Additional Comments on Alloy & Pressure Matching for Accuracy, the Myth

Details and background can be found in this prior post. 

I noticed some interesting data from my test records: All data is from testing with my 357 magnum, a Taurus 66, 6inch:

With a 358-429 168 Keith bullet: the most accurate loads & alloy:

700X at 28-30,000 PSI wiht BHN 7-8
HP38 at 18-20,000 PSI with BHN 7-8

These two loads are capable of groups less than 1 inch at 25 yards, from a rest.  The reason I favor 700X is the consistency of the tight groups.  It's just a bit better.

With the same cast boolit, the most accurate load with the 2 different powders is with different pressure levels.  It turns out the most accurate alloy was the same for both pressures.  That makes the comparison very relevant to disproving alloy and pressure matching for accuracy.

The most accurate load for a 158 SWC is:

HP-38 at 24-25,000 PSI with BHN 7-8

This is another pressure level for the same alloy and is the most accurate load I've found for a Lee 158 SWC TL cast boolit.

Looks to me that the most accurate loads depend on "boolit design & weight" matched to the powder.  The pressure ranges from 18,000PSI to 30,000PSI for the same alloy.  This pressure range is not even close to the 10,370PSI the formula from Lee provides.

When pursuing the best accuracy, the calculations don't work in a 357 revolver.  Different pressure levels have proven to be the most accurate with the same alloy, when using the most accurate powders.  Maybe I'll have to refine that claim, however magnum/slower powders just don't beat or even equal 700X and HP-38 for accuracy.

Pressure and Alloy Matching for Accuracy. Fact or Fiction in a handgun?

The engineering on this topic is fun to read about and for discussion. There are BHN charts, lead deformation charts, calculations to provide obturation pressure, accurate-pressure and a way to determine the maximum pressure for cast boolits. However taking it to the range and validating something like "matching pressure to BHN for accuracy" to me reveals the truth of this widely accepted and commonly promoted & quoted “claim”.

The reason I even bring it up is there are plenty of articles and books about this that get read and then recited as fact.   Many people are trying to figure out what’s wrong with their gun because of their bad results at the range.  This concept is often promoted by pundits and then is passed along as fact in various online forums by folks that have assumed it's valid.


But is it?

First, the Context

My goal is the best accuracy possible and all my comments should be read with that in mind.  What I’m about to cover may not/will not apply to someone who has decided they need a max charge of H110 with their 158 or 168 boolit and want to then make it a bit more accurate, keeping it at the max charge.   


I have yet to get the best accuracy with full house loads therefore don’t work with them much, but hope to in the future.  But using a download charge of 10.3 grains of 2400 (168 Keith) is not bad with 1.2 inch groups at 25 yards very possible.  It’s a far cry from a max charge though and was derived by searching for the most accurate 2400 load, not trying to achieve maximum velocity.  


I hope that made the point and helps clarify the goal of this blog. 


What is Pressure and Alloy Matching for Accuracy?

Finding information that describes the approach is pretty easy.  Modern Reloading by Richard Lee is one of the better known sources so I’ll briefly give his formula.  Note that he tested with rifles and not handguns, just like many other proponents.  Richard Lee never claimed this works in handguns, as far as I know so this isn't a slam against him or the book.  From that, many others have assumed it applies to handguns too, they are the ones that promote this as fact:


BHN*1422*.9=Accurate-pressure for cast bullets, called Max pressure in the Lee book, another key formula is:
BHN*1422=Alloy-strength and part of the information distributed by Lee, also;

BHN*1920=Maximum-pressure for cast bullets (this isn't based on the Lee book and is much higher than the Lee alloy strength formula)


Based in these, the accurate-pressure for my BHN 8 alloy is 10,370PSI, the alloy-strength is 11,520PSI and the maximum pressure is 15,360PSI.  Using the same formula for accuracy the best BHN for a 30,000PSI load is roughly BHN 24.


Compare these numbers to the results. 


Testing in a 357 Magnum for Accuracy, Results 


After testing several thousand boolits of different hardness, different diameters, different OAL, with and without gas checks I have proven beyond any shadow of a doubt that, first, one of the most accurate loads with a 358-429, 168 Keith in my 357 magnum is:

A 700X 30,000 PSI  load is most accurate with BHN 7-8 (< 1inch groups using 700X) 


This is 3 times the ideal matched pressure/alloy and is 2 times the maximum pressure.  The results are starting to prove that pressure matching is a hoax, at least in a 357 Magnum revolver.


Now the question is, does lower or higher pressure perform best with correspondingly lower and higher  BHN?  If not, pressure matching isn't for real and is disproved,

The most accurate BHN with other pressures and using HP-38 (slightly bigger groups by .25 to .5 inch bigger at 25 yards, still <1.5inch which is very good) are:

A HP-38 10,000 PSI load is most accurate with BHN 7-8
A HP-38 20,000 PSI load is most accurate with BHN 7-8 (this equals 700X, but isn't as consistent)
A HP-34,000 PSI load is most accurate with BHN 7-8

Any increase in BHN opens the groups and is less accurate for each of these loads. The harder the alloy the bigger the group.  The same BHN at all pressures is the most accurate with the same or similar powders.  That's worth talking about in another post as it turns out to be important.

 

Matching or increasing the alloy BHN with the pressure caused bigger groups.  Accuracy suffered!

I’ve tested a bunch and let me say this isn’t my entire database.  But it is one striking example that I trust makes the point. 


The Conclusion

This completely disproves Pressure and Alloy Matching for Accuracy, in a 357 Magnum Revolver.  It isn’t even helpful when trying to achieve better accuracy.   

Added: I've been told that once an accurate load is worked up, the alloy and pressure is matched.  This interpretation of pressure and alloy matching is limited and mistaken in this context. That's simply the most accurate charge for a given power with that bullet.  

To test this, change to a different powder (especially one faster or slower) and work up the load.  There's a good chance it is most accurate at a different pressure.  

Which pressure is correct for that alloy, according to the formula there is only one, but in practice it changes with the powder used.

Alloy and pressure matching does use peak pressure as the measurement.  That's what is being addressed here.  If someone tries to complicate the issue by pointing out the pressure curves change with a powder change, knowing that fact doesn't make the pressure-alloy matching valid or predictable. It means the most accurate load is at different peak pressures for different powders.  The most accurate powder is most often at a pressure very different than derived by alloy-matching.

It also means the most accurate load for a given powder must be worked up the old fashion way.  By shooting and measuring groups at the range.  Not by using pressure and alloy matching formulas.

Does matching work in other handguns?  I’d be speculating as I haven’t proven it doesn’t.  It wouldn’t be outrageous to assume another revolver or even a semi-auto would be more like my 357 Magnum than a rifle though.

I'm not claiming that BHN 7-8 is the most accurate alloy in every gun, there are many other factors are at play.  My test results indicate that bullet design and how it fits in the throat/barrel grooves is more important.  Powder choice is critical and tied in importance with fit, as it can and will limit just how tight the groups are (past 15 yards).   Followed by alloy and last of all, diameter (that relationship is important to understand, more coming in a future post).

With the right bullet, like the 358429 Keith loaded at 1.620, any diameter bullet shoots at any pressure without leading (in my Taurus 66 at least).

Though fatter boolits give smaller groups at the 25 yards (my test standard as that's how long the range is).  This is not common knowledge or commonly accepted.  However I’ll post more on other myths soon. 

CLOSING POINTS

After several thousand boolits of testing across alloys, moulds, OAL, crimp, etc... the results are in as far as I'm concerned. At one time I tried to achieve accuracy using pressure & alloy matching.  I accepted this "matching connection w/pressure" concept as valid, it caused me to spend many hours and many boolits trying to figure out what was wrong with my boolits, my gun, or my casting approach. In hindsight it was a good learning experience. But I wish someone just let me know up front...

Those that write about this concept, those that I've read, have extensively tested with rifles ONLY.  I'll try it again if I ever get interested in rifles.  But for my revolver, and probably handguns in general, working up loads based in starting recipes and testing the other variables (including loads) is time much better spent. Alloy/Pressure Matching for Accuracy is fiction in this case.  If you cast for a handgun, it's most likely fiction for you too.

The last word: Pressure isn't an important part of the equation when loading for accuracy.  Knowing what the PSI or CUP is really doesn't matter.  You and I already know that 5 grains of HP-38 is higher pressure than 3 grains of HP-38.  Beyond that, it doesn't matter what it is, as long as it's safe for gun.

Taurus 66SS6 (357 Magnum, 6 inch barrel) and Tasco Red Dot

This gun is the most fun to to shoot tuned cast and handloaded ammo in.  Great feel, doesn't break the bank and very accurate.  With older eyes the Red Dot works out great.  Glasses that are needed to focus on iron sights make them tough to shoot at 15 and 25 yards.  The targets are just to blurry.  The Red Dot doesn't magnify at all and is large enough so both eyes can look through it, focus on the target and still see the dot.


For accuracy testing my rest is an old rolled up rug with tape holding it together.  It moves a bunch and isn't the best but it inexpensive and seems to work well enough.  To help compensate for my error I shoot 4 groups of 5 rounds each when testing at the range.  I measure the groups and record them, always force ranking the best to the top of the list.

My Taurus with some test results from earlier in 2010:

168 Keith Boolit, an Excellent Design

I've spent a lot of time buying, casting, loading, testing, and then selling moulds.  The design that keeps rising to the top as consistently accurate is the Keith.  For instance the 168 or a SWC which is fashioned much like a Keith. Everything else gets sold off unless it can group less than 1 inch at 25 yards.

The best so far is a 168 Keith cast from a Night Owl Enterprises (NOE) mould.  I really like it, as it has the plain base, squared off large grease groove and 3 equal size driving bands.  I suspect the crimp groove is modified a bit from the original design of Elmer Keith, but it works well and that's what I care about.  Most important is the 1 inch or less groups that it is capable of. Off a rolled up carpet rest.  That's pretty good in my book.  The best group is .6 inch measured center to center.  I judge the mould, the design and the final boolit by how well they perform and this is excellent performance.

I grabbed a few that I cast this morning and took this picture:

There's at least one that's rounded and will be recycled, but this should give you a good idea of how they look.  As a footnote: these are 10 lbs of pure lead with 1 oz of solder for tin.  This is consistently the most accurate alloy in my 357 revolver.

A 145 SWC from NOE just showed up so sometime in the next month or two I'll post those test results.

The Lee 158 SWC TL is also an incredibly accurate design when loaded in 357 brass and crimped into the second TL groove.  Lee Alox works well as a lube, but I prefer the shiny barrel left by a conventional homemade lube such as Darr lube. Since I force rank the boolits, even this mould got sold off to help fund testing another.

Right behind the 168 Keith and the 158 SWC from Lee is the 148 TL Wadcutter from Lee.  It's very accuracte, however it groups slightly bigger.  So it got sold too.

The various other boolits like the 105 SWC, the 158 RF (flat nose) and several other flat nose designs didn't group well at 25 yards.  So they all got sold too.  Some are from high end mould makers and are costly.  If they don't group less than 1 inch, they are sold.

I'm looking for the best accuracy in my Taurus 66, 6 inch revolver and can't imagine starting a casting session excited about using the second best or third best mould.  It takes some time to cast, lube and handload so why not use the best most accurate boolit all the time  I'm sure I'll find something I really like and may end up with 2 or 3 keepers.  But they will have to have something very special about them, or they will all get sold.

The NOE 168 Keith is very special, it's a keeper.  I'm looking forward to casting and testing the 145 and begin evaluating it.

Find the most accurate design that works with a good throat fit and everything else works better.  Once you get something capable of less than 1 inch, work with it, practice with it and enjoy the results.  Even shooting off-hand the groups are excellent, that's actually how most of my 1,000 rounds a month are shot.

More Accuracy Tests, Keith 168 Bullet with 700X Powder

I did some testing for accuracy today and thought I post the picture of the best group of the day.

This is with the same 358-429 Keith bullet previously mentioned in the 357 mag post.  They were cast yesterday and test at 7-8 BHN today.  OAL is 1.620, lubed with Darr and 360 diameter.  On paper the velocity is 1,200 FPS.  It shot great, felt great and no signs of leading.  Although more rounds are needed to verify the clean shiny barrel is for real.

700X with this bullet produced a .6 inch 5 shot group measured center to center.  This 5.1 grain load equaled the best HP38 load so far.  That's early results with very limited testing.  I'm looking forward to shooting more of this load.  Hope the lead doesn't get much harder with age as the groups get bigger when it does.

This is good as 700X is one of my favorites, it can be extremely accurate.  It's a flake powder that meters well in my Dillon powder drop.  It worked well with Lee auto-disks before I switched to a Dillon Square Deal B.  Some folks report feeding problems, but if you want a great fast powder that's bulky, give it a try and see how it works for you.

Results from extensive testing, in pursuit of accuracy.

Working on accuracy in my 357 magnum Taurus 66, 6 inch barrel is great fun and an excellent hobby.  My goal is to obtain the best accuracy possible with cast bullets, or boolits in some circles.  Let's get started.

Accuracy can be achieved in all the moulds tested at a distance of 15 yards and less.  The big news to me is that some bullets that are accurate at 15 yards completely lose it at 25 yards.  On the other hand, everything that is accurate at 25 is extremely accurate at 15, that I did expect.

The loads and bullets listed are all capable of 1.5 inch groups or less at 25 yards.  Everything else didn’t group at all and won’t be the focus of this update.

The most accurate rounds to date are all using 357 brass as the length is critical.  The alloy for each bullet on the most-accurate list is 98% lead and 2% tin (more about alloys later):

1 - 358-429 Keith from NOE Moulds, .360 diameter at 168 grains over 4.9 grains of HP-38 and OAL of 1.620.  Groups of 1 inch or less are possible with this combination, with a best of .6 inch.  This bullet is big and may not fit in all revolvers.  It almost sticks out of the cylinder.  This is barely a +P load and was pan lubed with Darr lube.  Lyman lists 4.6 grains as the max standard pressure charge for 38 Special.

2 - 358-158-SWC tumble lube from Lee, unsized (roughly .3595) at 158 grains over 3.5 grains of HP-38 and OAL of 1.60.  Groups of 1 inch are possible with a best of .7 inch.  This is crimped into the second groove to get some length and is a 38 Special load.

3 - 358-158-SWC tumble lube from Lee (same as above), this time over 5.1 grains of HP-38 and the same 1.60 OAL.  Groups from 1 to 1.5 inches are possible with this light 357 load.

3 – 358-148 WC tumble lube from Lee, unsized (around .3595) at 148 grains over 3.5 grains of HP-38 and OAL of 1.40.  This is a tie for third best with groups from 1 to 1.5 inches and is a 38 special load.

Key factors to achieving tight groups, in the order of importance, at least in my view, are:

1 – Bullet design with good throat fit and the correct OAL.  Best accuracy is achieved with designs that help to center and align the boolit with the barrel, sometimes this requires a long OAL.  Not all revolvers will work well with these exact OAL’s, however keeping the bullet nose approx .03 inch from the front of the cylinder can sometimes help.  The Keith is actually .01 inch from the face, not much, and it’s accurate.

2 – Next in importance is the alloy.  This list is short.  The most accurate is BHN 7-8, a little bigger grouping with BHN 11-12, and even bigger grouping with BHN of 16 and greater.

3 – Last in the critical tuning controls is diameter.  Another short list, the most accurate is .360 followed by .359 and then .358.

Powder is key and HP-38 works well with lead.  I expect other powders may work as well but haven’t verified or tested very many.  I'll also be testing more with 700X which is another proven favorite.

Added later:  Crimp is also important.  A good medium to firm crimp results in the best groups.  It's also very important that bullets don't pull out a bit and lengthen as as may prevent the cylinder from advancing. You will need to experiment with this to see how it works with you die set.  Too lose and the bullets pull and groups are bad, too tight and groups are bad, just right and the groups get tighter.

I wanted to highlight what worked the best and won’t go into the thousands of bullets that didn’t work quite so well.  Accuracy with Magnum powder testing is ongoing and the results aren’t all that impressive so far.  Gas check didn’t improve or even duplicate the best results, so these are all plain base cast bullets.

The bottom line: soft and fat bullets loaded to fit the throat (sometimes long) over lighter loads are very accurate.  Bullet designs that don’t fit the throat well just aren’t as accurate as those that do.

Sorry to go so long, I tried to keep it short… ttyl

P.S.  Best accuracy for TL bullets is with LLA (used on all TL test bullets) with 2 medium coats followed with motor mica.  This is different than the light coating, or mixing the LLA with mineral spirits or Johnson Paste Wax that others seem to have good results with.

P.P.S.  Sizing to throat size and/or .001 to .002 over groove are not very accurate in my revolver.  These suggested sizings can be found in various places and didn't work.  Water dropping them didn't work either.  My revolver's throats slug at .358 and it has a .357 groove.

P.P.P.S. My rest is a rolled up carpet (taken when my wife wasn't looking) with some tape around each end.  Achieving decent groups off-hand will take many more thousands of boolits.

Multi-forum Poll: Most Popular Powder for Handguns

Below is a chart of the poll results. On several different forums I asked the same question.  Each person could vote for up to 3 favorite powders.  A total of 1,571 votes from 555 voters make up the chart.  It's interesting data, it did change which powders I plan to test next in my 6 inch 357 magnum revolver.


The question posed on each forum:

Please select up to 3 powders that you use the most when loading for handguns

---

The selections are heavily influenced by what I load. Sorry if your favorite is missing from the list.

By favorite, I mean the one you use the most of. You buy it more often than the others. If you really love a powder but don't buy it because it fills a niche you can vote for it if you'd like.

The reason I suggest 3 votes per person is to allow for a fast, medium and slow powder. However vote as you see fit.

Again, this is for handguns. You should be able to change your votes if you think it through and change your mind.


Click on the graph to make it larger: