berger 6.5 thick jackets grouping issues?

T

tim in tx

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i just cannot get the thick jacket bullets to group tight at 100yds,vld or bt, in 2 different [lawton& broughton ]barrels.the thin jackets shoot better but i am zipping them so it is a concern. has anybody had this problem?,i dont know what to do other then just switch but i will have to lengthen the throat to go back to the 142 sierra but would rather stick with berger if possible.the sierras shoot fine so it isnt the gun isnt the problem.bullet depth isnt an issue as well.any ideas or exeriences on this ? tim in tx
 
Tim in Texas,

Regardless of who's bullets you shoot, here are a few points to consider from a person who swages his own...

There is always some trade off concerning projectile weights, profile, and certainly jackets. The Berger/J-4 jacket is essentially the "gold standard" for both home and professional custom bullet makers.

I have no scientific evidence but strongly believe that thin jackets are the greatest contributor to making a good projectile. Bullet swaging dies are manufactured in tolerances that most of us have no accurate means to measure. Bullet dies are by nature of their intended use, extremely straight, lapped to an exact size and hardened and heat treated to a narrow Rockwell range. The presses used for swaging are also indicated and bored for straight " ram to punch to die" alignment.

Consider all the painstaking process in ensuring a good platform, specifically, the union between dies, press and ram to making match grade projectiles. This union can be diminished when jacket run out is introduced. Jacket inconsistancy is an old topic discussed at length here so I won't add to it.

The question that concerns me is...If a bullet is swaged with a thicker jacket at the same weight of a bullet with thinner jacket, Does that potentially mean that:

1.The thicker jacket bullet will have a higher lead slug column inside the formed bullet? HBC came to the conlusion that high columns of lead aren't so good when trying to red line VLD bullets and prevent bullet failure.

2. If there is an issue of run out in the jacket, does a thick jacket cause the true centerline of the lead column to be further from center than that of a thin jacket with the same run out value? This might cause pronounced cork screwing while going down range resulting in inconsistant impact points.

I have a couple other thoughts but I have to go now. I hope HBC, Eric Stecker, Dave Tooley and Brian Litz weigh in here, they are qualified and have the education to support various theories here. My contribution is limited to field trial failure.

Happy Thanksgiving, Mike

ps I kind of rambled, shoot the 6.5 at lesser pressure, I know its tempting to milk it for all its worth. Bullets that don't print the target result in DQ...it aint worth it!!!
 
Thick Jackets

Tim,
I shoot F-Class, not BR but I have shot 1300+ thick jacket naked 140 grain Berger VLD’s this year. Over 1,100 of those have been in National level competitions against the best F-Classers in the world. I don’t believe I have finished an agg below 3rd during that time so they must be work quite well.

Perhaps I am doing something that you aren’t so here is how I load. New Norma 6.5-284 cases; expand and neck turn cases to 0.013” neck wall thickness. Size case in Redding neck die using 0.287” bushing. Seat Russian primer using Sinclair primer tool, load H-4350 to give me 2995 fps. The loaded neck diameter is 0.2905. Chamber is a 0.294 neck. Jam the bullets into lands till I get a mark about half as long as it is wide (About 0.030”?). I test loads at 300 meters.

Perhaps the thick jackets require more neck tension and/or more jam than you are using. What I have described is the same techniques I used in the past for Sierra’s and Berger thin jackets. I changed nothing when I changed to Berger thin jackets and then to thick jackets.

I hope this helps, I know for sure Lot 1231 that I am using is a great bullet. FWIW, I am using Bartlein 5r barrels.
 
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When we first tested the thicker J4 jackets in the 6.5mm 140 gr VLD we observed something that I did not expect. While shooting regular J4 jackets we were able to produce failures. When we switched to the thick J4 jackets we had no more failures but we blew several primers (I have attached the testing results for those who ave not seen them already). Unfortunately, the chronograph was not functioning so we were unable to see if their was a velocity difference.

We shot 440 shots in each barrel in less than 6 hours so primers may have blown due to reasons related to the number of shots in each barrel. Having said this I believe it is possible that the thick jacket creates a situation where it acts essentially like a completely new bullet. What make the standard jacket 140 gr VLD shoot well may not shoot the thick jackets even though the external dimensions are the same.

To expand upon Henry Childs core column thoughts, we do know that there is a point where the nose of the bullet will experience slump (nose deformation). This slump is a result of high pressure. If the thicker jacket produces higher pressure (than the regular jacket) then it is possible that the nose of these bullets is being deformed. This result can show up on the target as poor precision. Nose slump was not found to cause bullet failures.

If higher pressures are causing nose deformation then it is easy enough to prove by backing off the load to see if precision improves. If a reduced load brings the bullets together then it will be a strong indicator that nose deformation resulting from high pressures is the cause of poor precision. The 6.5X284 is already up there when it comes to pressure so it is not unreasonable that adding a thicker jacket to the combination pushes the bullet over the line.

If someone can conduct this test (with chrono data to back it up) it could help a lot of shooters. If this can be proven then we can go back to the bullet and see what can be done to resolve this result (understand that I am not saying that this IS the cause but it is worth looking into).

It is also very possible that the thick jackets changes the harmonics compelling shooters to redevelop their loads for this change. I'd certain rather be able to tell you that "all you have to do is A, B and C to make them shoot" but I don't have those answers yet. I do know that they are shooting well for many but not for everyone. This is similar to when the VLD was first introduced. What we need now is open communication and an understanding that we will continue to work on getting these bullets to shoot best for everyone. Please keep the feedback coming.

Regards,
Eric
 

Attachments

  • Test 6.5mm 140 gr VLD Reg and Thick.xls
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