Wildly innacurate GP-100 load?

thevest

thevest

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Loaded up some 158g TMJ bullets over 13.8g of 2400 powder for my (new) 4.2" GP-100. Lee's reloading guide indicated the maximum load of 14.9g is the "potentially most accurate" but I didn't want to start at the maximum.

Testing them out of the range today, and accuracy was abysmal! At about 10 yards it looked like I was patterning a shotgun. :(

I'm not exactly a bullseye shooter, but I could easily keep my shots on a 3" shoot-n-see target at 10 yards with my 686. I find it unlikely that either the Ruger is that inaccurate, or that my shooting skill has devolved that badly in the past month or so.

Anybody have any experience reloading for the 4.2"? I don't get out to the range very often, so I'd like to keep the trial-and-error to a minimum if I can help it.

Any comments appreciated.
 
There are quite a few factors to consider. Are the bullets at least 0.358" in diameter? Is their weight varying a lot? Are your charges weighted?

Is the trigger smooth? (Watch your aim point while dry firing.)

Try shooting some factory loads with supported hand (on a sandbag or something). This should tell you something about accuracy. Then try your loads supported.

If it is still inaccurate, load and shoot some subsonic loads and then increase the load towards maximum (I use 15gr of 2400 with no ill effects in my GP100).
 
I found I was not as accurate with my 4.2 GP100 as my 6" 586. I think the shorter sight radius and my lack of practice is more of an issue than the ammo/reloads.
 
mmattockx said:
Did you happen to crimp them? Was there a cannelure to crimp into?
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There was a Cannelure, and I did crimp them. I'm not sure if you'd call it a roll or taper crimp..... whatever the lee carbide dies accomplish.

legi0n said:
Are the bullets at least 0.358" in diameter? Is their weight varying a lot? Are your charges weighted?
Click to expand...

Charges are being thrown with an auto-disk. I weigh about one in every ten, so it's possible that I'm not catching the fluctuations. (if any) Not weighing the bullets (scale only goes to 110g).

I certainly need to shoot from a rest next time to be sure, but it's got to be more than just that.
 
this almost sounds like the nut behind the wheel needs a little adj . anything out of anything has to give @ least 3" at 10 yds, other than the wheel nut , check the bore/bullet dia, if it's out[loose] by more than .001, get a fatter bullet & squeese don't pull , diff primers, powders/ weights/ seating depth, crimping, don't mean sh-t @ 10 yds, if the bullet is ratteling down the barrel, thats a prob, hope to see 1" @ 10yds, good luck
 
My .02 only.

TMJ Totally Metal Jacketed Bullets are Plated with a soft-lead core, not Jacketed.

Manufacturers of TMJ such as Berry's and Rainier usually limit maximum velocity of these heads to 1,200 FPS, basically a medium .357 magnum load. What brand are your bullets?

13.8 grains of 2400 is probably driving these projectiles around 1,350 FPS, and you are stripping the plating as the bullet travels down the bore and the plating is either totally or partially stripped away from the lead core, or the bullet/soft lead core is just forced straight through the bore's rifling without spinning. Hence, bullet is not stabilized.

I shoot 158 grain Speer JHP over 14.0 grains 2400 through my GP100. Last time, I got a 3-shot 1 inch group at 15 meters, double-action, standing two-hand hold. Not wanting to risk enlarging the group further, I packed the GP away, happy that I had a good story to tell the boys over drinks, and very content with the gun/ammo/myself:D
 
easyrider604 said:
My .02 only.
13.8 grains of 2400 is probably driving these projectiles around 1,350 FPS, and you are stripping the plating as the bullet travels down the bore and the plating is either totally or partially stripped away from the lead core, or the bullet/soft lead core is just forced straight through the bore's rifling without spinning.
Click to expand...

A quick check on some other sites suggests that this might be the problem. People saying that over 1,200 fps with plated bullets "starts looking like a bad shotgun pattern", which is exactly how I'd describe it.

I'll reduce the loads and see what that looks like, then try something other than plated bullets next time and see if that helps.
 
Hmm, good advice, i just loaded 100 rounds of 158gr Plated HP from Berry with 7.4gr of Unique with a OAL of 1.570, should get me about 1000fps. hmmm hope it works well :)
 
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