Keyholing Reloads

[watsona]

I have a late 90's mini-14 that does not like my reloads. It has always had accuracy/tumbling issues and I assumed it was just that the barrel was worn out from heavy use back when Wolf 223 was under $90/case. Today I brought 3 loads to the range: American Eagle .223 55grn, Tulammo 55grn, and my reloads (22.5 grn H322 + 55grn hornady FMJ. All shots were taken from 50yards on a semi-stable bench. My reloads key-holed terribly with many missing the paper plate completely, tulammo didn't keyhole but was all over the place, and the American Eagle shot a decent group. I repeated the test twice with identical results. The only difference I noticed when shooting was that my reloads ejected at the 90 degree angle to the gun while the AE pattern was further back. All bullets were 55grn and I have had a lot of success with these reloads in various AR-15's. Does anyone have suggestions for why my reloads suck in this rifle?

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[Kruel J]

I'd guess the twist rate vs the bullet weight vs the FPS have something to do with it. Either that, or we can fall back to the obvious that it's a Mini 14. Have you ever chrono'd your load?

 

[watsona]

I'd guess the twist rate vs the bullet weight vs the FPS have something to do with it. Either that, or we can fall back to the obvious that it's a Mini 14. Have you ever chrono'd your load?

I haven't but today got me wondering about what kind of velocity I'm getting. I might need to invest in a chrono before I spend too many more hours on my Dillon 650!

 

[Certaindeaf]

Probably a 1/7 twist for that year. I'd try heavier slugs after checking the crown for damage.

 

[Kruel J]

Probably a 1/7 twist for that year. I'd try heavier slugs after checking the crown for damage.

That would be a heck of a lot of crown damage. I'm gonna guess the 55 grain projectiles are being pushed too fast for the twist rate and are shedding their jacket, leaving the core to tumble. Just a guess.

 

[Certaindeaf]

That would be a heck of a lot of crown damage. I'm gonna guess the 55 grain projectiles are being pushed too fast for the twist rate and are shedding their jacket, leaving the core to tumble. Just a guess.

Oh yea, hadn't thought of that. As to damage, improper cleaning could easily cause it, and the mini is commonly cleaned from the muzzle.

 

[old11bravo]

Probably what KruelJ said but also check your brake and see if it's threaded to the barrel correctly and look for strike marks on the inner diameter of it.

 

[ConcernedCitizen]

Probably a 1/7 twist for that year. I'd try heavier slugs after checking the crown for damage.

Good call.
1986: 1/10 & 1/7
1987-1996: 1/7
1997: 1/7 & 1/9

Still shouldn't have mattered though, as 1/7 usually shoots 55gr just fine. I've heard some reports of decreased accuracy, but not keyholing. Trying some 62gr would be a good test, though.

That would be a heck of a lot of crown damage. I'm gonna guess the 55 grain projectiles are being pushed too fast for the twist rate and are shedding their jacket, leaving the core to tumble. Just a guess.

If it was crown damage it should be evident on all 3 loads, not just 2 out of 3. Velocity shouldn't be a problem either, as I've shot plenty of 55gr out of 1/7 barrels. The exception would generally be thin-skinned varmint bullets at high velocities, which can come apart completely mid-air. The Hornady 55gr FMJ-BT is usually considered the best (and most accurate) plinking bullet available for reloading, and shouldn't be the problem. Something else is going on here...

I also looked up his load data, and 22.5gr of H322 is warm, but below the max of 23.1 (per Hornady #6). Velocity should be 3,050 out of a 26" barrel, which should put his velocity around 2,900 fps, give or take. I believe TulAmmo is on the slow and weak side, but the American Eagle should say 3,240 fps on the side of the box and be roughly equivalent to XM193. I'm starting to wonder if his bullets are going too slow to grab the rifling, but that seems unlikely. If the barrel is really worn though, maybe the reloaded bullets aren't obturating enough to fully grab the rifling, but the faster (higher pressure?) American Eagle is. First thing I'd do next is check the bore size at the muzzle using a cartridge, and inspect the crown as you gentleman recommended.

Definitely an odd scenario. It might be worth having a gunsmith mic or slug the bore, or possibly even do a chamber cast to see if the throat's shot out.

 

[Kruel J]

Probably what KruelJ said but also check your brake and see if it's threaded to the barrel correctly and look for strike marks on the inner diameter of it.

That's a possibility as well, and one I thought of. But for the round to exit the muzzle and tumble due to a misaligned brake would hopefully be obvious.

 

[Kruel J]

Good call.
1986: 1/10 & 1/7
1987-1996: 1/7
1997: 1/7 & 1/9

Still shouldn't have mattered though, as 1/7 usually shoots 55gr just fine. I've heard some reports of decreased accuracy, but not keyholing. Trying some 62gr would be a good test, though.


If it was crown damage it should be evident on all 3 loads, not just 2 out of 3. Velocity shouldn't be a problem either, as I've shot plenty of 55gr out of 1/7 barrels. The exception would generally be thin-skinned varmint bullets at high velocities, which can come apart completely mid-air. The Hornady 55gr FMJ-BT is usually considered the best (and most accurate) plinking bullet available for reloading, and shouldn't be the problem. Something else is going on here...

I also looked up his load data, and 22.5gr of H322 is warm, but below the max of 23.1 (per Hornady #6). Velocity should be 3,050 out of a 26" barrel, which should put his velocity around 2,900 fps, give or take. I believe TulAmmo is on the slow and weak side, but the American Eagle should say 3,240 fps on the side of the box and be roughly equivalent to XM193. I'm starting to wonder if his bullets are going too slow to grab the rifling, but that seems unlikely. If the barrel is really worn though, maybe the reloaded bullets aren't obturating enough to fully grab the rifling, but the faster (higher pressure?) American Eagle is. First thing I'd do next is check the bore size at the muzzle using a cartridge, and inspect the crown as you gentleman recommended.

Definitely an odd scenario. It might be worth having a gunsmith mic or slug the bore, or possibly even do a chamber cast to see if the throat's shot out.

Good points!

 

[Kruel J]

Maybe a bad lot of projectiles? Reaching here, but trying to explore all options.....

 

[ConcernedCitizen]

Good points!

What's funny is that I actually have had my Mini-14 blow up bullets mid-air!

 

[Kruel J]

What's funny is that I actually have had my Mini-14 blow up bullets mid-air!

OP says he has had good luck with many AR's........hmmmm..............

 

[ConcernedCitizen]

OP says he has had good luck with many AR's........hmmmm..............

My issue was due to something entirely different, and we wouldn't see keyholing if OP had the same issue. My bullets never even made it to the target!

I'm seriously wondering if OP's initial hunch is correct, and perhaps the barrel really is shot out. I'd definitely take a good look at the crown and bore diameter.

If it is shot out, that gives OP the perfect excuse to rebarrel it in .300 Blackout!

 

[Goosebrown]

What's funny is that I actually have had my Mini-14 blow up bullets mid-air!

Some of the Sierra bullets are labeled as being a problem at high velocities. I shot 22-250 at a certain point going up in velocity they simply stopped hitting anything

 

[Kruel J]

My issue was due to something entirely different, and we wouldn't see keyholing if OP had the same issue. My bullets never even made it to the target!

I'm seriously wondering if OP's initial hunch is correct, and perhaps the barrel really is shot out. I'd definitely take a good look at the crown and bore diameter.

If it is shot out, that gives OP the perfect excuse to rebarrel it in .300 Blackout!

Very well could be. I'm just guessing here.

 

[Goosebrown]

"I'm seriously wondering if OP's initial hunch is correct, and perhaps the barrel really is shot out. I'd definitely take a good look at the crown and bore diamete"

If that we're the case I'd think it more likely that the American Eagle would fail too. Inconsistency is symptomatic of ammo differences more than barrel problems.

Hodgdon shows that's a good load but in a 1:12 twist. Might just need to slow down for a 1:7 twist. Berger twist stability calculator says that combo might be unstable.

Twist Rate Stability Calculator

Something to think about

 

[ConcernedCitizen]

Very well could be. I'm just guessing here.

Aren't we all?

 

[ConcernedCitizen]

"I'm seriously wondering if OP's initial hunch is correct, and perhaps the barrel really is shot out. I'd definitely take a good look at the crown and bore diamete"

If that we're the case I'd think it more likely that the American Eagle would fail too. Inconsistency is symptomatic of ammo differences more than barrel problems.

Hodgdon shows that's a good load but in a 1:12 twist. Might just need to slow down for a 1:7 twist. Berger twist stability calculator says that combo might be unstable.

Twist Rate Stability Calculator

Something to think about

If he needs to slow down, how does that explain the higher velocity American Eagle shooting the best?

Having a slower bullet would reduce RPM, but it's the slow bullets he's having problems with.

*Edit*

Using your stability calculator, everything looks good to me.

 

[Member 5605]

Stability also has a lot to do with speed of the rounds.

• What are your reloads running for velocity? Have you chron'd them?
• What's your barrels twist rate? Not MFG, but brush down bore method.
• When was the last deep cleaning?

@Baseacegoku and I were working through an issue with his AR. My reloads ran fine, everything else keyholed. No solution yet with his.