Why all the lube grooves in cast bullets?

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  • Last Post 28 November 2014
John Alexander posted this 22 November 2014 

             I recently finished a series of tests to see the effects of filling the lube grooves in a multi-groove bullet in addition to the small gap ahead of the gas check on the gas check shank. A full report will be in a future Fouling Shot describing the test, reporting the results, and discussing the possible implications of the results.

One of the conclusions was that lube in the additional grooves ahead of the gas check “groove” did nothing positive that I could tell.

Does anybody have any results from a planned test showing that lubing additional grooves provides any benefits in accuracy, consistency, etc? If such testing has been done and the extra lubing showed that it is worthwhile, it would be nice to know of it and in what type of situation was it found necessary for best load.   Unless there is good evidence that lube in the forward bands is beneficial, the obvious question is why are we still designing bullets with multiple lube grooves when the space they take up might be better used to increase the length or either the driving bands or the part of the bullet that aligns it in the throat and bore. It is also unlikely that all those grooves improve the ballistic coefficient compared to a smoother bullet at least as some velocities.

John     

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goodsteel posted this 28 November 2014

Ken Campbell Iowa wrote: i am interested in how much leverage you need to seat a bullet to ” fully engraved ” ... looks like you have about 10-1 leverage. i had been thinking closer to 50 to 200 to one was needed. which would point to screw threads or hydraulics. heh or rack y pinion.

based on bolt camming leverage is about 60-1 .

hydraulics would allow the input force source to be clear of the action.

ken I figured this would be about right and it was just fine. Took about as much force as it does to cock a break barrel air rifle. Bullets are not soft either. There are now four people who have used the tool. I tested it yesterday, and I think its going to hold up very nicely. 

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bjornb posted this 28 November 2014

Ric, you get it!

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RicinYakima posted this 28 November 2014

I like to think of this as “fun” benchrest shooting, and not competitive shooting! Ric

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bjornb posted this 27 November 2014

nimrod wrote: I was reading through the rules and I don't have any idea what most the guys plans are for all this breech seating but the breech seating allowed would be in the Plain Base Class and the Unrestricted Rifle Class, just saying. Of course in the Plain Base class there would be NO gas checks. I don't know about the Unrestricted Class maybe gas checks would be allowed I really don't know why not?

Rb Nimrod,our purpose for this breech seater is High Velocity shooting (why? why not?), and we are attempting to get the bullet started in the throat/rifling as straight as possible, with full support. As muzzle velocity increases, accuracy decreases once you get into the 2500fps+ area, and we are attempting to mitigate this by engraving the bullet fully before launching. 

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frnkeore posted this 27 November 2014

Ken, The key to BSing is in throating and as cast bullet size or both.

Typically, a tapered bullet for that use has the first band about 1/2 (or less) of the groove diameter and tapers to ~.001 over groove or throat dia (which ever is larger). With a GC you might get away with size for size. PB needs that extra .001 to make sure we get a seal and don't gas cut.

One other thing to keep in mind with all cast bullet shooting is sizing. The more you do, the more chance you take of things not going as planed. That goes for both sizing before you load and the sizing that occures when the bullet is either launched from the case or BSed.

Custom bullet molds are expensive and hard to get made to your dimensions but, they are the way to go.

Frank

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Ken Campbell Iowa posted this 27 November 2014

i am interested in how much leverage you need to seat a bullet to ” fully engraved ” ... looks like you have about 10-1 leverage. i had been thinking closer to 50 to 200 to one was needed. which would point to screw threads or hydraulics. heh or rack y pinion.

based on bolt camming leverage is about 60-1 .

hydraulics would allow the input force source to be clear of the action.

ken

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nimrod posted this 27 November 2014

I was reading through the rules and I don't have any idea what most the guys plans are for all this breech seating but the breech seating allowed would be in the Plain Base Class and the Unrestricted Rifle Class, just saying. Of course in the Plain Base class there would be NO gas checks. I don't know about the Unrestricted Class maybe gas checks would be allowed I really don't know why not?

Rb

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goodsteel posted this 27 November 2014

Dang, don't leave out the finished product! Came out looking pretty snazzy I thought.Thanks for the tip Frank. I just started thinking about doing a through the action breech seater Sunday, and was going to try to attach the handle to the body of the seater itself, but then Bjorn texted me and told me about your suggestion of using the boltstop stud as an anchor point. Brilliant suggestion! Made it happen and here she is:

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bjornb posted this 27 November 2014

Thanks John, I'm glad you cleared that up. When I first asked the question about breech seating GC bullets I didn't envision the discussion and pictorials that would follow. Goodsteel is shipping the seater to me over the holiday weekend, and I'll be posting more on installing it on my rifle and also on actually loading and shooting with this device once it has been installed. Thanks to everybody for posting pictures and comments.

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John Alexander posted this 27 November 2014

Go right ahead with the interesting discussion on breech seating tools and such.  I have started another thread to pursue the questions about lube grooves and reducing their number so a bullet can be designed that will come close to to breech seating with fixed ammunition.  

Threads the drift off seem to be normal and starting another thread is easier than moving all the posts.

John

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bjornb posted this 27 November 2014

You are correct and I shouldn't have started the thread drift but I really don't know how to move posts into another thread. So with a final picture of the MBT Breech Seater I promise I'll leave the thread or wait for a mod to move the breech seating stuff somewhere else.

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tlkeizer posted this 26 November 2014

Greetings, UMMMM, I'm missing somptin.  Isn't this chain about lube in grooves and is it required for all grooves or sumpin like that?  How do pistons relate to lube required in grooves?  Could most of these replys go to another track or am I not following the beginning of the thought?  I'm kind of weak minded so I can't quite put the head screws and mock chambers in perspective of lube required in grooves other than the proper lubed bullet should find the bunny at the end of the trail.  Please enlighten my if I am off base.   TK

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jhalcott posted this 26 November 2014

I tried several different lubes in the Loverin .30 caliber bullet years ago. I also tried filling ALL the grooves and only SOME of them. The type and amount DID make a difference in accuracy. I was more interested in minute of ground hog than X ring accuracy. The groups with ALL grooves filled were always larger than when only SOME grooves were filled. I cleaned the bore after each test and fired 3 shots to season the bore before the next test.

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DR Owl Creek posted this 26 November 2014

Bjornb,   Thanks for posting those pictures. That really helps.   Dave

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frnkeore posted this 26 November 2014

Note the button head screw, it isn't taped quite all the way through, used simular to a lock nut, that is a second BS adjustment. Frank

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frnkeore posted this 26 November 2014

This is the one I made for my Borchardt, same idea with the push lever style. Here I use press fit and slip fit dowel pins for the pivots. Frank

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nimrod posted this 26 November 2014

Yep that's about what I had in mind.

RB

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frnkeore posted this 26 November 2014

I can't find a way of posting mulitple pics in one reply

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frnkeore posted this 26 November 2014

This might be something like Nimrod is suggesting? I made this one for my wifes HW but, if made longer, with a case or case shape on the end, the ears could side in the bolt raceway, then rotate the handle, up or down, just a little, to catch the bolt lugs and pull back or, put the toggle on the other side and push as your lever would do. I suggested the bolt release as a anchor, because you had no provision for for anything on yours. Frank

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bjornb posted this 26 November 2014

Handle in all its glory:

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