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# High BC .257 bullets?

#29
10-17-2006, 05:30 PM
 Silver Member Join Date: Jan 2003 Location: Wallaroo, South Australia Posts: 201
Re: High BC .257 bullets?

Kirby, That certainly is interesting research, and I am impressed by the way you go about solving these problems.

I realise that I am getting old and senile, and my mathematics needs a brush up, but how do you calculate the percentage of bullet compression? Perhaps can you expand on how you arrived at the figures you quoted for the 4 and 6 groove Lilja.

I am probably missing something obvious, but if the lands and grooves are of equal width, do you simply divide by the number of grooves to get the percentage of bullet compression?

If the lands and grooves are not of equal diameter, would I have to contact the barrel manufacturer to get the land width specifications to enable me to do the calculations?
Regards, Brian.
#30
10-17-2006, 07:00 PM
 Silver Member Join Date: Sep 2003 Posts: 347
Re: High BC .257 bullets?

Kirby what you are saying does make sense. Those big bullets do have more bearing surface than any other bullets out their. And lessening the stress on the bullets and contact with the lands should reduce pressure. But thin 6 groove barrel's with big bore magnums might reduce barrel life. Time and testing will tell. It take time patience and balls to try the new and unproven and I give you credit for pushing the enevlope. Thanks for the food for thought
#31
10-17-2006, 08:06 PM
 Official LRH Sponsor Join Date: Jun 2004 Location: Fort Shaw, Montana Posts: 6,841
Re: High BC .257 bullets?

Brian,

My method of figuring this is pretty damn simple but it allows a comparision between the different land widths for speicific bore diameters.

First off, I figure the circumference of a specific bore diameter, lest say 7mm. The equation I use is 2(pi)r=c

So to figure this: 2 x 3.141592654 x 0.142= 0.892 rounded up.

Now I take and with a good light and my calipers, I get as close a measurement as I can of the lands at the muzzle. Just get as close as you can. YOu will easily be able to get within 5 thou of the actual land width with good light and possibly a magnifying glass.

Just for example I measured the following: THese numbers are just from memory as I do not have my notes in front of me now but you will get the point:

These are the widths of each land:

Rock 5R 1-8 twist(standard land width).....0.065"
Lilja 1-7 3 groove.........................0.075"
Lilja 1-9 4 groove.........................0.045"
Lilja 1-9 6 groove.........................0.025"

I then added the total wideth of the lands surface of a cross section of the barrel. Know I know that the lands are on a smaller circumference then the groove diameter and you could adjust for that if you wanted more accurate numbers but it is not that critical, I wanted to know the percentage of the circumference that was land width and compare those for each design.

If you take the Rock 5R barrel with 0.065" wide lands you come up with a total land width of 0.325. If you figure that into a ratio of the total circumference you come up with roughly 36% of the circumference is ladn width so it is pretty safe to say that 36% of the cross section of the bullet is compressed by lands.

If you look at the others you will find the following percentages:

Rock 5R...........36%
Lilja 3 gr........25%
Lilja 4 gr........20%
Lilja 6 gr........17%

Now the Rock 5R barrel was tearing the 200 gr ULD RBBT apart nearly all the time. Not the fault of the barrel, just not a good match with this bullet. In fact this barrel shoots well under 1/2 moa with the 160 gr Accubond with velocities near 3600 fps!!!

The Lilja 3 grooves have been working very well but on a couple occasions there have been instances where bullets have come apart with barrels that have gotten some wear on them. Again, not the fault of the barrel, actually more then a bullet baring surface compression issue it is more to high of RPMs more then anything combined with the wide lands.

In the Lilja 1-9 4 groove barrel, velocites pushing 3400 fps were possible and in the testing I was able to do never did I see any sign of bullet failure. All bullets made it to target predictably out to 1500 yards. THis is fully 250 fps more then what the Lilja 3 groove will allow but again, this is in large part to the overly fast twist rate come to find out we did not need such an extreme twist.

The Lilja 1-9 6 groove has the highest number of lands but also the narrowest and as such have been performing perfectly well.

The issues is largely twist rate but also land width as well.

The Rock standard 5R should not be overly hard on these bullets with a 1-8 twist at 2800 to 3000 fps which is terribly slow for the 7mm AM but we ever tested to this velocity and still had a very high rate of bullet failure.

Even the Lilja 3 groove with their very wide lands, widest of the group on average performed extremely well with this bullet because they only compress 25% of the cross section of the bullet.

The new Rock 5R barrel I am about to test which was made specifically for these bullets is a 1-8.7 twist, slower then the first one tested and the lands have been thinned to around 20 thou. Thats a bit over 11% compression.

Keep in mind though that the side of the 5R lands are not sharp edged like the Lilja barrel so there will be more compression then the land width predicts but still should be well under 20% which should work perfectly.

This is not an exact numbers figuring excersice, just one way to compare one rifling design to another and get a reasonably accurate comparision between the bullet cross section compression %.

With a set of calipers and a good light you can get extremely close to the actual land width of the rifling in your barrel.

TO test this theory I hope to get Rock to make me a 22 cal barrel with roughly 15% cross section compression and test it with the 100 and 107 gr ULD RBBTs in the 224 Allen Mag. This round has the potential to be a 3450 fps round in a 27" barrel with these bullets but so far the barrels I have tested will not allow this to be reached. Not even close.

Will need to talk with James at Rock Creek and see if a 22 cal barrel is possible. Thats a project for this spring though, to many irons in the fire for this fall and winter!!! [img]/ubbthreads/images/graemlins/grin.gif[/img]

Did I clear anything up or make it alot worse!!! [img]/ubbthreads/images/graemlins/grin.gif[/img]

Kirby Allen(50)
__________________
Kirby Allen(50)

Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

Farther, Faster and Flatter then ever before.

Web Page: www.apsrifles.com

allenmagnum@gmail.com
#32
10-17-2006, 08:15 PM
 Official LRH Sponsor Join Date: Jun 2004 Location: Fort Shaw, Montana Posts: 6,841
Re: High BC .257 bullets?

Reed,

Of course you are right in your comments that thinner lands will erode faster then wide lands. That was the whole reason for using the Lilja 3 groove in the first place. If a Lilja 3 groove in a 1-9 twist was available I suspect it would perform extremely well in 7mm with the 200 gr ULD RBBT but experimenting with Lilja barrels requires me to pay Dan to get a new rifling button every time I want to try something new. If I knew exactly want I wanted this is practical to do this one time but over and over testing would get EXTREMELY expensive.

Rock Creek has the ability to change twist rates down to .3" per inch and also the ability to change the wideth of the lands with no extra charge, ALOT LESS EXPENSIVE to test these things out!!!

Yes the origins of the lands will erode faster but remember that the 5R rifling are not sharp edged rifling so there is more meat in them then a traditional land of the same surface width so they will last longer, how much longer, yet to be seen.

Most feel barrels are pretty expendable. A custom rifle will run you anywhere from \$1900 to as much as you want to put into it. A replacement barrel will run \$300 to \$500 depending on length and if you want it fluted. Add \$200 to 300 on that and you have a new barrel installed so for \$500 on the low end you have basically a new rifle.

This is not chump change in any way or form but some feel it is more then worth it to get an extra 200 fps on a .9 BC bullet. I would probably fall into that catagory and give up 200-300 rounds on a 1200 round barrel life for big game hunting.

Sometimes I question my patients and sometimes I think the only balls I have are rolling around between my ears when I do something really stupid in testing but so far it has been alot of fun and we are doing some interesting things.

Richard just needs to keep making the bullets and I will figure some way to put 100 grains of powder under them to find the limits of the barrels, bullets and powders!!!

All in the name of having fun I guess!!! We are all in it together anyway, thats the good thing about LRH!!!

Good Shooting!!

Kirby Allen(50)
__________________
Kirby Allen(50)

Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

Farther, Faster and Flatter then ever before.

Web Page: www.apsrifles.com

allenmagnum@gmail.com
#33
10-17-2006, 10:00 PM
 Silver Member Join Date: Jan 2003 Location: Wallaroo, South Australia Posts: 201
Re: High BC .257 bullets?

Kirby, I just did the numbers on my Krieger .257 7 twist barrel (4 grooves, I think) and it comes out at 32.21% using these numbers.

Land width: 0.065 (I think I measured it correctly)
Total Land width: 0.260
Barrel Circ: 0.807

So it is safe to assume that the 32% land compression is putting considerable stress on the 156 grain Wildcat which as you would know has a large bearing surface.

The barrel has currently 90 shots down the spout and you would think that it is broken in. However, right from the first shot to the latest the accuracy levels are good, but I have been surprised by the amount of copper fouling it is creating.

However, it does seem to clean up most of it after just 2-3 patches of Tetra, but I usually am getting small spots of copper left on the edge of 2-3 lands in the last half inch from the muzzle.

These small deposits are left after using Tetra copper solvent and sometimes Sweets. The rest of the barrel cleans up quickly, but I seem to have to go to extra trouble to remove these 2 or 3 spots of copper.

Do you think that it is a barrel problem near the muzzle, or just a result of the bullet being shredded by the lands and more copper being deposited there.

My new Krieger .224 6.5 twist barrel is still in its wrapper in the cupboard, but I am now wondering whether I should take that off and measure the lands.

Thank you for a thought provoking article. Regards, Brian.
#34
10-17-2006, 11:20 PM
 Silver Member Join Date: Sep 2003 Posts: 347
Re: High BC .257 bullets?

The more you shoot the more disposible barrels are. In my little world I think the biggest thing to do with barrel life is the hardness of the barrel steel. I have had a douglas 22 br and a pac-nor 22 dasher barrel give up there accuracy with the throats fire cracking in under 700 rounds. One three groove the other 6 groove. But i noticed both barrels machined noticeably easier than the benchmark barrels and i have used. Then on the other hand you have 270 allen mags with 700 rounds and little wear, why has to hardness of the steel used. I think to many barrel manufactures are using softer lots of steel to get a barrel to machine easily and they will shoot well for a limited time. Who can complain about a barrel that shot a record group but only lasted 500 rounds. This is not sientific tested just my common sense observations. I don't think that it hurts anything using 5 or 6 groove barrels. How much of a difference is there in barrel life, is it cost effective enough to worry about. After shooting my 3 groove pacnor this summer 650 rounds through it with a 22 dasher and it gave up its accuracy , the 3 groove thing hasn't proven anything to me. I had a 22-250 ackley 8 twist benchmark go 1000 rounds with peak accuracy and it was a 6 groove. In theory a three groove should last longer, but with the problems associated and differences in the steel used, how many more rounds will we get? If you want you should try the 22 dasher with the wildcats. It shot real well at 3000 fps and 35.0 of powder. Shoot me an e-mail your welcome to borrow my reamers if you want to give it a try. You might rechamber that promblem 22 allen mag to a dasher, and you should have a real shooter on your hand. You said that barrel shot great around 3000 fps. And the dasher would put right there at that velcioty node. I have resize and finish reamers. Thanks for the information, it never hurts to learn something new [img]/ubbthreads/images/graemlins/smile.gif[/img]
#35
10-19-2006, 07:33 AM
 Official LRH Sponsor Join Date: Jun 2004 Location: Fort Shaw, Montana Posts: 6,841
Re: High BC .257 bullets?

Brian,

I have not had a serious problem in any way with the 25 cal 156 gr ULD RBBT in my Lilja 3 groove barrels. Only issue I had was when I got a barrel way to hot and a couple bullets let loose. This was the idiot rifle owners problem(me), not the barrel or bullets.

Other then that I have been using them to 3300 fps with great results. I will admit I do not have alot of rounds down my 257 AM barrels so time will tell is a worn 3 groove will start showing these signs or not.

Your Krieger does have a pretty high percentage of baring surface compression but at the velocity levels you are using you may never see a problem at all. Time will tell.

With a baring surface that long you will always get some copper fouling. The good thing is that it cleans up relatively fast.

I have customers wanting to know how to keep their 50 BMG from severely copper fouling, I simply tell them if they want to keep their BMGs from copper fouling, don't shoot them!!! [img]/ubbthreads/images/graemlins/grin.gif[/img]

When you have alot of baring surface there is really nothing you can do to eliminate copper fouling, clean often and regularly and it will not be an issue just as you are doing.

Kirby Allen(50)

I am really excited to try the new Rock 5R 25 cal barrels though when they are ready.
__________________
Kirby Allen(50)

Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

Farther, Faster and Flatter then ever before.

Web Page: www.apsrifles.com

allenmagnum@gmail.com

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