Newly Energized Interest in "Fiddling"

Started by gitano, January 29, 2021, 09:23:09 AM

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gitano

#15
Good to "see" you, Nels!

You have me over a barrel with cast bullet stuff. You well know that I've never had much luck down that path. If I was sticking to 6.5 caliber and a Mauser milsurp action, I'd be hard-pressed to deviate very far from the x57 case.

That said, if I were considering cast bullets at 2000-ish f/s muzzle velocities, I'd look hard at the 7.92x33 Kurz case. A case I know you have 'fiddled' with before. Which, has me thinking about that case again!

Paul
Be nicer than necessary.

Nelsdou

I actually got to handle a 7.92x33 Kurz chambered K98 once, assembled as a replica by a collector. My understanding is that the bolt action carbines manufactured in this chambering were late war and very few in number. If I remember right the one I examined had a block in the magazine to assist the bolt head in cartridge pick up.

The downside to the 7.92X33 for cast bullets is the short cartridge neck which makes it easy for the typical cast bullet to misalign during chambering. Instead of wildcatting the cartridge I thing I'd rather run with a more standard cartridge.
I love my Super Kurz, but it gets to be a PITA to manufacture the individual pieces from 284 brass.

For this 6.5mm barre I was dreaming about a 6.5x47 Lapua since it is a .473 case head and similar length to a 308 that feeds reliably in a Mauser action. The 6.5x47 in a 10 twist barrel should be able to push 140g cast bullets using moderately fast powder or jacketed bullets not exceeding 129g at high velocity.

 But when I consider the possible costs in reamer, gauges & gunsmithing, I can buy a chamber cut 6.5x47 barrel as a switch barrel for my Savage for about $300. I'll ponder with the analysis-paralysis in the mean time.
Put it into perspective; we live on a rock hurtling through space, what could be scarier than that?

gitano

Yup. I forgot about the general need for long necks in cases for cast bullets.

The 6x47 is "good", as almost all of  'them' are good. :D Nowadays, I just can't get around the .338x57 MAI in a Mauser action. (Or most other bolt actions for that matter.) I really don't care about the Ackley Improvement, but it does allow more positive cartridge seating, and it is supposed to improve case life. Although, I find that if I don't hot-rod a cartridge, I don't have any problems with case life. Besides, the cases I have now are likely to outlive me!



Paul
Be nicer than necessary.

Nelsdou

Before discarding the suggestion by Paul on the 8x33 Kurz,  I  checked the LW barrel website where they have 98k military drop in  c-moly barrels chambered in 8x33 Kurz for $256.50. Not sure about the  "drop-in" description, I assume one would need to check fit and do a  final finish ream on installation.
Anywho, I was bit surprised  by the availability and price, and I just happen to have a post-war  Czech 98k build that has the characteristics of a late war 98k carbine  with laminated stock, stamped metal barrel bands, stamped steel trigger  guard and a bolt that lacks the center guide rib. If I re-chambered it  to 8x33 Kurz I could have a close clone/example of a last ditch WW2  German carbine.


 The LW barrel is a 4 groove .311/.323 bore and  9.4 twist in a 600mm or 23.62 inch length. I don't understand why the  need for 9.4 twist with standard 125 grain pills for this cartridge but  it is probably a carry over twist from the 8x57js barrel design. With  that in mind I went into QuickLoad to see what I could wring out with  this barrel/cartridge combo.

The rated pressure for this  cartridge is 49,300 psi, a limitation which I suspect is due to its  application in the automatic/semi-automatic weapons of the era, and not  by its use in a bolt action rifle. However I used that limitation in my  QuickLoad analyses because small deviations in powder loads in small  cartridges can make big changes in pressure. By using a variety of fast  to moderately fast powders I came up with 2,500 fps for the 125g Hornady  bullet, 2,200 fps for the 150g Hornady bullet and sub-2,000 fps for the  200g+ bullets. Now what I found fascinating about the 200-220g bullets  in this cartridge was being able to attain subsonic performance  fairly easily (1,000 fps) using fast pistol powders. There are several  heavy 8mm bullets with high BCs that make this interesting and this  particular barrel provides plenty of twist to help stabilization.


I  have no experience in tuning a subsonic rifle load or modulating the  rifle sights to compensate for the drop but this could be interesting to  learn. One question I have on the big pills is the barrel groove depth  of .311/.323. The Shilen barrel I used on my Super Kurz was a six groove  at .315/.323 barrel intended for 8mm magnum bullet choices. Could  squeezing the heavier 8mm bullets down the .311.323 barrel be a  challenge at the pressure regime to attain subsonic speeds?
Put it into perspective; we live on a rock hurtling through space, what could be scarier than that?

gitano

In a word, "No". However, maybe you are aware of the option in QL to input barrel-specific information including number of lands and groove depth. I would encourage you to use those options to get the best data out of QL.

Second, at MVs below the speed of sound, AND shooting at ranges less than 300-ish yards, BC  is essentially irrelevant. That said, I would still use the Sierra 220-grain Game king if I could get what I wanted in terms of internal and external ballistics. However, since you're interested in cast bullets, the two Lee bullets, I think they're 230 and 250-grains, should be great subsonic candidates. I wonder how those deep grooves will effect leading?

Paul
Be nicer than necessary.

Nelsdou

Thanks for the advice Paul.

I checked the bore cross sectional area in QL given for the 7.92x33 and it matches most of the other listed non-magnum 8mm cartridges using .311/.323 dimension barrel bores. My reference books on military Mausers appear to correlate to that value as well and depicts four groove/four land machining configuration with the grooves considerably wider than the lands. However QL provides a slightly larger bore cross sectional area for the 8mm magnums, such as the 8mm RemMag. This is consistent with the 8mm barrel I received from Shilen that is .315/.323. I agree the differences in bore cross sectional area appear to be very small so the bullet engraving forces and deformation differences are insignificant.

But I started to wondered about bullet seating and the effect upon powder volume in this small of a cartridge.

I have a Husqvarna 8x57 sporter rifle that is .311/.323 and shows little to no throat wear.  I ran some checks on bullet seat outs using a Hornady OAL gauge. Using a Hornady 150 and 195 spiral points and Sierra 220 boat tail I quickly made contact with the lands. Both the Hornady 150 and 195 bullet contact with the lands occurs right as the bullet crimp cannelure meets the cartridge neck lip. The OAL for the Sierra on contact with the lands is 3.050”. In my Shilen barrel, I can seat all of these bullets out easily to some degree.

So my take is that depending how one finish reams the LW barrel, there likely isn’t much wiggle room on 7.92x33 case volume from what QL indicates.

To make a decision on subsonics, it will take some more playing with the powder and bullet choices to strike a reasonable case. I’m not interested in a subsonic if it requires a great deal of handloading precision to attain. Hopefully my analysis will indicate where the sensitives lie.

When it comes to cast bullets, my favorite 8mm is a silhouette style from a past Cast Boolit group buy.  It is a 195g bore-rider. The bullet nose expands to .316~.318 then about midway its length it taper expands to .325~.326 into the lube grooves and base. Works great in deep four groove Mausers however I believe the key to this bullet is the bore rider keeping the bullet centered on launch. Although this cast bullet fits smooth to snug in my military Mausers, it will not feed into my Husqvarna sporter.

I don’t know if this is due to the Husky having a different throat configuration than the military Mausers or it is a difference in throat wear. Again, it may come down to what kind of throat the LW barrel is configured to.
Put it into perspective; we live on a rock hurtling through space, what could be scarier than that?

gitano

I don't want to belabor this, Nels, but I do want to make sure we are actually communicating. When I refer to the ability to input specs for an individual firearm, I'm talking about this page:


Accessed from this page:



And unique case specs input from this page, accessed from the same page above:
 

Am I correct in assuming you're using those input portals?


Paul
Be nicer than necessary.

gitano

#22
I have no feel for how bore cross-sectional area, (hereafter, "BCSA"), relates to max chamber pressure, (hereafter, "MCP"). Neither did I know whether QL actually USED the BCSA when calculating internal ballistics. Just because it allows adjusting/setting it, doesn't mean it uses it in its calculations. So... I decided to do some fiddling with QL to see if and how MCP varied with BCSA.

Using the QL input portal I posted above, I started with an 8mm bore with groove diameter of 0.323", (groove depth of 0.006"), bore diameter of 0.311", 4 lands and grooves, groove width of  0.1645" and land width of 0.0845". (Approximately a 2:1 ratio.) The resulting QL-calculated BCSA was 0.080110 square inches (51.6841 square mm). Changing only the groove depth to 0.004", (groove diameter of 0.315"), the  calculated BCSA was 0.080693 square inches (52.0604 square mm). The difference in square inches was 0.000583 square inches (0.3763 square mm).

I then had QL calculate a load for the 7.9x33 Kurz, (the bullet, powder, and charge don't really matter for comparing 'apples to apples' as long as they are the same for both bores), and then had it calculate MCP for that load with the two different BCSAs.

With the .315" bore, the calculated MCP was 49,391 PSI.
With the .311" bore, the calculated MCP was 50,066 PSI.
The difference is 675 PSI higher for a difference in BCSA of 0.000583 square inches (0.3763 square mm).

The magnitude isn't really too important relative to what I was suggesting, which was that you can get 'better' data out of QL by setting all the input parameters as close to real as possible, and QL allows one to do that for BCSA. One might argue, and I would agree, that an increase of 675 PSI is "decimal dust" relative to the other sources of variance in the calculation of MCP. Nevertheless, internal ballistics are 'finicky', and when doing timing calcs for finding precision sweet spots, I am willing to tweak all the knowns I can in order get output that is as close to observed as I am able to get.

After this little exercise, I now have a rough idea of how MCP varies with BCSA, and I know that QL does in fact use the BCSA in calculating internal ballistics.


Paul
Be nicer than necessary.

Nelsdou

Yes, Paul, I'm using the same QL data file pages that you are referring to. My QL is V3.9 but the pages appear to be the same.

Instead of calculating different bores in the 7.92x33 file I compared the difference from it to the 8mm Rem Mag file because I had established a benchmark to it from my Super Kurz project barrel based on measurements. Back on that particular project I took the cut off barrel stub and by using pin gauges validated a .315 bore and estimated the land/groove widths by wax impression. By manipulating any of the mauser cartridge bore cross sectional calculators using .323 grooves, inputting a .315 bore and the associated land/groove width estimates I came up with .08086 which is coincidentally close to the QL data base file .080864 given for the 8 Rem Mag (and 325 WSM, as well).

With the information from the LW catalog on the 7.92x33 having .311/.323 and four groove, I simply compared the two QL data files, 8 Rem Mag and 7.92x33:  .080864-.080259=.000605 or about 0.7% difference in cross sectional area. In my judgment that's fairly insignificant, but I do appreciate that you actually calculated it fully out to derive pressure using the base 7.92x33 cartridge file itself.

One thought is that the difference in pressure (or portion thereof) is consumed in engraving the bullet, similar to the QL value for shot start initiating pressure, but again, likely not of much significance.

As a side note and due to the weather lately and being stuck indoors, I've been cleaning and oiling firearms. For grins, I pulled out a post-war Yugo 98k from the safe that appears to be near new in appearance and finish, and checked by pin gauge to have a tight .311 bore. Using my Hornady OAL guage, this rifle accepts bullet seat outs a bit more liberally than my Husky sporter, but nothing that I consider excessive either.  I am beginning to think that my Husky sporter was cut to minimum throat specifications.
Put it into perspective; we live on a rock hurtling through space, what could be scarier than that?

gitano

Yeah, I'd agree that 0.08086 is 'pretty close' to 0.080864! :D Also agree that the delta of 0.000605 is 'insignificant'.

Your Yugo with the .311 bore is going to have me checking all of mine now!

Lots of 'stuff' to fiddle with, but like I said, when I finish paper-whipping all sorts of things, I have a difficult time turning away from the .338 MAI. About the only thing I like as much is the .338-06. In fact, I consider the -06 version to be 'not quite' as good, and that's NOT because of my attitude about the .30-06. I think the shorter Mauser case is 'better'. The extra 6mm of the 06 case doesn't really improve anything because the 57mm case "gets there" without excessive pressure. The longer '06 case is just that - longer. Nevertheless, the .338-06 is my second-favorite .338 cartridge. ;)


Paul
Be nicer than necessary.

Nelsdou

I consider my 9.3x57 swede to be a distant (low pressure cousin) to your 338MAI but in the past have not gotten it to be much better than "average" or 3~4 MOA at 100yds with iron sights. Before chasing a new cartridge, I may hone back in on that one and see if I can do better. It's in excellent shape for an old rifle and very easy to handle in the field. For a while I played around with .367 cast lubed and .358 paper-patched bullets but never achieved very consistent results. With more powder choices in QL and exercising greater precision on the barrel inputs, I think it is worth a swing. I've got three different jacketed bullets and and a new .368 260g cast bullet mold to try. Couple of challenges is how to account for the amount of freebore that this rifle has and the fact that the cartridge does not have much of a shoulder that may influence its modeling closer to a straight wall case. Anyway, it's worth a dive back into my shooting notes and QL analysis.
Put it into perspective; we live on a rock hurtling through space, what could be scarier than that?

gitano

Sounds like fun, Nels. I recall your accounts of the 9.3x57 Swede. The following is not intended to be "selling" the .338 MAI cartridge, just my observations/rationalizations.

Once I broke through the psychological .30 caliber barrier, I started looking at all the bigger calibers. In the end, I settled on the .338 primarily for external ballistics reasons. The 'big deal' for me is that the .338 has more high-BC bullets available than the bigger calibers do. There's not a single .35-or-larger caliber hunting bullet with a BC higher than a couple of .338 bullets, regardless of the weight of the bigger caliber bullets. (There is an 'experimental' .416 FMJ BTSP target bullet with a crazy BC over 1, and of course the .50 BMG, but really now. :no: ) Add to that the terminal performance of the Accubond, and the .338 lands right in the 'sweet spot' of delivered energy, trajectory, and 'friendliness-on-my-end'. Put that .338 bullet on a "nice" case like the x57 Mauser case, and voila', you get my favorite hunting cartridge. (It also doesn't have a shoulder akin to snake hips like the larger calibers do when put on the x57 case OR the -06 case. Meaning, as you point out, positive headspacing from cartridge to cartridge.) By the same token, .338 doesn't 'go down' from the 57mm case particularly well. On the 51mm case of the .308 Win, the case capacity is just on the small side for those high-BC .338 bullets. Barely, but too small, nonetheless. In a barrel of reasonable length, it simply can't drive the 200g+ bullets with the high BCs, fast enough to compete successfully with the 57mm case.

Like I said, I'm not 'selling' here. Just explaining why I have become infatuated with this cartridge and why I haven't moved on up the caliber ranks in seeking a "better" general big game cartridge for North America.


Paul
Be nicer than necessary.

Hunterbug

Gitano, a quick look just showed me that Grafs has the Hornady. 330 205gr bullet in stock.
Ask not what your government can do for you. Ask how your government can go away and get out of your life.
 
 
The unarmed man is is not only defenseless, he is also contemptible.
Niccolo Machiavelli

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