Beware Setback

[sqlbullet]

While doing some reading to validate my comments about the Delta Elite and pressure, I stumbled into a thread on one of the 1911 forums by a guy that had some seriously bulged brass from a new Delta Elite using a load that was right between min and max.

But, he didn't have that issue with every round from the batch, just some.

He finally tracked it down to bullet set-back causing pressure spikes.  The brass was not holding enough tension on the bullet, and they were being set back, sometimes quite a bit.

So, last night I created a calculator to tell me how much pressure does up for a given amount of setback.  The spreadsheet depends on Boyles law that states, for equal temperatures:

    P₁V₁ = P₂V₂

So, starting with the known values of case length = 0.992", case volume = 1.56 CC, Bullet Diameter = 0.400" and COAL = 1.250", and assuming a near max load with a pressure of 35,000 PSI, I began running pressure calculations for setback all the way into the case.


Nosler 135 Grain JHP
Measured Bullet Length: 0.485"

Setback	Volume	pressure
0.000	1.093	35000
0.010	1.072	35672
0.020	1.051	36371
0.030	1.031	37098
0.040	1.010	37854
0.050	0.990	38642
0.060	0.969	39463
0.070	0.948	40320
0.080	0.928	41215
0.090	0.907	42150
0.100	0.887	43129
0.110	0.866	44155
0.125	0.835	45788
0.130	0.825	46359
0.140	0.804	47546
0.150	0.784	48796
0.160	0.763	50112
0.170	0.742	51502
0.180	0.722	52971
0.190	0.701	54527
0.200	0.681	56176
0.210	0.660	57929
0.220	0.640	59794
0.230	0.619	61784
0.240	0.598	63910
0.250	0.578	66188

Lee 175 Grain SWC TL
Measured bullet length: 0.600"

Setback	Volume	pressure
0.000	0.856	35000
0.010	0.835	35863
0.020	0.815	36770
0.030	0.794	37723
0.040	0.773	38728
0.050	0.753	39787
0.060	0.732	40906
0.070	0.712	42090
0.080	0.691	43344
0.090	0.670	44676
0.100	0.650	46092
0.110	0.629	47600
0.125	0.598	50057
0.130	0.588	50934
0.140	0.567	52782
0.150	0.547	54770
0.160	0.526	56913
0.170	0.506	59231
0.180	0.485	61745
0.190	0.464	64483
0.200	0.444	67474
0.210	0.423	70757
0.220	0.403	74375
0.230	0.382	78383
0.240	0.362	82848
0.250	0.341	87852

Berry's Plated 180 Grain
Measured bullet length: 0.595"

Setback	Volume	pressure
0.000	0.866	35000
0.010	0.845	35853
0.020	0.825	36748
0.030	0.804	37688
0.040	0.784	38679
0.050	0.763	39723
0.060	0.742	40824
0.070	0.722	41989
0.080	0.701	43222
0.090	0.681	44529
0.100	0.660	45918
0.110	0.640	47397
0.125	0.609	49803
0.130	0.598	50660
0.140	0.578	52465
0.150	0.557	54404
0.160	0.537	56492
0.170	0.516	58747
0.180	0.495	61189
0.190	0.475	63843
0.200	0.454	66738
0.210	0.434	69907
0.220	0.413	73393
0.230	0.392	77245
0.240	0.372	81523
0.250	0.351	86303

NOE 180 Gn HP Cast
Measured bullet length:  0.625"

Setback	Volume	pressure
0.000	0.804	25000
0.010	0.784	25657
0.020	0.763	26349
0.030	0.742	27080
0.040	0.722	27853
0.050	0.701	28670
0.060	0.681	29538
0.070	0.660	30459
0.080	0.640	31440
0.090	0.619	32486
0.100	0.598	33604
0.110	0.578	34802
0.125	0.547	36768
0.130	0.537	37473
0.140	0.516	38969
0.150	0.495	40589
0.160	0.475	42349
0.170	0.454	44269
0.180	0.434	46372
0.190	0.413	48684
0.200	0.392	51239
0.210	0.372	54077
0.220	0.351	57247
0.230	0.331	60813
0.240	0.310	64852
0.250	0.289	69466

Nosler 200 Gr JHP
Measured bullet length: 0.685"

Setback	Volume	pressure
0.000	0.681	35000
0.010	0.660	36092
0.020	0.640	37254
0.030	0.619	38494
0.040	0.598	39818
0.050	0.578	41238
0.060	0.557	42762
0.070	0.537	44403
0.080	0.516	46175
0.090	0.495	48095
0.100	0.475	50181
0.110	0.454	52456
0.125	0.423	56284
0.130	0.413	57687
0.140	0.392	60714
0.150	0.372	64077
0.160	0.351	67834
0.170	0.331	72059
0.180	0.310	76845
0.190	0.289	82312
0.200	0.269	88616
0.210	0.248	95967
0.220	0.228	104647
0.230	0.207	115054
0.240	0.186	127759
0.250	0.166	143619

As you can see, and as expected, shorter (lighter) bullets are more forgiving of setback.  I only tested what I had on hand.  If someone can post up lengths on 155 grain and 165 grain JHP's I will gladly update the above results to include those.

Hopefully this data will help create awareness of just how dangerous bullet setback can be.  Also, it might be prudent if you are experiencing bulges to start ejecting every other loaded round to see if some set-back is occurring.

(If anyone see's that my math is wrong, let me know. I build the formulas on my phone during a child's basketball practice, so an error is possible, though the results pass a basic smoke test)

[Benchrst]

I have a few lengths listed here: http://webcity.net/benchrest/10MMPublished/40calbulletdetails.html

Can also run some #s on QL.

[The_Shadow]

I had taken some water capacities of some 10mm casings a while back and they showed slightly different than what QL was using in the program.  I am trying to find that data.

Case capacity 10mm (water weight in grains)

Double Tap 10mm length 0.9880" weight of case un-sized with spent primer    75.0 grains

With water un-sized weight with water 99.8 grains            diff   24.8 grains
With water re-sized weight with water 99.2 grains (case mouth sized)   diff   24.2 grains

Cor-Bon 10mm length 0.9880" weight of case un-sized with spent primer    74.6 grains

With water un-sized weight with water 99.2 grains            diff   24.6 grains
With water re-sized weight with water 98.8 grains (case mouth sized)   diff   24.2 grains

JAG 10mm length 0.9805" weight of case un-sized with spent primer       74.8 grains

With water un-sized weight with water 99.4 grains            diff   24.6 grains
With water re-sized weight with water 99.2 grains (case mouth sized)   diff   24.4 grains

Star Line 10mm length 0.9855" weight of case un-sized with spent primer    77.4 grains

With water un-sized weight with water 102.2 grains            diff   24.8 grains
With water re-sized weight with water 101.4 grains (case mouth sized)   diff   24.0 grains

CCI Aluminum 10mm length 0.9875" weight of case un-sized with spent primer    27.2 grains

With water un-sized weight with water 51.8 grains            diff   24.6 grains
With water re-sized weight with water 51.2 grains (case mouth sized)   diff   24.0 grains

With water un-sized weight with water adv               24.7 grains / 24.68 grains (CCI added)
With water re-sized weight with water adv               24.2 grains / 24.16 grains (CCI added)



http://10mm-firearms.com/reloading-10mm-ammo/case-capacity-10mm-(water)-1911/msg22402/#msg22402

[sqlbullet]

Thanks Benchrst!

I have captured this data in my spreadsheet.  Later today i will try to get the first post updated, and formatted so it fits more data in the space.

[10mm-Admirer]

I use the Lee undersized die with thinner 10mm brass. Gives it better neck tension.

[Geeman]

Its just my guess that the brass he had problems with is PPU.  I believe this is exactly the cause of my Glock 's case head separation.  If the brass springs back after sizing, it is only a matter of the bullet being set back when stripped from the magazine.  The higher the tension of the recoil spring, the greater the possibility.

Greg

[Geeman]

The computation would be complex. 

First would be what the volume is in reality.  The bullet is not stationary during the pressure rise.  Quickload shows that the bullet moves about 1/3 inch with a max load of Power Pistol to reach maximum pressure.   That would lead toward faster burning powders being more of a problem than slower ones. 

QuickLoad is not very accurate with pistol rounds so take it with a grain of salt.

135g Nosler w/Power Pistol (OAL vs PSI)

1.26" @ 32,698 (Bullet travel at Peak pressure is .32")
1.25" @ 33,713
1.24" @ 34,772
1.23" @ 35,913
1.22" @ 37,118
1.21" @ 38,445
1.20" @ 39,831
1.19" @ 41,352
1.18" @ 43,016
1.17" @ 44,799
1.16" @ 46,794 (Bullet travel at Peak pressure is .23")

1/10" setback leads to 14,000 PSI difference.



1.06" @ 85,158 (Bullet travel at Peak pressure is .13")

2/10" is BOOM in any handgun designed for 10mm.

Greg

[sqlbullet]

Those quickload values track right with the calcs I did.

[Benchrst]

All my QL calcs are based on 1.558

[The_Shadow]

All great information guys! 
Case expansion based on chamber area to allow it would also play into equation. Also clearly not all brass is the same either.  Some like Starline are softer (great for handloading), others harder/stiffer/brittle and less malleable (some will not hold their resized dimensions), PPU is not a quality brass, its web maybe too thin for anything but light target loads.

Not all chambers are the same as is evident with say Glock at 0.434" and S&W 0.428".  Also freebore and tapered throats can be vastly different.
It would seem pressure would spike quicker in the tighter chamber pistol, this is why not all are the same.
Either that or the amount the bullet moves is proportional to that difference.

I had started checking things over as loaded a little closer...such as pushing, pulling and twisting the projectiles of finished rounds.  Back some time ago, (about the time Double Tap started with his good stuff), I bought the LEE FCD to use as a finish crimp die because of the Glocked brass.  When I started using it I found my finished cartridges with loose fitting bullets.  Try as I might no adjustments helped.  I went back to my RCBS die for seating and crimping in separate steps. 
What I found was that my cast bullets were being squeezed down slightly so they were able to be twisted inside.  I also had some jacketed bullets that didn't hold securely but they may have been PPU brass related.

Therefore, I utilized LEE FCD as a Pass-Through sizing die, this was very beneficial to provide reliable chambering especially the tight chambers.  This Pass-Through resizing reached the area not being reached by the conventional dies due to shellholder and carbide being radiused...One of the best improvements I ever did.

Then regular sizing and depriming with the RCBS die, I also hand prime my cases, (yes these steps take longer but I get to handle and see the cases looking for issues).
Hand weigh powder charges (because most are the upper end performance very close to DT, UW, SF).
Bullets are seated to proper COAL without any crimp being applied I place a 1/8" spacer to raise the die for this operation.
Then finish crimping is done by passing back in the crimp die buy removing that 1/8" space ring to drop the die back to crimp position.

Now going back to the Set Back, since I started doing things this way, I have had NO SET BACK ISSUES!  I have tested all of the 10mm loadings from Double Tap, Underwood and even SwampFox from the pull-downs with no issues other than those that are known to "SMILE", so I adjusted my loadings by backing off on those for my setup.

I had outright written Underwood and they say their loads are inside the SAAMI pressure specs, but if they are I'd be surprised...

[The_Shadow]

One other thing that I have seen while doing the pull-downs, is the use of bullet sealants.  This may infact be also helping to prevent Bullet setback issues.  I have seen it used by the Speer, CCI, Federal, Winchester Law Enforcement, defensive types of ammo. 

While providing a better moisture seal, its adhesion properties could help prevent set backs and provide more uniform performance/velocities.

[REDLINE]

Not sure if this would help toward figuring pressure vs setback in 10mm Auto, but in 2005 ATK/Speer (or whoever) worked up some data regarding pressure vs. setback length in Speer's own product number 53918 which is 357 SIG load with a 125gr Gold Dot.  They do show some formulas in the bottom right corner of the graph.  I don't know if those formula are of use with 10mm Auto but maybe one of you will.

Here's the link to their .xls document;  http://le.vistaoutdoor.com/downloads/technical_bulletins/357_SIG_Setback_Length-vs-Pressure.pdf

[Geeman]

They do show some formulas in the bottom right corner of the graph.  I don't know if those formula are of use with 10mm Auto but maybe one of you will.

Here's the link to their .xls document;  http://le.vistaoutdoor.com/downloads/technical_bulletins/357_SIG_Setback_Length-vs-Pressure.pdf

That would seem to be a polynomial curve fitting equation.  In other words, the data was measured and a simple ax^n + bx^(n-1)+cx^(n-2)..... equation was fitted for graphing purposes.  That equation is only good for that exact loading and will fail if any variable is changed.

What I found interesting is that of the compressed powder and how it limits the pressure.  There was one of the copper bullets in the tear down data that Shadow pulled out a pellet of compressed powder that seemed was a big overcharge.  Now I know where that comes into play.

The Quickload numbers I put up in this thread was compressed in a huge way, and I don't think Quickload models that into its equations.  According to the Speer data, that curve would flatten and produce lower pressure than Quickload predicts.

Interesting!

Greg

[The_Shadow]

That compressed Loading was Buffalo Bore's 10mm with the Barnes 155gr TAC-XP and 11.0 grs Power Pistol.
Buffalo Bore data;
This is a full power 10MM load that is within SAAMI spec and is thus safe for use in ANY/ALL 10mm pistols. Loading this long-for-weight all copper bullet in the 10MM case, causes powder capacity limitations that we do not experience with shorter/heavier lead alloy bullets and thus our advertised 1500 fps velocity cannot be reached, regardless of how may internal ballistics charts tell us that we should be able to launch a 155gr. bullet @ 1500 fps from a 5 inch barrel, that long light weight bullet simply uses too much of the available case capacity to do so.
1455 fps - Custom 1911 with Nowlin 5 inch barrel     Energy 728 ft.lbs
1429 fps - Colt Delta Elite, 5 inch barrel        Energy 702 ft.lbs
1401 fps - Glock Mod 20,  4.6 inch barrel        Energy 675 ft.lbs

I duplicated that loading for Intercooler using a 155 gr COP (Copper Only Projectile) a similar all copper HP to the Barnes.

His resultswere; COP 155gr All Copper HP 11.0gr's Power Pistol (Buffalo Bore load) 1422, 1435, 1456, 1413. Average = 1431.5 FPS/ 706 LBS. Really happy with this level of performance and would love to see them in gel!