The 6mm GT (aka 6GT) cartridge was conceived as a “bigger Dasher” for PRS and NRL competition. The 6mm GT’s creators wanted 6mm Dasher accuracy and moderate recoil delivered via a cartridge with a slightly longer case body for better mag-feeding, longer neck for seating flexibility, and more moderate pressures. So far the 6GT has performed very well in PRS competition. Today’s story is a bit different — this is about an experiment — running a 6mm GT in an F-TR type rifle. Understand that, under current NRA rules, you may only shoot .223 Rem (5.56×45) or .308 Win (7.62×51), in official, sanctioned F-TR competition, but the 6GT is fine for F-Open. Mike McCasland wanted to see the potential of the cartridge for long-range target shooting, so he put a 6mm GT-chambered Bartlein barrel on a nice custom rifle with McMillan XIT stock and Kelbly F-Class Panda action. The results were impressive.
6mm GT — New Cartridge with Multi-Discipline Potential
Story by Mike McCasland, Texas Precision
The 6mm GT began garnering attention within PRS circles in early 2019. It promised to shoot 105-110gr 6mm bullets at 2950-3000 FPS, yet not suffer from mag-feed issues sometimes found with 6mmBR variants such as the 6 Dasher, 6BRX, and 6BRA. Moreover, since it burned less powder, the 6mm GT promised increased barrel life compared to the 6mm Creedmoor or 6XC. The 6mm GT case size should still work with the accurate powders in the Varget burn-range. I found the 6GT also worked great with H4350.
As someone who aspired to building a repeater and jumping into the PRS game, and had a spare F-TR rifle sitting around, I thought it would be fun to build up a 6mm GT to see if there was any merit to the hype. My smith, Wes Ripley of RIP Precision in Texas, builds a lot of PRS rigs, and already had the reamer on hand (a 0.120″ freebore variant).
Whidden Gunworks had some 6mm GT FL bushing die kits in stock, so I figured why not see what all the fuss was about? At the very least I could play around with the 6mm GT in F-Open Class at local club matches to see how it compared to the 6BRA, 6 Dasher, and other popular 6mm cartridges.
How the Project Got Started with Backup F-TR Rig
My 6mm GT build really started as a project spawned purely from COVID-19 Isolation boredom. This rifle primarily serves as a backup F-TR gun, and it had been relegated to performing some load development on .308 barrels, so I could spin new ones on my main match rifle. The only problem was, I had run out of .308 barrels that needed load development. So, I basically had an ideal test platform just collecting dust in the safe. All I needed was a 6mm GT-chambered barrel, since (like the 6mmBR) the 6mm GT works in a short action with a .308 Win-sized bolt-face.
6mm GT Rifle Specifications:
Action: Kelbly Panda F-Class SA RB/RP
Stock: McMillan XIT with RAD 2A
Barrel: 30″ 5R Bartlein 1:7.5″-Twist, HV Contour
Scope: Vortex Golden Eagle 15-60x52mm
Trigger: Jewell Benchrest, about 2 ounces
Bipod: Phoenix Precision
About the 6mm GT Cartridge
BRASS — The first thing you’ll find is cartridge brass choices for the 6mmGT are rather limited currently. At present, the only commercial options are Hornady and Alpha Munitions. For the die-hard Lapua fans, you can technically make 6mm GT brass from 6.5×47 Lapua, however that process is very labor-intensive.
I have used both Hornady and Alpha brass in this rifle and haven’t noticed much difference between the two. I will say that my batch of Alpha brass was slightly softer than Alpha brass I’ve used in other calibers; you could feel a difference when neck turning cases. I’m unsure if that’s a batch issue, or something specific to their 6mm GT brass as a whole. As far as performance, there was little discernable difference. Oddly enough, the Hornady brass seemed to have slightly less case capacity than the Alpha; with most other cartridges it’s the other way around.
POWDERS — The 6mm GT was designed with Hodgdon Varget in mind, and that popular powder works exceedingly well in this platform. That said, the 6mm GT can work with a wide variety of powders, some yielding better performance than Varget.
I’ve tried a multitude of powders during my initial 6mm GT load development: Varget, Shooters World Precision, RL16, VV N140, H4350, and RL-15 to name a few. In my barrel, Hodgdon H4350 seems to deliver the best velocity/accuracy combination. SD and ES also seemed to be the lowest with H4350.
Load Development for the 6mm GT — Many Powders Tested
BULLETS — The most common 0.120″ freebore chamber allows for the majority of high-BC 6mm projectiles found in both F-Class and PRS. I had good luck with the pointed 107gr Sierra Match Kings (SMK), as well as the 110gr Hornady A-Tips in my rifle. For those looking to run the heavier 112-115 grain 6mm offerings, I believe GAP designed a 0.160″ freebore reamer that gets those bullets out of the neck/shoulder junction. Shown below is the 0.120″ freebore JGS reamer print:
SUMMARY — Good Cartridge with Much Potential
Generally speaking, I think the 6mm GT is a good little round. Some may not subscribe to this theory, but I believe some cartridges are inherently easier to tune than others. I’m not sure the 6mm GT is as easy-to-tune as a 6mmBR, 6 Dasher, or 6 BRA, but I don’t think it lags that far behind.
With relatively little trouble, I was able to find loads with both Varget and H4350 that would consistently shoot very well — 0.2 to 0.3 MOA. Moreover, I found the 6GT cartridge lives up to the velocity claims made by G.A. Precision. I was easily able to push the 110gr A-Tips to 2950 FPS, and the 107gr SMKs to low 3000 FPS range without any pressure signs, or unnecessary wear and tear on the brass.
As a fun test, I ran my 6mm GT rifle in a local 1000-yard F-Class match with the 110gr A-Tips, just to see just how well they would perform. Although wind conditions of the day and some E-Target issues prevented my 6mm GT rig from getting the better of the larger 7mm and .30-Cal rifles, the 6mm GT proved itself an accurate little round at distance. Here is a 1000-yard ShotMarker target:
After putting several hundred rounds through my 6mm GT rifle, I anticipate building another 6GT on a repeater action to give PRS a try. I think if you are looking for a dual-purpose rifle that can run tactical matches (with 100% feeding reliability), and can also be used for mid-range, F-Open Class competition, the 6mm GT would be a very good option.
About the author, Mike McCasland:
Mike McCasland is an avid shooter who competes regularly in F-Class matches. Based in Texas, Mike is the creator of the Texas Precision YouTube Channel. There you’ll find many videos covering reloading, gun projects, and marksmanship. Mike has done some notable product reviews including a comparison test of Micrometer Competition Seating Dies. To access Mike’s YouTube Channel, CLICK HERE.
.009” Group Record Stood for 40 Years
In 1973 Mac McMillan shot an amazing 100-yard, .009″ five-shot group in a benchrest match. The .009″ group was measured with a 60x microscope for verification. Mac McMillan shot the group using a handbuilt prototype McMillan rifle with an early McMillan stock.
Mac’s .009″ group was the “Holy Grail” of rifle accuracy. This .009″ record was considered by many to be unbreakable, a record that would “stand for all time”. Well, it took 40 years, but someone finally broke Mac’s record with an even smaller group. In 2013, Mike Stinnett shot a .0077″ five-shot group using a 30 Stewart, a .30 caliber wildcat based on the 6.5 Grendel. Stinnett’s NBRSA record .0077″ group now stands as the smallest 100-yard group ever shot in registered benchrest competition.*
Read About .0077″ group HERE.
Stinnett’s success doesn’t diminish the significance of Mac McMillan’s .009″ group in the history of benchrest competition. For four decades Mac’s group stood as the ultimate standard of rifle accuracy*. For those of you who have never seen Mac McMillan’s .009″ group, here it is, along with the NBRSA World Record certificate. The target now hangs in the McMillan Family Museum.
*Somebody else might claim a smaller group, but unless moving backers or electronic targets were used, it cannot be verified. Moving target backers are used at registered benchrest matches to ensure that five (5) shots are actually fired in each group. That eliminates any doubt.
Sellier & Bellot is one of Europe’s older ammunition manufacturers, producing a wide variety of rifle and pistol ammo. The video below shows ammunition being made from start to finish, starting with raw materials. This is a fascinating video that is well worth watching. It shows some amazing machines in operation.
EDITOR: Guys, this really is an exceptional video that shows every aspect of production. I have watched dozens of videos about ammo making. This is definitely one of the BEST. Take the time to watch.
Based in Vlasim, Czech Republic, Sellier & Bellot was founded in August 5, 1825 by Louis Sellier, a German businessman of French lineage. His family were royalists who fled France during the French Revolution. Louis Sellier began manufacturing percussion caps for infantry firearms in a factory in Prague, Bohemia on the request of Francis I, the Emperor of Austria. Sellier was later joined by his countryman Jean Bellot.
Sellier & Bellot has also produced an interesting CGI video that shows what happens inside a rifle chamber and barrel when a cartridge fires can’t be seen by the naked eye (unless you are a Super-Hero with X-Ray vision). But now, with the help of 3D-style computer animation, you can see every stage in the process of a rifle round being fired.
In this X-Ray-style 3D animation illustrates the primer igniting, the propellant burning, and the bullet moving through the barrel. The video then shows how the bullet spins as it flies along its trajectory. Finally, this animation shows the bullet impacting ballistic gelatin. Watch the bullet mushroom and deform as it creates a “wound channel” in the gelatin.
Watch Video – Cartridge Ignition Sequence Starts at 1:45 Time-Mark
If you’ve been thinking about a big purchase at Brownells, here are some money-saving codes. Now through the end of August, Brownells is offering $50 Off a $500+ purchase or $25 Off a $250+ purchase. That’s a great deal, effectively a 10% savings. Use Code VTH to save $50 on $500+, or use Code VTG to save $25 on the purchase of $250 or more.
Coupon Code: VTH — $50 Off $500 or more
Expiration date: August 31, 2020 at 11:59 PM CDT
Coupon Code: MFX — $25 Off $250 or more
Expiration date: August 31, 2020 at 11:59 PM CDT
More Brownells Discount Codes
If you miss these deals listed above, Brownells is still running some discounts for $99-$200 purchases. With a purchase of $200 and up, save $20 with Code M8Y. Or, with a purchase of $99 or more, you can save $10 with Code MDX. You can also get free Shipping/Handling for all purchases over $49 with Code VB5. That free shipping/handling could save you another $10-$20 easy. NOTE: These codes have no listed expiration date, but Brownells could terminate them at any time, so you should still act soon.
NOAA photo of flooding after Hurricane Floyd in 1999. The Colt Python Revolver once belonged to Elvis Presley (Rock Island Auction).
This past week, Tropical Storm Isaias has hammered the East Coast of the USA. The BBC reported: “From North Carolina up to New York, Isaias left more than 3.4 million residents without power. It spawned tornadoes, uprooted trees, damaged homes and caused floods and fires.” This article explains what to do if you have experienced flooding.
Firearms owners who have seen their guns and stored ammunition submerged by flood waters in storm-wracked areas are probably wondering if their firearms and ammunition can be salvaged and safely used. To answer these questions, the NSSF and the Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI®) created two documents outlining the proper response to submersion of guns and ammo. If you’ve got wet guns and/or ammo, download these two PDF files and read them carefully.
The SAAMI document “Guidance on Firearms That Have Been Submerged or Exposed to Extensive Amounts of Water” points out two major concerns about firearms that have been exposed to water: parts susceptible to moisture and rust damage such as metal parts, wood stocks and grips, and optics; and, secondly, infiltration of the action, barrel and safety systems by grit, silt and other foreign debris.
#1 Always unload firearms before beginning any treatment process.
It’s important to limit moisture and corrosion damage to the component parts of the firearm. This can be accomplished by disassembling the component parts and using up to two coats of a moisture-displacing lubricant such as Hoppes #9 MDL or WD-40 to clean and stabilize the parts while, importantly, following the product’s directions so as not to damage, for instance, plastic or synthetic parts. Another tip is to allow wood stocks and grips to air-dry and not be force dried by exposure to heat.
The document emphasizes that once the firearm has been thoroughly dried, consideration must be given to having the firearm inspected and serviced by the manufacturer, an authorized service center, or a qualified gunsmith before putting the firearm back in service.
Dealing with Ammunition That Was Submerged
Bottom Line, if your ammo has been submerged — DON’T USE IT. SAAMI explains why…
To help firearms owners determine what to do with ammunition that has been affected by water and moisture, SAAMI offers another helpful document, “Guidance on Ammunition That Has Been Submerged in Water.” This document covers differences in moisture resistance between centerfire, rimfire and shotshell ammunition, and potential hazards associated with “drying out” cartridges, including possible deterioration and damage to cartridges due to drying methods.
Another serious hazard that could result from using compromised ammunition is the potential for a bore obstruction due to partial ignition of either the priming compound or the propellant powder charge, or both. Firing a subsequent round through an obstructed barrel can result in bodily injury, death and property damage.
SAAMI provides the following cautionary conclusion: “It would be impossible to ascertain for certain the extent of the deteriorating affect, if any, the water may have had on each individual cartridge. Therefore, the safe answer is that no attempt be made to salvage or use submerged ammunition. The ammunition should be disposed of in a safe and responsible manner. Contact your local law enforcement agency for disposal instructions in your area.”
If you wonder how ammo is made, starting with raw metal, check out this video from Hornady. It shows how bullet jackets are formed from copper, followed by insertion of a lead core. The jacket is then closed up over the core with the bullet taking its final shape in a die (a cannelure is applied on some bullet types). Next the video shows how cartridge brass is formed, starting with small cups of brass. The last part of the video shows how cases are primed and filled with powder, and how bullets are seated into the cases, using an automated process on a giant assembly-line. CLICK Link below to watch video:
Hornady’s New 150,000-sq-ft Ammo Production Center
In 2018, Hornady opened a new, state-of-the-art factory. The 150,000-sq-ft Hornady West Facility, featured in the video below, handles ammunition production and product distribution — Hornady produces millions of rounds annually. Hornady cartridge brass and bullets will continue to be produced at Hornady’s 100,000+ square foot factory in Grand Island, Nebraska. The Grand Island factory is open for tours Monday through Thursday. Hornady Manufacturing was founded by Joyce Hornady in 1949, so 2019 marked the company’s 70th anniversary.
Here is an article Glen Zediker wrote for the Midsouth Blog. In this article Glen gives important advice on selecting, handling, seating, and testing primers. The right primer choice can and will affect your load’s performance and accuracy. And proper primer handling is essential for safety.
by Glen Zediker
The primer is one component in the collection that might not get all the attention it warrants. That’s because it is the one thing, above all other components, that you don’t want to just swap and switch around. We’ve all heard cautions about testing new lots of every component, especially propellant, but primers not only change lot to lot, they vary greatly in their influence on any one load, brand to brand.
The difference in one brand to the next can equal a good deal more or less pressure, for instance. While there are “general” tendencies respecting the “power” of various-brand primers, always (always) reduce the load (propellant quantity) when switching primers.
This has become more of an issue over the past few years as we’ve faced component shortages. I can tell you without a doubt that going from a WW to a CCI, or from a Remington to a Federal, can have a major influence on a load. I establish that from chronograph readings. No doubt, it’s best to have a good supply of one primer brand and lot that produces good results, and when that’s not possible, it’s a hard sell to convince someone to stop loading ammo and get back to testing. But. It is important. I can tell you that from (bad) experience. How I, and we all, learn most things…
When I switch primers, whether as a test or a necessity, I reduce my load ONE FULL GRAIN. There can be that much effect.
The Elements of a Primer
A primer is made up of a brass cup filled with explosive compound (lead styphate). Lead styphate detonates on impact. Primers don’t burn – they explode! In the manufacturing process, this compound starts as a liquid. After it’s laid into the cup, and while it’s still wet, a triangular piece or metal (the “anvil”) is set in. When the cup surface is struck by the firing pin, the center collapses, squeezing the explosive compound between the interior of the cup and the anvil. That ignites the compound and sends a flame through the case flash hole, which in turn lights up the propellant.
Primers Can be Dangerous — Particularly When Stacked
Don’t underestimate that. I’ve had one experience that fortunately only created a huge start, but I know others who have had bigger more startling mishaps. These (almost always) come from primer reservoirs, such fill-tubes. Pay close attention when charging up a tube and make sure all the primers are facing the right way, and that you’re not trying to put in “one more” when it’s full! That’s when “it” usually happens. What will happen, by the way, is akin to a small grenade. Static electricity has also been blamed, so keep that in mind.
Sizes and Types of Primers
Primers come in two sizes and four types. “Large” and “small”: for example, .223 Rem. takes small, .308 Win. takes large. Then there are pistol and rifle in each size.
Rifle primers and pistol primers are not the same, even though they share common diameters! Rifle primers [normally] have a tougher cup, and, usually, a hotter flash. Never swap rifle for pistol. Now, some practical-style competitive pistol shooters using their very high-pressure loads (like .38 Super Comp) sometimes substitute rifle primers because they’ll “handle” more pressure, but they’ve also tricked up striker power. That’s a specialized need.
Further, some primer brands are available with a “magnum” option. Some aren’t. My experience has been that depends on the “level” of their standard primer. A magnum primer, as you might guess, has a more intense, stouter flash that travels more “deeply” to ignite the larger and more dense powder column. It reaches further, faster.
Flash Consistency Counts Flash Consistency is very important, shot to shot. The consistency of every component is important: bullet weights, diameters, case wall thicknesses, and all the way down the list. We’re hoping to get more consistent behavior from a “match” or “benchrest” primer, and we’re paying more for it. I can tell you that some brands that aren’t touted as “match” are already consistent. That all comes from experience: try different primers, just respect the need to initially reduce the load for each test.
Primer Dimensional Differences and Primer Tools
One last thing — there are small variations in primer dimensions (heights, diameters) among various brands. These variations are not influential to performance. However — small diameter variations can influence feeding through priming tools. This can be a hitch especially in some progressive loading machines. Manufacturers usually offer insight (aka: “warnings”) as to which are or aren’t compatible, so find out.
This article is adapted from Glen’s books, Handloading For Competition and Top-Grade Ammo, available at Midsouth HERE. Learn more about Glen’s books at ZedikerPublishing.com.
The NSSF has posted a video featuring Bryan Litz of Applied Ballistics. Bryan also serves as Chief Ballistician for Berger Bullets and ABM Ammo. In this short video, Bryan explains the importance of ballistics for precision shooting at long range. Bryan covers key elements — drop, wind drift, angle correction and more. And Bryan also explains the key difference between Accuracy and Precision.
The principles Bryan discusses are covered (in greater detail) in the Putting Rounds on Target instructional DVD set. This 3-Disc collection boasts a total run-time of 3 hours and 37 minutes. The three DVDs, with many graphics and video segments, deliver as much information as a weekend shooting seminar… at a fraction of the cost. The 3-DVD set sells for $44.95.
Disc 1
• Accuracy & Precision
• Tall Target Test
• Chronographs & Statistics
• Ballistic Coefficient
• Trajectory Terms
• Run Time: 1 hour, 4 min
Disc 2
• Primary Elevation (Wind)
• Secondary Effects
• Using Ballistics Solvers
• Short & LR Equipment
• Run Time: 1 hour, 11 min
Disc 3
• On The Range: .308 Win
• On The Range: .284 Win
• On The Range: .338 LM
• Extended Range Shooting
• One Mile Shooting
• Run Time: 1 hour, 22 min
Brownells is a well-known retailer of guns, gun parts, tools, accessories, ammo, and pretty much everything gun related. What you may not know is that Brownells has a very active video production department that releases new “how-to” and product information videos every week. These videos offer helpful advice on gun cleaning/maintenance, reloading, as well as selecting/assembling components for various kinds of rifles. And every week Brownells serves up a new products video. There now over 1000 videos on the Brownells YouTube Channel, this really is a remarkable resource.
Here are six of our favorite recent videos from Brownells. AR owners will find some good advice on spare parts, new reloaders can learn how to use the OAL tool, and all gun owners should watch the video on ammunition storage.
Introduction to PRS Competition
In this video, Tom Beckstrand, former Special Forces Sniper Team Leader and Guns & Ammo magazine staffer, looks at the Precision Rifle Series (PRS). Tom covers the types of stages in a typical PRS match using unconventional, real-world shooting rests. He also discusses the equipment you’ll need including bag supports, bipods, tripods, and optics. As most ranges aren’t set up for PRS, Tom offers tips on how to train at your local range.
How to Use Hornady OAL Tool and Hornady Bullet Comparator
Gun Tech Steve Ostrem explains how to properly use Hornady’s Overall Length Gauge to determine length-to-land precisely. The OAL Gauge uses a “Modified Case” that theads onto the tool and holds a bullet. Push on the back of the gauge until you feel the bullet just touch the rifling. (We do this gently at first, tapping the rod a couple time to ensure the bullet is aligned correctly). Once you’ve got the length, then use the tool with a comparator on your calipers to get the lenght-to-lands. NOTE: We recommend taking the measurement 3-4 times in a row to get a reliable number. With a little practice your should be able to get repeatable measurements within .0015″.
New Bog Pod Tripod and Caldwell Electronic Muffs
Brownells staffer Paul Levy showcases the impressive new DeathGrip Tripod from Bog Gear. The DeathGrip’s adjustable jaws clamp firmly to the rifle’s forearm. This is a useful device for both PRS shooters and hunters. The head assembly has 25-deg front/rear tilt and 360-deg swivel. And the jaws’ non-slip, rubberized padding won’t scratch that stock. The legs snap open to three pre-set hard stops, and there’s plenty of length extension. Easily switch between rubber feet and steel spikes without removing a single part from the trippod. This video also features Caldwell’s E-Max™ Pro noise-cancelling electronic muffs. These affordable 23 dB NRR units boast dual microphones and digital volume controls, and two sizes are offered — Youth and Adult.
How to Store Ammunition Safely and Securely
Notably, this is the single most popular Brownells video this year, with 494,000 views since March 2020. Here’s the deal — ammunition WILL keep for a long time if you store it properaly. DO store ammunition in a cool, dry place that doesn’t have wide temperature swings. Temperature cycling will also degrade primers and powder. Put it in airtight ammo cans to keep out the moisture. Tupperware containers will work too. Brownells also recommends putting moisture-absorbing silica packs in your ammo containers. DON’T just keep ammo in factory cardboard factory boxes stacked in the basement, attic, or garage — especially not on the floor! The ammunition boxes will absorb moisture which will degrade primers and powder and corrode the brass cases. Yes, sealed military ammo will usually handle this kind of storage for quite a while, but it’s still not wise.
Must-Have Spare Parts for AR-Platform Rifles
This is one of Brownells most popular recent videos, with 154,000 views in just four months. Two gun technicians answer the question: “What spare parts should I keep on hand for my AR-15?” On the list are: Gas Rings, Buffer Spring, Extractor Spring and Pin. NOTE: You may want to try the one-piece spiral gas ring rather than the standard rings which require alignment. The cotter pin and cam pin can also easily get lost when the Bolt Carrier Group is disassembled for cleaning. On the lower receiver you’ll want spare springs and detents for the pivot/takedown pins. If you’re using lighter-power springs, keep standard-power spares on hand. If your rifle stops working, swap in the factory-spec springs to find out if the problem is the gun or your ammo. Also, if you have upgraded your trigger, always keep the original trigger as a backup.
Cleaning Advice for .22 LR Rimfire Rifles
Gun Techs Steve Ostrem and Caleb Savant debunk some myths about cleaning .22 LR barrels. One myth is that cleaning will harm the accuracy of a .22 LR barrel. Caleb thinks this myth is the result of people cleaning a barrel from the muzzle and damaging the muzzle crown, which CAN diminish accuracy. If it’s done right, cleaning won’t damage the bore. However, you certainly do NOT have to clean your 22 LR’s bore every time you go to the range. But DO clean the action every time you shoot the rifle, especially on a semi-auto. What about shooting a lot of lead bullets? Won’t that lead up the bore? The guys give us the straight skinny on lead fouling, too. When you see your .22 LR rifle’s groups opening up, you may want to consider cleaning.
Do you shoot long, pointy Hybrid Ogive bullets? If so, you may need to modify the Hornady L-N-L Bullet Comparator tool commonly used to measure the distance from bullet base to bullet ogive.
With modern, high-BC match bullets, so much of the bullet may extend forward of the ogive that the bullet tip actually contacts the inside of the red comparator body BEFORE the bullet’s ogive contacts the gray caliber-specific insert ring attached to the red body. When this happens you will NOT get an accurate Base-to-Ogive (BTO) measure. And likewise you will not get a proper Cartridge-Base-to-Ogive (CBTO) measurement with loaded rounds.
Watch this video — it shows exactly how this measurement “fail” can happen with a .338-caliber Berger Elite hunter bullet. The tester was getting a false bullet Base-to-Ogive reading of 1.175 (0:25 timemark) before modifying his tool. The true BTO measurement, with the bullet actually contacting the gray comparator ring, is 1.121 (1:25 timemark):
How to Fix the Problem
What’s the fix? With a drill, you must relieve the back “wall” inside the red comparator holder bore. This will provide more clearance for the bullet tip. With more clearance the bullet ogive will seat properly on the gray, caliber-specific insert. The tip will no longer bottom out on the red clamping half of the tool.
The maker of this helpful video, EuLRH explains: “As we all know the CBTO (Cartridge Base to Ogive) measurement is [more useful than] COAL (Cartridge Overall Length). There are lots of products that can do this. One of them is Hornady L-N-L bullet comparator. Attention! With modern long range bullets it is possible that the bullet tip is touching the comparator body instead of the bullet ogive touching the gauge.” In this example, EuLRH worked with the 300gr Berger elite hunter bullet in .338 Caliber.
Why You Need to Check with Your Own Loads
If your bullets have this “tip touching” issue, when you measure your loaded rounds you will be seeing COAL instead of the Cartridge Base to Ogive (CBTO) length. Take a moment, test with your own bullets and your comparator to determine if you have this measurement problem. If you do, try the drilling solution shown in the video.
As someone who aspired to building a repeater and jumping into the PRS game, and had a spare F-TR rifle sitting around, I thought it would be fun to build up a 6mm GT to see if there was any merit to the hype. My smith, Wes Ripley of RIP Precision in Texas, builds a lot of PRS rigs, and already had the reamer on hand (a 0.120″ freebore variant).
BRASS — The first thing you’ll find is cartridge brass choices for the 6mmGT are rather limited currently. At present, the only commercial options are Hornady and Alpha Munitions. For the die-hard Lapua fans, you can technically make 6mm GT brass from 6.5×47 Lapua, however that process is very labor-intensive. 
SUMMARY — Good Cartridge with Much Potential
.009” Group Record Stood for 40 Years
If you wonder how ammo is made, starting with raw metal, check out this video from 
Flash Consistency is very important, shot to shot. The consistency of every component is important: bullet weights, diameters, case wall thicknesses, and all the way down the list. We’re hoping to get more consistent behavior from a “match” or “benchrest” primer, and we’re paying more for it. I can tell you that some brands that aren’t touted as “match” are already consistent. That all comes from experience: try different primers, just respect the need to initially reduce the load for each test.
Get Midsouth products 
Do you shoot long, pointy Hybrid Ogive bullets? If so, you may need to modify the Hornady L-N-L Bullet Comparator tool commonly used to measure the distance from bullet base to bullet ogive.
