“Thunk” Test and Using Lead Bullets

“Thunk” Test and Using Lead Bullets

Link to Source

I would say not.* I admit to not having tons of experience, measured in the low four figures, with hard cast/gas checked bullets, but one time we shot 500rds and removed the gas tube for inspection and there was no tube fouling.* I have a customer that has 30+ years of shooting this style of bullet in AR’s and he, with absolutely no reservations states, that the hard cast/gas checked bullets are no problem, what so ever.* Feeding should be no problem either, as the 450b will with a great deal of reliability, not absolute, feed empty cases.Crimping?* With the lead bullets stay out of the crimping grove with the case mouth, which may mean adjusting the OAL or using a different hard cast/gas checked bullet, just stay as close to 2.250″ as possible, remember for any given load, the pressures go up the deeper the bullet is seated into the case or shorter the OAL.* For jacketed bullets, any proper made taper-crimp die cannot over crimp.* For proper ignition and to prevent any bullet travel in the case, use a heavy taper-crimp.* I personally want to see visible denting of the bullet.* Just double check your loads by removing the bolt/carrier and dropping the loaded round onto the chamber, you must hear an auditable “Thunk” when the case mouth seats against the end of the chamber.* If you don’t hear the thunk then you may have a crimp die that can over crimp (something I’ve never seen), which can give excessive head space, or the bullet has possibly caused the case to over expand (bulge) and is impeding the forward travel and preventing proper seating in the chamber.* “Carefully“, full length resize the loaded case again and that should take care of any bulge problems, be careful to clean any case lube off the cartridge, lubes in the chamber will induce excessive bolt thrust, keep those chambers dry.* Of course you could resize the bullet down a little in any of the various Luber/sizer dies (BTW – using a .451/.452 luber/sizer die and standard lubed .458 lead bullets, will lube the die just right for resizing jacketed .458 bullets down to .451 standards and you’ll end up with some really cheap lead plinking bullets to boot, just do not move them very fast or you’ll lead up the barrel.* I use one lubed lead bullet for every five jacketed bullets, there have been no jacket problems to date, heck you’re only taking the bullet down .003 per side).** If you see that your reloads do have the stated bulge do the thunk test, if you hear it, don’t fret the bulge.

By admin on October 17, 2009 | Uncategorized | A comment?
Tags: , , ,

The History Behind the .450 Bushmaster

Link to Source

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.