Keyholing

[MI2600]

Last week I shot a newly-acquired Mauser C96 7.63X25 and all the bullets keyholed. Last night I changed bullet types and shot it again and it was perfect.

Keyholing bullets:
100gr LFP bullets, .309", 4.5gr Bullseye.

Good loads:
90gr Hornady XTP, .309", 4.5 and 5gr Bullseye.

What am I missing?

 

[Wil Terry]

Stabilty of a longer softer projectile.

And so it goes...

 

[Hondo 60]

Were the 100 gr bullets really .309"?
Sometimes keyholing can occur because the bullet is a hair small.

But you've found out that not all components work perfectly in all guns.

I have a couple of .38Spls 1 of which doesn't like 158 gr bullets.
Plated 125 gr are MUCH better in that gun.

Also had a 9mm that didn't like 115 gr bullets.
Tried all sorts of profiles, including factory ammo.
Still stove piped about once a mag full.
Never had any problems with 124 gr bullets.

 

[MI2600]

The lead bullets did measure in at .309. Even if there some smaller, I doubt if all ten bullets were.

 

[murf]

you may want to slug your barrel. the .311" bullets will probably do better in your mauser.

murf

 

[Walkalong]

The 100 Gr LFP bullets may be skidding in the barrel, while the JHP is holding the rifling.

 

[lckdnldd]

Something to consider. When I use paper targets I use cardboard for a backboard. I was getting what I thought was keyholing. In reality I had used the same backboard for for previous target practice sessions and had blown out about a 8" circle in the center. The bullets were tearing the paper instead of cutting a clean hole because the backboard was shot out.

 

[MI2600]

I had not considered that. Good thought.

I'll also try to slug the barrel. From what I understand these old Mausers can widely vary.

 

[noylj]

Was the bore perfectly clean for each? Did the lead bullets also lead the bore (since they appear to be slightly too small)--lead bullets generally should be at least 0.001" larger than actual groove diameter. For some old milsurp gun that most likely fired corrosive ammo, a determination of actual groove diameter and an inspection of the bore before ever shooting lead bullets should have been done. Shooting jacketed may be best option no more what.

 

[Mauser69]

Do some research on rifling twist rates and how it affects stability with specific bullet weights in different calibers. Not all guns of the same caliber use the same twist rate, so perhaps your specific gun is already at the limit of what it can handle with 90g bullets of that specific shape and construction?

 

[Jim Watson]

Probably a diameter mismatch, maybe in combination with a worn barrel in an old gun.
I doubt it is the twist rate. One source says the Broomhandle has an 8 twist which is common in the .300 BO with MUCH longer/heavier subsonic bullets.

I have seen a lot of 9mms to keyhole with cast bullets, everything has to be right to run lead in these European autos.

 

[Steve C]

I would try reduction in load and if there s room to go up I'd try that too. I've occasionally had keyholing issues with lead bullets and have been able to solve the problem with load adjustment.

 

[grumbles_in_mi]

30 mauser, in broomhandle

Be sure you use the correct load data the for C-96. The C-96 is not a proper 7.62 x 25 it is correctly the 30 Mauser (or 7.63 Mauser) and is loaded to different (lower) pressures than the 7.62 x 25. The cartridge dimensions are close enough to be considered by some to interchangeable, but the actual loading is different. Neither my Hornady nor my Lyman books show load data for a 100gr bullet for the 30 Mauser.

 

[MI2600]

I think I'll back off and start tests at 4.0gr of BE and work my way up.

 

[MI2600]

Update.

I loaded some test loads from 3.8gr to 4.4gr. I still got about 1 out of 5 keyholes with the lead bullets. I should have tried the loads in my other 7.63s and Tokarevs.

Look like I have a barrel-bullet mismatch on this gun.

 

[Trent]

Well, you learned something valuable.

I always look at "what doesn't work" as just as valuable as "what does work"... assuming there's no rapid-unplanned-disassembly-happenings-stuff. (Such as what happened when I was messing around with 223 pistol length gas system load development...)

 

[Reefinmike]

Check your bore. A badly leaded barrel will keyhole a bullet real quick.

 

[Curator]

Jacketed bullets are significantly harder than any lead bullets. An under-size jacketed bullet will usually shoot accurately because it will 'self-center" in the bore and will not have metal eroded off their sides by hot gasses escaping up the grooves like will happen with lead. Under-size lead bullets will not only deposit lead fouling in the bore but also key-hole. Lead bullets in a high pressure round like .30 Mauser need to be a couple of thousandths over groove diameter and hard enough to resist pressure melting. (about BHN22) Gas checks will also help both with leading issues and accuracy.