Powder Coat Bullet Accuracy

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Powder Coat Bullet Accuracy

Post by 10sandxs on Sun Feb 28, 2016 4:50 pm

As the accuracy of powder coated bullets has been the subject of discussion of late, Al and I did a methodical study to determine the effects of powder coating on bullet accuracy.  To accomplish this, bullets were cast using a 5 cavity NOE mold # 453-200-SWC and a mixture of Wheel weight and linotype which when water dropped and aged gives a hardness of roughly 14 brinnell. Bullets from this mold and allow combination drop at 216 gr +/-.5 gr when I do my part well. 



These bullets were weight sorted into groups of +/-0.3 gr and the heaviest group was used for testing.  Of this group, half were lubed and sized with White Label Lube X-Lox2500+.  The other half were coated with polyester powder coat (red) sourced form www.powederbythepound.com.  Un-sized bullets were coated by the “Airsoft BB dry tumble” method and baked for 20 minutes at 420 degrees F. Thickness was determined to be between 1 and 3 thousandths by measuring coated and uncoated bullets prior to sizing.  Once baked and cooled, these bullets were sized using the same sizing equipment (Star) that the previous bullets had been lubed and sized in.



These bullets were loaded using IMI Match brass which had been cleaned and prepared using normal loading methods.  The load consisted of 4.5gr of Titegroup over a Federal Premium #150 Large Pistol Match primer seated to a depth of 1.230 +/-0.002 and crimped to 0.001 less than the body diameter with bullet seated.



This load was initially ransom rest tested from a base bolted to a concrete floor at an indoor range at 50 FEET.  Three ten shot groups ranged from 0.431” to 0.615” for this load.  The ransom rest on the indoor 50 YARD range consisted of the rest clamped to a 700 lb. (approximately) concrete and steel bench.  The test protocol consisted of firing 5 ten shot groups of powder coated and traditionally lubed cast bullets.  Previous 50 FOOT ransom rest testing indicated that within 1 or two “fouling” shots, the groups had stabilized and no significant effect was observed when switching between lubed and coated bullets (long line to short line simulation)



The test program was performed using two guns, a 45 I built on a Caspian frame and slide with a 5” Kart Exact Fit Barrel.  This was the gun used for 50 FEET ransom rest testing.  The second was a Rock River 6” gun that has shown excellent accuracy (>1.5”) in numerous previous ransom rest sessions.  The second set of experiments with the Rock River was conducted for reasons discussed below.  There was effectively no difference observed in the accuracy of these two guns.



Groups from the 50 YARD range were somewhat disappointing, ranging from a minimum of 2.065” to a maximum of 3.669”.  Interestingly, these extremes were fired using the same gun/ammunition combination so user error or rest stability are possible factors. In many cases groups were reasonable with the exception of one or two flyers.  To get a better understanding of the overall accuracy potential, group sizes are reported as both 10 shot and 9 shot groups.



Rock River powder – 2.466+/-0.072* and 2.153+/-0.235



Rock River lead – 2.825+/-0.578 and 2.356+/-0.522



Caspian powder – 2.589+/-0.672 and 2.008+/-0.426



Caspian lead – 3.088+/-0.289 and 2.231+/-0.422



* 4 groups, ran out of ammo.



In both guns for both 9 or 10 shot groups, power coating was MORE accurate in these tests by between .25 and .5” on average.  Of course there appears to be some issues with either load development or ransom rest technique/anchorage which may not be allowing the guns/ammo combination to be performing to their highest level.  I've also attached a graph of the average group sizes for all conditions for both 9 and 10 shot groups.



It should also be noted that while the average powder coat group size is better across the board then the lubed group size, the difference is still within the margin of error.  I interpret this to mean that while power coat may (or may not) increase accuracy, it certainly doesn’t negatively affect accuracy.



Now with all that said, I’m open to questions, critiques, comments or suggestions for future experiments.  Some things I’m planning, are to optimize load data for the range and bullet, chronograph testing to determine velocity and distribution. 

10sandxs

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Re: Powder Coat Bullet Accuracy

Post by Ghillieman on Mon Feb 29, 2016 10:41 pm

Very interesting, I'm glad you did this test.

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Re: Powder Coat Bullet Accuracy

Post by rich.tullo on Tue Mar 01, 2016 11:54 am

Great test hope you do it again with a better Ransom Rest set up. 

I also think you came to the correct statistical conclusion: the difference in coating had not difference in accuracy. 

If you have more data with a better test i would be happy to do a Z test for you.

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Re: Powder Coat Bullet Accuracy

Post by 10sandxs on Tue Mar 01, 2016 12:26 pm

Thanks rich, I'm going to try some different loads once the weather gets better at a local ransom rest.I'll let you know what I come up with.

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Re: Powder Coat Bullet Accuracy

Post by KevinB on Wed Mar 02, 2016 12:32 am

Certainly in my plans for 147 gr. 9mm run and gun stuff now.

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Re: Powder Coat Bullet Accuracy

Post by noylj on Wed Mar 02, 2016 8:05 am

If you fired enough groups for statistical analysis, you should report the S.D. and do a student t-test at 90 or 95 "confidence" level to see if there is any real statistical difference.

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Re: Powder Coat Bullet Accuracy

Post by 10sandxs on Wed Mar 02, 2016 9:03 am

I tried to attach the data file but it didn't work. The standard deviation (1 sigma) is reported as +/- after the group size. Looking at it graphically with 1 sigma error bars, it's pretty obvious they are stastically equavelent. Yes, i could do all kinds of various stastically calculations to prove it, but I don't feel the need to prove the obvious, ive got ammo to load and a famity to follow. If you like I'll send you the data file and you can crunch numbers till your hearts content. There are some potential outlier groups that you could examine if you want.

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Re: Powder Coat Bullet Accuracy

Post by BE Mike on Wed Mar 02, 2016 10:50 am

Thanks for sharing all the hard work. I've been wondering about coated bullets and their application to bullseye shooting for a long time. So much "accuracy" testing on the internet involves 5 yds. and is useless IMHO.

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Re: Powder Coat Bullet Accuracy

Post by troystaten on Thu Mar 03, 2016 1:29 am

Nice write up, a friend of mine did a comparison limited to 25 yards and two hands and sandbags from a bench with 3 different pistols (2 Wilsons and one Salyer built bulleye pistol) and there was very little difference between powder coated bullets (bayou brand and conventional lead bullets, most of the groups for both types of bullets where all in the 1 inch range for 5 shot groups. The conclusion was that for his skill level it made no difference and the cleaner powder coated bullets where the way for him to go.  Of course your results may vary and maybe at 50 yards there might have been a difference.

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Re: Powder Coat Bullet Accuracy

Post by lablover on Wed Mar 09, 2016 7:00 pm

I like this..I was on the fence to powder coat and now I think I'm going to...Also, this makes me want to cast my own hence the PC interest.

Now to go buy a mold...Pot...lead..read till my eyes bleed....I LOVE IT

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Re: Powder Coat Bullet Accuracy

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