Clark bbl is keyholing (Model 41)

Shooting BE indoors @ 50', I was getting some very fat, oblong hits, maybe 3 or 4 per tgt of ten shots.  Commented on by various shooters when they scored me over the last several months.  CCI std vel was the ammo. *

I sent it off for a crowning even though it wouldn't snag the first wisp of cotton from a Q tip.  Back it comes and no change.......grrrrr.

Same results tonight on the first group of targets.  I changed to S&K Std - nothing fancy or even the Pistol Match flavor and NO funny holes.  I'm going to mic the CCI Std vel fodder and do some cogitating and testing.  I'm wondering if CCI may/may not have a bit of a mfrg QC problem?

Results will be posted.

Quick question:  Which older Lapua .22 rf ammo was a bit larger diameter?  Older Midas L or M?  Seems I read that in the last year or 3......

*No, I wasn't limp wristing that mighty recoil, a la Model 52, to get'em sideways....

I have a S&W 5.5" 41 barrel that did keyhole CCI sv at 50ft.  Other ammos keyholed or tipped less but to a lesser degree than the CCI.  Eley tipped the least.  I have since had the barrel relined by Alex Hamilton.  The barrel is about a 1977-8 vintage.

Roddy and I looked the bore over, slugged it and scrubbed it.  No effect at all.

Does it do this at longer ranges? I have never seen keyholing not get worse at longer distances.
I assume that you know this, but just in case:
What looks like keyholing is sometimes no more than a target just hanging in the air and producing oblong holes.
I solved the problem by putting a length of cardboard on the bottom of the target.

Borrow a bore scope and look at the chamber and how it was cut

I have tested various rimfire ammo in my M41, mid 70's vintage, organial barrel.  In each case CCI Std Vel produced the largest group at both 25 and 50 yards.  Last week I ransom rest tested the same gun using Eley Target, Eley Sport, Aguila Match and CCI Std Vel.
Eley and Aguila Match all grouped well withing the X-Ring and the CCI had two just outside the X-Ring in every 10 shot group.

At 25 yards Eley and Aguila grouped one hole with the Eley Target grouping at 1/2" with the CCI grouping about 3/4".

This gun is stock and has had a lot of rounds through it.

A couple years back I found CCI did not group well in this gun and was able to use a chrono while testing.  My M41 shot better groups with faster ammo and I recall that CCI Std Vel was at least 50 fps slower than Eley or Aguila.

I've never experienced any keyholing with this gun.

Could be the Ammo, I had a batch of CCI STD that key holed a couple, still in the 9 and 10 rings. 

RE Velocity, All Aces, I found my Model 41 really likes Federal Match White Box. Its advertised as 1200 FPS but its only seems a little hotter than SK. My bet its in the 1100 to 1150 range out of a rifle. I use a std spring and a recoil buffer. 

If you do another test I would be interested to see if in fact it is the case that that ammo runs well in a Model 41. 

I will also note that sorting the Aguilla match or ELEY Target by rim thickness makes that ammo more accurate than most anything.

I bought my 41 PC new last April and it keyholes a couple of times every 10 shots on CCI Standard. I got a ransom rest and tested about 15 kinds of ammo and SK Standard Plus was about the best popular priced ammo and seems to have totally stopped the key holing. I can't say why it is better as each brand had several parameters different. CCI was the largest diameter by about .001. It was also the longest. And of course SK has a much different lube. I can verify that the lube makes a lot of difference. I know this because I would shoot 10 fouling rounds followed by 2 groups of 10 rounds of the same ammo from a ransom rest. Then change nothing but the ammo and do the same thing with the next brand. Then I went back and did the same tests but cleaned the barrel between each brand change. The difference was very significant.