115 DTAC Blowups!

[rcw3]

This thread sounds like an extreme velocity fest. I truly wonder if any of these extreme velocity shooters rifles are actually consistently accurate,I doubt it, but of course we'll never know because their bullets never make it to the target).

Robert Whitley

 

[GLC]

Robert,

With respect, 3100-3250 in my opinion is not extreme, this cartridge will push the DTAC to 3300+ without breaking sweat, It's a personal choice....

The other rifle in 6x284 at 1000yrds hit 4 out of 5 of the string into the 5" V in a 8MOA wind, last shot was a 5, so this rifle has not missed a beat,2nd string of 5 was very similar.
The whole point of this discussion is to find out why my barrel blows up bullets at any reasonable velocity,slowest was 3087)

If your personal preference is to shoot lower velocity cartridges no problem, there are plenty of us that want and like to shoot faster, the velocities we are aiming for are all well within range safetly limits on our range.

Regardless of this, this thread will make others think before ordering a 7.5 twist.....

With regards

Gary

 

[BlackHawk95]

The last time I shot my .243AI with 107gr Matchkings I could see comet trails on the target at 100 yard on 3 consecutive shots at 3100fps.

Im interested in trying the Final Finish on my Lilja barrel, as I dont have anything to lose now.

Jerid

 

[rcw3]

GLC
Gary
I get a kick out of the slow it down band-aid fix for bad bullets myself. . . . .
Lynn

Hey that is pretty funny - take heavy long 6mm bullets, drive them super fast through a very fast twist barrel - they blow up and then they're "bad bullets"?

By that logic, you run an engine over the "red line" and it blows up and it's a bad engine?

Robert Whitley

 

[rcw3]

Lynn

I am not trying to be a pain but the whole thread seems funny to me.

You're all on the "ragged edge" with a 6mm doing what you're doing and it's almost as if everyone is in denial about it.

I have done a lot of work with 6mm's,big and small 6mm cartridges) - run them hard - run them fast - out of fast twists - with the big bullets too - yes, even blown up some myself. My conclusions:

Forget a 7" twist - with a big bullet, it's over the line, or so close to it you'll be lucky to get one to shoot right,the twist is so sharp, when the bullet hits it and trys to engrave it's like hitting a wall rather than a ramp - and it needs to be a ramp not a wall). Let's keep in mind the bullet has to go from zero to 200,000+ rpm in fractions of a second - big big stress and longer bullets need even more rpm to keep them stable.

A 7.5 Twist is close to the edge but just off it - but very tight for very high velocity loadings,i.e. over 3000 fps) and it puts a lot of stress on bullets when you run them fast, particularly the 115's,but then you need that or close to that to stabilize some of the 115's).

An 8 twist is better from the engraving perspective but getting very close to the edge the other way,non-stabilization). I found at an 8.1875" twist I had trouble with some DTAC's stabilizing and the Berger 115's would not at all.

So here you are - you have the "thread the needle" on the twist - do the balancing act, make the compromises and all the planets have to be in proper alignment for everything to be well. A 7.5 twist is good but not if you're going to hammer the velocity then there are other issues that crop up.

The 115 gr bullets are also on the "ragged edge" of being too big and long a bullet for the 6mm bore size,there's a limit to what the 6mm bore size can effectively and reliably handle - the DTAC 117's were over the edge - he brought them back to 111's for that reason - the 115's are right there near or on the edge). There's a reason why bullet maker stayed away from making bullets over 105-108's for many years - too close to the edge - too temperamental - especially with those who want to "push the envelope",like some of the shooters on this thread).

For day to day consistent reliable accurate shooting, I never found the 115's to deliver reliably accurate results much over 3000 fps. I have plenty of cartridges that can easily drive them much faster,and have done a lot of testing there), but when I have done 20 shot group testing, I never found the groups to hold together well and go 20 straight when they were run fast,over around 3000 fps). The group may hold for 12, 14, 16 shots or so and then let out a flyer, then again another a couple or few shots later. Too much stress, twist, heat, etc. for something on the "ragged edge". That's why I doubt you will get consistent reliable accuracy up at those higher velocities,and I mean .5 or better MOA accuracy for a full 20 shots - not just a 5 or 10 shot group).

So that's where I am coming from.

Robert Whitley

 

[JOHN708]

Robert,

Thanks for your info regarding your testing with the 115 6mm bullets at high velocity. You just saved me alot of money from trying yet, anouther experiment with the heavy 6mm bullets, that was probably doomed to failure.

John Skowron

 

[GLC]

Lynn/Robert/John/Jerid

All of this information is helpful and as I see it here there are two camps, both of which I live in!

My 6x47SM shoots fantasticly at 2980 with a DTAC I have won many F class comps beating 6.5x284 etc BUT as soon as the wind gets really tricky,especially in the UK) I will drop points, you may say brush up on your wind reading skills, however we all look for an advantage and a fast shooting ballistically superior low recoil rifle is it. The "other"rifle,the one that hits the target)! will kick my backside everytime in anything but low to moderate conditions, that is why I ordered one!,who wouldn't)

Robert I do see where you are comming from and after your explanation I can see the point, but it still doesn't answer the question WHY identical barrels differ so much. In fact a fellow Shooter and Top UK Br shooter Vince Bottomly is shooting the same cartridge and bullet with a 8.5 twist! at 3250fps..?

Lynn is spot on, I would go back to my 6x47 if plenty others were not beating me with "hotter" cartridges!,particulary my shooting buddy!

Unfortunately I cannot shoot the 107's @ 3400 but I will try the new 111's.

Finally I would be very cautious with the final finish, I really do not like the idea of firing an abrasive projectile down a match grade hand lapped barrel, I do not think the issue here would be fixed by doing this, and after my experience with JB paste I personally would not go down that route ,only my humble opinion though) however Jerid if you have nothing to lose before junking the barrel it's worth a try!

Gary

Gary

 

[BlackHawk95]

Thanks for all the great info guys. IN my case it shouldnt be much longer before my Broughton 8 twist gets here. Im ready to try it out and see what happens. Now the question is what can I do with a left over 7 twist Lilja ive got laying around?

Thanks Jerid

 

[rcw3]

Robert,

Thanks for your info regarding your testing with the 115 6mm bullets at high velocity. You just saved me alot of money from trying yet, anouther experiment with the heavy 6mm bullets, that was probably doomed to failure.

John Skowron

John

I am not saying don't try out a long range 6mm, but I am saying to be realistic in what you are dealing with. Some of the benchrest shooters feel they to have to push a very fast velocity with their bullets or they don't feel they are competitive. We must bear in mind they only need to run some sighters and then 5 or 10 record shots typically and then they get a break in their shooting. If you shoot f-class or prone courses of fire, you typically need to be able to go 22+ shots in a row, and a lot of hot loads won't do that and stay tight,i.e. look at a lot of the successful prone and f-class 6.5 x 284 shooters, they are running the 139-142 gr bullets in the 2950-2975 fps range because that's where they need to to stay tight for 22+ rounds straight). In my testing with the 6mm and the 115's, after I clean the gun or if the barrel is cold, I can usually fire a few sighters and 10 more shots and everything will stay tight, but if I keep going on another target for 10 more rounds the hot load groups invariably fall apart. I do a lot of 20 shot group testing when I do load work ups to make sure the load stays tight the whole way, and it's surprising how many won't go the whole way. Now if I only needed to find a load that would stay tight for 8 or 9 rounds, a lot of hot loads would do that. If I only needed to go 12 or 13 rounds, there are also a lot of hot loads that will do that too. So I don't know what these benchrest guys need, but what may work for them won't work in other settings.

One of the last matches I was at a shooter was shooting a 243AI and was kind of proudly touting how he was running his Berger 105 VLD's at somewhere like 3200+ fps,I did not say anything when he told me but I thought - "we'll see how this turns out"). Well he shot 14 x's in a row then dropped two or three points at the end of the 20 shot match,surprise surprise). I plugged along with my Berger 115's at 2950 fps and shot a 200/10x. The point of the story - velocity without accuracy and consistency means nothing in our game,it's a three legged stool, any one leg missing and you are not going to be competitve).

Robert Whitley

 

[sparker]

Robert has done a fine job of pointing out the difference between selecting a load for LR bench-rest vs long range prone. I do not believe you will find many folks spitting out 115s above 3100 fps. Likewise, I do not believe anyone is shooting 107s at 3400 w/ consistency. anything near the ragged edge either in twist or velocity will fail in high power. Some people may get by in bench-rest, however, most will not. I would approach a load in either game the same way. Fire for consistency first and velocity second. Many many cartridges that are both accurate and efficient shoot their best in a range from 2950-3050 fps.

To accomplish this, use the rule of 3.2. Take one's desired bullet weight and divide by 3.2 that will give you the charge weight needed to achieve that velocity range.

Scott Parker

 

[CPorter]

Scott,

Your rule of 3.2 doesn't work, and there is too much variance in powders, barrels and bullets for it to possibly work.

 

[sparker]

If we interpret the rule within the context of the thread, i.e. long range shooting w/ heavy bullets, I believe you will find the rule works quite well. It is not designed to give you the magic load. It is designed to point you to the case volume needed to get you to 3000 fps. I believe the rule applies to sectional densities of .23 and greater.

Scott Parker

 

[sparker]

Yes Lynn.
As I said some people may get by in bench rest. 20 shots for record is a different horse race.

Scott

 

[JOHN708]

Robert,

I do shoot prone, any-any and F-class, and your point is well taken. A great load that's only consistant for 5-10 shots, won't cut it. ANY cartridge taken to the ragged edge of it's performance parameters can inconsistantly fail. Not necessarily in every gun,barrel, twist combination. But they will fail. I was shooting in the same relay with John Widden a couple of yrs. ago. It was a long range regional match. He had a 6mm bullet blowup on him. I believe he was shooting a 105 Berger at 3250-3300+ fps. To me that's on the ragged edge regarding velocity, and the blowup proved it. I'm not sure, but I believe he's reduced the velocity somewhat, and guess what, no bullet blowups.

Pushing the limit works for some of the shooters some of the time, but it doesn't work for all of us all of the time. That's why the national F-class team is shooting 142 serria's in their 6.5-284's at around 2950fps.

John Skowron

 

[HPMike800]

Robert:
I'm in the middle of a 1,000yd build and using 6XC dedicated to 115 Bergers for a prone gun. The barrel is a 7.5tw .237 bore and I was planning to use moly. With RL-17 I was hoping to get a good load at 3050fps. Do you think that's off the bleeding edge enough to be reliable?

Mike

 

[mikecr]

Gary, did you check your actual twist?
Push a dry patch and measure one rev of your cleaning rod.
Thanks

 

[rcw3]

Robert:
I'm in the middle of a 1,000yd build and using 6XC dedicated to 115 Bergers for a prone gun. The barrel is a 7.5tw .237 bore and I was planning to use moly. With RL-17 I was hoping to get a good load at 3050fps. Do you think that's off the bleeding edge enough to be reliable?

Mike

Mike

I did not have luck up that fast with the 115's with RL17, I tried 3100 fps and 3050 fps, both loads started out shooting great but fell apart up around shot 12 to 14, I backed things off and when I got down around 2950 - 2965 fps, I could make it the whole way with a tight group so that's where I will be if I shoot my 6XC with the 115 Bergers. That's more than I was able to get from my 6XC barrels before however.

People have great hope that RL17 will be a "miracle powder" but I don't know about that. One thing I'll give RL17 is that it can deliver plenty of speed. While in my testing I have been able to get substantial additional velocity increases with the powder, I have not been able to retain accuracy and consistency up at the high velocities. I have not done a great deal of testing, but enough to realize that while there may be some capacity for increased velocity with accuracy and consistency here and there, it won't be as simple as just using RL17 and running your velocity up 100-200 fps more than you could before. That powder is different than any other powder we currently have and use in the US. ES and SD chrono numbers with the powder seem larger and more finicky than I am used to. It's going to take a while before we will really know what the ideal uses for the powder may be. It may be that RL17 will turn out to be a great powder for hunting applications due to its capacity to deliver velocity and bullet power, but it may not turn out to be an ideal powder for target use. Right now I simply cannot make that call. RL17 is a powder worth giving a try, but don't throw out your favorite steady performing load and powder as you may need to go back to it if things don't work out.

Robert Whitley

 

[TonyR]

Robert.
Have you done any accuracy testing with the RL-17 in your .284?
Thanks
Tony

 

[rcw3]

Tony

I have not had time, but based on the results I had from chrono testing I would try the loading I had that ran around 2950 fps with the Berger 180's. The load that was right at 3000 fps was a little hot and instincts tell me that for accuracy and consistency it would probably be better backed off a little. 2950 fps with Berger 180's for a prone or f-class course of fire is certainly nothing to scoff at.

Robert Whitley

 

[sparker]

Robert.

About how much R 17 are you using behind your 180s?


Scott Parker