.224 - 95 SMK bullet failures

[linebaugh]

Just an FYI on the 95SMKs but please read everything before making generic assumptions.

I was shooting a 22BR +.050 for about 1.5 seasons in PRS matches. I am running a 30" tube and admittently I have been running excessive pressure and pushing the 95 SMK to 3030 fps in a 7 twist barrel. That equates to about 311,600 rpms. That RPM is probably not full value stable BUT I have regularly made hits to 1400 yards during matches and practice so its not exactly unstable.

My barrel was looking good up until about 1600 rounds and then it really started to fire crack the throat area badly. I shot a match in MO in the heat and humidity and ended up losing a good number of bullets. At the time the barrel would have had 1800-1900 rounds on it. I shot a match yesterday with the last of my reloads and I probably had about a 15% fail rate on bullets at the 2000-2100 round count. Again keep in mind I was running excessive pressure the whole time I shot this barrel.

I am chambering up another 7tw in 22-6GT today throated to the 95s and will see if lowering the pressure helps extend barrel life. I will report back in a year when I am back in that 2000 round count range or if I experience failures prior to. It may be worth noting that none of my fast twist 22 calibers have ever exceeded 2000 rounds of usable barrel life. This last one got close and I am hoping to get over that edge this time.

 

[Jdne5b]

.218 bore? It might be worth switching to a .219 if you haven't already. They stay together for me at 330k rpm in a .219.

 

[sfinn1]

.218 bore? It might be worth switching to a .219 if you haven't already. They stay together for me at 330k rpm in a .219.

I agee with Jeremy on .219 bore.
Not having shot the 95SMK's, I'm wondering if the 7 twist is good to go or 6.5 twist would be better.

 

[PigButtons]

How often do you look at the chamber and throat with a bore scope? I ask because I've noticed that most times when I have a cracked casing, there is a small "burn crater" in the area where the crack occurred. I'm pretty sure that this happens because there is probably a jet of hot gas that exits the crack just before the bullet leaves the case; it is very focused and very hot.

I don't get a lot of cracked cases so there are only a few such craters and that makes it easy to spot with the bore scope. I would imagine that once you get more than 50 such craters the friction they represent to the case's flexing under pressure will start a spiral of ever more frequent split cases and more craters leading to more friction,... You get the idea.

If you are running at high pressure anyway the effect is likely to be more rapid and dramatic. If you could post some pictures of the area of the throat where the cracking is occurring it might help us appreciate the situation.

 

[Jdne5b]

I agee with Jeremy on .219 bore.
Not having shot the 95SMK's, I'm wondering if the 7 twist is good to go or 6.5 twist would be better.

7 has been fine in my 223. I dont think one needs to go faster, especially in a bigger case like the BR or GT.

 

[Ranger188]

I would think you would get less life with the 22GT
Your burning more powder than the BR case.
It's the heat that causes the fire cracking which leads to the jacket failures
more than just the RPM's alone.
When my barrel was clean, I was spinning them pretty fast
but once I got some fire cracking, it was all over. Poof

 

[linebaugh]

I would think you would get less life with the 22GT
Your burning more powder than the BR case.
It's the heat that causes the fire cracking which leads to the jacket failures
more than just the RPM's alone.
When my barrel was clean, I was spinning them pretty fast
but once I got some fire cracking, it was all over. Poof

I will be burning only slightly more powder but hopefully cutting pressure 10kpsi. I dont have the answers to any of this yet but I am literally one barrel away (this one) from not messing with the fast twists anymore. If this one makes it to about 2000 rounds again I will be out of 95s and thats gonna be a wrap from this guy. From there on I am going back to 8 twist and 88s and 90s.

I don't actually know what this barrel diameter is as I got two of them through sponsorship. I will assume .218
I already ordered a .219 in 8 twist so I hooe to keep.the 88s and 90s 100% intact next year. I fully believe I will have no more bullet issues with the 8tw.

 

[Ranger188]

If I could get 1600 rounds, I'd be building a 22x47 tomorrow..
I got a bad taste in my mouth with my 7 tw 22 creed.
Got 400 rounds out of it and it would keep changing constantly.
Shoot bugholes for a few rounds, next week crap. Work on it again
shoot bugholes, then crap. Then started blowing up bullets.
Took barrel off and moved on.
I think high speed heavier 22 cal's are a fine line.
I think the 22br @3000-3100fps is about the best combination of a long range
caliber and barrel life you will find.

 

[topclass2017]

If I could get 1600 rounds, I'd be building a 22x47 tomorrow..
I got a bad taste in my mouth with my 7 tw 22 creed.
Got 400 rounds out of it and it would keep changing constantly.
Shoot bugholes for a few rounds, next week crap. Work on it again
shoot bugholes, then crap. Then started blowing up bullets.
Took barrel off and moved on.
I think high speed heavier 22 cal's are a fine line.
I think the 22br @3000-3100fps is about the best combination of a long range
caliber and barrel life you will find.

If I do the math correctly, 3000 fps suggests just over 308K rpm's in a 7 twist barrel. From what I can deduce, staying under 300K, and preferably closer to 275K (approx 2700 fps) will help maintain bullet integrity.

I am keenly interested as I have a 7tw 22BR and am searching for a load in the 85-95 bullet grain range.

 

[jelenko]

FWIW. I called both Hornady and Sierra tech support on their recommended RPM's for H75 and S77's respectively.
Hornady => don't go over 280K
Sierra => recommend max of 250K to 260K.

 

[Ranger188]

That's the whole problem with the 22's the math.
You want a high BC bullet, ( 85g+)which equals a long slender bullet that requires a fast twist
to stabilize it. You want something to equal your 6mm or 6.5 drop and drift.
So you have to push it fast and use a fast enough twist to stabilize it at distance
plus most are overbore so your putting the same amount of powder threw a smaller hole.
All that equals heat and RPM's that are close to pulling your bullet apart,
then add fire cracking to the equation.
So you slow it down, now you don't have the drop or drift you want
or use a slower twist and now can't stabilize the heavier higher BC bullets.
It's a no win situation.
That little white dot in the middle is a 90g bullet coming apart.

 

[Ned Ludd]

Using a .223 Rem with a 30", 5R, 0.218"/0.224", 6.8-twist barrel pushing 90 VLDs at ~2850 fps, or Hornady 88 ELDMs at ~2875 fps, I have experienced jacket failures with both bullets. I strongly suspect the twist rate is a contributing factor with these two bullets. In contrast, I have never blown up a single Sierra 90 or 95 SMK in that same barrel. Clearly the Sierra bullets have the tougher jackets, although clearly no bullet made can ever be guaranteed 100% immune. It's also worth noting that I have never had a single jacket failure with any of these four bullets out of the exact same spec. barrel, except having a 7.0-twist.

There are likely a number of factors that go into producing jacket failure with the .22 cal heavies. Twist rates faster than 7.0 (i.e. RPM greater than 250-275K), a 0.218" bore configuration, really long barrels, really high velocity cartridges, and certain types of barrel land/groove patterns are but some of the factors that likely increase the odds of jacket failure. You may get away with any one, maybe even any two under the right circumstances. Nonetheless, the more of these factors working against you, the higher the odds of jacket failure.

As has been suggested, the approaches to mitigating jacket failure with the bullets that are prone to it would include using the minimum twist rate that will effectively stabilize the bullet. A 90 VLD at 2850 fps from a 7.0-twist barrel would have a gyroscopic stability coefficient (Sg) of 1.46 at 70 degrees and 1000 ft elevation, and is predicted to give up approximately 1% of the intrinsic BC. Giving up one or two percent BC isn't even worth discussing if the alternative is jacket failure. You can easily run the 90 VLDs at an Sg of 1.4. Yes, you'll give up a little bit of the intrinsic BC, but they won't fall out of the sky, or keyhole at the target.

Like James Tiberius Kirk, I don't believe in the no-win scenario. If you want to run a hot rod .22 cal cartridge with 88, 90, or 95 gr bullets, use a twist rate calculator together with your expected velocity and order a barrel twist rate that will get you in the ~1.4 Sg range, while keeping the RPM below ~275K, if possible. Barrel manufacturers today can readily cut any twist rate you want to the tenth of an inch. That's not a guarantee against jacket failure, but would certainly help put the odds more in your favor without dramatically degrading BC or bullet performance. At velocities markedly higher than 2850 fps, where a 7.0-twist is plenty, maybe a 7.1- or 7.2-twist would be sufficient. Stick with barrels of 30", or even less, so as to reduce friction between the lands and the jacket, a factor known to contribute to jacket failure. You could also go with a 0.219" bore, and preferably in a 5R land/groove pattern, which seems to be a little less problematic.

In other words, choose the barrel carefully in order to minimize the potential for jacket failure in every way possible. Your best bet for ordering such a barrel is directly from the manufacturer, as most barrel vendors don't carry such specialized barrels. If ordering such a barrel and waiting several months seems like a lot of trouble and extra work, ask yourself how much extra effort and work it is to purchase a barrel and have it chambered, then work up a load, only to find a significant number of the bullets are blowing up.

 

[linebaugh]

Using a .223 Rem with a 30", 5R, 0.218"/0.224", 6.8-twist barrel pushing 90 VLDs at ~2850 fps, or Hornady 88 ELDMs at ~2875 fps, I have experienced jacket failures with both bullets. I strongly suspect the twist rate is a contributing factor with these two bullets. In contrast, I have never blown up a single Sierra 90 or 95 SMK in that same barrel. Clearly the Sierra bullets have the tougher jackets, although clearly no bullet made can ever be guaranteed 100% immune. It's also worth noting that I have never had a single jacket failure with any of these four bullets out of the exact same spec. barrel, except having a 7.0-twist.

There are likely a number of factors that go into producing jacket failure with the .22 cal heavies. Twist rates faster than 7.0 (i.e. RPM greater than 250-275K), a 0.218" bore configuration, really long barrels, really high velocity cartridges, and certain types of barrel land/groove patterns are but some of the factors that likely increase the odds of jacket failure. You may get away with any one, maybe even any two under the right circumstances. Nonetheless, the more of these factors working against you, the higher the odds of jacket failure.

As has been suggested, the approaches to mitigating jacket failure with the bullets that are prone to it would include using the minimum twist rate that will effectively stabilize the bullet. A 90 VLD at 2850 fps from a 7.0-twist barrel would have a gyroscopic stability coefficient (Sg) of 1.46 at 70 degrees and 1000 ft elevation, and is predicted to give up approximately 1% of the intrinsic BC. Giving up one or two percent BC isn't even worth discussing if the alternative is jacket failure. You can easily run the 90 VLDs at an Sg of 1.4. Yes, you'll give up a little bit of the intrinsic BC, but they won't fall out of the sky, or keyhole at the target.

Like James Tiberius Kirk, I don't believe in the no-win scenario. If you want to run a hot rod .22 cal cartridge with 88, 90, or 95 gr bullets, use a twist rate calculator together with your expected velocity and order a barrel twist rate that will get you in the ~1.4 Sg range, while keeping the RPM below ~275K, if possible. Barrel manufacturers today can readily cut any twist rate you want to the tenth of an inch. That's not a guarantee against jacket failure, but would certainly help put the odds more in your favor without dramatically degrading BC or bullet performance. At velocities markedly higher than 2850 fps, where a 7.0-twist is plenty, maybe a 7.1- or 7.2-twist would be sufficient. Stick with barrels of 30", or even less, so as to reduce friction between the lands and the jacket, a factor known to contribute to jacket failure. You could also go with a 0.219" bore, and preferably in a 5R land/groove pattern, which seems to be a little less problematic.

In other words, choose the barrel carefully in order to minimize the potential for jacket failure in every way possible. Your best bet for ordering such a barrel is directly from the manufacturer, as most barrel vendors don't carry such specialized barrels. If ordering such a barrel and waiting several months seems like a lot of trouble and extra work, ask yourself how much extra effort and work it is to purchase a barrel and have it chambered, then work up a load, only to find a significant number of the bullets are blowing up.

From a practical standpoint I am saying that you are correct in using the minimum twist to stabilize a bullet as I believe the RPMs are indeed the number one contributor to bullet failure. That said you quote the stability factor calculators like gospel and I am not certain they can be given that much credit. I would agree they are a guide but using them as hard factual data leaves me a bit skeptical as I have personally shot bullets to great distance quite accurately not obeying the stability calculator outputs.

My last bbl was 30" and made it to 1900 +/- 100ish without a failure. I just cut another 30" barrel yesterday and hope to repeat. Does it contribute, probably. How much is uncertain to me.

I would bet bearing surface has more to play than barrel length... but admit I do not know. I do know I have shot a pile of 75gr ELDs at 3060fps in a 7 twist and I can't get one to blow up. I have a second 7tw bbl in the box and I am probably going to cut another 223AI @ 30" and shoot for the 3150 fps range. That should at some point tell me if they are going to let loose in flight.

So every fall we have a farm shoot here called snipergeddon where we start at 800 yrds and work out to a mile on steel targets. Shooters prone out and get 5 rounds per distance to clear a stage. Every year so far every competitor goes out about 1500 yards and I think last year we made it to 1600 for a winner.
Okay considering the above scenario I have went out 2 years in a row at 1400 and 1500 yards and that stability calculator says I am underspun. The entire crowd goes out at the same time and its becsuse bullets are hitting the transonic zone. At 1500 yards I cant use the same holds twice as there are no ryme or reason for impacts. Everyone there experiences this. High BC bullets just do not lend themselves to transonic flight.

I am attaching my actual BC values from strelock for the 95s in my rifle for reference to what the BC does at different velocity levels. Also a pic of the new bbl installed yesterday.

 

[linebaugh]

Pictures attached

 

[linebaugh]

That's the whole problem with the 22's the math.
You want a high BC bullet, ( 85g+)which equals a long slender bullet that requires a fast twist
to stabilize it. You want something to equal your 6mm or 6.5 drop and drift.
So you have to push it fast and use a fast enough twist to stabilize it at distance
plus most are overbore so your putting the same amount of powder threw a smaller hole.
All that equals heat and RPM's that are close to pulling your bullet apart,
then add fire cracking to the equation.
So you slow it down, now you don't have the drop or drift you want
or use a slower twist and now can't stabilize the heavier higher BC bullets.
It's a no win situation.
That little white dot in the middle is a 90g bullet coming apart.
View attachment 1187390

My gut tells me from experience there is a win in there but we need to stop over spinning. Forget using the twist rate as a rule and start paying critical attention to RPMs.
At one point I didnt think you could blow bullets up and now after 6000 rounds and 4 barrels I have learned some things that I think will be true. I have blown 88s, 90 bergers, 95 SMK now with regularity. I have not blown a 90 SMK though I do think if you pair it with the 300k+ RPM it will eventually give you greif as your barrel ages. I do believe the 90SMK is probably the toughest of the lot however.

I personally would steer clear of the 90 bergers all together and I tell you that even as I have a gun shooting them and about 1000 bullets on my bench. That gun is an 8 twist 22250AI single shot and I expect it to be reasonably safe from bullet failure until deep into its barrel life. I dont over heat it and im not ramming RPMs. Its running about 285K rpms.

The 90 SMK is probably number one tough scale and I personally think if you dont spin it to hell it will probably survive quite well. Find a twist in the 285-300k range and I think you will have your magic bullet. You will have comparable everything to the 6mms you are comparing to but you will have minimal if any gains and thats what I think all of us are trying to do here. We are trying to beat the 6mm ballistically with .224, at least thats my angle. For me less recoil and higher ballistics values.

I would personally suggest to deviate slightly from your bullet stability/twist rate calculators and error on the UNSTABLE side slightly. It's a mathmatical calculation and although I think it's a very good guide the real guide for me has been experience. Experience has shown that I am able to drop below that 1.5 number and maintain results down into the 1.4 range and slightly lower. Am I losing BC at that point? I dont know and doubt anyone on here has the ability to figure that out for certain. Every barrel and load combo has enough nuances to make such a determination un-scientific.

I can tell you that I am going to start testing the new combo asap and I am geared up to shoot 95 SMK's. I am going to run them from 2950-3030 fps depending on what accuracy tells me. That lower end is 303k RPM and using the berger chart will yield me about 1.36 for stability in my environment. I'm willing to try them down to 2900 fps which is only 298K RPM.

I will see what testing shows and report back to you all. I will be shooting matches next month and will be doing a trial by fire then.

 

[Evan]

I am keenly interested as I have a 7tw 22BR and am searching for a load in the 85-95 bullet grain range.

Have you seen my log: http://forum.accurateshooter.com/threads/my-new-22br.3981971/
I've got loads and info in there from my 7 twist 22BR for most of the real heavy 22 bullets.

To this conversation - my 7twist 22BR will blow up anything and has blown up everything I've tried in it once it gets hot, even 90 and 95 SMK. I can't use it effectively for competition. It will shoot 3 shot groups just fine. The first couple 5 shot groups are ok and then it starts blowing up bullets. 10 shot groups almost always blow a bullet up. I think my barrel has a bore that is slightly tighter than usual. My next barrel will be an 8 twist and I'll stick to 80gn bullets. I now have the rule going forward that I will not spin a bullet over 300k which in general means nothing faster than an 8 twist in any caliber.

 

[linebaugh]

Have you seen my log: http://forum.accurateshooter.com/threads/my-new-22br.3981971/
I've got loads and info in there from my 7 twist 22BR for most of the real heavy 22 bullets.

To this conversation - my 7twist 22BR will blow up anything and has blown up everything I've tried in it once it gets hot, even 90 and 95 SMK. I can't use it effectively for competition. It will shoot 3 shot groups just fine. The first couple 5 shot groups are ok and then it starts blowing up bullets. 10 shot groups almost always blow a bullet up. I think my barrel has a bore that is slightly tighter than usual. My next barrel will be an 8 twist and I'll stick to 80gn bullets. I now have the rule going forward that I will not spin a bullet over 300k which in general means nothing faster than an 8 twist in any caliber.

Good point on the any caliber comment. Agree.

 

[Ranger188]

I'm with you on Berger's twist calculator. It's much too conservative.
Will you loose some BC probably, will it keyhole if it's in the 1.3 range
probably not. As long as it stays supersonic and out to 1000yds.+ -
should be fine.
Here's another twist calculator and it's a lot more lax.
https://thebarreloutlet.com/twist-calculator/
Just put in the 3 variables and hit the blue tab (INCHES:REVOLUTIONS)

 

[Evan]

I'm with you on Berger's twist calculator. It's much too conservative.
Will you loose some BC probably, will it keyhole if it's in the 1.3 range
probably not. As long as it stays supersonic and out to 1000yds.+ -
should be fine.
Here's another twist calculator and it's a lot more lax.
https://thebarreloutlet.com/twist-calculator/
Just put in the 3 variables and hit the blue tab (INCHES:REVOLUTIONS)

I agree. I think the Berger calculator has lead a lot of people to a faster twist, mistakenly believing that the couple percent loss in BC is a problem. I, perhaps arrogantly, thought it wouldn't matter much to me if I blew up a bullet here or there since I mostly just target shoot for fun. I was thinking it'd be fun to experiment with the slightly cheaper 22 heavies as an alternative to the commonplace 6mm. My reality, however, is that blowing up bullets kills all the fun and stresses me out, regardless of if I'm just shooting for fun or trying to compete at a match. I'll stick with conservative, safe bullet and twist choices from here on out and never again have that sinking feeling of "why isn't there a hole in that target?"

 

[Ned Ludd]

I'm with you on Berger's twist calculator. It's much too conservative.
Will you loose some BC probably, will it keyhole if it's in the 1.3 range
probably not. As long as it stays supersonic and out to 1000yds.+ -
should be fine.
Here's another twist calculator and it's a lot more lax.
https://thebarreloutlet.com/twist-calculator/
Just put in the 3 variables and hit the blue tab (INCHES:REVOLUTIONS)

The reason the Berger Twist Rate Calculator might be viewed as overly conservative has to do with the gyroscopic stability coefficient (Sg) Berger has listed as necessary to achieve the full intrinsic BC of the bullet (i.e. Sg >/= 1.5). This came from Bryan Litz's work. Notably, just a few years ago, Bryan was recommending an Sg of only 1.4 as the minimum necessary to obtain the full BC. That was more recently updated to an Sg of 1.5, presumably after further testing/modeling.

FWIW - I've fired plenty of bullets out of barrels with twist rates that only generated Sg's in the 1.35-1.40 range, which according to Berger's calculator would be giving up approximately 3-5% of the intrinsic BC. One example is the 200.20X bullet, which I run at ~2650 fps out of an 11-twist barrel in one of my .308s. I've posted some good scores in F-TR matches with that particular rifle/barrel, so the 4% BC loss to me is just a number, as it shoots very, very well. In my hands, a bullet won't usually start to become unstable until the Sg gets down around 1.1 or below (i.e. oblong holes in the target and/or full keyholing).

As long as the Sg remains in the 1.30 range or above, gyroscopic stability shouldn't typically be an issue. This is due, in part, to the fact that a bullet's linear velocity decreases much faster than its rotational velocity. So at least out to the bullet's trans-sonic region, the gyroscopic stability usually increases the farther the bullet travels.

One caveat to running bullets at an Sg in the range of 1.3 to 1.4 is if you're really pushing the envelope in terms of maximum range and precision. The OP mentioned shooting 95s out to 1400 yd. That's asking a lot from a .22 cal bullet that is relatively lightweight in comparison to larger caliber bullets. I can totally understand not wanting to go with a slower twist rate and give up even a single scrap of BC in such a circumstance, but a jacket failure is even worse than a modest decrease in precision. In the end, it may be possible to largely mitigate jacket failures with the .22 cal heavy bullets as I described above, but it will likely come at the cost of some reduction in BC, which may or may not be a deal breaker.