AR-15 Chamber Selection, Part Two

Continuing with common AR-15 dimensions, I suspect I’ll ruffle some of my fellow gunsmith’s feathers in the section on "encyclopedic error." We will start on the short end of the spectrum and end up on the long side. The SAAMI chamber is old but that doesn’t mean it isn’t applicable to certain AR-15 projects today. When the .223 Remington first came out it was used mostly for varmint hunting in bolt guns.

The long heavy bullets of today hadn’t been invented yet and most of the ammo was of a length to fit in the integral magazines of bolt action rifles. Because the chamber was designed to accommodate short ammo, the leade is short. I don’t normally build varmint rifles and don’t have a SAAMI reamer but references say it measures about 2.42" with an 80 grain Sierra Match King bullet.

Shorter chambers tend to pressure up more and the conventional wisdom is to not use the SAAMI chamber with military 5.56mm ammo as it is loaded hotter than some civilian ammo. ARs have recently become quite popular for varmint hunting and if the customer plans to use light short bullets this could be a very good chamber. You should remind your customer to check the game regulations for the state where he plans to hunt as semi auto rifles are not legal everywhere for hunting.

My home state, Pennsylvania, does not allow them. Of course we don’t have prairie dogs either but we do have woodchucks. Quite some time ago when NRA bullseye shooters started to make the switch from the old M14/M1A, some ARs were chambered with SAAMI reamers. As bullets for the AR got longer and heavier, shooters with such chambers found they had to seat bullets further down in the case. This caused pressure problems and lots of blown primers.

Powder charges had to be cut to compensate, reducing velocities and shooter happiness. A fair number of disgruntled shooters threw these barrels out, which was wasteful as judicious use of a throater reamer likely would have fixed the problems. Some had their barrels completely rechambered and that also worked. If you get a customer complaining that an old "safe queen" from back in the day is blowing primers, you might want to take a quick Stoney Point reading and determine if it has one of these short chambers.

A chamber popular with Service Rifle shooters is Compass Lake Engineering’s proprietary chamber designed by Frank White, and it’s a good one. Overall cartridge length, measured with the Stoney Point using an 80 grain SMK is 2.450". Derrick Martin at Accuracy Speaks has a similar reamer resulting in a chamber not much different at 2.442". For the Across The Course Service Rifle shooter these chambers are my top picks.

By starting a bit on the short side these chambers offer stellar results with magazine length ammo while offering hundreds, if not thousands, of rounds of additional service life. There will be a small reduction in powder charge with these chambers when shooting 80s compared to the next chamber. A very popular chamber in a number of circles right now is the Wylde. Bill Wylde didn’t design it specifically for High Power, instead, he wanted to optimize 62 grain Canadian ball ammo.

Regardless of his original intent back in 1984, it turned out to be a very versatile chamber. It has a gradual 1 degree 15 minute leade angle which is friendly to thin jacketed bullets like the Sierra 90 grain Match King. You can safely shoot military ball ammo in it and I have never experienced any pressure problems doing so. It is longer than either the CLE or Accuracy Speaks chambers, measuring 2.475".

Because of the longer length you can safely add about a half grain (work up to this gradually) more powder than the CLE chamber and gain about 50 feet per second with 80 grain bullets. While I recommend this as my second choice for customers building 80 grain guns, it is my first choice for shooting 77s at the 200 and 300 yard lines and 90s at 600 and 1000. The longer freebore of the Wylde allows me to seat my 90s ahead a bit more so not as much of the bullet is buried below the case neck.

That, coupled with my gain twist barrel design, allows me to hit my target muzzle velocity of 2,600 fps with Berger 90 grain boat tails and stay strong supersonic (1,249 fps remaining) out to 1000 yards. I do not recommend any chamber longer than a Wylde for normal use with 77, 80, and 90 grain bullets. The longer a chamber begins life, the shorter that life will be.

Perhaps some full time military shooting teams have enough money to rebarrel frequently but most folks paying for their own barrels out of pocket would much rather have barrels last hundreds or thousands of rounds longer. The next chamber we will look at is the Holliger, designed by John Holliger of White Oak fame. It is a whop-

ping 2.530" long and has the gradual 1 degree 15 minute leade angle that like. John designed it to optimize 90 grain bullets. I would recommend this chamber to those few customers who want to build an AR strictly for long range shooting and never plan to shoot magazine-length ammo. The added leade of this chamber optimally positions the long 90 grain bullet’s base in relation to the case neck while making room for more powder.

I would expect this to wear out quickly but long range shooters don’t fire that many rounds in a season so it is an option. While there are limited use chambers around 2.50" in length’about midway between the Wylde and the Holliger’t hey have never caught on much. They tend to perform questionably with magazine length 77 grain bullets and wear out fast. Last is the NATO chamber measuring 2.550" long and fat in just about every dimension.

All that slop makes it reliable in dirty battlefield conditions but sure doesn’t do anything to enhance accuracy. If you are building a genuine go-to-war gun this chamber is the ticket. Otherwise, for shooting military ball ammo, go with the Wylde. You should not expect this chamber to give accurate performance for I very long.

PPC Revolvers PPC stands for Practical Police Combat and is a sport and training course that I practiced quite a bit in the early 1970s after returning from my "senior trip" to Viet Nam when I began a 28 year career in law enforcement. Cops were finding out that traditional one handed bullseye shooting wasn’t practical for teaching and developing skills needed to survive gun battles. Revolvers were about all that cops carried at the time and the .357 Magnum with jacketed hollow points was very popular.

Matches were held but there were very few rules regarding firearm modifications, resulting in "funny guns" because they barely resembled anything a cop carried on duty. Great big bull barrels with ribs on top so massive that couldn’t fit normal duty holsters.

Every possible advantage was also gained on the ammo side of the house as well and the jacketed hollow point Magnums were left in the cruiser and replaced by match lead wadcutter bullets seated flush with the end of .38 Special cases loaded with very light "talcum powder" propellant charges to reduce recoil. Such bullets fired in .357 chambers jumped the length of a football field before entering the back of the barrel. This enormous jump (about 1/2") was of some concern regarding accuracy.

A very smart hombre by the name of Fred Schmidt created an ingenious solution. He cut all that excess front part of the cylinder off down to the center part on which it rotated. At the same time he extended the back part of the barrel rearward through the frame by an equal amount so there remained only a few thousandths of gap needed for reliable rotation of the shortened cylinder. He even patented the modification. Guys who had his revolvers swore by them!

Other gunsmiths, prohibited from performing the modification by Schmidt’s patent, tried to say (loudly and repeatedly) that the overly long jump didn’t degrade accuracy (riiiiight…) but none of them came up with any test data to substantiate their claims. Perhaps this was an early example of encyclopedic error. More on how this pistol bullet jump ties into AR chambers in a bit.

In an interesting side note, the Police Revolver Distinguished Match was held to higher "as issued" equipment standards and the wadcutter ammo was replaced by rounds similar to what officers actually carried on the street. Mr. Schmidt is deceased now but Mark Hartshorne, a member of the American Pistolsmiths Guild, is offering short cylinder conversions through Pinnacle High Performance (pinnacle-guns.com, [contact withheld]

Encyclopedic Error Do any of you really believe that each time anew edition of an encyclopedia comes out little worker bees diligently researched everything from the Big Bang to the Edsel? Probably not. In reality, most of what was previously researched and published just gets reprinted, a cut and paste.

So, if the distance from the Earth to Mars was off by a few miles way back when it was first calculated, that error just gets carried forward from one edition to the next until someone notices the mistake and gets it corrected. I am told that cartographers are notorious for copying previous maps. Some map makers were even rumored to have in- 357 was both carried on duty for part of his 28 year career in law enforcement and also used to earn his first of three Distinguished Shooter Badges.

Note the difference in length between .357 JHP ammo and the match .38 wadcutter. The wadcutter bullet jumps slightly in excess of 1/2"if fired in a full length cylinder.

serted bogus fictional streets in some of their city maps to catch other cartographers when they copied them. I kept hearing that it is OK to jump magazine-length 77 grain bullets long distances in the AR-15 because it allegedly wouldn’t hurt accuracy. None of the people who kept repeating this ever offered any studies or proof of their assertions, however. The whole idea on its face made no sense to me because throat erosion is one of the prime factors in barrel wear.

Doesn’t throat erosion cause bullets to jump further? Roughness of throat erosion is also a factor regarding barrel wear out and a barrel that begins life with a short chamber and erodes to a given point is going to be much rougher than one that starts out long because the customer or gunsmith selected a reamer with a lot of freebore. Eventually I began to wonder if the whole idea of excessive bullet jump not harming accuracy was a prime example of encyclopedic error.

I was also talking to a lot of Compass Lake Engineering customers, many of them swearing their 77 grain performance in Frank White chambers was noticeably better than in longer chambers. I spoke to Frank about my concerns and he said that part of the reason he came out with the chamber was to improve 77 grain accuracy while also helping barrels wear longer.

I measured the jump distance in barrels with new Wylde chambers and determined that 77 grain bullets seated at magazine length travel 0.116" before contacting any rifling. That is enormous! I decided to set up my own study to see what the truth was. I had recently purchased 34 barrel blanks from two well known and respected barrel makers and they were due to be processed by CLE. These were 1:8 twist barrels for shooting 77 and 80 grain bullets.

I had Frank chamber half of each brand with his CLE chamber and half of each brand with Wylde chambers. When they arrived I built temporary guns around half of them and broke them in using a noninvasive process and machine rested the 17 temporary guns with several known lots of ammo. When I was finished, I cleaned everything up, tore the guns apart and reassembled with barrels with the other chamber.

Same receivers, float tubes, match bolt carriers, flash suppressors, torque specs, ammunition, etc., as the first group for a total of 17 barrels with Wylde chambers and 17 with CLE chambers. This is a nice size sample and a lot of work! When the gun smoke cleared the CLE chamber had smartly spanked the Wylde by a substantial 23.3% average reduction in group size. Very significant! I wanted to test my methodology so I dug out my throater reamer and went to work on some of the barrels with the CLE chambers.

I throated them out to 2.475" Wylde specs, 2.50" length, and even took some to NATO 2.550" length. Then I tested them a second time using the same ammo lots. Going the 0.025" from the CLE starting length of 2.450" out to the 2.475" of the Wylde resulted in group sizes becoming about 23% larger, just as in the initial method of testing. Going an additional of 2.50" made the groups even worse and you can pretty much guess what the additional 0.050" to NATO specs did to my groups. Horrible!

The gunsmiths who push these long chambers make two promises. The first promise is the claim that the long jump distances that magazine length ammo is subjected to doesn’t degrade accuracy. My study says the exact opposite and to a very noticeable degree. According to my study they are sacrificing short line performance. In most matches fired in NRA High Powder competitions, 60 – 75% of the competitor’s score comes at the 200 and 300 yard lines.

I believe the more accurate statement regarding 77s is that they are jump resistant, not jump proof. There are two reasons why long jumps may degrade magazine length ammo’s performance. First, the longer the distance traveled the further from the center of the bore any bullet not seated perfectly concentric is going to strike, causing more deformity. Second, bullet skid. This is a theory from Smith & Wesson when they brought out a very high power hunting revolver some years ago.

S&W theorized that any bullets launched into a fast twist barrel will "skid" along over the lands for a short spell before engraving enough to start rotating. They make up for this with again twist barrel starting the bullet rotating very slowly at the back (1:20") and the twist rate doubles over the eight inches of barrel and spins 1:10 at the muzzle. Obviously bullets that have accelerated more are going to skid further and incur more damage than those traveling slower.

Barrels with greater jump will allow their bullets to be traveling faster when they impact with the throat than bullets with less jump. Did Fred Schmidt have some inkling of this bullet deformation by skidding and the exacerbation caused by excessive jump allowing bullets to impact with greater speed back 40 years ago? Hence part of the reason for his short cylinder PPC revolver conversion. The second promise is for improved performance with 80 grain bullets used for 600 yards.

These bullets will be seated long, nearly touching the lands, and will not fit in magazines. Even if this was true, is it possible to make up the points lost at 200 and 300 when the 600 yard phase is only 25-40% of the total match aggregate? Look at the "Long Chamber Theories" diagram and consider two notions the long chamber proponents base their assumptions on. The cartridge drawing on the left indicates part of the bullet below the case neck swelled out to look egg shaped.

The theorists posit that when the expanding gas from the burning powder "smacks" the base of a bullet which has no support, the bullet will begin to obturate and the back end will swell out. When that swelled out section is later swaged

back down when going through were true, would be to use a chamthe rifling, damage to the bullet is ber with a longer leade and throat to caused. allow the bullet to be seated forward Their second theory is explained so that none or very little of it exby cartridge on the right. The logic tends below the neck, which would here is that not all times is the powoffer needed support to keep these der ignited evenly nor does it always accuracy robbers from taking their burn evenly in the case. In around toll.

I gave the theories every chance where there is uneven combustion, to prove themselves and at the end for whatever cause, more gas (picof the study neither 80s nor 90s imtured coming on the right of the proved one iota by shooting them bullet) and pressure can be generin longer chambers, however, long ated on one side of the bullet than chambers sure did degrade the poor the other.

Bullets subjected to these 77 magazine-length ammo jumping uneven pressures can tilt to the their bullets huge distances. side and enter the barrel crooked. This is not the first time in my This is very close to seating a bullet shooting career have I looked at crooked when the ammo is loaded. the supposed benefits of something This run out has been verified nuwhich on the surface made sense but merously to degrade accuracy to a didn’t pan out in real life.

We will significant degree. get into some of the other failures in I must admit that both theories sections on loading ammo because make sense on paper.

I stipulate that a person can waste a whole bunch the obvious solution, if the theories of time doing things over in that stable that just are not necessary. will tell you straight up that I did Cartridge graphics by ISM Services not test the 80s during the initial helps clarify long chamber theories. experiment for two good reasons. consider the 80 to have been made obsolete by the 90 and I have no desire optimizing it when a better bullet is on the market.

Secondly, I had already spent an enormous amount of time building 34 temporary guns to do the testing that the study was originally designed to test. I was the Armorer for the Army Reserve Shooting Team at the time and just didn’t have the time to spend doing any more testing. That said, as I fielded the barrels with the shorter CLE chambers during either rebarreling or custom gun builds, I did my normal 80 grain load work ups to find the bullet seating sweet spots for each.

While I had to reduce the powder charges by 1/2grain in each of them from the charge used in the longer Wylde chambers’re sulting in a 50 fps reduction in muzzle velocity which translates to less than 1/4 MOA windage at 600 yards’I saw no degradation in 80 grain grouping in the shorter chambers, which runs counter to the long chamber theorist’s notions.

Chambers And Boat Tails One of the reasons to order a custom reamer is because, at least in the case of the Wylde chamber, it is abundantly clear to me that not all reamer makers know or adhere to true Wylde specs. I have received barrels with chambers purported to be true Wylde that were as short as the CLE chamber or as long as the NATO one. That is an enormous spread and was making my life miserable. The shorter chambers obviously pressured up more and I had to cut my loads resulting in lower velocities.

The longer chambers shot magazine length 77s (usually about 2.25") poorly! The only "good" thing that came out of all these varying chamber lengths was that I got to test the theory that long chambers I shoot heavy bullets better. The longer chambers didn’t shoot the 90s better at all. They did allow for I higher powder charges and I did get faster muzzle velocities but the groups weren’t better than with the shorter chambers.

The shorter chambers did position the bottom of the long 90 grain bullets well below the case necks but their group sizes were just as tight as those shot with long chambers. In all fairness, I am somewhat comparing apples to oranges. When Berger and I were brain storming the idea of a reliable 90 grain boat tail bullet, one point of early agreement between us was that it needed to have a thick jacket to avoid the blow up fate of the thin jacket Sierras.

It may be the thicker jacket of the Berger 90 boat tail makes it more user friendly to deep seating, however, the 90 is a longer bullet than an 80 so more of it is bound to extend down into the casing below the neck. The long chamber theorists insist that this should result in fat groups yet my 90 grain groups are averaging 7.7% tighter than 80 grain groups! AG