Mountain Molds 6 EXP

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Paul Pollard posted this 16 June 2016

Mountain Molds sent a 6mm mold which arrived on Monday. The designation is 6 EXP and it is designed with the body of the Eagan MX2-243. The sharp pointed nose takes the place of the truncated cone of the Eagan. The intent of this exercise is to take the design of a good shooting bullet with a flat nose and determine if the sharp point nose makes a difference for wind drift while maintaining accuracy. The rifle is a 6ppc with a Shilen 1:14 twist barrel. According to most ballistic calculators, the Eagan bullet will not stabilize. Some weight is lost when going to the pointed nose bullet. Maybe with luck, we can stretch the pointed nose bullet a little more and gain some weight.

The overall length of two cavities is 0.800” and the center cavity is 0.815” long. These were cast of linotype and the shorter bullets weigh about 75 grains while the longer bullet weighed 77.5 grains. I started casting at 625°F, but turned the heat down as it took quite a bit of time for the sprue to harden. I ended the session at 600°F, but may try a little lower yet.  For the first time with this mold, I didn't weigh and sort, just inspected for fill out and discarded unfilled bands or bases. 

In order to size the pointy noses, I had to alter my gas check seater top punch. It had been flat on top for the Eagan flat nose. I found one for the LBT 65 grain which still had a 0.080” meplat. The first attempt was to insert a .177 pellet in the punch; after 8 bullets, the sharp nose poked through the lead and hit the flat part of the punch with a resulting flat on the bullet nose of about 0.050”. I drilled a small hole for the point and reinserted the lead pellet. This time it had enough cushion for the sharp point. The mold came with a top punch, which I put in the RCBS lubesizer along with a Lyman .244 die. This worked fine. Finally, for the taper/bump die, I swapped out the Eagan die for the LBT taper die. Also had to alter the top punch. I ran some through the sizing operation and checked fit and overall length with some dummy rounds. Everything looks very close to the Eagan sizes. One noticeable area was the nose is a little bigger on the 6 EXP at 0.239” and shows better engraving when chambered.

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onondaga posted this 16 June 2016

No pictures? No mold!

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Paul Pollard posted this 16 June 2016

Here's half a mold, showing the cavities. The middle cavity is the 77.5 grain at 0.815” long. The outboard cavities are the 75 grain at 0.800” long, same length as the Eagan MX2. 

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Paul Pollard posted this 16 June 2016

Two dummy rounds were loaded to check for chamber fit. The one on the left is the 75 grain at 2.210 OAL. The front band is sized the same as the Eagan MX2 and is loaded to the same OAL. The one on the right is the 77.5 grain with OAL at 2.235. Because the bullet is longer, it is loaded longer. The front band on it also fits the same. The nose engraves lightly. It actually is slightly larger diameter nose than the Eagan. Both these bullets show full engraving on the nose; the Eagan only shows contact points at the nose/ogive junction.  It's hard to see, but there are light engraving marks on the nose and the first band.

 If you check mtngun's 6BR thread, you can see photos with lengths which match up with my finished sizes also. His photos are much better than mine.

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onondaga posted this 16 June 2016

http://www.castbulletassoc.org/view_user.php?id=216>Paul Pollard

Thanks for the pictures! I hope you do well with the bullets.

Gary

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Loren Barber posted this 17 June 2016

Paul,You are one step away from fame. I will be very interested in your accuracy results.  I have a 6 PPC bench rest rifle with a 14 twist Hart barrel.  Someday, I would really like to try some cast bullets in my rifle.  Please keep me informed. Maybe I'll see you in KC.Loren Barber

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Paul Pollard posted this 20 June 2016

Saturday, June 18, 2016.

Shot the Mountain Molds 6 EXP in 75 grain and 77.5 grains. Accuracy seemed so-so, but the bullets seemed stable. The pointed noses tear the paper, making it difficult to determine if there is any tipping. The Eagan flat point punches out nice holes without tearing. The only powder used was H4198 with CCI450 primers. Cases were Lapua 220 Russian. Lube was Voodoo Red. One new thing for me was Gator gas checks. I used up the last of the Hornady gas checks on the Eagan bullets cast over the winter. Shilen barrel, 1:14 twist, 6ppc. The wind was only about 5 mph which was not the cause of the mediocre groups. Temperature was 85°F to 88°F and humidity started at 35% at noon and dropped to 28% by 3:00 pm.

The 75 grain cavities were shot first with varying powder charges of H4198. I tried a few thousandths variation in seating depth. These averaged 1.207 for 10 groups of 5 shots.

Next was the 77.5 grain with a few different powder charges and mostly the same seating depth. After smoothing the bullet holes, I couldn't see any tipping with this bullet either. There was one group shot with 30 clicks of powder and it may have been a little slow to stabilize this bullet. This was the largest group with this bullet. The average was 1.269 for 9 groups of 5 shots.

For comparison, I shot some Eagan bullets loaded with 32 clicks H4198 all at 2.205 seating depth. These also had Hornady gas checks. During these groups I had a primer misfire. This was on shot #2 and after poking out the bullet and blowing out spilled powder, shot #3 went way low. This opened the group to 2.100 for 4 shots. Ignoring this goofy group, the average of five 5-shot groups was .983.

None of the bullets showed stellar accuracy (even my old stand by). I'll try a bit better casting techniques and see if the weights will be a little closer. It looks like the bullets are stable, even the .835 long 77.5 grain one. 

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OU812 posted this 20 June 2016

I know I sound like a broken record, but it would be interesting to see what softer and heavier 20-1 alloy and Titegroup powder would do in that rifle. Maybe even Hardball alloy (50 percent linotype, 50 percent pure lead).

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Paul Pollard posted this 21 June 2016

It would be interesting to try 2 or 3 different alloys. However, I'm still trying to figure out how to cast good bullets in 3 cavities at one time. I've been using a single cavity mold exclusively for 8 years. Yesterday's casting session of linotype (again) gave me about 300 bullets. Scrap rate was about 20%. With 90°F ambient temperature, the sprue took forever to harden. Turning the pot temperature down was not a good idea. Complete fill out became worse. 

For the casting, I used a one pound Rowell ladle to get plenty of metal into the mold. I haven't run the numbers for the weights yet, but I did weigh each bullet and charted it on paper. It's not in the spreadsheet yet. As mtngun predicted, the front cavity weighs a bit more than the rear cavity.

For these bullets I'll be using Hornady gas checks again. I'm also trying different sizing dies, trying to get what works best. I may go back to sizing just the gas check in the Lyman die, then run the bullet into the taper/bump die for the final size. This tends to close the open end of the gas check a little better.

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OU812 posted this 21 June 2016

You need a Lyman or RCBS ladle. Holding the tapered spout against tapered sprue plate opening is a form of pressure casting, just at a lower pressure. I have always cast hot...this gives me best fillout of bullet.

Bottom pour pots are trickier to learn, but work just as good as ladle casting. Flow rate adjustment is most important and changes as level drops...lower level equals lower pressure.

No two molds or alloys cast exactly the same, so adjustments must be made. Sometimes it can be difficult to find sweat spot.

...

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45 2.1 posted this 21 June 2016

OU812 wrote: You need a Lyman or RCBS ladle. Holding the tapered spout against tapered sprue plate opening is a form of pressure casting, just at a lower pressure. I have always cast hot...this gives me best fillout of bullet.

Bottom pour pots are trickier to learn, but work just as good as ladle casting. Flow rate adjustment is most important and changes as level drops...lower level equals lower pressure.

No two molds or alloys cast exactly the same, so adjustments must be made. Sometimes it can be difficult to find sweat spot.

...
Stay with the Rowell ladle Paul..................... Everyone should try the methods for themselves to see just which method delivers the best results as to uniformity in weight and as cast diameter. Weigh all the bullets cast via each method and plot the distribution curve. Bottom pour versus Lyman/RCBS ladle versus Rowell ladle. Then see what happens on the target!

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mtngun posted this 22 June 2016

Thanks for the detailed report, Paul.

BTW I had no problems getting good fill with a drilled out (#21) RCBS ladle and linotype at 715F.     I'm sure the 3-cav does run hotter than your 1-cav.     I don't want to second guess your casting style since you obviously have plenty of experience, but reading in between the lines it sounds like your lead thermometer is out of calibration ???

I don't know why the MX2-EXP would shoot any different than your MX2, since the part that is in contact with the barrel is very nearly the same.   But my 6BR did not like the MX2-EXP's at all.  :(    If it is not an accurate design then we go back to the drawing board.   

I've been using Gator checks for the 6mm and they work fine.  I don't have any Hornady checks to compare them to.   For some calibers Gators are identical to Hornadys, while for other calibers there is a slight difference in thickness.

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mtngun posted this 22 June 2016

Paul Pollard wrote: The nose engraves lightly. It actually is slightly larger diameter nose than the Eagan. Both these bullets show full engraving on the nose; the Eagan only shows contact points at the nose/ogive junction.   You would think that, to the extent that it made any difference, the increased engraving would improve accuracy.    But I can imagine one way that increased engraving might actually hurt accuracy.     I'll test the theory in my barrel when time allows.

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Loren Barber posted this 25 June 2016

Paul,Do you have an estimate of the velocity of your loads?Loren Barber

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Paul Pollard posted this 25 June 2016

Loren, 32 clicks (17.7 grains) of H4198 or LT30 will give about 2200 fps with Fed 205m primers. That's with the 80 gr bullet. CCI450 primers give about 2300 fps, I think. I need to recheck. LT32 will need one more grain to equal that velocity.

With the 75 gr Mountain Molds bullet, CCI450, 17.7 gr H4198, velocity was 2350 fps; with the 77.7 gr, it was 2330 fps.

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OU812 posted this 26 June 2016

NOE may be working on a scaled up version of John Alexander's 223 caliber 227-80 bullet. I requested to close up the gap between gas check and first band. My theory is hydraulic pressure caused by excess lube in this area is causing gas checks to pop off when exiting barrel  (occasional flyer or flyers). He would also shorten bore ride length slightly. This bullet would work perfectly in 6mmPPC, 6mmBR , 30 BR rifles without throating. Any other ideas before going into production?

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Paul Pollard posted this 26 June 2016

Mtngun wrote, “You would think that, to the extent that it made any difference, the increased engraving would improve accuracy.    But I can imagine one way that increased engraving might actually hurt accuracy" I looked more closely at my taper dies. The MX2 die which was using a flat push out pin sized the nose at 0.2385. The LBT die tapered the nose 0.2385 up to 0.2405 in front of the front band. After sizing 2 of each die, I made up 2 dummy rounds of each. When chambering dummy rounds, the LBT-sized ones were tight chambering and one pulled the bullet when extracting. The MX2-sized ones chambered easily and extracted without trouble. The LBT die may be sizing the nose too big and holding the bullet's tapered front band away from the taper in the throat.

Attached is a really rough sketch of the nose sizes.

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Paul Pollard posted this 29 June 2016

June 28, 2016.

Re-prepped the 75 grain bullets. Resized these in the MX2 taper die which sized the nose to 0.2385 for the full nose length, as opposed to the 0.2385-to-0.2405 taper of the LBT taper die. Hornady annealed gas checks. Tumble lube. These bullets finished at 0.814 long x 0.2442 diameter at the base band and gas check. The front band is tapered from 0.2435 to 0.2425, as near as I can measure. This should be the 3° taper included angle.

The target is marked up to show clicks of H4198. 30 clicks is about 16.5 grains and 32 clicks is about 17.8 grains. The measure will usually throw in a .3 grain spread, and it doesn't seem to make too much difference. The one thing I noticed about this bullet was that it was predictable. When a shot went out, then a glance at the wind flags would confirm that I wasn't paying attention.

So far, I can't tell if there is less wind drift with the pointy bullet vs the flat point. This was one of those days when things shot well. The 7 group agg was 0.643. Still needs some fiddling. The 31 click load looks like it would work better with the 75 gr bullet vs the 80 gr Eagan.

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mtngun posted this 29 June 2016

Thanks for your report, Paul.   I admire your attention to detail and willingness to try different things. :)

Dunno what the BC of the Eagan bullet is, but the EXP is pretty close to a G1 form so I figure its BC will be the same as its sectional density, about 0.200.   So perhaps the EXP drifts less than the Eagan but even with a pointy nose the BC is still nothing to brag about.

If I ever get into CBA competition I may be inclined to go with a slow twist 30BR or 30PPC.   18” twist can stabilize up to 150 gr. spitzer (using reclaimed shot),  16” twist up to 165 gr..    That should drift less than a 6mm 80 gr. yet with a 16” - 18” twist could be just as accurate as your 14” twist 6PPC if not more so.   Recoil would be the only downside.

What kind of accuracy do you need to be competitive?    Has your PPC barrel lost accuracy with age?   

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OU812 posted this 30 June 2016

That's it !!! Hornaday “annealed” gas checks

Verygood shooting Paul

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Paul Pollard posted this 30 June 2016

Competitive accuracy in unrestricted rifle class is .500 and under. A couple times the 5 shot agg at 100 yds was won with .330 to .350.

If there any 75 grain bullets from the previous casting with Gator checks, I'll resize those in the MX2 die. That seemed to be the key to accuracy with any of these bullets.

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