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keyholing 7mm Rolling Block (Read 412 times)

George Babits Frequent Elocutionist Offline Posts: 1151 Joined: Sep 27^th, 2012	keyholing 7mm Rolling Block Jun 5^th, 2026 at 3:54pm	Print Post
	I've got a really nice 7mm rolling block. It shoots fine with 175 grain jacketed bullets at 2350 fps. But, my preferred load is a 168 gas checked bullet which runs about1820 fps. The problem is that the cast bullet keyholes 2 shots out of 5. The same load shoots fine in my 7mm rolling block carbine so I don't think it is the ammunition. Any ideas? George


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jimmy Senior Forum Member Offline Now available in Oklahoma. Posts: 466 Location: Skiatook Joined: May 12^th, 2009	Re: keyholing 7mm Rolling Block Reply #1 - Jun 5^th, 2026 at 4:21pm	Print Post
	Check groove diameter and bullet size.


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GunBum Senior Forum Member Offline Posts: 293 Location: SW Missouri Joined: Oct 30^th, 2021	Re: keyholing 7mm Rolling Block Reply #2 - Jun 5^th, 2026 at 4:35pm	Print Post
	What is the twist rate? I’ve had several 7x57 rifles that shot 175gr bullets fine and keyholed with lighter bullets.


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George Babits Frequent Elocutionist Offline Posts: 1151 Joined: Sep 27^th, 2012	Re: keyholing 7mm Rolling Block Reply #3 - Jun 5^th, 2026 at 5:26pm	Print Post
	The cast bullet is 168 g +/- and the jacketed bullet is standard 7mm spitzer. The cast bullets are sized to 284 and work fine in my 7 mm rolling block carbine. I haven't a clue what the twist is, but I'd guess 1 in 10 as that is standard for the 7mm and both rifle and carbine are "standard." With the cast bullets I usually get a nice 1.5 inch group for 3 shots (sitting) at 80 to 100 yards with two keyholes. I suppose I should see where the keyholes fit in the order of rounds fired? George


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GunBum Senior Forum Member Offline Posts: 293 Location: SW Missouri Joined: Oct 30^th, 2021	Re: keyholing 7mm Rolling Block Reply #4 - Jun 5^th, 2026 at 8:01pm	Print Post
	I have several 7x57 95 Mausers (yeah I know, not a single shot) that will do 1-1/2” at 100 yards with 175 grain bullets, and anything under 170 grains keyholes. It is 1:220mm (about 1:8.7in). Once the bullet gets too short, it isn’t stable anymore.


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George Babits Frequent Elocutionist Offline Posts: 1151 Joined: Sep 27^th, 2012	Re: keyholing 7mm Rolling Block Reply #5 - Jun 6^th, 2026 at 2:23pm	Print Post
	The 175 grain jacketed spitzer is 1.355" long; the cast 168 grain bullet is 1.175" long. Assuming that the 7mm carbine has the same twist as the rifle, if the length was the problem, the lead bullet would be keyholing in the carbine too. George


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frnkeore Frequent Elocutionist Online Posts: 7645 Location: Central Point, OR 97502 Joined: Jun 16^th, 2010	Re: keyholing 7mm Rolling Block Reply #6 - Jun 6^th, 2026 at 8:19pm	Print Post
	Have you tried linotype? With that fast twist, a soft alloy may strip sometimes. I would also check the crown on the muzzle.

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George Babits Frequent Elocutionist Offline Posts: 1151 Joined: Sep 27^th, 2012	Re: keyholing 7mm Rolling Block Reply #7 - Jun 6^th, 2026 at 9:14pm	Print Post
	cast bullets are Lyman #2 alloy


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GunBum Senior Forum Member Offline Posts: 293 Location: SW Missouri Joined: Oct 30^th, 2021	Re: keyholing 7mm Rolling Block Reply #8 - Jun 6^th, 2026 at 10:59pm	Print Post
	George Babits wrote on Jun 6^th, 2026 at 2:23pm: The 175 grain jacketed spitzer is 1.355" long; the cast 168 grain bullet is 1.175" long. Assuming that the 7mm carbine has the same twist as the rifle, if the length was the problem, the lead bullet would be keyholing in the carbine too. George I wouldn’t assume that unless you measured the twist rate.


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George Babits Frequent Elocutionist Offline Posts: 1151 Joined: Sep 27^th, 2012	Re: keyholing 7mm Rolling Block Reply #9 - Jun 7^th, 2026 at 5:02pm	Print Post
	I've tried to measure the twist and for some reason I can't get it done. Good tight patch but rod hardly rotates. Tried two different rods, both with ball bearings in handle. Both the carbine and rifle acted the same. Not sure what is happening there. Twist "looks" pretty fast. I don't think the problem is related to the twist or bullet length. I have a friend in Arizona who was doing pretty well with a 154 grain bullet in his 7 mm rolling block rifle. George


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bullshop Senior Forum Member Offline Posts: 363 Joined: Sep 14^th, 2017	Re: keyholing 7mm Rolling Block Reply #10 - Jun 7^th, 2026 at 5:17pm	Print Post
	Try dropping the powder charge by 2 grain.


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frnkeore Frequent Elocutionist Online Posts: 7645 Location: Central Point, OR 97502 Joined: Jun 16^th, 2010	Re: keyholing 7mm Rolling Block Reply #11 - yesterday at 4:16am	Print Post
	What you may have is rifling that has well worn edges from wear and erosion. Take a casting of the rifling. Lino could help, it's about 50% harder than #2

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George Babits Frequent Elocutionist Offline Posts: 1151 Joined: Sep 27^th, 2012	Re: keyholing 7mm Rolling Block Reply #12 - yesterday at 9:49am	Print Post
	I think I'll take the simple solution and just stick with the jacketed bullets. The have never shown any sign of keyholing. Thanks for all the suggestions. George


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