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.310 FMJBT bullets for larger bored rifles (Read 3817 times)
madsenshooter
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.310 FMJBT bullets for larger bored rifles
Jan 9th, 2018 at 7:10pm
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Speaking of bored, the winter doldrums have set in, I've nothing better to do than physically compare a couple 174gr FMJBTs that are available to us.  After having some success with the 174gr FMJBTs that I pulled from Russian made .303 British, I thought I'd check out a couple of commercial offerings.  So, I ordered 100ea of PRVI and Hornaday's offerings.  The Hornady offering measures pretty close to as listed, I get .3103". PRVI bullets are about the same and both are very consistent in this dimension.  Weight-wise, the Hornady bullets were very consistent, ranging from a low of 173.3gr to a high of 174.2gr.  Over 40 out of the 100 weighed exactly the same 173.6gr.  The PRVIs were not as consistent, weight ranged from 173.1gr to 175.8gr with a good concentration in the range 174-174.5.  Still a lot less variation than I experienced with their 190gr HPBT bullets.  It must be easier to maintain consistency when stuffing the jacket from the rear.  The Hornady is a secant ogive design, the PRVI a tangent ogive.  The Hornady will have a bit less jump to the rifling if loaded to same OAL as the PRVI and has a longer bearing surface.  BC of the Hornady is listed .470 and that of the PRVI was calculated by Parashooter as .492.  the PRVI has a slightly sharper boat tail and a rounded annulus.  The Hornady has the same sharp jacket edge at the rear that the 150gr FMJBT has.  The meplat is a bit smaller on the PRVI, might help feeding.   Perhaps I can get out sometime before spring and give them a bit of a shooting test.  I'd really like to find the RL19 that I have somewhere in these boxes!  Both bullets are close in length to the Russian 150gr steel core bullet.  My goal is to take away some of the time of flight advantage that the 06 has over the Krag.  Whether or not that will really make a difference, I can't say.  L-R, Russian 150gr, Hornady 174gr, PRVI 174gr.
  
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Parashooter
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Re: .310 FMJBT bullets for larger bored rifles
Reply #1 - Jan 9th, 2018 at 10:42pm
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If competing up to 300 meters, you won't see much advantage with the higher BC's of such projectiles unless the wind is really blowing and/or the target small. At 200 yards on the big SR target, we rarely see conditions where a small reduction in wind deflection yields a higher score.

For a .310"+ groove Krag, you might check out the .311" Sierra 180 FB (which works well in many .303's) - or even their .311" 150 FB.

Main problem with the boattails is a propensity to yaw in long, wide throats like the Krag's, engraving off-axis*. They're all worth trying though. Never know 'til you fire some for group.

*Crude sketch of yaw in long throat, BT vs. FB.
(You need to Login to view media files and links)

Wind graph shows significant advantage for higher BC at 600, not so much at 200.
  
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madsenshooter
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Re: .310 FMJBT bullets for larger bored rifles
Reply #2 - Jan 10th, 2018 at 4:36am
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I've always thought a FB would be better in a Krag with a standard throat.  A few of those 173gr Thomas bullets would be nice to try.  These bullets are getting up there in length at 1.245" for the PRVI and 1.26" for the Hornady.  Their major diameter is still in the case neck when the ogive hits the rifling, especially that of the Hornady.  That ought to at least minimize yaw or tip.
  
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madsenshooter
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Re: .310 FMJBT bullets for larger bored rifles
Reply #3 - Jan 18th, 2018 at 9:37pm
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I've been pondering your yaw illustration, which I know is exaggerated.  What I'm thinking is fill up that space around the boat tail with powder. It'll be there, under pressure, even when the neck is expanded, and as the bullet travels through the neck and starts into the throat.  That should further minimize any chance of yaw.  I can think of a few slow burning ball powders that ought to do that, Norma MRP or Hodgdon's Superformance.  Those suggestions are for those of you who can afford them.  Me, I have some dirty burning WC860 to play with.  I wish I had quickload to play with, it'd be interesting to see what those ball powders would do with a 174gr bullet out of a 30" barrel.  They'd likely need to be fired with magnum primer to get the most out of them, at Krag pressures.
  
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Parashooter
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Re: .310 FMJBT bullets for larger bored rifles
Reply #4 - Jan 18th, 2018 at 11:25pm
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madsenshooter wrote on Jan 18th, 2018 at 9:37pm:
. . .What I'm thinking is fill up that space around the boat tail with powder. It'll be there, under pressure, even when the neck is expanded, and as the bullet travels through the neck and starts into the throat.  That should further minimize any chance of yaw. . .
I wish I had quickload to play with, it'd be interesting to see what those ball powders would do with a 174gr bullet out of a 30" barrel. . .


I think that's pretty insane. Granular powder, especially spherical, has about the structural stability of dry sand - if sand could burn away.

In my limited experience (only been handloading since 1958), using super-slow powders in low-pressure, relatively small cartridges is a waste. They never get hot enough to burn much before the bullet exits the muzzle.

Here's QuickLOAD estimates for H870 (supposedly very close to WC860) in .30-40 with the 175 Sierra BTHP. Note the penultimate column showing the % propellant burnt.

Cartridge          : .30-40 Krag
Bullet             : .308, 175, Sierra HPBT MatchK 2275
Cartridge O.A.L. L6: 3.089 inch or 78.46 mm
Barrel Length      : 30.0 inch or 762.0 mm
Powder             : Hodgdon H870

Predicted data by increasing and decreasing the given charge,
incremented in steps of 1.0% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step    Fill. Charge   Vel.  Energy   Pmax   Pmuz  Prop.Burnt B_Time
%       %    Grains   fps   ft.lbs    psi    psi      %        ms

-10.0   90    42.30   1679    1095   14434   3309     52.9    2.469
-09.0   91    42.77   1698    1121   14809   3393     53.6    2.441
-08.0   92    43.24   1718    1146   15198   3477     54.4    2.413
-07.0   93    43.71   1737    1172   15596   3562     55.1    2.385
-06.0   94    44.18   1756    1199   16012   3648     55.9    2.358
-05.0   95    44.65   1776    1226   16439   3736     56.7    2.330
-04.0   96    45.12   1796    1254   16880   3824     57.4    2.303
-03.0   97    45.59   1817    1283   17339   3914     58.2    2.276
-02.0   98    46.06   1838    1313   17810   4004     59.0    2.249
-01.0   99    46.53   1860    1344   18300   4096     59.8    2.223
+00.0  100    47.00   1881    1375   18808   4189     60.6    2.196
  
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Hamish
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Re: .310 FMJBT bullets for larger bored rifles
Reply #5 - Jan 19th, 2018 at 1:25am
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WC860,870, and 872 are amazingly useful by themselves in many different cartridge configurations. 

EDIT:

Pondering on this overnight.  I must admit that I have no personal experience other than research online about these particular pull down powders with jacketed bullets. 

However, noting that the .308 and the 30-40 are nominally within a grain of water capacity, I would think that a fair initial comparison could be made with the example of the 311440 over 48.0 grains of WC870 in the .308.  Yes there are a few mummies in the barrel after each shot, but accuracy is good enough to hit swingers out to 250 yards.  I really should chronograph it.


« Last Edit: Jan 19th, 2018 at 1:42pm by Hamish »  
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madsenshooter
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Re: .310 FMJBT bullets for larger bored rifles
Reply #6 - Jan 19th, 2018 at 5:17pm
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Rich knows what I'm up to.  Ve haf ways of turning up the heat!  The only chronograph results I have shows I got the 30H, probably around 180gr, up to 2206fps with no problem.  I really should get me a chronograph before starting on this project.  The whole problem with those 50BMG powders in smaller cases is the difference between a LR primer and a 50BMG primer.  As parashooter said, they (the powders) never get hot enough to burn much before the bullet exits the muzzle.  That's true, unless you turn up the heat.  I'll see how it goes and let you all know.
  
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madsenshooter
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Re: .310 FMJBT bullets for larger bored rifles
Reply #7 - Feb 28th, 2018 at 5:18pm
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I managed to get a little shooting time yesterday.  I had a variety of loads made up using the Hornady and Prvi 174gr FMJBTs.  The Hornady was outshooting the PRVI, but not by a lot.  The best of the day was 5 of the Hornady bullets over 48.4gr of RL19 that shot a 1.6"wx1.3"tall group.  50gr of H4831SC shot a slightly larger group with the group being about 4" lower than the RL19 loads and the boosted 860 loads impacted between the two.  With the Hornadys, I seated the bullets to the crimp groove and used the Lee factory crimp die.  PRVI bullets were seated to max magazine length and no crimp used.  I used the CCI #34 primer for all loads.  Though quite bulky, I've got good results with RL19.  An Alliant powder, it is made in Sweden.  I've got one of the lenses from my dad's glasses glued onto my sunglasses for shooting.  I still see the up and down double of the bull at 100yds though.  That's no longer a problem, just cover the bottom one with the front sight.  I'm waiting on my third pair of glasses from the VA.  I mention my vision problem cause I had a really tight group going using WC860, plus a bit of booster.  5gr of Blue Dot, 46.2gr of WC860.  The first three went into less than .5", but I lost the other two.  One went really low, like I picked the wrong one of the double bulls!  The other just slightly off the paper, about 3/4" out of the group of 3.  I'm going to get back to that load, use up the cheap 860.  It worked very good for some fire forming loads with 150gr FMJBTs.
« Last Edit: Mar 5th, 2018 at 4:59pm by madsenshooter »  
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