Can I get some feedback on this boolit design?

[Castloader]

So here's the concept:
115883
-6 ogive
-30 cal (.310)
-200 gr (ish)
-smooth-walled (because I don't mess with lube) for Powder Coating or copper plating
-Rebated boat tail
-Purpose is subsonic use
-Overall boolit length is 1.541"
-Ogive length is .720" (this would be the minimum boolit nose length sticking out of the case)
-I'm not really hung up on the crimp groove, I could take it or leave it I was just messing with my new drawing program, but it shows where the ogive begins.

On the boattail: I know boat tails IN GENERAL are a bad idea with cast, but I wondered if a rebated tail would exit the muzzle more like a Plain Based boolit, but mostly enjoy the flight profile of a regular boat tail.

Here's what I'm looking for in feedback:
1) Can a mold like this be made with existing equipment? (some require wide meplats etc.)
2) Has anybody tried a REBATED boat tail in cast before? I know the standard boat tail failed, I have the LEE 230gr TL
3) Does anybody anticipate issues with the actual casting process with a mold like this; fillout, release etc.?
4) Any related thoughts on how a powder coat would affect the shoulder step on the tail.

What I'm NOT looking for in feedback:
a) Anything related to standard boat tail cast boolits
b) Any wild guesses not based on empirical data or your personal experience. ie; if you don't make molds or know A LOT about how to make molds, please don't reply to #1 If you don't powder coat, I'd rather not hear any comments from you on #3
c) Suggestions for other boolit designs

Thanks

[leadman]

Might help to post the application for this boolit you are considering. Since you have the Lee 230gr you probably know of some of the challenges to get this to shoot well.

[Castloader]

I plan to load in either/both a .308 AR-10 with a 1:11.25 twist or 300AAC Blackout AR-type with 1:7 twist.I could get the Lee 230 grain to stop tumbling if I apply gas checks, thats it. It hates having a regular boat tail. After reading on Corbin's website about the ballistics of a rebated boat tail, I'm intrigued about the possibilities with cast. I really want something to mass produce for short range competition and plinking. 2 MOA accuracy would be fine for me. I don't want to have to use gas checks, and I'd like repeatable accuracy at 100yds and in.

[leftiye]

Old time Lapua match.

[Tatume]

b) Any wild guesses not based on empirical data or your personal experience. ie; if you don't make molds or know A LOT about how to make molds, please don't reply to #1 If you don't powder coat, I'd rather not hear any comments from you on #3

Telling people what to do or say is rude. If you'd rather not hear comments from everybody then don't post the question on an open forum. Find someone you do want to hear from and ask your question as a PM.

[Moonie]

Here's what I'm looking for in feedback:
1) Can a mold like this be made with existing equipment? (some require wide meplats etc.)

I believe this mold can be made, it would have to be made with a cherry and there might be some issues with a tip that narrow. I am not a mold maker however so I can't really comment on the strength of a tip that small on a cherry.

2) Has anybody tried a REBATED boat tail in cast before? I know the standard boat tail failed, I have the LEE 230gr TL

I'm sure it has been tried, everything has, the designs that do not perform well are discarded.

3) Does anybody anticipate issues with the actual casting process with a mold like this; fillout, release etc.?

With the exception of the step it should do very well in actual casting, I'd add a small angle to the step rather than straight as that could cause some hang up.

4) Any related thoughts on how a powder coat would affect the shoulder step on the tail.

I don't think PC would affect anything on the shoulder step.


With all of this said, please note that this boolit design goes against most every cast boolit design that is conducive to accuracy. Long unsupported nose sections do not normally contribute to accuracy and usually are difficult to get to shoot well. All the boat tail designs I've heard of over the years have failed. I do wish you luck, none of the above criticisms are designed to dissuade you from your plan. PC does change the game somewhat, enough to make this design easier to get to shoot? I don't know, but I do hope so. I think your problem will be finding someone that will make the molds for you as a lot of the industry has moved away from cherry's and to CNC machines that generally have to make molds with at least a small meplat.


Also note, Tatume is quite correct, telling this forum what you do NOT want in responses usually doesn't go over well with those best equipped to help you as we tend to be gentlemen that do not like being told what not to do, especially when it appears to be a bad idea.

[Wayne Smith]

Humm, methinks you will need a nose pour to get that point. I'm sure it can be made, but at what cost?? Definitely a non-traditional approach, but if you have the capacity to copper plate and can get enough on to prevent nose slump it might work. You will have to do the math if you are going to plate to figure your actual diameter of lead needed to get the final size you need. I assume you are thinking long range target shooting? You will need to specify your alloy ahead of time to accomplish consistent weight and diameter, and then only use that alloy.

[DeanWinchester]

I think the rebated boat tail is a waste of time. For subsonic use, a plain base will do just fine if they are cast square and smooth with sharp corners. There's just not gonna be a benefit for the work and expense making a rebated boat tail will require. With the time and money invested in making it work, with no gaurantee it will, you could already be shooting good groups with a rgualr plain base.

[leadman]

If you are only going to shoot to 100 yards there are many molds out there that will cast a boolit that works. I'm going to try the Lee 200gr RN GC without the gas check and coated with Hi-Tek in a 300 Whisper just to see what it will do.
Have you ever seen a picture of the 22 LR heeled boolit in flight after it is fired? The heeled section has obturated to bore diameter and the boolit is shortened. Could possibly happen to the rebated boat tail.

[runfiverun]

that nose is doable, lyman and ideal have both done it.
I'd drop the crimp groove for sure, it will just make trouble in the cutting and the casting.
I'd keep the flat for your planned use.
dunno how P/C will affect the base but you could do the tumble and size p/c method, and then use a custom base punch to help square it up fully.

[Castloader]

leadman- I do have some Lapua 200gr Rebated boat tail Scenars, but they're $0.45 each! They shoot like a dream though, I'm basically trying to copy them, but make a few changes to allow for some of the idiosycracies of cast and PC or plated.

I also have the Lee 200gr GC. I haven't fired it without the GC, but it's the most accurate boolit from my 300 BLK so far. Feeds like a champ too. I just don't want to mess with GC's either if I can help it. I'm looking for lowest cost (after setup costs) and high output. I read on the Corbin page that the rebated boat tail has the greatest benefit in subsonic use! Up to 40% improvement in BC with subsonic! That's a benefit worth exploring to me especially since I need to squeeze all the efficiency I can out of a sub in order to get repeatable performance at distance. I can shoot supers just fine, but that's not the goal here.

Tatume- I didn't think that being specific about the feedback I'm looking for quallifies as being rude. If people take offense, feel free not to comment. No offense intended.

Moonie- thanks for the input on angling the step, I'll work that in

Popper- I actually own the C.O.D. mold in a 5-cav plain base. It won't shoot for sour apples in my 7-twist, and I don't have my 11.25 twist available to try at the moment, but all the evidence from my own tests compared with others seemed to indicate that I wasn't getting a nose slump, I just had a twist that the COD doesn't like, at least when fired at "normal" 300 BLK velocities. I did a chambering exercise, and couldn't detect any nose bending with PC'd boolits that 'cured' for a couple weeks.

shank length, or bearing surface is .621" based on measuring my drawing

I didn't think gas velocity was subsonic, I'm pretty sure it's not, though I could be wrong... why else have a suppressor if not to grab a hold of all that supersonic gas around your subsonic boolit?

This 6 ogive nose is significantly less pointed than the COD, but I'll probably widen the meplat by another hair or two just to make sure there's no bending issues. I wish the COD had a shorter nose and a wider meplat, but hey, what can you do? I appreciate the input.

I emailed Mr Nelson at NOE and he said the cherry shank needs to be .284 or possibly .280 minimum, so my rebated boat tail can't really be smaller than a GC shank anyway, at least if the mold is made on his equipment. He said the nose is no problem at all.

I'm planning to get a benchtop mini lathe pretty soon, and if I make a mold for this, it'll probably be made in 2 parts, one for the nose and shank, and a second "layer" for the rebated boat-tail. I'm just screwing around, and I don't need to produce more than 1 mold, I just want to see if it will work. If I ever manage to get to the pouring stage I'll let y'all know. Once again, that's for all the input.

[303Guy]

I've toyed with the idea of a two-piece 'solid' mold which casts through either the nose or base. Gas venting takes place around the casting spout which protrudes into the mold, leaving a conical hollow after the sprue is plucked off. Currently I only nose pour making base shapes easy to play with. But alas, I don't have range data for plain cast, only paper patched. The main problem I had been trying to solve was trailing edge feathering and to that end I added a small rebate and chamfer. A secondary objective was to shoot a plain based, fairly soft boolit with reasonable pressure. I seem to have succeeded on both counts but I do need to complete my testing which has been on back burner for a while now.

From my findings I'd suggest looking at making that rebate only groove depth so that the rebate will support the step and prevent base dragging at the rifling impression. Then again, that may only be of any relevance where oversize chambers are involved. I'd also consider angling that step as already suggested. That too reduces feathering and base dragging.

[JeffinNZ]

I'm with DeanWinchester. Forget the boattail. I doubt you will be shooting over ranges that will matter.

The nose looks like a lot of unsupported lead to me also. I'd shorten up the nose.

[Fluxed]

The features you propose for this bullet are appropriate for a high velocity long range cartridge. To meet your requirement of 100 yards and under at subsonic velocities, you're wasting your time with this. A plain base bullet with a small flat meplat (a more common design as has been used for over 100 years) will do what you want.

[Elkins45]

I'm still stuck on the part where you said the Lee 230 failed. I've had very good results with it at subsonic speeds.