Experimental barrel weight advice

[johnk]

Not all tuners are of significant mass & forward of the muzzle. Those typical of the batch that Keith Hills supplied 15-20 years back were back of muzzle affairs of very modest mass (2 ounces or less in the old currency). They didn't tune with the same precision as the current styles, but they certainly were more forgiving over a range of distances or atmospherics.

You'll still see them used with more or less success (depending on the understanding of the users) by TR & MR shooters in particular.

[DenisA]

Absolutely John. From what I understand of discussions on this forum though, barrel weights, barrel tuners and then dampeners are all different things each intended to combat different issues.

Barrel weights increase node length focusing on barrel whip and gravity.
Tuners allow you to adjust the position of the node V's the muzzle with the same load with no difference in node length (or slight increase I guess)
Dampeners are intended to reduce lower order vibrations.

I'm probably off the mark but that's by general layman understanding of it.

[ShaneG]

One thing about this sport which no one can deny - it keeps the old grey brain cells working!?

[DenisA]

I got to the 100y range on Sunday to break in this barrel using a mix of old odd bod 180 VLD's and hybrids with a very light charge of ar2209 and then an initial ladder type test just to identify where the nodes are, what the speeds are and what the pressure signs are like.

The tested load is 168 VLD's jammed 0.015", AR2209 and FEDGM210M primers. The Lapua brass is near the end of its life and has fairly loose primers pockets. I was amazed to see that the primers didn't start showing pressure until the end. I think I can see what Alan was saying about 168's being much easier pressure wise.

The results weren't awe inspiring but they're results and worth sharing for any one interested. It'd be interesting to know if anyone who has tuned a solid barrel weight can immediately identify any obvious difference between these results and theirs whether they're good or bad. Curious to know if the rubber bonding might have had a positive or negative effect.

This is the first time I've played with a barrel weight and actually seen results to compare against other barrels I've developed loads for.

It looks like I started off in a low node which obviously extends through 1gn of powder. Then there's almost 2gn's between that and the next node starting to form again. Unfortunately primers are starting to show some pressure signs at 54.1gn and it was a mild day. I think I'll have to try ar2213sc and see if I can get a node between these two.

The barrel was cleaned and fouled with 2 rounds prior to the sighters.




Admittedly, I did get excited when I started, thinking "I hope this is the bad node". Hahaha.

[plumbs7]

Dennis 53.5 is worth trialling by the look. Also 50.5 for the lower node and brass saver looks the goods too!

The only problem with round robin results is human error . Slight flinch etc. can skew results.

[DenisA]

Dennis 53.5 is worth trialling by the look. Also 50.5 for the lower node and brass saver looks the goods too!

The only problem with round robin results is human error . Slight flinch etc. can skew results.

I don't think that 53.5 is a node. It doesn't look long enough to be consistent with the first node and the in between.

Also 3 rounds isn't enough to be statistically accurate. That could easily be a fluked group given both groups next to it.

Something I've seen a few times developing loads for other barrels is that there will be an accuracy node followed by vertical spread which gets larger then smaller, then there will be a really tight group just before horizontal spread starts, gets bigger and pulls back in and finally the next accuracy node comes along. That could be coincidence that I've seen that a few times but I'm wondering if that's what's happening here.

I'm pretty sure the next nodes up a little further which I don't believe is achievable with this barrel, barrel weight, AR2209 V's chamber pressure.

Don't know. Further testing will tell the story.

[plumbs7]

Don't know. Further testing will tell the story.


Yes Dennis that's right ! But that group looks good with a low Sd and 3 shots nearly through the same hole, smack bang in the middle of 2 equal conical groups . It looks sexy! Lol!

[williada]

Denis try 53.3, 53.4, 53.5 with different seating depths. Suggest you try jam .010", .005" off, .010". Look for the best group where all three groups have the least elevation variance when three aiming marks across are shot with the same seating depth but different charges. Shoot the next row with a different shooting depth and so on. Think this will fix him Plumbs. David.

[plumbs7]

Denis try 53.3, 53.4, 53.5 with different seating depths. Suggest you try jam .010", .005" off, .010". Look for the best group where all three groups have the least elevation variance when three aiming marks across are shot with the same seating depth but different charges. Shoot the next row with a different shooting depth and so on. Think this will fix him Plumbs. David.

Hi David , hope ur Cows have plenty of feed and Merry Christmas . Regards Graham.

[DenisA]

I'm sure most already know this stuff, but I thought I'd conclude this for interest sake if anyone's interested.

I think its safe to say that my rubber bonded weight had a negative effect.

I explored these loads with varying seating depths with the best results (though not brilliant) at 51.1gn (2880 fps). The next node looked like it was starting to form much further up the powder charge scale though not within safe chamber pressures.

Today I removed the barrel weight and re tested and found that the accuracy nodes had dropped from 1.2gn approx. to 0.6gn in length. The upside is that because the good and bad node lengths have shortened, I now have a faster node at 2935fps.

Things I've learnt:

1. Barrel weights extend good AND bad node lengths. This means that unweighted and weighted nodes are at different MV's and powder charges. It doesn't just lengthen the existing good nodes.

2. If your intending on using an unweighted node close to a range MV restriction, the chamber pressure limit or case pressure threshold, lengthening these nodes can have a negative effect by pushing the fast node out of reach.

3. 50mm O.D barrel weights need scope rings high enough to keep the weight out of the scope picture. It wasn't obvious on high magnification (which is where it always sits), but I wound the mag back at one stage to spot another shooter on and the weight was causing an aberration in the bottom of the picture.

I'm not sure if the poor groups of my dampened barrel weight were due to the ability of the weight to vibrate independent of the barrel, different light levels reflecting off the weight through the scope, the aberration in the picture or the weight being positioned flush with the crown and interfering with exiting gases, but all in all it was a negative effect.

In my opinion, I think solid mounted barrel weights are ideal if your working with a moderate speed node, well enough below the range MV restriction with a cartridge that has lots of spare room to play pressure wise like a Shehane, SAUM or a WSM.

I would like to re-do this test again when bullets are more readily available. I'd use much higher rings and mount the weight back from the muzzle a few inches to make sure there's no interference with the exiting gases and maybe shorten the 1.2gn node length to .8gn - 1gn if that's how it would work. I imagine it might. Retesting this way should tell me whether the rubber bonding is the problem or not.

Anyway, here's a pic of todays non barrel weight results. Fine tuning is still to happen and seating depth tests might get that SD down to <5 but the current results are good enough for local club shoots out to 700m.

[Old Trev-39]

Hi Dennis,
I think that mounting the tuner flush would have no effect on gas/projectile interference. I have 6.5x55 rogue and std .284 win. both using the Purdy system for tuning. With this the tuner can be up to 1.25" in front of crown (depending on figures used) with excellent results. However in my experimenting with this system of tune I found that a harmonic of at least 19 and I.D of device to be over 3/4" to work. With I.D. under this I found what I believe is that the gasses then upset the projectile as there is to much gas trying to move foreward with the projectile and up-setting it. If you want to investigate the formulas just search The Purdy Prescription and down load. Happy to discuss this further with you if you like.
Cheers,
Trevor.

[DenisA]

Hi Dennis,
I think that mounting the tuner flush would have no effect on gas/projectile interference. I have 6.5x55 rogue and std .284 win. both using the Purdy system for tuning. With this the tuner can be up to 1.25" in front of crown (depending on figures used) with excellent results. However in my experimenting with this system of tune I found that a harmonic of at least 19 and I.D of device to be over 3/4" to work. With I.D. under this I found what I believe is that the gasses then upset the projectile as there is to much gas trying to move foreward with the projectile and up-setting it. If you want to investigate the formulas just search The Purdy Prescription and down load. Happy to discuss this further with you if you like.
Cheers,
Trevor.

Thanks Trevor, I will read up on the Purdy Prescription.

I'll get back to you. Cheers.

[DenisA]

Hi Trev,

It looks like the Purdy Prescription is a formula to tuning certain types of tuners and by the sound of it, applies best to rimfire??

The theory is pretty interesting to try and understand. I guess this why you pointed me down this path.

How do we know how many harmonics a given barrel has and how do you know which one you want to tune to?

[Old Trev-39]

Hi Denis,
Yes I forgot to mention that the article actually delt with R/Fires. However I was interested to see if it would work with C/F. I discussed it with the author and he said it should work on C/F but to start at, at least 17th. harmonic. I have found that both 19 &21 have worked for me. As to how many harmonics there are in a c/f barrel I would not have a clue. I have 2 .284 and 1 6.5 barrels working on the 19th. and the latest 6.5 on the 21st. The first 3 have a sleeve over the barrel tuned to the required measurement. The last 6.5 barrel was a straight 1.25 Krieger which came as a 31" blank. I did the calculations and came up with the figures that if I had 29.5" of usable barrel, counter bored with a 20 mm. recessed crown I could get my tune without using a sleeve, just by cutting barrel back to the measurement calculated. It worked. I just loaded up my 45.8grof 2209 and 140 jlk projs. at varing seating depths. After ru nning in I proceeded to fire groups at seating depths of >010 in. .020 -.030- .040 jumps.. The .010 2 groups not to bad .020 jump .178 & .087 .030 was shocking and .040 2 groups .108 &.102. Next lot of testing will be to confirm the .020 &.040 results. All these shot at 100yds.
When I set up my 2nd .284barrel I used the same load data as the first and the results were that it worked as good as the 1st. so did not do any other load development on that barrel.. It gave me the group win at the 2014 Southern Cross 1000yd B/R champs with a 4 target agg. of 7.116 and comp small group of 4,291. This was my No,2 barrel.
That is good enough proof for me that the system works. In 2013 at the champs I used my 1st .284 barrel and that gave me 2nd. place with a 4 target agg. of 6.645 and comp. small group of 3.828.
Hope this convinces you to give it a go.
Cheers,
Trevor.

[DenisA]

Trev, thanks so much for the info. It's really sparked my interest. Time and resources permitting, I'd love to have a play with the PRX one day. I might be inclined to start off on a .22lr until a I get a good understanding of it. Ill have to think about get myself a Harrells style tuner for the Annie.

Back to CF. On initial setup, how do you come up with a powder charge? Just base it on the MV you want? Or do you have to develop a great load for the barrel with out the tuner first?

I can't see anywhere in the formula that includes MV so I must be missing something.