266 grain cast bullet, the Dolomite special

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dellet
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266 grain cast bullet, the Dolomite special

Post by dellet » Mon Mar 06, 2017 12:53 am

A few months ago Dolomite started a project to get a heavy cast bullet. He was kind enough to send me some to test for him. I do not know if this will be the final version, I'll let him pipe in on that one.
viewtopic.php?t=99010

I got a chance to run a few through a couple rifles this weekend and they were surprisingly forgiving.

First the bullet.
Image

1.385" long and weighing in at 266 grains, it's about the same length as a 175 TMK.

The bullet shape/design is a little different than anything I have loaded before. I do not shoot a lot of cast in modern rifles so there are many things I don't really understand about them. There were a couple surprises for me.

Image

I always start a new bullet in a Sheridan gauge. It gives me a visual of how it will fit in the chamber. It's tough to see in the above photo, but if you look at the top one you can see the shape of the bullet is basically stepped, the front section is designed to ride the lands as a snug fit. Bore rider. This bullet will likely fail more chamber gauges than it will pass.

Chambering a dummy round left very slight marks from the lands, more of a polished spot on the coating. The coating was still intact.

Dolomite and some of the more knowledgable cast shooters can chime in on this type of design.

Image

First shots to check for stability. I shot first at 5 yards and had the confidence to step back to about forty. There was a genuine worry about stability with this bullet barrel combo. A long heavy cast, shot from a 1/10 twist.

Image

Next up was to test the stability at a fast rpm. The lower holes are from a 1/5 twist. In round numbers the 1/10 twist was spinning at only 74,000 rpm. The 1/5 146,000. A 1/7 spins it at 105,000.

All loads/brass were prepared the same, only powder and charge weight varied.

I did not use an over size neck expander, I used an aggressive chamfer. I did not see any evidence of shaving the coating. No crimp was applied.

Load data.

Remington once fired 300 AAC BLK brass
Remington 7 1/2 primer
2.145" Col

Image

The above target is three different rifles, three different twists. All shot at 50 yards within a 15 minute span, so temp and weather was basically the same. 34 and lightly snowing and wind.

Five shots circled
18" AR 1/10 twist
9.5 grn N120

998 avg.
85 ES
35 SD

Five shots unmarked
16" 1/7 twist Micro 7 bolt action
6.7 grn N105

1006 avg.
45 ES
17SD

Five shots hash marked
8" AR 1/5 twist
7 grn N105

964 avg.
22 ES
9 SD

A note, disclaimer, excuse on the SBR group. This was the second time shooting a new trigger. I installed a 2 stage flat trigger and it's different. It's possible that the fast twist was also an issue. I will revisit that after getting a few hundred rounds on that trigger, right now I have less than 25.

The flyer in the bolt action group is an anomaly. That was the only shot in 25 that got away.

All in all I think it was a good first day with a new bullet. Running it in three completely different rifles and having pretty reasonable results. I have a pretty good idea of charge weights to work with. I think as some more experienced cast shooters get their hands on these groups will improve.

Any suggestions for me are always appreciated.
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xdmalder
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Re: 266 grain cast bullet, the Dolomite special

Post by xdmalder » Mon Mar 06, 2017 5:59 am

That long of a bore rider design would probably greatly benefit from being nose sized as well.

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Re: 266 grain cast bullet, the Dolomite special

Post by bangbangping » Mon Mar 06, 2017 9:14 am

Interesting that you got the best results from a 1:10. I would not have expected that.

I had planned to run some through my Micro 7 yesterday, but we had over 5" of rain.

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Re: 266 grain cast bullet, the Dolomite special

Post by dellet » Mon Mar 06, 2017 10:22 am

bangbangping wrote:Interesting that you got the best results from a 1:10. I would not have expected that.

I had planned to run some through my Micro 7 yesterday, but we had over 5" of rain.

All things considered, it does not surprise me. It fits me the best and has the best trigger.

The short AR I recently changed the trigger and moved the scope forward to make room for an iron rear. I am having trouble with eye relief and length of pull.

The Model 7, if you pull out the flyer it's not that different than the long AR. I was loading single shot because there was trouble feeding from an AI mag. It was basically fire, stand up, load, sit and shoot.

Then if you look at the flyer hole, it's very oblong. I'm guessing I damaged the base loading it since I did not bell the case mouths. Out of all the shots, that was the only one that was not where it was pointed, and the only one that showed instability.

I would like to think I'm pretty critical of my shooting, without making excuses, but no one likes to be the week link. I'll load another round for the bolt gun and get some trigger time with the sbr with ammo I'm more familiar with and see what happens.

I worked up a load for this bullet as a super that I expect to be at least 1400, so I will be able to find out where too much spin is.

I really thought I would be able to find bigger issues across the twist rates. So far I'm pretty impressed for a cast bullet.
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Re: 266 grain cast bullet, the Dolomite special

Post by 45r » Mon Mar 06, 2017 1:02 pm

M-dies from lyman makes things a lot easier and more accurate with cast bullets.
They like being seated straight and not too much squeeze being seated.
Bullets that heavy should be lightly crimped with a LFC also.
That keeps the bullet from sliding forward on it's rough trip from the mag to slamming home into the chamber.
Helps with powder burn and lowers ES also.
You can use the Sheridan chamber gauge as a bore rider bump die by coating the bore rider lightly with lanolin type case lube before inserting it and use a wooden dowel to push out the cartridge if it gets a little bit stuck.
Then rub off the lanolin and GTG.

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Re: 266 grain cast bullet, the Dolomite special

Post by L1A1Rocker » Tue Mar 07, 2017 10:01 am

Has anyone thought of hollow point options? Or is that counter to trying to get the heaviest heavy out there?

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Re: 266 grain cast bullet, the Dolomite special

Post by dellet » Tue Mar 07, 2017 10:28 am

L1A1Rocker wrote:Has anyone thought of hollow point options? Or is that counter to trying to get the heaviest heavy out there?
Probably a little bit of both I am sure. There has been a lot of people aking about the hollow point, Dolomite tends to listen to what people want.

My contribution to the project is just being able to run it through a bunch of twists and cause it to fail if possible. I'll slow it down some in the 1/10 to look for minimum spin for the lower limit, it already has potential for many .308's as sub bullet. I need to work it down to about 800 fps to mimic a 1/12. We'll see how close I can get.

I hope this weekend to be able to stretch this out to at least 100 yards, it will be interesting to see if the slow twist is still stable.
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Re: 266 grain cast bullet, the Dolomite special

Post by L1A1Rocker » Wed Mar 08, 2017 10:26 am

dellet wrote:
L1A1Rocker wrote:Has anyone thought of hollow point options? Or is that counter to trying to get the heaviest heavy out there?
Probably a little bit of both I am sure. There has been a lot of people aking about the hollow point, Dolomite tends to listen to what people want.

My contribution to the project is just being able to run it through a bunch of twists and cause it to fail if possible. I'll slow it down some in the 1/10 to look for minimum spin for the lower limit, it already has potential for many .308's as sub bullet. I need to work it down to about 800 fps to mimic a 1/12. We'll see how close I can get.

I hope this weekend to be able to stretch this out to at least 100 yards, it will be interesting to see if the slow twist is still stable.
Thanks for being the guinea pig on this. You know, looking at the nose profile, I'm thinking that anything other than a "cup" type hollow point will result in the bullet collapsing in, rather than expanding out.

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Re: 266 grain cast bullet, the Dolomite special

Post by Dolomite_Supafly » Thu Mar 09, 2017 8:53 am

This bullet was never meant to have a hollow point. It won't work well with a hollow point. The manufacturer has said he is willing to produce a hollow point bullet. We have talked several times regarding producing a bullet with a hollow point and he is on board but we need to figure out the perfect hollow point bullet. So if anyone has a favorite let me know and maybe it can start to be made commercially. The manufacturer is a great guy who puts his customers first. His #1 priority is to produce a top quality cast bullet.

The coating is my home job of a coating which is far form perfect. The coating will be much more uniform when it gets into production.

Hey L1A1, I can send you some of the prototypes if you want. But remember these are not the production bullets. These are being hand cast using a prototype molds so they will have imperfections in the coating or the bullets themselves. Once a machine is making these the consistency will improve and along with consistency you will get accuracy. If you want I can send you some that are naked so you can use whatever coating you want for coating.

In the coming weeks as long as the results continue to be favorable I will be ordering a single production mold made of iron. It will be modified to use as a hand cast mold. That way I can make sure the dimensions are going to stay the same when we go to iron. As long as that happens, or it can be corrected, I will be ordering a complete set of molds for the manufacturer to begin production.

And if anyone wants to check out his bullets, here is the website. He is expanding so there will be a lot more bullets available very shortly.
http://www.acmebullet.com/index.php?route=common/home
He really is a great guy.
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Re: 266 grain cast bullet, the Dolomite special

Post by Dolomite_Supafly » Thu Mar 09, 2017 10:16 am

bangbangping wrote:Interesting that you got the best results from a 1:10. I would not have expected that.

I had planned to run some through my Micro 7 yesterday, but we had over 5" of rain.
I have personally found that the slower the twist the tighter the groups tend to be when all else is as equal as can be. I think the reason is every bullet is slightly out of balance and when you spin those bullets the out of balance begins to show up. Like driving a car without a tire that is properly balanced. If you are doing 5 mph you would never feel an out of balance tire but go 100 mph and it will feel like something is seriously wrong.


The bore rider portion is supposed to do as the name implies and ride the bore. With heavier bullets this helps the bullet itself center itself in the bore and helps improve accuracy or at a minimum help it shoot more accurately in a wider variety of firearms than a typical cast bullet. There is a reason why these bullets are working equally well in a wide variety of firearms with different twists. I will not get into detail what those changes are just yet but those changes were by design, not by accident. This was my take on what a HEAVY "universal" bullet should be and so far it seems to be shooting well in a very, very large sample of firearms. I have been sending out bullets or the mold to a lot of people and the testers seem surprised at the accuracy. Especially those who were not working up loads for accuracy. Testers are just throwing cartridges together and getting decent results for a cast bullet. I have personally shot 1" groups at 50 yards WITHOUT load development. Dellet told me he was getting 3/4" groups at 50 yards, again without working up loads. I can live with 1.5 MOA, especially with a cast bullet that uses 1/3 less powder.

Because this bullet is heavier and different than a typical bullet it uses less powder than a typical bullet used in subsonic loads. The space for the powder is also very specific and that was done to ensure consistent ignition and consistent powder burn times. It is this consistency that leads to a more accurate load. But not only that, when you are using less powder your gun will be quieter with a silencer. The reason is this bullet uses less powder so that means less gas and less gas means your silencer is better able to mitigate the gasses that cause muzzle blast.

One more thing I haven't mentioned much is this bullet WILL feed from a magazine in an AR. It will not work with all magazines but so far we are seeing reliable performance using Lancer magazines. Hopefully the 300 Blackout specific magazines will be on the market soon.

Once these go into production I will do a write up on how to load this bullet for the best accuracy in YOUR individual firearm. I will also go into greater detail as to what changes it has and how to take advantage of those changes. A lot of people look at bullets as just a bullet but it is a very important part of the "system" that is your firearm.
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