257 Roberts keyholing

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jimmyraythomason

jimmyraythomason

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Okay I finally got out to zero my Mauser 98 in .257 Roberts. Three shots fired and three perfect 90 degree keyholes. Ammo was 117 gr. WW Power Points. I had had high hopes for this rifle......What causes keyholing and more importantly, what can I do about it?
 
You probably need to try some lighter bullet weights to see if it's the heavier bullets causing stability issues.
Is the twist a 1in10"?

Check the muzzle crown for damage or poor uneven crown.



NCsmitty
 
Thanks NC smitty. The 117 grs was all I was able to find factory loaded. I don't know the barrel twist rate, it wasn't specified when I bought the barrel. The barrel was professionally recrowned when it was installed.
 
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Is it possible to re-chamber this rifle to 25.06? It is standard length action and the magazine will accomodate the 25.06 without modification. Barrel length is 24'' total length.
 
You can measure the twist with a swivel handle cleaning rod and a tight patch. Put a little tape flag on the rod and mark a starting point and the stopping point after one revolution.

Shilen recommends 10" twist for "up to" 100 gr bullets. I think there is a good deal of margin on that, but you have apparently gone beyond it.

I think a .25-06 reamer would clean up a .257 chamber but it would not necessarily let you shoot 117 gr bullets. Bullet stability goes up only as the fourth root of velocity, which is not much.
 
You probably can check the twist using the old cleaning rod and tight patch routine. It should be close enough to judge if it's a 1in10" or something else.
1in10" is pretty much standard for 1/4" bore.

Are you able to load the 257 Roberts at this point?



NCsmitty
 
I don't hand load but if that is what I have to do to get to shoot my bob...... It was like kissing an angel to shoot,sweet! I was thinking about more bullet choices and loads for the 25.06. I know they (factory loads) are much more available around here.
 
I have a mauser in .257 rbts.. definitely not a gun I will ever get rid of... not sure what to recommend that others have not mentioned... I would try different weights if/when possible.... there is just something different enough about the bob to make it appealing.. I definitely wouldnt rechamber into a the 25-06 if I hadnt exhausted every other option...
 
The last keyholing thread I read was fixed by not bouncing the bullets off the ground before they entered the paper. Not saying its your fix, just saying:D
 
I would much prefer to keep it in .257 bob. I have always wanted one. I did the tight patch and cleaning rod method and it is 1:10 twist.
 
I checked around and lighter 257 Bob ammo is harder to find and expensive.

Too bad that you cannot load some 85-100gr bullets to see if they behave properly.



NCsmitty
 
At what range is it keyholing being accomplished? Have you tried different ranges to see if/when in the bullet's flight it is destabilizing? Have you checked the headspacing?
 
Try a diffrent brand of ammo something like the Hornady superperformance rounds, could be your rifle just does not like those rounds.
 
At what range is it keyholing being accomplished?
Click to expand...
First round wasat 100 yards and the other 2 were at 50. The headspace was set when the barrel was installed and this was the first time it had been shot. I did have some Remington 117 Core-lokt cartridges but didn't try them.
 
I guess all you can do is work with different ammo and see if you can get improvement... may be time to start reloading... :what:


(is that really such a bad thing?):D
 
A fellow THR member who lives within easy driving distance has offered to load them for me if I will buy the dies(he currently doesn't load .257 Roberts) and components. I have more than enough hunting rifles in several calibers. This was just to be a "because I want one for the fun of it " gun.
 
I will be getting started in reloading some time this month and look forward to finding a pet load for my .257. I hope you are able to find what works.
 
You mention this was a brand new barrel. Did you thoroughly clean it before firing the first rounds and what sort of breakin procedure are you following ?
 
If I remember right... the old original 257 Roberts loads with 117 grains bullets used round nosed bullets. My older reloading mentor had to load those to get his 257 to shoot. He had a 244 Remington that had the same problem. If I'm not also wrong the first of 257 Weatherbys had to use 117-120 grain round nose bullets because of the same reason, barrel twist. But then I may be wrong too.

Jimmy K


http://www.midwayusa.com/viewProduct/?productNumber=440769
 
First thing I would do is measure the rifling twist with a cleaning rod like several folks suggested.
If it is in fact 1/10, it should shoot 117 grain flat base semi-pointed bullets just fine.
(If it is slower then 1/10, somebody put a slower twist 1/12 barrel on it for a varmint rig shooting light 60-75 grain bullets.)

Next, I would slug the bore and make sure it is in fact a .257" barrel.
(It would keyhole real bad if it happens to be a .264", or .270" barrel some jack-leg chambered for .257 Roberts by mistake.)

Other then that, crown damage, or lathe live-center damage to the muzzle is about the only other thing it can be.

BTW: It has nothing to do with break-in.
A new barrel should not be shooting bullets sideways at 50 yards, break-in or no break-in.

rc
 
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