Hollowpoint/Alloy-Velocity/Accuracy (4-Way) Testing

[Butcher45]

I wanted to test these one day after work, but there was a lot more gravel to be raked than I thought, so I only had time to shoot one shot string of these 245grain .456 HollowPointed RCBS Single Action Army (cast in 25:1 alloy) thru my tuned 909 using a 3000psi fill.  I figured it would be worth doing just to analyze the results, and base further testing off of them.

     1.  662
     2.  667
     3.  679
     4.  682
     5.  670 end psi 2200


     What to gather from these initial numbers?  My first curiosity with these particular slugs was whether or not velocity would suffer with this hard of lead.  Cast in 25:1 alloy, I'm guessing the BHN of these slugs is somewhere between 9.5 and 10.  I think this could very well be the hardest alloy I have shot out of this rifle.       

     Compared to the fastest 245grainer I have tried so far (practically pure lead .457 REAL's no harder than BHN6 tops), the power drops off a bit with the HP SAA slugs using the same 3000psi fill (which is a great fill pressure to use in my rifle for the 245gr. REAL).  The shot count with the 25:1 HP SAA's added another shot into a 20fps maximum variance, making this the first load I have recorded in this particular rifle that has given me 5 shots within a maximum 20fps variance.  It also used the same amount of air to make those five shots that most other slugs I shoot use-up in four shots.  The curve of this string indicates to me that further testing at different (likely lower) fill pressures could yield some improvement in power.....might even maintain the 5 shots within 20fps while doing so.  Hmmmmmmmm.......

     The .456 HP SAA, along with being cast from the harder .25:1 alloy, has a lot of contact area with those fat bands.  Aside from the alloy being harder, those fat bands could be a big contributor to why the HP SAA slug initially appears to be a bit slow.  Wish I had the same exact design in pure lead to compare with this alloy, to establish how much of a factor the lead hardness is.  That comparison would simultaneaously go a long ways towards establishing just how much of a factor those fat bands are.  The RCBS SAA design has a MASSIVE base band.

     I couldn't wait to get out to the ranch and get to more testing today.  I only had so many of the SAA's, so I had to test them sparingly.  I DID have plenty of HP #454424's cast in 50/50 clip-on wheelweight-pure lead that tested BHN8.5 the day after they were cast.  That was a while ago, so these may be slightly harder by now as can happen to cast boolits with age. I cannot come close to putting a dent in these boolits with my fingernail. 
     I have previously shot some pure lead versions of these HP #454424's cast from the same mold, and those were very accurate.   I only wished I had more of the REAL's on hand for this test as well, since I have yet to do a complete string of 245's with all the shots being out of the same batch of boolits.  Think I may very well get 5 shots within 20fps with those heavy .457 REAL's, too.

     Now for some answers, along with some more questions lol.

     Went back out to the ranch today to test these hollowpoints for accuracy, and see if the harder lead appears to have much of an effect on velocity.  Test rifle is a tuned SamYang 909 with a Zeiss Conquest 1.8-5.5X38mm scope set to 5.5 power.  Shots were taken from the prone position (I'm not used to it) using my tacklebox as a rest from a distance of a measured 50yards.  F-1 Chrony was set a measured ten feet from the muzzle, and leveled with a leveler.  Today I set things up for doing chrony testing, and accuracy testing simultaneously.  Paper targets were changed after every string.  I factor in a 25psi margin of error on all fill pressures, because it is tough to read the gauge much closer than that.

     Two designs were tested today.  The first design tested is the .456 (un-sized, but .456 for the most part) RCBS Single Action Army design modified to drop HP's, weighing 245-246grains cast from 25:1 alloy.  The mold pin used to make these boolits created a cavity just a tad over .25 inch wide at the nose, and just a bit shy of .5 inch deep (the boolit measures .75 inches long).

     Please excuse the poor pictures.



     The second boolit design was the original HP #454424 (pretty rare mold), dropping slugs that were .457-.458 un-sized (.457 for the most part), and weighed about 230grains (give or take a grain).  The cavity was .20 in width at the nose, and about .5 inch deep (these slugs are 11/16's in length).  These slugs were cast using a 50/50 alloy consisting of clip-on wheel weights/pure pb.  I have had excellent results in the past (accuracy wise) shooting these same slugs cast in pure lead.



     The first string/group of the day was 4 shots of the HP'd RCBS SAA design using a 2900psi fill.  Chrony string was 1)674.9  2)685.6  3)685.0  4.668.0 end psi 2100, and here is the "group" that resulted.



     Discouraging to say the least.  What happened here?  Granted these were the first shots of the day, but no way did I mess-up THAT bad shooting off a rest.  So I moved on to the next string, shooting the 230grain .457-.458 HP #454424's using a 2900psi fill.  The shot string was as follows:  1)696.4  2)709.8  3)704.8  4)690.6 end psi 2150



     Shot #1 was pretty low in comparison with the rest of the group, despite being very close in velocity.  I recalled seeing this happen before, but wanted to make sure it was the gun causing it, and not me.  So I repeated the test with the same fill pressure, and for string #2 using this boolit I got  1)682.0  2)695.5  3)702.6  4)689.8 end pressure 2150



     Well now.....it appears that despite the numbers being pretty tight, the rifle/valve/what have you just does not like to shoot this boolit at 2900psi, and throws the first shot low from the rest.

     I then went back to the 245grain HP'd SAA design, and shot this string:  1)672.7  2)682.6  3)690.2  4)668.9 (forgot to record end fill pressure on this one)



     This boolit makes nice chrony strings, but accuracy is looking pretty dismal at this point.

     So I went back to the 230grain HP #454424's, this time using a 2800psi fill in an effort to get rid of the low first shot I was experiencing.  I got a string of  1)702.5  2)709.1  3)697.9  4)678.7 end pressure 2025psi, and here are the results on paper.

     

     Despite falling outside my desired maximum variance of 20fps (by about 11fps), the low first shot was now gone, and the accuracy of these four shots showed to be very good.  The first two shots went into the same hole. 

     For the last string/test of the day, I shot 3 of my remaining 4 HP'd SAA boolits (saving the last one for a terminal ballistics test) using a 2800psi fill.  1)683.0  2)685.8  3)682.9, and got this on paper.

     

     General thoughts on the 245grain .456 HP'd RCBS Single Action Army design:  these slugs go about 25fps slower than the .457 245grain REAL's cast in pure lead (fastest boolit this weight so far).  It remains to be seen whether or not the velocity difference is due to the extremely fat bands on this boolit (especially the base), the 25:1 alloy, or a bit of both.  I will be ordering pure-lead versions of this boolit for further testing so I can try to figure out what is causing the reduced velocity.

     Accuracy was non-existent.  I am hypothesizing that this may be due to the cavity style used.  The caster has about 4 different mold pins that create four different styles of cavity for this mold, and the cavity/mold pin used for these boolits is the most extreme of the four cavity styles.  When I order more of these slugs, I am going to try all four cavity styles in an effort to see whether or not a different style of cavity will improve the accuracy of this boolit design.

     General thoughts on the original Lyman #454424 HP design:  This was quite interesting.  I established that the rifle's first shot did not like that extra 100psi in the fill despite the velocity being right where it should be.  I am hypothesizing that this has something to do with how the valve functions when shooting this booit, thus affecting the time spent in the barrel.  I will try a 2850psi fill next time, in an effort to tighten the numbers while avoiding that low first shot.

     Accuracy with these 50/50 alloy HP #454424 boolits was very good....apparently identical to the accuracy the pure lead versions displayed.  Good enough that this will probably be my new heavyweight target/plinking round.  I wish I had had the time to test some pure lead 230grainers for a velocity comparison.....I will do that soon.  Good power regardless, despite the alloy being on the hard side as far as airgun slugs are concerned.

     General thoughts overall:  No matter what the chrony says, you have to see what is going down on paper before establishing both the correct fill pressure, and how accurate that fill pressure will be with any given design.  The harder alloy used in this batch of HP #454424's does not appear to be slowing down the velocities a great deal, if at all.  The 50/50 WW-pb alloy APPEARS to be just as fast as the pure lead, but that remains to be seen.  Prior testing with this design in pure lead was done before my rifle had some work done to it that upped the power a little, so a comparison between the two alloys using the strings I recorded before the work was done to the rifle would not be valid.  I may be able to obtain more of the HP#454424's cast from pure lead for further testing.

     What next?  Testing the accuracy of the HP #454424's at further ranges, and requesting more HP'd SAA's cast in the same alloy, but with the other three cavity styles in an effort to establish whether or not the cavity is having an affect on the lack of accuracy I am experiencing with this boolit.  I will also request more of them made from dead-soft lead, with all four cavity styles being represented to see if the softer lead, and/or the different cavities result in some accuracy.  It will also be interesting to see if the softer lead improves velocity.

     Any comments, ideas, or observations are welcome, and encouraged.

[JonnyReb]

 Another awesome post Butcher, i have no intelligent observation to make but i'm sure looking forward to your future comments as you figure out what works best in your guns and why. All of us who shoot koreans can benefit from your findings, J

[rsterne]

If you can tell me the volume of the air reservoir I would love to do an efficiency calculation.... What we know so far is that the average velocity was 672 fps over 5 shots.... which with 245 gr. slugs works out to 245.7 FPE x 5 = 1229 FPE total....

Bob

[Butcher45]

If you can tell me the volume of the air reservoir I would love to do an efficiency calculation.... What we know so far is that the average velocity was 672 fps over 5 shots.... which with 245 gr. slugs works out to 245.7 FPE x 5 = 1229 FPE total....

Bob

I'm pretty sure it's either 385cc's, or 380cc's for the 2tube 909.  Could have taken more shots if I wanted to, but I handpump so I only shoot it down three, maybe four shots before refilling usually.

[rsterne]

OK, so let's do the efficiency calculation.... 385cc is 385/16.4 = 23.5 cu.in.... The 5 shot string used 1000 psi which is 1000/14.5 = 69 Bar.... Multiply the two together, 23.5x69 = 1622 cu.in. of air at 1 Bar....

From above, the 5 shot string was 1229 FPE total.... so we take 1229/1622 = 0.76 FPE/cu.in. air used at 1 Bar.... I would say that for the energy level of your gun, that's pretty decent efficiency.... I have limited experience with big bore guns.... but in .22 cal I have measured values from a low of 0.58 FPE/ci (in a 52 FPE modded Disco) to a high of 1.97 FPE/ci (in a regulated gun set up for tons of shots at ~600 fps)....

I'm very interested in getting as many efficiency values for various guns as I can collect.... so if anyone else wants me to do the calculation, just let me know.... I need the number of shots, the average velocity and pellet weight, the volume of the air reservoir, and the difference in pressure between the beginning and end of the string....

Bob

[JonnyReb]

 Hey Thanks Bob, i'll be sure to shoot you some figures at future points, it's good to have a genius or two or three on the site

[rsterne]

It will be interesting to gradually build up the knowledge of what is and what is not "efficient" in different calibers.... and be able to compare one gun to another....

Bob

[Butcher45]

OK, so let's do the efficiency calculation.... 385cc is 385/16.4 = 23.5 cu.in.... The 5 shot string used 1000 psi which is 1000/14.5 = 69 Bar.... Multiply the two together, 23.5x69 = 1622 cu.in. of air at 1 Bar....

From above, the 5 shot string was 1229 FPE total.... so we take 1229/1622 = 0.76 FPE/cu.in. air used at 1 Bar.... I would say that for the energy level of your gun, that's pretty decent efficiency.... I have limited experience with big bore guns.... but in .22 cal I have measured values from a low of 0.58 FPE/ci (in a 52 FPE modded Disco) to a high of 1.97 FPE/ci (in a regulated gun set up for tons of shots at ~600 fps)....

I'm very interested in getting as many efficiency values for various guns as I can collect.... so if anyone else wants me to do the calculation, just let me know.... I need the number of shots, the average velocity and pellet weight, the volume of the air reservoir, and the difference in pressure between the beginning and end of the string....

Bob

Better run your numbers again Bob.  The 5 shot string used only 800psi, not 1000.

[rsterne]

Excuse me.... but I was certain that the ending pressure stated was 2000 psi.... was it edited?.... If not, I apologize.... The corrected air usage would be....

800 / 14.5 = 55 Bar.... 55 x 23.5 = 1293 ci. at 1 Bar.... 1229 / 1293 = 0.95 FPE/ci....

Bob

[Butcher45]

Nope no editing....posted in it's original form from when I first wrote it back in March '10.  I was just reading back over it while going over your numbers, and noticed the end fill pressure.

I appreciate the formula....going to be putting that one to use in search of the most efficient boolit alloys/designs.

[rsterne]

What can I say.... ME BAD !!!....    

Bob

[lloyd-ss]

Butcher,
Again, a lot of info packed in there.  Not being a bullet caster I've got a few questions if you would indulge me, LOL.
It seems like the accuracy of deep hollowpoints like those 2 molds would depend greatly on how well the pin fit the mold.  If it had just a little bit a wiggle room it would throw the center of gyration off like an out of balance tire, and the deeper the cavity, the worse it could be.  I know you and others have mentioned filling the HP holes with leather or wax or such, which would help to negate any eccentricity in the casting.  But the filling would have to be pretty heavy to really help a bad mold.

Your mention of trying pure lead and hard lead out of the same mold to test velocity sounds great.  I'd like to hear about that if you get the chance.

Thanks,
Lloyd

[Butcher45]

Butcher,
Again, a lot of info packed in there.  Not being a bullet caster I've got a few questions if you would indulge me, LOL.
It seems like the accuracy of deep hollowpoints like those 2 molds would depend greatly on how well the pin fit the mold.  If it had just a little bit a wiggle room it would throw the center of gyration off like an out of balance tire, and the deeper the cavity, the worse it could be.  I know you and others have mentioned filling the HP holes with leather or wax or such, which would help to negate any eccentricity in the casting.  But the filling would have to be pretty heavy to really help a bad mold.

Your mention of trying pure lead and hard lead out of the same mold to test velocity sounds great.  I'd like to hear about that if you get the chance.

Thanks,
Lloyd

I try to get as much info on the alloy used in the boolits I buy as I can, and often order more than one diameter, alloy, or both of the same boolit design to try and see whats what. 

I've bought/tried more than a few designs, but have yet to cast any boolits myself.  I just got a ventilated work space set-up to do it though, so hopefully casting my own is not to far off.