6.5mm ARP Wildcat Range Report - Update

Andy

Andy

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Very preliminary, but encouraging and pretty much as predicted. The 6.5mm ARP is essentially a 6.5-300 Win Mag with the belt removed (2.620" length). No special dies needed, just neck down 300 Win Mag brass with a 264 Win Mag sizer and trim off the belt. No special expensive dies needed - F/L size with 300 Win Mag dies followed by 264 Win Mag, and neck size with 264 Win Mag neck sizer.

I removed the belt for two reasons (neither of which will make it shoot better than a 6.5-300 Win Mag): to see what was involved and how it would feed; and to make its appearance match its big brother the "8mm ARP" which is based on the 300 RUM case. Like all wildcats, it's nothing new, and my name for it "6.5mm ARP" has some vanity attached to it.

Case capacity is approx 90.0 grs H2O full to the top, so it has about 8% more case capacity than the 264 Win Mag. All things being equal, I should see about 2% more MV than the 264 Win Mag, or between 50-75 fps. If I get more, it's because of higher pressure. My platform is based on a Mauser action and sports a 24" barrel, so I am aiming to match published 264 Win Mag loads with a 26" barrel.

Here's a comparson:

L to R - 6.5x55 Swedish, 6.5mm ARP, 8mm ARP

6-5x55_6-5mm_ARP_8mm_ARP.jpg


As for powder choices, here's a comparison of Expansion Ratios (ER) of a variety of "overbore" cartridges. Generally cartridges of similar ER are suited to similar powders, in this case slow powders.

Expansion_Ratios.jpg


My initial powder choices were the slowest Hodgdon powders. Here's what I got:

6.5mm ARP, 120gr Nosler, 3.365" OAL (just off the lands), 24" barrel, 0 degrees C

H4831 - 67.0 grs - 3275 fps
H1000 - 72.0 grs - 3290 fps
Retumbo - 75.0 grs - 3370 fps
H50BMG - 81.0 grs - 3270 fps
US869 - 83.0 grs - 3300 fps

I'm guessing that a 140gr bullet would go about 3200 fps with the right powder.

I got erratic readings from the H50BMG and US869 in that the readings were not linear (i.e. MV would go down, then up again as powder was added), so I will re-do them to see if it repeats.

The reamer was designed to give an OAL of 3.500" with the Hornady 160gr RN. Being that it's a "bore-rider", the throat limits single diameter bullets like the typical 140's I'd use to a shorter OAL. As I won't make much use of 160's, I'd like to lengthen the throat so that I can an OAL of at least 3.450" with the 140's. The next barrel will be at least 28" long.
 
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Andy,

This is interesting. Other than appearance what did you learn about removing the belt from the cases? Seems to be a lot of extra work even if you have a lathe to use. Was there a big difference in feeding?

Wouldn't the erratic velocities with H50BMG be because the powder has rather large kernels designed for a much bigger case?


Fudd
 
ElmerFudd said:
Andy,

This is interesting. Other than appearance what did you learn about removing the belt from the cases? Seems to be a lot of extra work even if you have a lathe to use. Was there a big difference in feeding?

Wouldn't the erratic velocities with H50BMG be because the powder has rather large kernels designed for a much bigger case?


Fudd
Click to expand...

I didn't learn anything about feeding improvement by removing the belt, as I didn't have a belted "control" round with which to compare it. Intuitively I believe it will feed better, but I can't prove it. My belted 300 Win Mag feeds more than well enough, so that says something. Removing the belt causes this round to headspace on the shoulder as opposed to the belt, but that can be achieved in belted rounds as well. In fact the belt is an advantage for wildcat rounds that must be fireformed. I simply did it to see what was involved, and for looks - so that it would look like its big brother the 8mm ARP. I like it and do not regret the decision. Removing the belt was a one minute job. You can do it in a bit longer with a drill press and a file.

The erratic MV's with H50BMG and US869 with the 120gr bullet was due to low pressure. Once pressure got into those powder's "working zones" the MV's settled down and were consistent, but that didn't occur until the case was almost full (those powders are better with heavier bullets).
 
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Wow, this round really wakes up with Hodgdon US869. It's burn rate is a bit slower than wet charcoal and it takes a full case, but I am very impressed with the results, all with a 24" barrel:

120gr - 88.0 grs - 3580 fps (Full Case - perfect)
140gr - 83.0 grs - 3310 fps (Full Case - perfect)
160gr - 82.0 grs - 3150 fps (90% Full - if such a thing existed as a slower powder, I'd try it)

I cringe when I hear of people "who got" a certain MV and with "no pressure signs", and I am guilty of the same here. I can at least say that I have no primer pocket loosening after three firings and I did after three with some published 264 Win Mag loads (a smaller case), so I am comfortable that the pressure is sane.

With a 28" barrel, I can see 3450 fps with a 140gr and 3300 with a 160 gr.
 
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todbartell said:
very cool :D won't run into too many other guys out there who have a rifle so chambered
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That's true, but there are a few others (some in Canada too). To be honest though, it would have been a lot more practical to just buy a factory 7mm RUM if I wanted a big-ass cartridge in a small(ish) bore rifle. Instead of a 140gr, use a 150, and instead of the 160, choose the 175. Factory brass, dies - you know the story.

Except I wanted a 6.5mm........... ;)

P.S. my 8mm ARP ROCKS with that US869. A full case (104 grs) pushes a 200 gr at 3250 fps and a 220 at 3150 fps!
 
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Andy, another great wildcat project. That is all that needs to be said.

Fun, Fun, Fun....

How has the accuracy been?

Have you looked at the Steyr 375 case? That is pretty much a beltless magnum case. A number of wildcats have been based off this but I don't know if brass is available anymore?

Jerry
 
Jerry,

Yes it is fun.

To this point the load development has been pretty one-sided towards muzzle velocity. The accuracy is "good" (about 1 MOA for the one five shot group where I tried), but it's a fairly light rifle and the recoil is enough that it affects me. I imagine my best groups will come well below max loads. I have a much heavier 308 and I don't think I'll ever shoot this one as well as I do it.
 
Outstanding info, Andy!! It's no secret that I like the 6.5 bores a lot, and have had several 264 Win Mags over the past 30 years. Some were slower & some were faster, but a 26" barrelled 264 will make 3250 (140 gr) or so with a full case of some of the real slow burners. I was fond of H570 originally, and when that dried up, I went to H5010. Later, I had some excellent results with Retumbo and Vihtavuori N170. I never had a 28" barrel on one, but built one with a Pac-Nor at 26½" (1-9" twist) It would break the 3300 barrier with the same 140 grain loads as the shorter barrel made 3250 with. I would be tempted to build a long range wonder with this case. Some of those 6.5 match bullets should be just great in a 1-8" twist with a 30" tube. Regards, Eagleye.
 
So now I have to buy H - US869 and get my chrony fixed.Mine has the same case dimentions/case capacity but has a belt.I also have a 26" barrel.

Rich

Andy are you coming to Calgary Show this year?
 
RR said:
So now I have to buy H - US869 and get my chrony fixed.Mine has the same case dimentions/case capacity but has a belt.I also have a 26" barrel.

Rich

Andy are you coming to Calgary Show this year?
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Rich,

You're one of the guys in Canada I was referring to. ;)

Yes, you've got to try it. It's mucho slow, but also very dense and packs well, being spherical, so you can put a lot in the case. I'd love to hear how it works for you.

As for Calgary, I've got to go some time, but not this year, I'm heading to Tulsa in three weeks. :D
 
Can you guys give send me some data.. I too have a 6.5-300 WM and am just about to start loading it.. I was planning on using US869 and what I have read seems to validate that thought..

I plan to shoot 142 and 150-155gr wildcat bullets..but may shoot lighter just to try it out.

I used a Parker Hale 1200V and had the barrel rerifled to 6.5 and the 6.5 300 chamber cut.. 24"barrel..

I'll try to post a pic or two when it is done..

But please send any and all data.. blygy@yahoo.com

Thank You
 
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Have you tried the powders Andy mentioned above ?

If trying US869 with 140-142gr bullets I would start Around 70gr and work up watching for pressure signs.

let us know how it turns out !
 
I sent some info with the usual cautions/caveats.

I'd start lower than my maxes for sure given that every gun is different (chamber, throat, barrel, etc.) and that I deveopled my loads in the winter (cold = lower pressure, hot = higher pressure).

Still, I'd start at 75.0 grs. With US869, it needs a critical minimum pressure to operate consistently, and I found that I needed 80.0 grs with the 140gr bullet for it to settle down.
 
Andy said:
I sent some info with the usual cautions/caveats.

I'd start lower than my maxes for sure given that every gun is different (chamber, throat, barrel, etc.) and that I deveopled my loads in the winter (cold = lower pressure, hot = higher pressure).
Click to expand...


I can just imagine how hot that barrel gets around this time of the year. My 264 is just scorching after a group of 3.
 
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