Boosting BC of commerical bullets.....

[Fiftydriver]

Roy nailed it, main difference being I didn't have my looks to fall back on, when my skill level proved insufficient to the task. Very cool to see it done.

We are all studs in our own minds!!!

 

[Swamplord]

Fifty....


how about turning that boat tail on the 375 cal Accubond to reduce the bearing surface and increase the BC ? along with your tip of course !

put me down for 100 pcs..... pre-ordering now just in case you decide to sell a batch

 

[ICANHITHIMMAN]

Kirby

What type of time do you have invested in one bullet, ie. how long does this process take.

 

[Fiftydriver]

Fifty....


how about turning that boat tail on the 375 cal Accubond to reduce the bearing surface and increase the BC ? along with your tip of course !

put me down for 100 pcs..... pre-ordering now just in case you decide to sell a batch

The baring surface on the 375 cal, 300 gr Accubond is not a problem, its actually pretty good and does not limit velocity potential at all. Its the new 338 cal version that has a very long baring surface length and that is because they basically only increased the length of the body on the 250 gr version to get the 300 without changing ogive design or boattail design.

In all honesty, I do not think you could do alot with the boat tail to increase BC. Most of the BC is made with ogive design and meplat shape. You would only be looking at an increase in the thousandths range modifying the boattail. You may also weaken the solid base and if the Accubond looses its support cup, penetration will suffer dramatically.

Another issue is consistancy, I have no desire to mess with any part of the rear of the bullet because that is critical as far as accuracy is concerned. In reality, you can get away with more run out on the tip of a bullet then you can if you have run out on the base of a bullet where it contact the crown of the muzzle when fired.

I have tested some prototype 265 gr Aluminum Tipped 338 cal bullets from the old Wildcat bullet company that had very poor aluminum tip run out. At 1000 yards, I tested these in my 338 AM loaded to +3500 fps. One test lot of ammo was loaded with bullets that had tip run outs of less then 0.001". The other test lot of ammo had tip run outs that were all between 0.005 and 0.008". You could see the tips wobble as you rolled them across the loading bench surface.

I shot three, 3 shot groups at 1000 yards on paper and measured group size. The match quality run out bullets averaged 8.890" for three, 3 shot groups at that range. The bullets with poor tip run out averaged 9.783" for three, 3 shot groups at 1000 yards.

So while the poor tips did not shoot as well, at 1000 yards, they shot within an inch group size of the perfect tips...... I was amazed to see this. In my opinion, with a bullet of this mass, a very light aluminum tip will have very little influence if run out is less then 3 thou or so because the mass of the tip is not enough to influence the bullets center of gravity. Remember about the only amount of the bullet that is really out of alignment to any measurable degree is the very tip which weighs virturally nothing compared to the mass of these larger bullets.

Certainly we want everything to be as perfect as possible but having an absolutely perfect tip alignment is less critical then many would ever think. It suprised me!!! The difference is far less then most people would be able to tell down range as enviormental conditions can effect group size much more then a tip slightly off axis.

Now, as far as a boattail a bit off, that would cause serious accuracy issues because one side of the bullet could be released by the crown before the other and the escaping gasses would raise hell with the beginning flight path of the bullet and it would REALLY show up down range with poor consistancy and accuracy.

 

[Swamplord]

What if you were to reduce the diameter of the bullet slightly just in front of the ogive or at the boat tail ? just enough to shorten the bearing surface to an acceptable length

 

[Swamplord]

oops, ya answered my question just as I typed and posted it, disregard the last Q

 

[Fiftydriver]

Kirby

What type of time do you have invested in one bullet, ie. how long does this process take.

Once I had the collet system made, it took me around 15 minutes to figure out the correct amount to take off the ogive to match up to the tip diameter. That number is a given that can be repeated quickly from set up to set up so that is not something that needs to be done every time I set up.

Once I got a few ran and figured out the process, I timed myself to see how long it would take just or my information from a labor stand point just in case I ever decided to offer these bullets for sale(still undecided on that).

On the conventional cup jackted bullets, After a bit of time I could pump out between 2 and 3 a minute. So your looking at around 120 to 180 per hour. I am sure it would get quicker with more time and I can see possibly pushing this up to around 4 per minute pretty easily with so time and practice.

The simple version of the process goes like this:

1. Release the 6 jaw chuck pressure, insert a bullet into the collet, tighten down the chuck.

2. Use my part off tool which is set up in the correct position to take the correct amount of the ogive off the bullet. Part off the nose of the bullet at 430 rpms

3. Take some 0000 steel wool and remove the small burr left on the bullet by the part off cutter while the lathe is spinning at same rpm.

4. Use a small center drill to make a starter hole in the face of the larger bullet meplat. Not deep, only around 25 thou is plenty. Same 430 rpm

5. Replace center drill with #40 carbide drill (not needed for lead) and drill 0.098" diameter hole 0.400" deep into the nose of the bullet. Same 430 rpm

6. Run part off tool across face of bullet again to remove any left over lead scraps from drilling process.

7. Turn off lathe, insert 22 cal bullet seater stem into chuck in tail rest. Insert aluminum tip onto hole in bullet and use the tail stock to press in the tip into the nose cavity of the bullet. Done and repeat for next bullet.

the Barnes bullets are harder to do and I need to order in some different tooling to make it easier to do them. The solid copper bullets really like to gaul up so if you push the drill to hard then stick pretty tight so you have to go slower with these by a little bit. The tips have a 0.101" diameter shank post and in the lead bullets, the 0.004" press fit is perfect, on the solid copper bullets, its to heavy so I need to order in a drill with a 0.100" diameter which should be perfect for the Barnes bullets. Other then that, its the same process.

Again, not hard at all, anyone with a lathe and a bit of time can do this easily. I am going to sit down and sometime and try to figure out a system that could be used for a drill press as there are more guys that have a drill press then have a metal lathe. I think it could be easily done, just have to figure out the clamping system on the bullet, other then that it would be easy.

In fact, it may be better on a drill press as far as pressing tips in as well.

 

[Fiftydriver]

What if you were to reduce the diameter of the bullet slightly just in front of the ogive or at the boat tail ? just enough to shorten the bearing surface to an acceptable length

I have done some testing with this on the barnes TSX bullets that showed some promise. What I did was for example, on the 285 gr TSX-TAC bullets, it has 4 bands on the bullet body with obviously 5 relief grooves cut into the side of the bullet to reduce baring surface.

I have taken these bullets and experimented with these bands by removing some of them to see what would happen.

From my experience with 50 cal bore riders I knew that you need a certain amount of body baring surface to get good accuracy so I started at the front of the bands nearest to the ogive of the bullet. I parted off the first one on 20 bullets and did a quick load development to see of this would improve performance at all. I was mearly looking for velocity improvement. Removing one band did not do much compared to the standard bullet. Velocity and pressure using the same standard load stayed pretty much the same.

When I removed two bands, the velocity with standard load dropped by 30 fps.

When I removed three bands, the velocity with standard load dropped by nearly 65 fps.

When I removed all 4 bands, velocity dropped by just under 100 fps with standard load.

Why did the velocity drop, simple, less baring surface made it easier to push the bullet done the bore so there was a drop in pressure which resulted in a drop in velocity with a given load. Its kind of like backing the bullet way off the lands with the same load, this flattens the pressure spike and results in less velocity with a given load.

THAT SAID, this drop in pressure allows the careful reloader to increase the powder charge because the pressure curve of the load is dramatically flattened. As such, it would take more powder to regain the same level of velocity that the original load produced but at the same velocity, the pressure curve would still be significantly flatter with more area under the curve. This means that there is more pressure under the bullet while the bullet is in the bore.

As such, you can often increase powder charges even more and see an improvement in velocity performance with the lower baring surface bullets.

In my testing, I would increase the load by 1 grain at a time (in my 338 Allen Xpress so 1 grain is roughly 1% increase) and load up until i JUST started to see an ejector ring on the case head. I know, not scientifically pure but it works close enough. These were all fired in cases that had had one high pressure firing on them with no ejector ring marks at all.

When loaded to the same visual point based on the ejector rings marks on case head, again just looking for the first hint of a ring, the bullets with one band removed were only 15-20 fps over the standard load.

Bullets with two bands removed allowed close to 50 fps increase.

Bullets with three bands removed were in the 60-70 fps increase range.

Bullets with all four bands removed showed an 80-90 fps increase.

I was a bit suprised to see the velocity gains were slightly off from the velocity drops with the standard loads comparing the number of bands removed but I was still impressed to see the possible increase in velocity. Being able to increase velocity by nearly 100 fps is pretty much as close to a free or CHEAP lunch as you can get.

I machined up 25 bullets with all four bands removed and loaded them up. I had to use somewhat of an odd loading length and the throat had to be long enough so that I could seat the bullet so the base of the bullet body was still in the neck of the case to hold it solidly as the center of the bullet would just fall in the case. Luckily, I had a single shot rifle to test and was able to do this with its long throat set up for the SMK seated to the base of the neck.

At 1000 yards, it was instantly clear that accuracy was VERY poor. Groups could be measured in yards!!!! Was not impressed. Headed back to the shop scratching my head and thats when I remembered many 50 BMG bore riding bullets needing a certain amount of baring surface at the rear of the bullet to shoot accurately.

I machined up another batch of bullets with the front three bands removed and this time they shot MUCH better but still in the 1-2 moa range.

Tested more bullets with only the front two bands removed and these bullets shot to the rifles potential. So in the end, to maintain peak accuracy I was limited to a 50 fps velocity increase. Is it worth it...... Not really to me but it is possible.

Now, I did this testing with the solid Barnes bullets. The Accubond, while it has a thick jacket, its not thick enough to do this type of modifying on without weakening the jacket to the point that you would likely see problems on impact loosing the entire front half of the bullet at best and possibly, in the larger magnums, having bullet failure when the bullet leaves the muzzle. I have seen this alot but thats another story for another time.

 

[Swamplord]

This is probably the most interesting thread on this forum in quite a while,
got my eyes and ears wide open !!!!

Definately want to hear about your results with the drill press !

I've been using WS2 (Danzac) tungsten disulfide to coat my bullets for about 10 yrs now and get similar drops in pressure and velocity, and when gradually worked up I always see an improvement in velocity, often times exceeding 100 fps... and accuracy tends to improve also...

I've taken a boatload of moose with coated 30 cal A Frames and Accubonds over the years sizzling 100 fps faster than usual for the cartridges I used, although none were over 650 yards so It didn't really matter I guess.... other than the improved accuracy !

I wonder if removing a few of the bands on the Barnes bullets then coating them will produce a noticable improvement ....

a 200 gr LRX in my 300 RUM going 3300 fps would be ultra super !!! (pun Intended, lol)

 

[Fiftydriver]

Thats very fast anyway!!

 

[screech]

If some one has a Harding second operation lathe I bet you could do it pretty quick off of it. If you don't mind me asking were you loading them off the base of the bullet or the ogive on a stop ?

 

[westcliffe01]

Would you be willing to share your method for coating the bullets. I am familiar with WS2 grease. Did you manage to obtain powder and what is your source ?

I've been using WS2 (Danzac) tungsten disulfide to coat my bullets for about 10 yrs now and get similar drops in pressure and velocity, and when gradually worked up I always see an improvement in velocity, often times exceeding 100 fps... and accuracy tends to improve also...

 

[Fiftydriver]

If some one has a Harding second operation lathe I bet you could do it pretty quick off of it. If you don't mind me asking were you loading them off the base of the bullet or the ogive on a stop ?

Right now they are going off the base of the bullet. From the limited number of bullets I have modified, OALs have been running pretty consistant, less then 5 thou which compared to a SMK is GREAT and similiar to a Berger or other tipped bullets.

I have not found bullet OAL to have a huge impact on down range accuracy and consistany. Now, baring surface consistancy is critical to down range results but boat tail length and ogive length do not seem as critical to down range consistancy. Still, they have been very good so far.

 

[Engineering101]

Kirby

Since bearing surface consistency is critical to downrange accuracy, it follows that those bullets that control this parameter the best would be the most accurate. Is Berger then the most accurate of the major bullet makers at long range?