Reloaders Corner: Pressure Curves and Port Pressure – Part 2

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The following is a specially-adapted excerpt from the forthcoming book,” Top-Grade Ammo,” by author Glen Zediker, owner of Zediker Publishing. Click here to order.

Last time I gave a caution about respecting one of the differences between semi-auto and bolt-action rifles, and that was with respect to propellant burn rates. The summary reason for that is that different rate propellants will “peak” at different areas as the expanding gases and the bullet travel through the bore. Slower-burning propellants peak farther, and that means more pressure is available at the gas port location in an AR-15, for instance, as the bullet passes it. If the system is oversupplied, then the system is overworked.

Compared to ideal function when gas supply is delivered as engineered, mistimed peak pressures can result in the bolt unlocking too quickly and excessive bolt carrier velocity rearward. The system just gets hit too hard. The extractor tries to yank the case out of the chamber too soon, before the case is released from its grip on the chamber walls (from being expanded through firing). Spent-case condition shows a measurably more abused hull. Probably the worst popular example of these effects is the M1A. I’m doing an entire column or two on reloading for this beast. Essentially, a spent case from an M1A will show dimensions that don’t seem possible. These come from the bolt unlocking too quickly. AR-15s actually handle excessive pressure better than some other designs.

Always keep in mind that this is all happening in about 2 milliseconds. Average time a bullet spends in the barrel, for most modern centerfire rounds, is 0.002 seconds. Timing is everything.

Keeping in mind the behavior of a pressure curve, which is like a wave cresting, factors that influence the amount of gas-port pressure, using the same load, include barrel length, gas-port size, and gas-port location. When the bullet is sealing the bore, the longer the barrel, the more pressure is contained for a longer time. The smaller or larger the gas port size, the slower or faster the gas enters the system. The farther back or forward the port is located, the sooner or later. Bullet weight is a factor also: heavier bullets accelerate more slowly (and also the reason heavy bullets erode the chamber throat more than lighter bullets).

And, the amount of volume inside the bore has a huge influence on all this. That matters when we’re using another caliber than .224 in an AR-15 or .308 in a big-chassis AR (like an SR-25). For instance, in that rifle chambered for .243 Win., but retaining the gas system specifications (gas port size and location) of the .308 Win.–chambered rifle, there’s way more pressure only because there’s less space, less volume, in the bore. The opposite is usually true when we’re running an AR-15 with a larger caliber bullet.

Selecting a propellant with a suitable burning rate, which, again, is something in the vicinity of H4895, is really the only thing we can do on the loading bench to ensure that we’re not contributing to these symptoms. Beyond that, dealing with excessive pressure gets technical.

All my NRA Match Rifles, which usually have 26-inch barrels, get their gas ports moved forward one to two inches. These, of course, are custom-barreled. I also usually install an adjustable gas manifold.

Moving the port forward effectively delays the wave of gas moving through the bore, kind of repositioning its peak with respect to its outlet; there is more space available for expanding gases. It also allows a little slower-burning propellant, which can take more advantage of the longer barrel. It’s common in a similarly constructed AR-10 to get a port moved as much as 5 inches forward to accommodate a .243 Win. or .260 Rem. chambering.

The adjustable manifold allows some tuning. There are essentially two forms these take. One way is to restrict or limit the through-flow; the other just bleeds it off. I like the first kind the best.

Also, I have searched far and wide for a consensus on gas-port sizes, and came up empty.

All this changes with different chamberings and rifle configurations. Carbine-length barrels are particularly sensitive to port pressure because the port is located farther back.

There are a few surefire things that will alert you when your rifle is exhibiting “over-function” symptoms, such as spent-case condition showing excessively blown (extended) case shoulders, extractor marks on the case rim, and a generally explosive sensation in functioning.

In a more extreme circumstance, an over-accelerated carrier can “bounce” back from its rearmost travel so quickly that a round can’t present itself in time to be picked up by the bolt, or the bolt stop can’t engage quickly enough to hold the bolt carrier.

Sometimes what appears to be a “light” load is actually not. I’ve seen excess pressure leave a spent case in the chamber because the extractor lost its grip, and I’ve seen chunks pulled right off case rims. That’s severe. That’s also another cause for the “short-stroke” appearance of over-function: the extractor issue has slowed the carrier.

If you’re having any problems with “over-function,” solutions include retrofitting an adjustable manifold, increasing carrier mass, installing a stouter buffer spring. I do all those things on my rifles. Keep in mind that I am primarily a Service Rifle shooter, and I am trying to push an 80-grain bullet as fast as reasonably possible from a 20-inch barrel that can’t get the modifications mentioned. I know a thing or three about delaying bolt unlocking — I’ll cover more on this topic if you all want to know.

 

Sources:

Sun Devil Manufacturing

663 West 2nd Ave., Suite 16

Mesa, AZ 85210

(480) 833-9876

 

Medesha Firearms Ltd.

10326 E. Adobe Rd.

Mesa, AZ 85207

(480) 986-5876

 

Come February, Virginia to Sever CHP Reciprocity with 25 States 

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In a startling move, Virginia Attorney General Mark Herring announced on December 22 that Virginia will sever concealed handgun permit (CHP) reciprocity ties with 25 of 30 states. In particular, this will affect many Midsouth Shooters Supply customers who reside in Tennessee and other states bordering the Commonwealth.

Speaking about this audit and update, Attorney General Herring said, “Virginia, and nearly every other state in the country, have recognized that carrying a concealed handgun is a significant responsibility that should be extended only to those who have gone through a process to prove a level of competency and responsibility.”

Early next year, Virginia will no longer honor carry permits from the following states:

Alaska, Arizona, Arkansas, Delaware, Florida, Idaho, Indiana, Kansas, Kentucky, Louisiana, Minnesota, Mississippi, Montana, Nebraska, New Mexico, North Dakota, North Carolina, Ohio, Pennsylvania, South Carolina, South Dakota, Tennessee, Washington, Wisconsin and Wyoming.

virginia-ag-mark-herring
Virginia Attorney General Mark Herring Virginia Attorney General Mark Herring announced on December 22 that Virginia will sever concealed handgun permit (CHP) reciprocity ties with 25 of 30 states. Millions of concealed-handgun-carry permittees will be affected by the decision.

“The standards for proving competency and responsibility are up to each state,” Herring said, “and the General Assembly has established Virginia’s standards for whom it considers capable of safely carrying a concealed handgun. Those standards should be applied evenly, consistently, and fairly to anyone who wants to lawfully conceal a handgun in Virginia.

Herring added, “Under state law, the Virginia State Police can agree to recognize permits issued in another state if that state’s laws, disqualifiers, and safeguards are adequate to prevent possession of a permit by persons who would be denied a permit in the Commonwealth. For much of the last year, my team and I have worked with the Virginia State Police to conduct an audit and update of the states whose permits are recognized in Virginia. This has been a deliberate, thorough, professional review of the states which supposedly meet or exceed Virginia’s standards.”

The following permits will continue to be recognized: West Virginia, Michigan, Oklahoma, Texas and Utah.

The move also means several states will no longer recognize Virginia’s concealed carry permits because they require mutual recognition of permits. Those include Florida, Louisiana, North Dakota, Pennsylvania, South Carolina and Wyoming.

Border towns in West Virginia, Kentucky, Tennessee, North Carolina, and Maryland will be hardest hit, such as in Downtown Bristol, which sits on the Virginia/Tennessee state line. State Street in Bristol divides the city into Virginia and Tennessee sections. Soon, that could mean gun-carrying residents on the south side of the street in Tennessee become criminals on the north side in Virginia.

Members of the Virginia House of Delegates criticized the actions of Attorney General Herring.

“The House of Delegates will immediately begin a careful review of the Attorney General’s findings,” said Speaker William J. Howell of Stafford. “Unfortunately, I have little doubt as to his true motivations. He is damaging the integrity of the office he holds.”

“This is another Washington-style overreach from a nakedly partisan attorney general,” said Delegate Rob Bell (R-Albemarle). “The attorney general’s job is to faithfully interpret and enforce the law of the Commonwealth. Virginians who have concealed carry permits may lose the ability to protect themselves when traveling in 25 states. Instead of doing the job he was elected to do, Mark Herring continues to put the political goals of his liberal supporters ahead of sound legal judgement.”

Speaking about today’s announcement, Deputy Majority Leader Todd Gilbert (R-Shenandoah) said, “Attorney General Herring is endangering the lives of law-abiding Virginians as they travel for work, vacation or to visit their families. Virginia’s law on concealed carry reciprocity was created in 1997, when Democrats controlled both houses of the state legislature. This law gives State Police the discretion to determine the states with which Virginia should have reciprocity agreements based on consultation with the Attorney General’s office. There is no doubt in my mind, however, that the consultation provided by the Attorney General in this matter is based purely on his partisan, political goal of denying law-abiding citizens the right to protect and defend themselves.”

“People who lawfully carry a concealed firearm in Virginia want the confidence that when they travel to another state, that state recognizes the rights of Virginia citizens to protect themselves. The attorney general’s unilateral action likely means that many of the 25 states involved in today’s announcement will no longer recognize the legal rights of Virginia citizens,” said Delegate L. Scott Lingamfelter (R-Prince William), Chairman of the House Committee on Militia, Police & Public Safety. “If the Attorney General was truly interested in safety and security, he would have sat down with these states and resolved any potential issues instead of pulling the rug from under the feet of law-abiding Virginia citizens.”

Sierra Announces Five New SIG V-Crown Bullets

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Sierra SIG Sauer V-Crown Bullets Nov 2015

Sierra Bullets, in partnership with SIG Sauer, has announced the availability of five new members of the V-Crown self-defense-bullet line. The V-Crowns deliver Continue reading Sierra Announces Five New SIG V-Crown Bullets

Range Test: What’s So Smart About This Gun?

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America’s 1st Freedom magazine’s staff has shot the Armatix iP1 — a so-called “smart gun” touted by some gun-control groups to be the end-all answer to gun safety. However, when range tested by the magazine’s team under rigidly controlled circumstances, they found a number of problems Continue reading Range Test: What’s So Smart About This Gun?

Brooklyn Lawmakers Want to Severely Tighten Ammo Sales

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If two New York lawmakers from Brooklyn are successful at passing new draft legislation aimed at tightly restricting the sale of ammunition in the state, will legitimate gun owners there turn to reloading Continue reading Brooklyn Lawmakers Want to Severely Tighten Ammo Sales

Ruger Rolls Out ‘American’ Pistol Line

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Sturm, Ruger & Co., Inc. (NYSE: RGR) has announced a new line of full-size duty pistols, available in 9mm Luger and .45 Auto. The two 9mms are Model Nos. 8605 (17+1) and 8607 (10+1) and the 45 is Model No. 8615, and all will list for $579 MSRP. Continue reading Ruger Rolls Out ‘American’ Pistol Line

Hodgdon’s Step-by-Step Loading Help

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Midsouth Shooters Supply sells a ton of Hodgdon powders, because, of course, the company makes great products our customers love. But Hodgdon powders are also popular because the company’s experts are willing to help folks get started in the craft or guide experienced hands toward new reloading ventures. Whether you’re new to reloading or a seasoned vet, there’s always something more to learn.

That’s where Hodgdon’s Reloading Education section comes in. The company has stockpiled a wealth of information that can help take your handloading to the next level. Over the next few weeks, we’re going to look at Hodgdon’s online system for building top-rate rifle, pistol, and shotgun loads and give you some pointers on how to make time-saving and money-conserving choices on brass, bullets, and powders.

Click here to see the landing page on which Hodgdon begins the education process.

Select the Reloading for Beginners tab to learn the basics, from the effect of crimp depth in shotshells to reloading the .223 to matching shot type and size to reloading data.

Midsouth also recommends you spend some time learning about Safety. Click that tab to brush up on the do’s and don’ts of reloading, starting with the basic reloading precautions created by the NRA.

Then, select the Tips and Tricks tab for informative posts on key topics in the reloading community.

Here’s a sample of some of the things you’ll find on the site:

Reloaders Corner: Pressure Curves for Semi-Automatic and Bolt-Action Rifles

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The following is a specially-adapted excerpt from the forthcoming book, Top-Grade Ammo, by author Glen Zediker, owner of Zediker Publishing.

When you’re handloading for semi-automatic rifles and bolt-action rifles, it’s helpful to realize they are not to be approached the same way. Continue reading Reloaders Corner: Pressure Curves for Semi-Automatic and Bolt-Action Rifles

10 Great Things about Kel-Tec’s PMR-30

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A few years ago, one of our Midsouth staffers asked an FFL friend to find him a Kel-Tec PMR-30, which were in short supply at the time. He purchased one for $600. Now, at a vastly better price, “The Shot Report” e-letter readers have a chance to win one in our giveaway.

Besides just the sheer joy of getting something cool for free, there’s a lot to like about the PMR-30 pistol. So, to fill you in on some of the best aspects of this handgun, we compiled a top-ten list of great things to like about Kel-Tec’s PMR-30, and we wish you luck when it comes time to draw for it.

#10

Ammunition for the PMR-30 is affordable, if sporadically available recently. A lot of shooters love the similarly sized FiveseveN handgun, but just the 5.7 ammo that runs that handgun will turn a big wad o’ cash in your pocket into a small wad o’ cash PDQ. The PMR-30, on the other hand, chambered for the .22 Winchester Magnum Rimfire, offers a lot of load availability and pricing. We currently list 14 different .22 WMR packages from CCI, Hornady, and Federal in bullet or shotcharge weights of 30, 40, 45, 50, and 52 grains. You can shoot this surprisingly powerful round for as low as 20 cents a round (actually, 19.88 cents/round for the Federal FMJ 40-grain load #129-737).

#9

First reaction of most shooters who handle the PMR-30: “It is so light, it feels like a toy.” The gun and magazine together, unloaded, weigh only a pound, and with a full complement of 40-grain cartridges, it comes in at 20.2 ounces.

#8

You can shoot the heck out it. Our staff has poured about 1000 rounds through one PMR-30, and everyone who shot it has loved it. But note that Kel-Tec says, “The PMR-30 pistol functions best with high-power ammo, often with bullet weights of 40-grains and up. This includes, but is not limited to, the following: CCI Maxi Mag 40gr, Winchester Super-X 40gr, Remington Premier Magnum 33gr.” Also, Kel-Tec notes, “Low-power ammo and/or lightweight bullets may cause failure to feed problems due to the lack of energy to cycle the slide all the way back. The following are currently low power, and may not function reliably in the PMR-30 pistol, especially if the grip is not held firmly: Winchester Dynapoint 45gr, Winchester Supreme 30gr.”

#7

Capacity. The “full complement” mentioned above is 30+1 rounds. Start shooting the first of the month, keep shooting all month. If you like to do math and not have loose rounds in your range bag, then cipher this:

We added three steel magazines to the two polymer mags purchased with the handgun, which gives a loaded-round count of 150 rounds in magazines, or the tidy equivalent of three 50-round boxes of ammo.

#6

The PMR-30 uses a double-stack magazine, and loading 30 rounds into it takes time, and holding pressure on the cartridges to put 30 in can tire your hands. To make this process easier, loading tools are available and recommended. Just do an online search for “PMR-30 loading tools” and several sources will pop up.

#5

The trigger is a crisp single action with an over-travel stop. Our staff PMR-30’s trigger breaks at 3.9 pounds, with no creep and a clean reset.

#4

Another favorite feature on the PMR-30 is the fiber-optic orange rear-sight dots and green fiber-optic front-sight dot. Even newbies understand and can see how to align the three dots, and they’re very visible on almost every target color. In fact, the color scheme is superior in low-light conditions.

#3

The sights and good trigger translate to pretty good accuracy. With Winchester Dynapoint 45-grain JHPs  at 15 yards, we can shoot some 2-inch groups off sandbags, but the average group size is closer to 2.5 inches. Our older version also likes Remington Magnum Rimfire 40-gr. PSPs, which come in around 2.7 inches as a group average.

#2

The PMR-30 produces surprising power and penetration. Super-X 22 WMRs are rated at a muzzle velocity/muzzle energy of 1910 fps/324 ft.-lbs. out of a rifle barrel, and in the PMR-30 itself, we got 1339 fps/159 ft.-lbs., only a 30% decrease. In Ballistic Technology’s wax-like, easy-to-use Handgun Bullet Test Tubes, we were able to accurately measure penetration and wound-cavity size. We fired a round into two 11-inch-long, 3.5-inch-wide Handgun Test Tubes set end to end. The Remington PSP had enough energy to punch a quarter-inch-wide hole 4 inches deep into the second tube (15 inches overall penetration).

#1

We have tested ten .22 WMR samples in the Kel-Tec for function and reliability. We encountered no function problems with any of the 10 brands. Some of our friends have mentioned two instances where the 30th round stuck in the magazine and didn’t feed. It only happened with Winchester Dynapoints in both of the polymer factory mags, so it may be an ammunition-specific issue. More likely, it’s that they did not follow the recommended loading sequence religiously. Failure to load the magazine properly can result in rim-lock, which will lead to a failure to feed. Most likely, after they got 15 to 20 rounds in the magazine, they didn’t tap the magazine on the bench to seat rounds.

All in, the lucky winner of the PMR-30 we’re offering will likely have himself or herself a ball with this handgun — with a red-dot or laser, it would be a wicked squirrel gun out to… as good as you are. Most of us are happy when the gun is better than we are.

A heads-up: You’ll notice we’re currently out of stock on all .22 WMR. Unfortunately, right now, ammunition manufacturers just can’t keep up with demand, and they won’t give us any expected dates of delivery, so we’re leery of letting folks backorder, when it may be a while before it can be fulfilled. If some looks to be coming in, we’ll try to let you know as soon as it hits the receiving dock.

Magnum Research Rolls Out Two More All-Stainless Desert Eagles

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Magnum Research Mark XIX Desert Eagle .44 Magnum (DE44SRMB)
Magnum Research Mark XIX Desert Eagle .44 Magnum (DE44SRMB)
DE357SRMB-Lx72
Magnum Research Mark XIX Desert Eagle .357 Magnum (DE357SRMB)

 

Magnum Research has announced two new models of its stainless-steel Desert Eagle, these chambered in .357 Magnum and .44 Magnum. The company, based in Greeley, Pennsylvania, introduced the stainless-steel Mark XIX in .50 AE about a year ago.

“When we introduced the first stainless steel Desert Eagle Mark XIX in .50 AE last year, the demand was overwhelming, and it was difficult to keep up with that demand,” said Frank Harris, VP of sales and marketing.

The new Mark XIX Desert Eagle .357 Magnum (DE357SRMB) and .44 Magnum (DE44SRMB) have all-stainless-steel frames, slides, barrels, and rails accented with attractive black appointments. Both models have 6-inch barrels and integral muzzle brakes, which will replace the add-on brakes Magnum Research previously offered. Both list for $1,931 and are scheduled to ship during first quarter of 2016.

Handily, the integral muzzle brake makes the new models the same overall length as the company’s standard 6-inch-barrel handgun, so the same holsters will fit the new models. The DE357SRMB and DE44SRMB also feature new Picatinny bottom rails for accessories.

Harris said, “Unquestionably, the Desert Eagle Mark XIX series is the most popular handgun that Magnum Research manufactures, and now, in stainless steel, the .357 and .44 Magnum, as well as the .50 AE, look more commanding than ever before.”

Click here to peruse our .357 Magnum ammunition choices.

Click here to view our .44 Magnum ammunition choices.

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