OT---Bullets keyholing from .243 M-77

[Mustang Gregg]

 

This is a new one on me. A friend brought in a .243 M-77 that her son couldn't hit deer with. They wanted me to check it out. Well, I found a loose scope and a bad elevation turret. So I fixed those problems. I also cleaned the chamber and barrel.

 

Then I went to the range and found that it would keyhole at 40 yds with both 80 gr & 90 gr bullets. I think all Ruger M-77's have a 1:9 twist, which should work fine with both bullet weights. I don't have an erosion gage, but the rifle has not been fired very much, so I'm guessing that wouldn't be the trouble.

ANY IDEES, PARDS???

 

Much obliged,

Mustang Gregg

[Rex M Rugers #6621]

Wow , keyholing at 40 yards would make one think it was a smoothbore. Maybe it has a damaged crown. Might be somewhat enlightning to slug the bore , also.

Will be watching your progress on this one , keep us updated.

Rex

[Chickasaw Bill SASS #70001]

I think RMR hit the nail on the head , most likely recrowning will cure it .

 

Chickasaw

[Mustang Gregg]

 

I looked at the crown and it doesn't look like it was dinged up.

I just asked the owner if he ever had any keyhole and he said 'no'.

He only shoots factory Remington 100 gr SP's, too.

 

Anyhow I'm gonna shoot some 100 gr ammo tomorrow.

I will see if'n I can find a .243/6mm erosion guage or at least aome ball gages to mike the bore.

 

Hmmmmm????

 

MG

[Seldom Seen #16162]

Factory or reloads?

[Chili Ron]

Pard,

My bet is that the bullets are too heavy to be stabalized by that rifle barrel.

So try lighter not heavier bullets.

.243 are available all the way down to 56 grainers.

And guessing at barrel twist is a waste of breath.

Many mini14s have been given bad press because their owners werent patient

enough to find the bullet weight their particular barrel liked.

 

I have a 223 that will shoot little groups way out there but feed it 69 grainers

and it will pattern keyholes at 50 yards.

those same 69 grainers fed to my mini 14 will put 5 rounds in one inch in 15 seconds

at 50 yards. Give that a try with any rifle you have.

Best

CR

[Hacker, SASS #55963]

Assuming Correct bullet diameter and clean barrel with no damage, keyholing occurs because the bullet length and twist rate do not match.

The Greenhill equations used to determine this relationship use the bullet weight because they assumed FMJ.

The actual issue is the bullet length.

 

The Greenhill equations mentioned on this page.

Barrel rifling

[Steel-eye Steve SASS #40674]

Pard,

 

 

I have a 223 that will shoot little groups way out there but feed it 69 grainers

and it will pattern keyholes at 50 yards.

those same 69 grainers fed to my mini 14 will put 5 rounds in one inch in 15 seconds

at 50 yards. Give that a try with any rifle you have.

Best

CR

 

I have a FN FNC import with a 1/12 barrel and even with its heavy trigger will shoot very nice groups with 52 or 55 grain bullets, but feed it any ss109/m855 ammo and it's like a shotgun, with a fair number of bullets key-holing.

[Mustang Gregg]

 

Like I said in my posts---I have tried lighter bullets...Did not fix the problem.

And the owner of the rifle said it does shoot the 100 gr Rem factory stuff straight and true.

 

Still trying,

Mustang Gregg

[Iron Pony]

Greg I carried a 77 stainless weather proof or whatever they called it for several years as a deer rifle up here and settled on the Nosler 100 grain partition bullet for that purpose. Cant find my load info but IIRC it was with a fairly stout load of 4064 and the rifle would shoot 3 shot groups of right about an inch at 100 yards. The only thing I do remember is the large charge and slim profile bbl made it heat up quick at which point accuracy would suffer. It also had a tendency to blow up groups on light bullets when I tried to push them too fast, but thats my fault. The other thing about 243 is/was bbl life, lots of powder being used, lots of pressure and flame etc so they dont last as long as others. If you have another rifle to shoot the same loads through that might tell you if they are bad or if there is a problem with the rifle. I think erosion is a good bet, so a real good bore scope might help out.

 

Heres a link to some real good info about the 243, http://www.6mmbr.com/243Win.html.

 

Everytime I go to Rileys in Hooksett I eyeball a real nice Savage heavy bbl in the rack but being used I always get worried about bbl life.

[Ol Number4]

MG,

 

Yes try the heavier bullets, I found the same problem with one I have.

Too tight a twist for light ammo.

 

Ol' #4

[Stump Water]

Another thought... Thin paper targets (w/o some type of backing) will tear instead of punching nice holes, particularly at closer ranges.

 

If the bullets really are tumbling groups should be... there would be no group.

[Dubious Don #56333]

Before you re-crown this rifle check the following:

 

Barrel throat erosion.

 

Groove diameter (if you don't use bullets of the proper size, they'll keyhole too)

 

Barrel twist.

Actually, I'd check this first and see if the bullet weight you're using is compatible. Generally, the heavier the bullet, the faster twist you need to stabilize it. Remember this isn't rocket science. Internet advice is good. Charts and graphs are ok but NOTHING beats putting the rifle on paper and seeing where YOUR rifle shoots with YOUR loads.

 

If the 80-90's are KH, try 100gr bur first check the twist. Take a cleaning rod that can rotate with a tight patch or bore brush. Stick it down the bore and when it's in the rifling, mark the top of the rod by the handle and make another mark on the rod where it enters the chamber. Push down borw until it makes one revolution, make another mark by the chamber just like the first. Pull the rod out and measure between those two marks. If it's 9 inches your barrel is a one twist in nine. (1/9) If it's 11 then it's 1/11 and so on. the higher that second number, the heavier bullets (in theory) that twist needs. One old chart I've got says 1/14 = 70-75gr 1/12 = 85-100gr 1/10 100gr & up.

 

 

This is a new one on me. A friend brought in a .243 M-77 that her son couldn't hit deer with. They wanted me to check it out. Well, I found a loose scope and a bad elevation turret. So I fixed those problems. I also cleaned the chamber and barrel.

 

Then I went to the range and found that it would keyhole at 40 yds with both 80 gr & 90 gr bullets. I think all Ruger M-77's have a 1:9 twist, which should work fine with both bullet weights. I don't have an erosion gage, but the rifle has not been fired very much, so I'm guessing that wouldn't be the trouble.

ANY IDEES, PARDS???

 

Much obliged,

Mustang Gregg

[Stump Water]

the higher that second number, the heavier bullets (in theory) that twist needs. One old chart I've got says 1/14 = 70-75gr 1/12 = 85-100gr 1/10 100gr & up.

 

 

[Conejo Kid #51342]

Dubious Don is correct. However, I think he said it backwards -- it should be -- the higher the second number the lighter the bullet. The chart is however correct. A 1:9 twist (that's one rotation in 9 inches is a faster twist than 1:14. Heavier bullets need a faster rpm to stabilize the bullets. I have a heavy barrel Remington 700 in .243 that keyholed every light bullet I put through it. However, shooting 100+ grain bullets it does very well.

 

You may want to check the crown as well. Even a small burr can cause problems. You can do a poor man's re-crown (i.e. polish) buy putting some lapping compound (not valve grinding compound)-- about 500 grit on a metal ball bearing and rolling it around the crown opening for a couple of minutes. If there is a burr, it will generally remove it and leave a slight but even tapered crown.

 

Good luck, CK

[Four Bucks #36386 Life]

Well, I was all ready to tell you about bullet weight not matching the rate of twist...but our Pards have given you great advice and set you on the right track. Good luck.

 

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