Flat base vs Bevel base?

[hanover67]

I have Lyman mold 3118 that casts 115gr flat based rnfp boolits and I also have some similar commercial boolits which have bevel bases. I use them in a Colt Army Special .32-20 revolver.

What are the pros and cons of each base type, advantages or disadvantages. I would think a bevel base boolit would let gas escape past the base and cause barrel leading more that a flat base. Am I wrong? Your experience?

[ShooterAZ]

I have only one bevel based mold. It's the RCBS 45-185 SWC BB. The biggest drawback is when lubing the boolits. The lube wants to go into the void, thus creating a mess. I have been using styrofoam discs cut from an egg carton to remedy this. It shoots fantastic in my S&W M25, so I continue using it regularly.

[mdi]

http://castboolits.gunloads.com/show...e-or-flat-base
https://www.google.com/search?q=Beve...hrome&ie=UTF-8

[Outpost75]

Bevel base prevents "finning" when a larger, throat-diameter bullet is extruded into a smaller barrel groove diameter.

It also reduces "cupping" of the base in heavy loads. It also reduces risk of damaging the base during the loading process.

If the bevel is no more than necessary, about 0.02-0.03", it is "gone" by the time the bullet leaves the barrel.

If the bullet properly "fits" revolver cylinder throats, it is LESS prone to leading than a flat base in which a thin wire edge is dragged off the corner, which has lower heat capacity than the bevel.

Those who use the Lyman and RCBS style sizers don't like to have to wipe bullet bases to clean off the bevel. It takes only a second to drag the bullet base over a felt pad moistened with mineral spirits to have a clean, DRY base and to permit 100% visual inspection of finished bullets, which a fussy shooter would do anyway.

This problem is avoided by using a Star or Phelps sizer or using a film-coat lubricant such as 45-45-10.

[gwpercle]

The bevel is there only to speed production from the automatic casting machines that commercial casters use , they drop from the moulds easier . They are a tad easier to get started in a case but they do nothing for accuracy or to stop leading . You see a few in the 1 to 6 cavity moulds us home casters buy...but not very many.
I did a small test with 38 special loads , the 158 gr. SWC BB I had bought against the 158 gr. SWC FB I cast myself . All loaded over identical charges of Bullseye , Red Dot , HP-38 and Unique.
At velocities in the 850 fps range , no difference in accuracy or leading was noted .
The FB and BB were a wash.
That confirmed to me at those velocities , in the 38 special , the BB were OK to use... But
I didn't test 357 magnum or rifle loads ...that may be a totally different story .
The BB is only there to help the boolit drop from the mould...it's not a J-word Boat Tail rifle projectile ...that's a different animal .
Gary

[MT Chambers]

The bevel is there only to speed production from the automatic casting machines that commercial casters use , they drop from the moulds easier . They are a tad easier to get started in a case but they do nothing for accuracy or to stop leading . You see a few in the 1 to 6 cavity moulds us home casters buy...but not very many.
I did a small test with 38 special loads , the 158 gr. SWC BB I had bought against the 158 gr. SWC FB I cast myself . All loaded over identical charges of Bullseye , Red Dot , HP-38 and Unique.
At velocities in the 850 fps range , no difference in accuracy or leading was noted .
The FB and BB were a wash.
That confirmed to me at those velocities , in the 38 special , the BB were OK to use... But
I didn't test 357 magnum or rifle loads ...that may be a totally different story .
The BB is only there to help the boolit drop from the mould...it's not a J-word Boat Tail rifle projectile ...that's a different animal .
Gary

You are bang on, it is preferred by commercial casters because they fall from the mold easier, I see no other advantages.

[popper]

My solution is a stepped base, basically most GC shank cut off. Easy to cull poor base and no long shank to rivit.

[stubshaft]

All of the BB molds that I use get PC'd so I don't have to fart around with cleaning the mess in my lubrisizer.

[kevin c]

I ordered most of my molds as BB figuring it'd be easier for seating than FB, though the stepped expander I'm getting from Lathesmith may make the issue moot. I coat all of mine as well.

I would have thought the top of the mold face closing over part of the boolit base to make the bevel would actually make it harder for the boolit to drop out, not easier?

[trapper9260]

I have some BB ,mainly have FB I do not see any problem with any of them I use the Lyman sizer and make my own lube and normal wipe the base of the boolit. So I see no problem with any of them. I do not push them more then I need to. If I where to push a boolit, I would go with GC .

[McFred]

I use a 158 RNFPBB in 357SIG. It has a very short neck and I barely have to flare the case mouth to seat a bevel-bottomed bullet. This works well enough that I don't have to run a separate operation to crimp the case mouth back down. So win/win for me. I don't hotrod it so I've not had to deal with any leading or too hard/too soft alloy issues.

[gnostic]

I've lubed many BB bullets and many had excessive lube, where the bullet is beveled. At first I removed the excessive lube, then I didn't, and it didn't seem to make any difference. Try it for yourself and see if it matters, it sure didn't for me...

[tazman]

I've lubed many BB bullets and many had excessive lube, where the bullet is beveled. At first I removed the excessive lube, then I didn't, and it didn't seem to make any difference. Try it for yourself and see if it matters, it sure didn't for me...

This^^^^^.
I like the ease of seating a bevel based boolit.
Many great shooters have told me that plain based boolits are more accurate due to the base design. I haven't had that experience myself, but I simply may not be a good enough shot to tell.

[yeahbub]

The mold you have is a classic for the .32-20 and can serve you very well. You don't mention whether you'll be shooting smokeless or BP, or how hot you intend to run them, but in a classic Colt design, I presume you'll be staying within the region of BP pressure levels.

You can do okay with either design, but I prefer flat base because of reasons other than the possibility of leakage, mostly because of that objectionable annular rim of lube around the base of the boolit which occurs during the size-and-lube operation. This inevitably exposes the propellant to lube and may change the behavior of the load. Another has to do with consistent boolit heels. If the mold happens to cast a bit out of round, as many commonly do, or you're sizing them down quite a bit, the bevel around the base will be uneven and break contact with the muzzle on exit unevenly which has a negative effect on accuracy. A flat base boolit which was sized round will still have a flat base and sharp corner around its circumference, no rim of lube and no uneven heel. I have a bevel base Lee 6-cav mold which casts .003 fatter at 90 deg to the mold lines and when sizing them in a push-through die, the bevel is obviously uneven around the circumference. These do not do well out of a carbine where accuracy at distance matters. Flat base boolits sized the same way do better, but I don't have a flat base copy. I have shot bevel base commercial cast which had a consistent bevel on all the ones I inspected and had good results on target, but anymore I cast my own and I prefer flat base. Leakage has more to do with proper fit and alloy hardness than whether they're beveled or not. Soft enough for the load to make the boollit want to upset and apply some outward pressure to the sides of the bore, but not so much as to overcome the film strength of the lube you use, thus leaving you with lead on steel and ineffective lubrication. Too hard an alloy for the pressure of the load in use and sized smaller than chamber throats will cause leakage and leading since the boolit won't upset to fill the chamber throat/bore and seal properly. Most commercial alloys are harder than they need to be due to consumer misunderstanding of what causes leading, the popular assumption being that if there's leading, the alloy needs to be harder. I get very good results with range scrap at 9-10 BHN and stout but pleasant mid-range charges in .357, expansion too. WW's work well and are a convenient alloy, but harder than necessary unless I'm tending toward max loads, typically with a card wad and lube cookie. The lubes on commercial cast are also pretty stiff and intended to stay in the grooves so customers don't complain about ugly boolits gooped up with hunks of lube. Try both, YMMV.