6.5x55 Challenges

[Zeek]

I have a couple of these slinky Model 1896 Swedish Mausers. They are really fun to shoot with J-words, but tend to be heavily twist-limited with (cast) boolits ~~~> loads limit-out (highest MV with easy GC boolit accuracy) at ~1400 fps in the same way that most other chamberings limit out at ~2100 fps. Heck, even hard-as-the-hinges GC boolits gave only plinking accuracy at 1900 fps. That ~1:7 twist poses a serious limitation!

So, I thought that I would try PPCBoos instead, given that the paper jacket should be able to transmit torque far better. I tried from near-max pressure down to ~40 Kpsi loads on a Lyman 266673 (from air-cooled WW+Sn alloy using a 2X adhesive label PPatch with GC added) and got precisely ZERO positive-performance indications throughout that pressure range.

I sure would like to hear if anyone knows a means for achieving even 3 MOA accuracy, in the 6.5x55, with a PPCBoo load having an MV anywhere over 2100 fps.
Thanks for any help that you can provide,
Zeek

[StarMetal]

I have a couple of these slinky Model 1896 Swedish Mausers. They are really fun to shoot with J-words, but tend to be heavily twist-limited with (cast) boolits ~~~> loads limit-out (highest MV with easy GC boolit accuracy) at ~1400 fps in the same way that most other chamberings limit out at ~2100 fps. Heck, even hard-as-the-hinges GC boolits gave only plinking accuracy at 1900 fps. That ~1:7 twist poses a serious limitation!

So, I thought that I would try PPCBoos instead, given that the paper jacket should be able to transmit torque far better. I tried from near-max pressure down to ~40 Kpsi loads on a Lyman 266673 (from air-cooled WW+Sn alloy using a 2X adhesive label PPatch with GC added) and got precisely ZERO positive-performance indications throughout that pressure range.

I sure would like to hear if anyone knows a means for achieving even 3 MOA accuracy, in the 6.5x55, with a PPCBoo load having an MV anywhere over 2100 fps.
Thanks for any help that you can provide,
Zeek

Hi Zeek,

I suggest you read this thread:

http://castboolits.gunloads.com/showthread.php?t=64315&page=2

Joe

[303Guy]

PPCBoo - I like that one!:D

Have you considered/tried firelapping your bore?

How is the crown and last bit of bore?

I would suspect that the initial bore is somewhat larger than the bore at the muzzle due to wear. That is the case with my relatively new 303 Brit barrel (after 500 rounds of MkVIII machine gun cordite ammo!)

I determined the boolit size and shape by making a brass measuring rod with a mike'd end and measured how deep it entered. Then I turned off an increment and measured again until I had the throat and initial bore profile. I then made my mold to produce a boolit that size and shape with the heel section large enough to fit an unsized case neck. I then gave that boolit a layer of 'waxy-lube' which secured the boolit into the neck and contacted the throat and leade. When I switched to PPCBoo's, I used the same finished profile (or similar, anyway). This means the PPCBoo is tapered with a 3° step-down between the rear section and the bore-ride section which is also tapered to suite the initial bore. Work pressure has halted my testing for now but I can say that the recovered boolit shows good conformity to the bore. (This PPCBoo will actually headspace on the leade if seated too long). On firing, the rifling engraves into the bore-ride section and the paper comes off in small shreads even at low velocity.

That's not to say this will work for you, it's just the path I have taken.

I should mention that I size my prime castings. (That way, any bent castings get straightened and any casting weight can be used - only the bore-ride section varies in length. All my PPCBoo's seat to the same depth and just contact the leade and bore on chambering).

I hope this may be of some help.

[Zeek]

Hi Zeek,
I suggest you read this thread:
http://castboolits.gunloads.com/showthread.php?t=64315&page=2
Joe

Thanks, Joe. That helped quite a bit! I think I see quite a bit from the traces. If I am reading it correctly, then I see your point, as I have run into difficulties once when experimenting with that approach. If I try it again, it will be with FAR more caution. My problem is that most of my CBoo and PPCBoo R&D is for gunzene articles that I hope to write, and a success produced by following that approach would be useful only to me ~~~> no write-up is doable.

When working up loads under such an unpredictable approach, I have found a qualify blade micrometer (across the casehead at the same spanned place each time ~~~> and just barely forward of the extractor groove) to be the best pressure indicator. My rule is to never accept more than 0.0002" (two tenthousandths) free casehead expansion, as that is about what you can expect on most factory loads, in before/after measurements at that location. You have to practice with your blade mikes to get that reading reliably/repeatedly, but it IS doable.

Most other pressure indicators are extremely fickle, but THIS indicator, because it measures free-expansion is the gold standard. Think of it this way, if your load will give 0.0002" casehead expansion there, then in 10 shots the primer pocket is going to be perhaps a bit less than 0.020" larger in diameter (= no longer functional). Yes, Matilda, that IS a maximum functional load, and it is wise to keep a grain or so shy of that point for ANY load, especially if you get that indication on a cold day at the range!
Thanks again,
Zeek

[Zeek]

- I like that one! (PPCBoo):D

Have you considered/tried firelapping your bore?

How is the crown and last bit of bore?

This Swede shoots like a champ with J-words, and also shoots like a champ with GC CBoos, but only with light charges (e.g., 15 grains of AA-1680 and a lively primer = ~1400 fps). Therefore, there is no crown or near-muzzle problem. I may work with some JB Bore Paste on PPCBoos to smooth it out a bit, as the bore looks okay-but-not-bright.

The from-hell combination remains: scarry-quick twist; and deep-for-the-caliber rifling.

Talking about "caliber," please put up with my rant. "Caliber" is a measure, in 100ths of an inch, of the diameter of either the bore or the groove diameter of the barrel. One can chamber a 30 caliber barrel (nominal bore of 0.300") in any number of CHAMBERINGS, including: 30-30, 300 Winmag, 308Win, and 30-06, not to forget the incomparable 308 Transpuckerfier. So, "30-30" is NOT a "caliber"; it is a "chambering," and any real gun crank should know the difference. The only exception is a muzzleloader, for which one speaks ONLY of its caliber, given that it HAS no chambering. 303Guy, I have not seen YOU pull that way-Bozo ploy, but it is so very common, nowadays, that I thought it worth bringing up.
Regards, Zeek

[303Guy]

So, "30-30" is NOT a "caliber"; it is a "chambering,"You are so right! I never thought of it like that before. Yup, 'chambering'! I like that.

It's interesting how these 'funny' names of cartridges came about. Like the '38 special'. It's a .357 caliber! But the name came from the 38 which was a true 38 with a healed bullet just like the 22 LR. then the same case was used for a 'seated' bullet which happened to be .357 to suit the internal dimensions of the case mouth. So, same case, different bore, same name! 250 versus 257 !? And so on.:roll: But it's all fun!


My problem is that most of my CBoo and PPCBoo R&D is for gunzene articles that I hope to write, ...I do wish the best in that endeavor!:drinks: