MMP Sabots

MMP Sabots

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Yesterday I had loaded up 6 cases with the Hornady 45 caliber sabots. These sabots held a .400 caliber 200 grains SST Bullet. I used 5744 powder, starting at 20.0 grs and ending at 25.0 grains. I shot them over a Chronograph and had velocities that started at 1,259 fps with the 20 gr. charge and 1611 fps with the 25 gr. charge. My goal was to get to 2500 fps with this bullet. With the powder charges used the action would not lock open.

Recovered sabots had a small 1/2 circle piece of the sabot base missing. This missing piece was about .10 inches. Each sabot had this piece missing at the same location based up visual appearance of the rifling impressions on the sabot. This is most likely the diameter of the gas hole in the barrel. I am assuming that when the base of the sabot passes over the gas hole, the pressure blows the skirt into the hole because it is unsupported. All other portions of the sabot look OK.

At this point I am not going to proceed any further with shooting sabots in a gas gun — unless a sabot is designed specially for this — as it does have potential.

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Regarding the low charges — I started low and was working up until I hit a charge that would hold the bolt open — just didn’t get that far. With the sabot — the case holds about 32 grs.

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I shot 6 loads today using the 45 caliber sabots (with 40 caliber sst bullets). Using 5744 powder — 26.0 grains to 30.0 grains. Top velocity was 1750 fps at 28 grains. Velocity decreased with higher charges and also was a lot of unburned powder. I was hoping for 2500 fps, but it appears that will not be possible with 5744. Also, the case would eject, but action would not stay open.

I did have to modify the sabots by removing some of the rear of the cup — about .05 inches. The skirt was too thin and was blown apart when passing over the gas hole. Trimming helped a little, but still there was a “divit”. I am out of sabots — so I will put this little experiment to rest (maybe).

By admin on October 22, 2009 | Uncategorized | A comment?
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Crimping Effect on Velocity

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I reconfigured the crimp so that it only crimped into the cannelure. This is a 200gr Barnes bullet that has been crimped and pulled. 2 strong whacks with the puller to get it out. All rounds feed flawlessly.

I’ll post the actual numbers from my last range visit later, but here’s the short version.

The crimp increased the velocity by about 100fps and improved the accuracy, these 200gr bullets were giving me ragged holes at 100yds.

The 275gr bullets with 42.8grs of Lil’Gun also improved. Running around 2070fps and 1.5″ groups.

The spread I loaded with AA1680 was a major surprise with the velocities running a little over 1600fps to 1800fps, the last 3 loaded to 100% case capacity.

No signs of pressure on any of the loads.

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200gr Barnes 42.8grs Lil’ gun no secondary crimp 2414fps, light crimp 2475fps, heavy crimp 2564fps.

275gr Barnes 34,5grs Lil’ gun no secondary crimp 2050fps, light crimp 2093fps, heavy crimp 2128 fps.

275gr Barnes 39.2grs AA1680 heavy crimp 1708fps.

40.1grs AA1680 heavy crimp 1749fps

41.2grs AA1680 heavy crimp 1811fps (100% case capacity)

By admin on October 19, 2009 | Uncategorized | A comment?
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The History Behind the .450 Bushmaster

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Now, the 450b is directly based off the .284win., and thus, turning or reaming should not be an issue, but what to do in the mean time? First, assuming you have full length resized and then trimmed to the factory standard of 1.700” (plus nothing, minus .003” and use the order given – resize and then trim), load a dummy cartridge and try the “THUNKING” test. Pointing the barrel down “drop” your reload into the chamber, it better have a decided Thunking sound when the mouth of the cartridge hits the end of the chamber. If it does not, take safety precautions and again full length resize and re-crimp, the reloaded cartridge; it’ll go “THUNK” now! Second don’t worry about squeezing the bullet a little in the resized loaded case; the bullet is a little over sized and the barrels are ever so slightly undersized and the dies (assuming they were made right) will not over crimp the bullet, so as to let the mouth of the case go pass the end of the chamber (remember we have the same set of problems with the 45 ACP). With that in mind put on a heavy tapper crimp, “NEVER any kind of roll crimp”, into the case, enough so the bullet is visibly dented, again don’t worry about denting the bullet, in fact you want to see a slight dent (you wouldn’t have to do this if you had the bullet sealing gum that Lake City uses, but normally we don’t, so not to worry). This will not affect accuracy at all and will assure proper bullet pull, and will stop any bullet travel, in the case, that can occur in the shooting/cycling process and still yield minute of angle accuracy and better.

Now, what to do about over pressure signs? It is very normal for under pressured cases to kick the primer out first, before the case releases, thus a flat or detached primer. It is my opinion; you may be very much under pressured. Randal gave numbers that say 35,000 to 37,000 psi are dangerous pressures (based on the program Quick Load), nothing could be further from the truth (no offence Randal, also none of the bolt thrust formulas are accurate either, more on that latter). We normally load the 45 Pro to 60,000 psi with 230 ball or FMJ flat points my favorite. Yes, I know that the 458Socom and the 50Beo are loaded to the 35,000 psi area, but then again those great cartridges do not have the barrel thickness the 450b has in the chamber area. Here’s my example, a “Mountain Rifle”, bolt action weapon, chambered for the 284win case has a SAMMI spec in the area of 63,000 psi and has a barrel chamber diameter the same as the 450b. The other proof is Bushmaster told me that twice they loaded to these pressures and fired 6000 rds + each time with no ill effect and my friends and I load to these pressures and have done so for years, normally. So, why does Hornady load for 38,000 psi, as they have quoted? They tell me the Lawyers won or that they did not want to over stress their SST bullet, which is designed for magnum muzzle loader velocities of around 2000fps and would blow up on deer, like a varmint bullet would do, if you pushed them as we can actually do. My personal loads in the 450b, for the 250gr. bullet START at 2500fps and go up, but then who can afford those bullets, sold in twenty packs. I’ve tried the 200gr SST and compressed a load of 296 and achieved 2800fps, with only slightly flatting of the primers. If you need a pointed expanding bullet, Barnes makes excellent 200 & 275 grain varieties.

As for “Bolt Thrust” with these pressures (70,000psi +), Wayne State University’s Engineering Dept., in a published article, I forget which gun rag ran it now, actually ran “MEASURED” test, not calculated and found that at these increased pressures, the bolt thrust was just a little less that the .223 case and this because of a effect known as Bernoulli’s Theorem, which basically tells us that necked cartridges have way more bolt thrust than straight cases and all the bolt thrust formulas are based on those necked cases, hence not at all accurate for the 450b. My Buddies and I have never seen a bolt failure and don’t ever expect to and we only use, what you might call, max loads, we don’t think they are but others might and we’ve never had a problem and together we have maybe a million rounds down range or certainly many, many, 100,000’s at least.

My recommendations? Assuming you will take proper safety precautions and use great skill, use WW296 for the lighter 200 grain Barnes, which is a pointed-hollow point bullet and AA1680 for the Barnes 275 gainers, which is also a pointed-hollow point. But consider the Hornady 230 FMJFP, which the Flat Point will disrupt more tissue than an expanded bullet does. The flat point doesn’t really expand and will penetrate straight through an animal, as opposed to going squirrely, as is the case with many expanded bullets, on occasion, even to turning 90 degrees in side of flesh, been there, done that. Your loaded length of 2.1” is way short too, load the 230’s to 2.2” (but not much more, you still have to hang onto the bullet) or longer and the pointed bullets to 2.250”, max is 2.260″, but you do need some clearance in the magazine. AA1680 & 230’s will increase your speeds and lower your pressures and still yield 2800fps, which is more than enough for any animal on this planet, if FMJ’s are used. In fact this combo has twice been to the Cameroon’s and has dispatched Cape Buffalo and Elephant, with reported ease. Keep in mind that this is with a version that is .070” longer, the 45 Professional. The standard 230gr hollow pointers are cheap and because of these highly increased speeds just explode on anything, making them good for home defense.