGING with velocity. In other words, as the bullet moves down-range and slows down, the BC changes to lower and lower values. Therefore, the differential between a "fast" MV and a "slow" one is reduced the farther down-range the bullet travels.

By the way, here's why I'm still looking at the 8x284 Win:


And if the AR could easily handle "magnum" head diameters, 3700 f/s MV:


LOVE light-for-caliber bullets going really fast! :D

Paul

Quote from: gitano;140709LOVE light-for-caliber bullets going really fast! :D

Paul

:grin: who'd a thunk it!!!

RJ