One rifle shoots fine, the other not so much...

S

Schnitzjr

New member
One rifle (1:8 twist) shoots my reloads fine.
the other rifle (1:7 twist) keyholes every shot!

Under 3000 rounds through both rifles, bores look great (I clean after every outing) bullets are pulled M193 that look great and measure .224 wide.

I'm using 24.5-24.7 gr H335, loading on Lee Turret press.

I cannot fathom why one rifle functions flawlessly and the other does not!
I have test fired XTac, Wolf brass and M193 Federal Ball and they all went down range without a hitch in both rifles but my reloads just will not stop keyholing out of the one rifle.
I do not have a chrono but my reloads feel soft compared to the factory stuff.

Any ideas?
 
I am sure you listed a chamber, make and model, there are times I read too fast and miss somethings.

I went to the range with two new rifles, both were 300 win Mags, both were shooting the same ammo and shot by the same person. One shot one hole groups, the other shot like a shot gun, it shot patterns.

I contacted Winchester, they instructed me to shot it more. I wanted to know if there was something I do not know about large ugly chambers. I wanted to know how shooting the rifle would reduce the length and diameter of the chamber. We had words, eventually the gun shop sent the rifle back to Winchester because honing, reaming and polishing the chamber did not reduce the chamber in length and or diameter. I asked the smith why he sent the rifle back to Winchester, he said the chamber was too long and large in diameter, I then ask him when did that happen, I ask him if it was his honing, or his reaming and or his polishing. He said the rifle can that way, and I wanted to know why he could not measure the chamber before he started.

I ask for a chamber that would fit my dies or Winchester dies that would fit their chamber. It time we had more words and they sent the rifle back in a new box. One day I will take the rifle to the range, it has been 5 years + since I received the new box.

I would not shoot the same in both rifles.

F. Guffey
 
AR15, both 5.56. one is 1:7 twist (Complete upper bought from Primary Arms), the other 1:8 (Complete upper bought from DSG).

Not sure how your story fits the thread but I will smile and nod.:D
 
I would not shoot the same in both rifles.
Click to expand...

Use longer bullets, shorter and or heavier bullets. I have a friend that built a rifle for prairie dogs, the barrel manufacturer is a personal friend of his, the owner hand selected the barrel as a good gesture. the rifling was not even close to what my friend had ordered, it scattered bullets like a shotgun. The barrel manufacturer corrected the mistake, it was not in time to take the rifle on the next hunt.;)

F. Guffey
 
Keyholing is unexpected. Since bullets become more stable, and not less stable, as twist increases, and since other ammo shoots well in both guns, I suspect something is happening to these particular bullets in the faster twist. Your load level is middling unless you are using a magnum primer, in which case they could be nearer Hodgdon's maximum in actual pressure and velocity, depending on the primer brand, though that's still not quite up to the military's maximum.

My guess is you may be experiencing bullet core stripping. This is where angular acceleration by the rifling twist causes the jacket to spin up so quickly it breaks contact with the core, which then lags behind the jacket spin rate. When the bullet exits, the two rates of rotation find a compromise angular velocity as the the jacket loses spin to the core, and the core gains spin from the jacket. Being less massive than than the core, the jacket looses a lot more spin than the core gains in this exchange. The end result is a bullet spinning more slowly than the velocity and barrel twist would suggest it should be. The core is then also loose in the jacket, so the net projectile is poorly balanced and wobbles in flight and would tend to shotgun even if it weren't outright unstable.

The reasons I suggest core stripping are two-fold. One, you have pull-down bullets. The pulling process usually squeezes on the jacket some, and that squeezes the core. Copper gilding metal is more elastic than a lead core, so it springs back better. Add to this that the pulling was done to bullets already deformed by crimping, and you can see how it might weaken the contact friction between the core and jacket.

The second reason is that the bullets shoot well enough in a slower twist. All else being the same, the only thing the faster twist does differently is supply greater angular acceleration which increases the core stripping stress. If I'm right that this is core stripping, then I'd expect, unless they were made surplus because they couldn't pass accuracy testing in a 7: twist military rifle, that if the bullets were new and not deformed or pulled, they'd hold together for you.

Anyway, the core stripping hypothesis is easy to test. If you fire them in the 7" twist gun loaded for 7/8 as much velocity, they should then get the same rotational acceleration they do in the 8" twist gun. If they stop keyholing when you do that, the hypothesis is correct. Try 21.5 grains of powder and 19.7 grains of powder. I estimated by two different methods and got those two different numbers. Shoot the 21.5 grain load first, because if you find keyholing stops anywhere on the way down from below 24.5 grains, you have shown the bullets were likely to have been stripping.
 
I will load up several rounds at 21.5 and 19.7 grains as unclenick suggested.
I'm also going to load up more at 24.5 and fire through a third 1:7 rifle.
Lastly, I will load up a batch using some brand new 55g BT bullets I just received.

Will report back ASAP.
 
A quick update to this, bought some Hornady .223 bullets and loaded up a hundred rounds at 24.5 grains with H335.
Both rifles shot without keyholing this time but the 1:7 rifle is shooting 6 inch groups while the 1:8 is putting nickel sized holes in the paper at 50 yards.
I got similar results with factory ammo as well so something is up with my 1:7. I even bought a new barrel for it. :(. Don't know why it seems to be getting less and less accurate while my 1:8 kicks butt. Very confused.
 
This is going to sound stupid but, is the barrel fouled up with copper? I'm assuming they are being shot off of different lowers. If so, switch them and see if the 1:7 regains accuracy off of the other lower. If so, there is the problem. These to me seem the most obvious. I like to eliminate obvious before getting detailed. :^) God Bless
 
I think you just need to invest in some better bullets. measure the "pulled" bullets for consistency in diameter. my 1:7 shoots best with 70-80gr bullets
 
Those rapid twist barrels will do better with longer heavier bullets.
You can shoot 90 gr bullets in a 1:7" barrel, but it is no surprise you groups are worse with the faster twist when shooting 55 gr bullets.

You should try 69 Sierra MK's in the 1:8" and 75 gr Hornady OTM in the 1:7".

Forget about 55 gr or lighter in those twists, for exactly the reason you are experiencing.

Barnes all copper lead free bullets are also very long and the 70 gr should be perfect for your two twists.
 
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Bore and chamber are spotless.

What concerns me is the decline in accuracy. If the rifle was not shooting good groups all along I would attribute it to using the wrong bullet weight.

Metal God I didn't try the lesser charge because at this point the keyholing stopped by switching to the new Hornady bullkets. The Pulled M193's were keyholing badly.

I will try swapping lowers as WVmountaineer suggested.
 
Ok but If you get a chance I'd really like to know if the issue was bullet core stripping. The fact the rifle shoots other bullet ok would seem to point in that direction but does not confirm it . Only that there is likely something wrong with those bullets .
 
Core stripping is easy to test for. Just get some 4198 and load down at about 17 or 18 grains. That will slow the bullet enough that the core stripping, if it's happening, should stop. It's a good accuracy powder to have for this bullet weight anyway, even if it doesn't get maximum velocity.


Schnitzjr:

How are you checking that the bore is spotlessly clean? If you don't have a borescope, the next best thing is a copper dissolving bore cleaner that gives a strong color indication from the presence of copper. I like Boretech Eliminator for general cleaning and it produces such an indication. You have to use it with a plastic or other chemically inert jag, as it reacts with the copper in brass so fast a brass jag will color the patch light blue before it gets through the bore. Anyway, put some of that stuff in the bore and wait five minutes and patch it out to check for copper.

This article has more on the subject.
 
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