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Anyone shoot the 6mm GT cartridge? Login/Join 
Freethinker
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From looking at YouTube videos of various long range precision rifle events, it seems that 6mm cartridges are growing in popularity. The latest one I heard of was the 6mm GT that was discussed in an Outdoor Life article, among other places. That article makes claims about its superiority for several reasons, but I’m curious what other users or those who are familiar with it have to say.

https://www.outdoorlife.com/st...ecision-rifle-world/

Comments?

(To help save some electrons, I will ignore any “Why do you want that?” questions. If we look at the question I did ask, you’ll see that there is nothing about my wanting the cartridge or my intentions. I’m just looking for information and any discussion in that vein is what I’m seeking. And if this comes across as testy, yes it is. I have a bet with myself about how many posts there will be before someone asks, “Why do you want that?” so they can earn the Internet Clever Fellow Award for the day. But if people can post things like that on a fortunately open forum, I can post my testy pre-response. Smile )




7/93
 
Posts: 45893 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
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Why wouldn't you want that?

(double clever fellow award winner)
 
Posts: 19836 | Location: 18th & Fairfax  | Registered: May 17, 2003Reply With QuoteReport This Post
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6mm GT (commonly called gay tiger) was developed to use varget to get 3100ish fps from heavy 6mm bullets, and feed well from mags. From all accounts it works very well. It was specifically developed for PRS and benchrest competition. One of the developers and champions of the cartridge is George from GA precision. But you probably already found out that much from a quick google search unless you are super lazy. The backstory adds a little context. George has been a strong proponent of heavy high bc 6mm bullets for a very long time. Since even before PRS was a thing he has advocated the low recoil, wind bucking, and consistent performance of a high bc 6mm bullet for long range target shooting from bolt guns. He started with 243, and worked with 6mm lapua, 6 dasher, 6 creed, and 6 GT. It was George’s advocacy of 243 that got me to abandon 308 for match shooting and jump into 243 with both feet. I have since changed over to 6 creed, but still have one match rifle that is chambered in 243 that is not yet shot out. I used that rifle in a match last weekend and it still got the job done. Here is my take on the 6mm cartridge debate in a big nutshell. The goal is a 105-115 gr high bc bullet with a consistent bc to be propelled to 3000-3100 fps at the muzzle that feeds well from a offset double stack rifle mag, and is tolerant of the constant throat erosion of an over bore barrel eating load. 243 works, but the case is a bit to long and is not ideal for mag feeding, can be finicky to find loads for. 6 creed works, is easier to load for and feeds better from a mag. I don’t have a 6 GT, but I am sure it works as well and uses Varget instead of 4350. If you are not already reloading for a 6mm cartridge that is working for you and want a new chambering, get a gay tiger if you want to try it and have varget to burn, if you want to burn 4350 get a 6 creed. If your current system is working and you have components and rifles well chambered in a 6mm that is working for you it is probably not worth changing to the new cartridge on the block even if it is a little better. The great thing about long range shooting is that it is an entertaining way to turn money and time into clanging steel or holes in paper. Only an individual knows if the extra money and time is worth the effort in the end.
 
Posts: 1637 | Location: Spokane, WA | Registered: June 23, 2008Reply With QuoteReport This Post
Freethinker
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Thanks for that discussion, Stlhead. It expands on what little I have read thus far.




7/93
 
Posts: 45893 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
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I am actually in the =process of building a 6mm GT bolt gun (my end goal is to get a rifle together that I can use to try my hand at PRS). I'd stick with my 6.5 Creedmoor (which I absolutely love) but I haven't seen the Berger 140HT in a year and a half or so. Berger says they're not discontinued, but they're just never on the build schedule.

I had already planned on building a 6mm at some point, and was torn between Dasher and GT. What made the decision for me was the variety of powders I can use vs. the powders I have on the shelf right now - I have 15# of IMR 4451 that I have/use for my 6.5 Creedmoor. I plan on using Berger 105VLD bullets for the moment; ultimately I plan on getting my hands on 109 Hybrid Targets as they're what I'm told is the ideal projectile for this.

It's my understanding that Dasher is a bit more narrow in the range of ideal powders but is more "plug and play" while GT's usable range is from H4350 through Varget (4451 is the IMR equivalent to H4350; I also have some VV N550 and H4350 on the way) but requires some more care in load development.


"In order to understand recursion, you must first learn the principle of recursion."
 
Posts: 3150 | Location: Memphis, TN | Registered: August 23, 2010Reply With QuoteReport This Post
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A variety of issues have resulted in my not shooting competitions in 2022. So my information is dated by a year.

The PRS/NRL/steel match folks continue to search for cartridges that fly flat, buck the wind, and produce minimal recoil. 308 was easily eclipsed by the 6.5mm bores. Quick stages shot from barriers means the 6.5mm bores take a big back seat to the 6mm.

On the slow MV end, there's nothing like the accuracy of a 6BR. The fast cartridges (6x47 and 6CM) work great, but with short-lived barrels and a little more recoil. In between 6mm bores include Dasher, BRA, BRX, XC, and gay tiger. In reality, all the 6mm cartridges are capable of great accuracy -- probably better accuracy than is really required for the vast majority of steel target stages.

In one field match last year, a member of my squad shot a 6GT. I talked to another guy at the Steel Safari match who shot his 6GT in the Safari. Both of them said almost the exact same things:
- 6GT is really accurate. Right up there with Dasher and similar.
- 6GT has pleasant recoil. A little more than 6BR, but way less than 6.5CM.
- 6GT is theoretically long enough to cycle well in a standard 308-length magazine without modification, but don't count on it. Both shooters stated that slow & careful cycling almost always chambered the round well. Running the bolt fast & hard regularly resulted in a jam from a nose-down cartridge dive. Meaning that for PRS events, use a spacer on your AI mags. And maybe even bend the feed lips a touch.

Last year, the newest flavor of the day was the 25 Creedmoor. I saw a couple of guys do really well with it, including a match win. One guy hot-rodded his in the Nightforce ELR match -- and did amazingly well.
 
Posts: 7400 | Location: Colorado | Registered: January 26, 2008Reply With QuoteReport This Post
Freethinker
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Thanks for the new comments. As I say, I don’t anticipate acquiring guns chambered for new cartridges, but I do have an abiding interest in ballistics in general, and learning what other people know about issues relating to cartridges’ suitability for various disciplines plus things like barrel life and powders round out my own knowledge.

And I hope you don’t have any serious problems, fritz, and that you’re able to get back to competing. I always appreciate learning from your experience.




7/93
 
Posts: 45893 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
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Just too many items on my plate, and some things have to give -- rifles matches and skiing are at the top of the list.

At the office we're still trying to get current from last year's 2 ransomware attacks. Our systems and data are good -- but the processing backlog still exists. We just recently sold our building, then just went into contract for a new one. Downsizing and all. Prep for moving has been going on for a few weeks.

I continue to be the primary cleaner-upper at the family ranch for the devastating snow and wind storms of spring 2019. I'm working most weekends. Maybe 3/4 of the cleanup work on our forested area is now done -- broken branches, snapped trunks, downed trees.

In the past year I'm quite certain that my booger hook has spent more hours on chainsaw throttles than minutes on the triggers of precision bolt action rifles.

I haven't even started the big project of felling our ever increasing collection of dying Ponderosa pines. Whether it's beetles, drought, or phase of the moon, there's some kind of problem. I've lost count, but I'm guessing I've marked with spray paint at least 75 trees that require felling. Plus at least 25 "telephone poles" from 2019 that only the bottom half or so still stands. The smallest dead pines are around 10" in diameter at the base. The biggest ones are 30-34" in diameter and up to 70' tall.

A big rain storm in August resulted in a gully washer flood that likely sets me back a few months in cleanup. Shit.

Fortunately, there's the SF Postal Match. My rifle capabilities are suffering, but at least the Postal Match is keeping the fundamentals from completely going off the deep end.
 
Posts: 7400 | Location: Colorado | Registered: January 26, 2008Reply With QuoteReport This Post
Freethinker
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Ooog. Frown
Doesn't sound like any fun. All the best with all that.




7/93
 
Posts: 45893 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
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Originally posted by sigfreund:
Ooog. Frown

Yep.
I am now finding fewer dead trees per day than in the middle of the summer. Found 6 trees one day in early August. Marked only 1 new one for felling yesterday. Needles weren't deep green over Labor Day, so it was on my watch list. This one is 21" in diameter at my upper thigh -- the height at which I do felling cuts. Maybe 50-60 feet tall. This tree is near the middle of one of our worst areas for dead pines in 2022. Within 100-150 yards of this tree, there's at least 20 others that I've marked for cutting.



Part of yesterday's cleanup work, snapped by winds in 2019. The base cut will be at 24" diameter. Broken at 21" diameter, maybe 9-10 feet up. The remaining trunk is 28 feet long. I trimmed it with the Ego battery saw, will finish it later with one of my Stihl gas saws.



The previous 28' log is maybe 15 yards behind me, from this shot. Struck by lightning, this tree gave up the ghost in 2018 IIRC. Base is 21" diameter. Probably more than 60' tall. I need to fell this one right where I shot the picture, to avoid hanging it in surrounding trees. It leans a little and wants to fall to the right in this picture, but I hope to control its drop. The lower branches are getting brittle and falling. If I wait too long to cut it down, the branches could drop from the vibration of the saw -- such are called "widow makers" for a reason.

Working solo I should be able to fell, cut limbs, clean up the shattered branches, buck the trunk, and haul everything off in one day. If all goes well. This tree is probably is just slightly larger than the average dead tree I need to deal with.



Welcome to my world. And why it's tough to find time to shoot.
 
Posts: 7400 | Location: Colorado | Registered: January 26, 2008Reply With QuoteReport This Post
Freethinker
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Wow!
Are you experiencing beetle kill?

There are large swaths of beetle kill (evidently) in Summit County not too far from where I live, but thus far not so much at our higher elevation as far as I know.

(It’s my thread, so I don’t mind drifting it. Wink )




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Posts: 45893 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
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We aren't certain what's causing this year's rash of dying trees. Grampa said we've had pine beetle issues for as long as the land has been in the family -- which goes back to the late 1800's. Beetle kills were especially bad throughout the 1970's and 1980's, then cycled up and down over the following decades. Grampa always said that cold winters noticeably reduced the beetle kills in the following spring. In recent years we generally lost no more than 10 trees a year, which was fine for supplying the family with wood for winter burning.

Almost every newly dead tree I've cut in past couple of years has some level of blue stain from beetles. Maybe 1/3 of the blowdowns from 2019 show a little blue stain. What's different this year is the lack of marble-sized sap nodules on the bark. This is where the beetles bore into the trunk, and then the tree subsequently tries to encase the beetles and push them out. I believe I've only seen two trees with such sap nodules this year -- and they were clearly beetle kills.

We do see insect bore marks on the bark of some dying trees. We've chipped into these bores, following them into through the bark and into the sapwood. Haven't found any beetles. We generally find a touch of blue stain in such trees, but it's not really pronounced.

We don't know if the trees are too weak from the drought to produce enough sap to fill the insect bore holes. We don't know if this is a new type of beetle or some other insect.

In prior years, the pine beetles moved from tree to tree in the spring. By June, we pretty much knew which trees were infected and which were dying. Rarely did we see beetle kills in the heart of the summer. This year, I've marked a lot of trees in July and August.

Most of the trees we've lost are far from our primary seasonal creek bed, so water might be an issue. But here's a big one in the creek bed that started turning this year in May. All needles are now completely brown. Dig down a few feet and there's always water in this creek bed. The August gulley washer made this wide portion of the stream bed about 12-15" deep in water. I haven't measured this tree yet, but I suspect it's around 36" diameter, probably 70-80' tall.

There's an old dead snag on the right side of the above picture. The photo doesn't show another 5 recently dead mature trees on the right bank -- half way between the snag and the big tree.

This year's increase of dying pine trees seems to be occurring in a number of places on the front range -- from Denver to Evergreen, based on my direct knowledge. Our land is to the east, at about 6400' elevation.
 
Posts: 7400 | Location: Colorado | Registered: January 26, 2008Reply With QuoteReport This Post
Freethinker
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Interesting. Thanks for all that, and hopes it doesn't get worse.




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Posts: 45893 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
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